Home Hazards

What is Chronic CO Poisoning?

Chronic CO poisoning usually involves lower levels of the gas in the air and lower blood CO (COHb) concentrations. Exposure usually continues for many days to months. The boundary limit between acute and chronic exposure is indistinct.
The word chronic should be reserved to describe the type of exposure, not the subsequent condition or effect! A damaging effect of CO poisoning, or in fact, any change which persists, should be referred to as a residual effect.
Chronic CO poisoning may not elicit the typical symptoms of (acute) CO poisoning such as headache, nausea, weakness, dizziness, etc. Mucous membranes of the body will almost never be cherry pink. Chronic CO poisoning is often misdiagnosed as chronic fatigue syndrome, a viral or bacterial pulmonary or gastrointestinal infection, a “run-down” condition, immune deficiency, etc. Patients may occasionally present with polycythemia, increased hematocrit, etc.
Chronic CO poisoning is, in fact, difficult to diagnose by those not skilled in its presentation. As stated above, it is often mistaken for chronic fatigue syndrome, viral or bacterial pulmonary or gastrointestinal infection, excessive heat, etc. Similar symptoms seen simultaneously in more than one person, and which disappear upon removal from an environment are tip-offs that CO is involved. COHb is usually not excessively elevated. More often than not, by the time air CO or blood CO levels are measured, the presence of CO in the environment has been corrected, making measurement impossible. Computed tomography (CT) and magnetic resonance imaging (MRI) generally show no lesion, even when psychological/psychiatric and neurologic evaluations may detect functional deficits.
This is a subject about which many exciting new data have become available during the past 2 years. Summaries of some of these date are seen on this website. A body of animal data are also available which is of some value in understanding and predicting human responses. See the very useful British study by CO Support and the other studies contained in the section called Chronic CO Poisoning.

Definitions of Types of CO Exposure

Acute CO Poisoning – Exposure to CO occurs only once and lasts no longer than 24 hrs.
Chronic CO Poisoning –
Exposure to CO occurs more than once and lasts longer than 24 hrs.
Usually involves lower CO levels / lower COHb saturations
Exposure usually continues for many days to months
Boundary limit between acute and chronic exposure indistinct

Definition of the Word ‘Chronic

Chronic –
(Gk.) khronos = time
(Lat.) chronicus
(Fr.) chronique
1) Of long duration
2) Subject to a habit or disease for a lengthy period
Syn. continuing, lingering, persistent, prolonged, protracted
Webster’s New College Dictionary, Houghton Mifflin Co., 1986.
The term chronic is sometimes used as in definition #2 – “A history of CO inhalation and an awareness of the typical distributions of lesions are important for recognition of the effects of CO poisoning, especially when patients are in the chronic stage.” (Uchino et al., 1994, Neuroradiology, 36, 399-401)
Note: In this condition, ie. chronic CO poisoning, we are concerned with how long the insult (exposure) lasts, not how long the resulting effects last.

A Paradox of CO Physiology:

It limits oxygen delivery, binds to intracellular energy generating system, kills cells, causes damage to tissues and organs, and kills people.
Natural / Helpful:
It is generated by the human body as a by-product of hemoglobin metabolism
Along with NO (nitric oxide), it is an integral part of the vascular control mechanism.
Most blood vessels dilate as COHb increases, allowing more blood to flow through.
Elevated CO Concentrations are More Likely in:
  • Smaller multi-unit dwellings
  • Households using gas ranges for cooking
  • Dwellings heated by gas wall furnaces
  • Low(er) CO Concentrations are More Likely in:
  • Single family dwellings
  • Homes with forced-air furnaces
  • Residences with electric cooking appliances

Table of Indoor Air Pollutant Concentrations

PollutantConcentrationLocation / Condition
Carbon Dioxide860 ppmLecture Hall
Carbon Dioxide600 – 2500 ppmSchool room
Carbon Dioxide9000 ppmNuclear submarines
Carbon Monoxide2.04 +/- 2.55 ppmU.S. homes
Carbon Monoxide2.5 – 28 ppmOffices, restaurants, bars, arenas
Carbon Monoxide3.1 – 7.8 ppmHome kitchens with gas stoves
Carbon Monoxide1 – 5 ppmmedian outdoor concentration in cities, 1979
Carbon Monoxide0 – 3 -27 ppmMax. 1 hr. average outdoor concentration
Carbon Monoxide0 – 3 – 22 ppmmax. 1 hr. average indoor concentration
Carbon Monoxide20 ppmRoom polluted with cigarette smoke
Hydrogen Cyanide56 ppbRoom polluted with cigarette smoke
Nitric Oxide1.05 ppmRoom polluted with cigarette smoke
Nitrogen Dioxide5 – 110 ppbU.S. homes with gas stoves
Nitrogen Dioxide5 – 317 ppbEnglish homes with gas cookers
Nitrogen Dioxide20 – 66 ppbMedian outdoor concentration in cities, 1979
Nitrogen Dioxide25 – 177 ppbHomes, 48 hr. average
Nitrogen Dioxide200 ppbRoom polluted with cigarette smoke
Ozone2 – 68 ppbPhotocopying room
Ozone2 – 18 ppbHomes with electrostatic air cleaners
Ozone7 – 60 ppbMedian outdoor concentration in cities, 1979
Ozone0 – 700 ppbUsing an electronic air cleaner
Sulfur Dioxide8 – 37 ppbYearly averages in Chicago & NY
Methane2 ppmAtmospheric air

Non-Fatal vs. Fatal CO Poisonings

Furnaces (non-vehicular)19
Thus, for every CO death due to a malfunctioning furnace, there are 20 non-fatal CO poisonings.
Estimates Based on Statistical Data: 2
5,700 – 10,000 people seen in emergency rooms for suspected CO poisoning, 1992-94.
200 CO-related fatalities during same period.
7850 / 200 = 39.25
Thus, for every CO death, this suggests there are 39.25 people who present to the ER for CO poisoning. How many more people with CO poisoning don’t go to the ER, and thus are not found in the record?

Symptoms of Occult CO Poisoning

  • Headache
  • Fatigue
  • Dizziness
  • Paresthesias
  • Chest pains
  • Palpitations
  • Visual Disturbances
  • Occult – “hidden from view, secret, concealed”. Most chronic CO poisoning is of this type, at least at first.
  • Paresthesias – “abnormal or morbid sensation, as with burning, prickling, etc., but without objective symptoms.

Subjective Symptoms

SymptomFrequency %
Sleep Disturbances66
Cardiac Symptoms62
Nausea, vomiting42
Memory Disturbances40
Reduced Libido22
Loss of Appetite17
From: Jain, K.K. (1990) Carbon Monoxide Poisoning, Warren H. Green, Inc., St. Louis, MO
Chronic CO poisoning often masquerades as lethargy, listlessness, lack of motivation, sleepiness, etc. and is often characterized as chronic fatigue syndrome, clinical depression, or an endocrine disorder. The changes are frequently subtle and only recognized as being related to CO exposure after a period of time. Recognition of CO involvement often only occurs by accident or by happen-stance and documentation of abnormally elevated CO in the air and blood is frequently not possible.

Characteristics of CO

  • Often goes long undetected
  • Masquerades as flu, fatigue, etc.
  • Often many people “sick” simultaneously
  • May go away upon leaving poisoning site (to work, on vacation, etc.)
  • Nearly always misdiagnosed by physicians
  • May involve pets “sick”, dead at same time
  • Rarely involves sinus congestion, cough (when present, it may be due to other compounds {eg., NOx, SO2} in exhaust gases)

Clues to Discovery

  • Lethargy, headache, etc. of long duration
  • Long-standing “illness” intractable to medical solutions
  • “Illness” that suddenly improves when leaving site
  • Multiple cases at one location
  • Morbidity / mortality of pets
  • CO alarm sounding, once or repeatedly
  • Presence of malfunctioning furnace, water heater, etc.

Differences From Acute Poisoning

may not elicit the typical symptoms of (acute) CO poisoning:
  • headache
  • nausea
  • weakness
  • dizziness
  • mucous membranes almost never cherry pink
COHb is usually not excessively elevated
CT and MRI generally not useful

Common Misdiagnosis 

  • Chronic fatigue syndrome
  • Viral or bacterial pulmonary or GI infection
  • “Run-down” condition
  • Endocrine problem
  • Immune deficiency
  • Psychiatric/psychosomatic problem
  • Allergies
  • Bad/tainted food

 Problems in Dealing With Chronic CO Poisoning

  • Fact of exposure usually recognized only later
  • Good COHb level measurements usually not obtained
  • Air CO level measurements often not obtained
  • Residual effects commonly occur, but often subtle; thus usually unrecognized by physicians.
  • Less medical/scientific literature available than for acute CO poisoning
  • Seldom produces damage recognizable by high-tech scanning techniques (MRI, CT, SPECT)
  • Changes seen by neuropsychological testing usually most useful
  • Considerable variability of effects from one inpidual to the next

 Why is CO Poisoning Not Better Recognized by the Medical Profession?

  • It almost invariably presents with too many disparate, seemingly unrelated and often non-specific symptoms. This tends to confuse physicians who act mainly on pattern recognition of one or a few symptoms to come up with a probable diagnosis, or at least a “short list”. The result of being presented with 5, 10, 15 or more symptoms is likely to yield a diagnosis of hypochondriasis (faking), psychiatric condition, or both.
  • Presentation in urgent care settings is such that it usually appears not to require emergency measures – absence of unconsciousness, no obvious provoking agent, low or normal COHb values, skin/mucous membranes not pink, etc.
  • It has been difficult to study in animal models because rats, mice, etc. are far more resistant to CO than humans, and also are unable to report the many psychological, cognitive and emotional changes that result. Thus we have little understanding the underlying cellular mechanisms at play.
  • Lack of training in the area, thus a low index of suspicion for the condition and the resultant shockingly high rate of misdiagnosis.

 Long Term Effects (Based on CO Support Data)

  • Tiredness, weakness
  • Pains, cramps
  • Headaches
  • Nausea, sickness
  • Loss of Concentration
  • Dizziness
  • Digestive Problems
  • Cardiac Problems
  • Flu Symptoms
  • Difficulty Breathing
  • Pins & Needles, Stiffness
  • Vision Problems
  • Memory Loss
  • Personality, Emotional Problems
  • Sleep Disturbance
  • Mouth/Throat Problems
  • Unable to Walk / Work
  • Clumsiness
  • Hallucinations, Zombie-like State
  • Depression
  • Panic Attacks
  • Loss of Hearing
  • Trembling

Furnace Concerns – U.K. vs. U.S.

Chronic carbon monoxide problems are potentially worse in the U.K. than in the USA, because of the many very old buildings and the past and present construction approach which consists of building solid walls, floors and ceilings. This usually precludes the use of ducted forced air heating/cooling. Instead, building are fitted with “gas fires”, ie. gas heaters that are usually located in old fireplaces, exhausting into the fireplace chimney.

Problems with Gas Fires/Fireplaces

  • Most use air from within living space for combustion
  • Inadequate installation / maintenance
  • Possible exposure of inhabitants to heat, flame and fumes
  • Possible leakage of unburned heating gas into living space

Other Specific Problems With Gas Fires

  • Chimney outlet too low
  • Cold chimney, leading to water condensation, then rusting of metal parts
  • Exhaust fan creating negative pressure in living / combustion space
  • Unusual geography near chimney
  • Wind conditions around chimney
  • Doors/windows open, additions to structure

Exhaust Gas Removal

  • Leakage of fumes from flue – masonry/metal/plastic (lined/unlined)
  • Partial/complete blockage of flue – cement, condensates, birds nests, etc.
  • Age of fire/furnace, flue and chimney

Hypothetical Case Report

Mrs. Betty Jones is a 35 year old homemaker. She and her husband George, 37 years old, live in a city in the mid-west. She has an Associates degree in accounting, while her husband has a Masters degree in Business Administration. Neither of them are smokers.
In early 1995, they purchased a home in a suburban community through a real estate brokerage company. The home was built in 1958. It was inspected and major appliances in the home were guaranteed for 5 years. The home has three bedrooms, a living room, family room and a glassed in back porch. It is heated by a forced-air, natural gas furnace in the basement. Hot water is provided by a gas-fired water heater, also in the basement.
Beginning in the autumn of 1995, Betty Jones began having headaches and feeling very tired. Her two children, John (12 years of age) and Cathy (9 years of age), and her husband George occasionally awoke in the morning with headaches, dizziness, and nausea. They believed that they all had a touch of “flu” or had eaten tainted food.
Mrs. Jones continued to feel “out of it” for the remainder of 1995 and into the spring of 1996. Her physician, Dr. Blackstone, gave her a “physical”, obtaining chest X-rays, blood for complete CBC, and samples for a Pap smear test. He found nothing wrong, saying that “flu” has been going around. A furnace company who regularly serviced the heating system found “everything in good working order.”
During the summer of 1996, Betty Jones and the whole family felt much better, although she and the children continued to have frequent headaches and to feel slightly fatigued. They felt better when they went away for vacation for two weeks.
In late October, 1996, Betty Jones again began to have frequent severe headaches and to become extremely fatigued. She was becoming so lethargic that she could not accomplish her normal housework. She was forgetting tasks that needed doing, and finding it increasingly difficult to maintain the family checkbook. She was also feeling depressed and defeated in her daily life.
On several visits to Dr. Blackstone she was told that there was nothing wrong with her. He said her perceived state was psychosomatic, and that she should seek counseling or schedule regular visits with a psychiatrist.
By spring 1997, the Jones’ children John and Cathy, previously excellent students, were on academic probation at school. John, a 7th grader, was in danger of failing and being held back a year. Cathy was now getting C’s and D’s in her classes in elementary school and her teachers were concerned. Mr. Jones, who all his life had been an ambitious and successful employee at a national insurance company, believed he now was in danger of being fired.
To gain extra space in their modest 1300 square foot home, the Jones family contracted to have a fourth bedroom added during the summer of 1997. Because the old furnace in the home was the original unit and would not be adequate to heat the new larger house, the contractor installed a new one. In doing so, he discovered that the heat exchanger in the old furnace was badly rusted through, that the near horizontal run of flue pipe to the chimney was also rusted through, and that the old brick chimney was oversize, unlined, and partially blocked near the top.
Upon learning of these problems, Mr. Jones asked that the old furnace be fired up and measurements of CO made by the gas company. He had recently seen a program on TV about the dangers of CO and wanted to be sure. With the family safely outside, CO levels in the house were observed to attain 176 ppm after one hour. The whole family then went to see Dr. Blackstone, who drew blood for the measurement of carboxyhemoglobin. COHb levels came back at between 0.5% and 1.4%. The physician, not familiar with the effects of the gas, told them that since the CO was now out of their bodies, they would be well again.
Mrs. Jones continued to suffer from severe headaches, fatigue, depression, and irritability. She also continued to have cognitive and memory problems, and began to develop muscle and joint pain, to hear a buzzing sound in her head (Tinnitus), and to have various visual problems. Mr. Jones continued to find it difficult to do his job. He could not make decisions (loss of executive functioning) and lost track of details in his work. The children continued to struggle academically and socially – cognitive testing at school suggested recent significant declines in I.Q. in both children.
As of early 1999, the Jones family is attempting to recover from the health problems caused by their old, leaking furnace. They have been seen by a number of health professionals with varying results: neurologists, toxicologists, and neuropsychologists. To the Jones’, it appears that few people in the medical community have much understanding of the long-term health effects of chronic CO exposure. They have retained legal counsel and are discussing options which might lead to compensation from responsible parties. Fortuitously, they have kept the old furnace, flue and other parts as evidence.

What Important Points does this Case Illustrate?

  • Have a thorough inspection when you buy a house, especially an older house.
  • The multiple symptoms reported (headache, dizziness, nausea) should have increased suspicion of CO poisoning.
  • Similar symptoms in several people should also increase suspicion of CO poisoning.
  • A CO detector should have been purchased and installed in home.
  • The physician should have been strongly encouraged to promptly order COHb tests.
  • Furnace and “gas” inspectors should always test for CO.
  • Fatigue and lethargy combined with headache are strong indicators of CO presence.
  • If you can’t get satisfaction with one physician, see another – a G.P. or a specialist with experience in CO poisoning.
  • While the leaking furnace, flue ducts and faulty chimney were discovered by chance, Mr. Jones did the right thing to immediately have the house tested for CO.
  • Blood samples for COHb measurement were taken way too late, ie. they must be done within 2-4 hrs. after leaving the site of the poisoning).
  • The residual effects elicited by all members of the Jones family are consistent with chronic CO poisoning.
  • The health effects of the CO poisoning continue at least 1-1/2 years after the CO poisoning was discovered/ended.
  • Mr. Jones was wise to have kept the faulty furnace, flues, and other parts, should legal action be necessary.

Carbon Monoxide Alarms

What they can and cannot do

  • CAN – sense unacceptable levels of CO in the air
  • CAN – provide early warning, before a healthy adult might show symptoms
  • CAN – act as round-the-clock monitor of CO
  • CAN – only sense CO that reaches it – Where you hang a detector is important
  • CAN – breakdown like any other electronic device
  • CANNOT – work without electrical power (batteries, AC)
  • CANNOT – sense smoke, natural gas, propane, etc. (It is not a smoke detector!)

Where to put (or not put) your detector

  • PUT – near a bedroom, or other room where people spend most of their time; where its alarm can be heard.
  • READ the instructions that come with your Detector.
  • DO NOT PUT – in garage, furnace room, near cooking stove, etc.
  • DO NOT PUT – in dead air space, corner of room, near floor, in peak of vaulted ceiling.
  • DO NOT PUT – near open windows or doors.
  • DO NOT PUT – in excessively hot or cold areas, or excessively damp or dry areas.
  • DO NOT PUT – a cloth or plastic cover over the detector.
-Used with permission from the author David G. Penney, PH.D

Carbon Monoxide Fact Sheet

Consumer Protection Safety Commission Document #4466

The Hazard

What is carbon monoxide (CO) and how is it produced in the home?
CO is a colorless, odorless, toxic gas. It is produced by the incomplete combustion of solid, liquid and gaseous fuels. Appliances fueled with gas, oil, kerosene, or wood may produce CO. If such appliances ar not installed, maintained, and used properly, CO may accumulate to dangerous levels.
What are the symptoms of CO poisoning and why are these symptoms particularly dangerous?
Breathing CO causes symptoms such as headaches, dizziness, and weakness in healthy people. CO also causes sleepiness, nausea, vomiting, confusion and disorientation. At very high levels, it causes loss of consciousness and death.
This is particularly dangerous because CO effects often are not recognized. CO is odorless and some of the symptoms of CO poisoning are similar to the flu or other common illnesses.
Are some people more affected by exposure to CO than others?
CO exposures especially affect unborn babies, infants, and people with anemia or a history of heart disease. Breathing low levels of the chemical can cause fatigue and increase chest pain in people with chronic heart disease.

The Data

How many people die from CO poisoning each year?
In 1989, the most recent year for which statistics are available, thee were about 220 deaths from CO poisoning associated with gas-fired appliances, about 30 CO deaths associated with solid-fueled appliances (including charcoal grills), and about 45 CO deaths associated with liquid- fueled heaters.
How many people are poisoned from CO each year?
Nearly 5,000 people in the United States are treated in hospital emergency rooms for CO poisoning; this number is believed to be an underestimate because many people with CO symptoms mistake the symptoms for the flu or are misdiagnosed and never get treated.

 CO Prevention

How can production of dangerous levels of CO be prevented?
Dangerous levels of CO can be prevented by proper appliance maintenance, installation, and use: :


A qualified service technician should check your home’s central and room heating appliances (including water heaters and gas dryers) annually. The technician should look at the electrical and mechanical components of appliances, such as thermostat controls and automatic safety devices.
  • Chimneys and flues should be checked for blockages, corrosion, and loose connections.
  • Individual appliances should be serviced regularly. Kerosene and gas space heaters (vented and unvented) should be cleaned and inspected to insure proper operation.
  • CPSC recommends finding a reputable service company in the phone book or asking your utility company to suggest a qualified service technician.


Proper installation is critical to the safe operation of combustion appliances. All new appliances have installation instructions that should be followed exactly. Local building codes should be followed as well.
  • Vented appliances should be vented properly, according to manufacturer’s instructions.
  • Adequate combustion air should be provided to assure complete combustion.
  • All combustion appliances should be installed by professionals.

Appliance Use

Follow manufacturer’s directions for safe operation.
    • Make sure the room where an unvented gas or kerosene space heater is used is well ventilated; doors leading to another room should be open to insure proper ventilation.
    • Never use an unvented combustion heater overnight or in a room where you are sleeping.
Are there signs that might indicate improper appliance operation?
Yes, these are:
  • Decreasing hot water supply
  • Furnace unable to heat house or runs constantly
  • Sooting, especially on appliances
  • Unfamiliar or burning odor
  • Increased condensation inside windows
Are there visible signs that might indicate a CO problem?
Yes, these are:
  • Improper connections on vents and chimneys
  • Visible rust or stains on vents and chimneys
  • An appliance that makes unusual sounds or emits an unusual smell
  • An appliance that keeps shutting off (Many new appliances have safety components attached that prevent operation if an unsafe condition exists. If an appliance stops operating, it may be because a safety device is preventing a dangerous condition. Therefore, don’t try to operate an appliance that keeps shutting off; call a service person instead.)

Are there other ways to prevent CO poisoning?

Yes, these are:
  • Never use a range or oven to heat the living areas of the home
  • Never use a charcoal grill or hibachi in the home
  • Never keep a car running in an attached garage

CO Detection

Can CO be detected?
Yes, CO can be detected with CO detectors that meet the requirements of Underwriters Laboratories (UL) standard 2034.
Since the toxic effect of CO is dependent upon both CO concentration and length of exposure, long-term exposure to a low concentration can produce effects similar to short term exposure to a high concentration.
Detectors that meet the UL standard measure both high CO concentrations over short periods of time and low CO concentrations over long periods of time. The effects of CO can be cumulative over time
Detectors sound an alarm before the level of CO in a person’s blood would become crippling
Detectors that meet the UL 2034 standard currently cost between $35 and $80.

Where should the detector be installed?

CO gases distribute evenly and fairly quickly throughout the house; therefore, a CO detector should be installed on the wall or ceiling in sleeping area/s but outside individual bedrooms to alert occupants who are sleeping.
Aren’t there safety devices already on some appliances? And if so, why is a CO detector needed?
Vent safety shut-off systems have been required on furnaces and vented heaters sine the late 1980s. They protect against blocked or disconnected vents or chimneys.
Oxygen depletion sensors (ODS) have also been installed on unvented gas space heaters since the 1980s. ODS protect against the production of CO caused by insufficient oxygen for proper combustion.
These devices (ODSs and vent safety shut-off systems) are not a substitute for regular professional servicing, and many older, potentially CO-producing appliances may not have such devices. Therefore, a CO detector is still important in any home as another line of defense.
Are there other CO detectors that are less expensive?
There are inexpensive cardboard or plastic detectors that change color and do not sound an alarm and have a limited useful life. They require the occupant to look at the device to determine if CO is present. CO concentrations can build up rapidly while occupants are asleep, and these devices would not sound an alarm to wake them.

Consumer Protection Safety Commission’s Role

  • CPSC worked closely with UL to develop a safety standard for CO detectors (UL 2034).
  • CPSC embarked on an extensive public awareness campaign in 1993 to reach consumers and educate them about CO through the media. Activities included a message from President Clinton declaring the last week of September “CO Safety Awareness Week.” CPSC also developed stories for television, radio, and newspapers, as well as brochures and posters for consumers.
  • CPSC is proposing that the national model building code organizations include a provision for the installation of state of the art CO detectors in all new residential construction. The proposal calls for installation in sleeping areas, but outside individual bedrooms.
  • Under CPSC’s proposal, battery-operated units would be allowed only in existing homes, not new construction. Even homes with no permanently-installed fuel-burning appliances would have to install them because CO deaths have been associated with the use of portable kerosene heaters, wood-burning stoves, charcoal grills wrongly used indoors, and auto fumes from an attached garage.
  • CPSC staff is working with state and local code jurisdictions to incorporate CO detector requirements into state and local legislation.
  • CPSC is working with the National Fire Protection Association to develop a national installation standard.

CO Detector Requirements in the U.S.

  • On September 15, 1993, Chicago, IL became one of the first cities in the nation to adopt an ordinance requiring the installation of CO detectors that bear the mark of a nationally-recognized testing laboratory in all new single-family homes and in existing single-family residences that are being equipped with new oil or gas combustion furnaces.
  • Kingston, NY has approved a code to require the installation of CO detectors in multiple dwellings with four or more dwelling units.
  • Bel Air, TX requires CO detectors in some single-family dwellings.
  • The Recreational Vehicle Industry Association (RVIA) requires CO detectors in motor homes made after September 1, 1993. RVIA requires CO detectors in all recreational vehicles that are motorized and in towable recreational vehicles that have a generator or are prepped for a generator. RVIA’s membership includes approximately 90% of all U.S. recreational vehicle manufacturers.

Carbon Monoxide is Not Well Understood


Properties, Presence & Detection:

  • CO is easy to detect.
  • CO is lighter than air and therefore rises (to the ceiling) and stays there.
  • CO is not combustible.
  • CO and natural gas are the same thing.
  • You can always tell if CO is present because of a peculiar odor that will be present.
  • A brand new, well designed, perfectly “tuned” heating/cooking device cannot produce toxic/lethal amounts of CO.
  • Diesel engine exhaust never contains adequate CO to cause harm.
  • HVAC and gas company personnel always check for CO when performing maintenance/service on home heating systems.
  • CO will be detected immediately by service personnel if it is present in a home heating system.
  • When your home CO detector shows low levels of CO, it is probably just an instrument malfunction.
  • Cracks in heat exchangers are responsible for production of CO.
  • Home CO detectors/sensors are the best devices to ferret out CO because they react to very low levels of the gas.

More Misconceptions


  • CO binding to hemoglobin is irreversible.
  • CO (caused) hypoxia is no more serious than any other type of hypoxia.
  • CO poisoning is no more serious than an anemia in which there is a comparable amount of hemoglobin able to carry oxygen.
  • Small animals (birds, mice, etc.) die more quickly because their hemoglobin binds CO more avidly than that of humans, thus they were used as alarms for CO in mines.
  • The fetus is protected from CO by the maternal body.
  • Good COHb measurements can be obtained one day to a week after a person leaves the site of the CO poisoning.
  • Breathing “clean” air for 2-3 hours will eliminate all CO from the body.
  • Breathing 100% oxygen for 20-30 minutes will eliminate all CO from the body.
  • Breathing (filter) masks protect the wearer from inhalation of CO.

More Misconceptions


  • The skin, nail beds, etc. of people with CO poisoning are invariably red or pink in color.
  • Fever is a symptom of CO poisoning.
  • Nasal congestion, cough and hoarseness are symptoms of CO.
  • The lungs are inflammed by low to moderate levels of CO and will show pathology on X-rays.
  • Symptom clusters involving prolonged headache, dizziness, nausea, and fatigue of the whole family should be blamed on viruses, bad food, or group craziness.
  • Everyone responds to CO in the same way, ie. show the same symptoms.

Even More Misconceptions

Treatment, Outcome

  • Inhalation of 100% oxygen from a re-breathing mask or from nasal prongs are recommended best immediate means of removing CO from the body.
  • Victims of CO poisoning should be released from medical care immediately following 1-2 hours of oxygen treatment, whether or not their symptoms have disappeared.
  • There is no need for repeat COHb measurements, psychometric tests, or other clinical tests following medical treatment for CO poisoning.
  • People who recover from CO poisoning are always completely normal.
  • Depression and personality change never result from CO poisoning.
  • CO exposure never produces brain damage unless there is a period of unconsciousness.
  • Low / moderate CO exposure cannot produce brain damage or significant changes in functional performance.
  • In environments containing CO, the levels of CO2, oxygen and other gases are unimportant in the degree of poisoning.


  • Physicians receive adequate training in the diagnosis and treatment of CO poisoning in medical school.
  • Physicians obtain adequate experience with CO poisoning in treating their patients.
  • Psychiatrists and neurologists are the best medical professionals of choice to determine the extent of CNS damage caused by CO.
  • High-tech imaging devices (CT, MR, SPECT) always shows areas of brain damage from CO poisoning, if it exists.
-Used with permission from the author David G. Penney, PH.D

Steps to Carbon Monoxide Production

The most common carbon monoxide (CO) problems involve a lack of oxygen – either because there is simply not enough, or because the flames cool off before the carbon can join with it. CO is produced whenever a fuel is burned without enough oxygen on hand. Carbon atoms in the fuel that normally join up with two oxygen atoms to form carbon dioxide, which is harmless to human health, end up with only one oxygen atom and instead form CO.

Basic Steps to Getting CO Into Your Life

It is not enough to understand how to create CO, we need to examine all of the coordinating factors which can create it and allow it into the living space.
Five basic factors not only lead to the production of CO, but will aid in getting it into your homes. Any one major failure can get CO into your home, but typically three of these factors must go awry to produce a major problem.

The Flow of Fuel

As you add fuel to a fire, the fire produces more Btus of heat. It also requires more oxygen to combine with the carbon and hydrogen to form carbon dioxide and water vapor (H2O. As you continue to add fuel, the amount of available oxygen needs to keep up or CO will be produced, which is incompletely burned carbon. In engineered systems (all modern combustion appliances) the amount of air that can move through the unit is limited by the design. Any additional restriction (dirt, lint, carbon) will result in the air flow being reduced. The air flow is controlled by the laws of nature (hot air rises). The flow of fuel is controlled by the pressure applied to the fuel and the size of the hole it is forced through. Any problem with the pressure of fuel input can lead to problems with the fuel/air mixture.

Competition for Air

We refer to many kinds of air when describing a standard combustion appliance (combustion air, primary air, secondary air, dilution air, return air, supply air, and so on). Air, or more precisely the oxygen in the air, is fundamental to the combustion process. The amount of air than can come into standard appliances is typically controlled by two basic systems. First is the mix of gas and air before combustion (primary air). This is controlled by the design of the burner, the pressure of the gas, and any control of the air stream. The secondary air, or additional air that is needed to supply oxygen to the flames, is simply controlled by the amount of air that is drawn through the heat exchanger.
In order for these two simple systems at the appliance to supply adequate oxygen for complete combustion, there needs to be sufficient air to the area around the appliance. Any competition for the air needed for the combustion process can lead to problems. The power of the competition does not need to be strong to overcome the natural forces of the combustion appliance.

Venting: The Wild Card

Getting all of the combustion products out of the living space, a matter of indoor air quality, is fundamental to the safety of our clients. Codes and venting systems are designed to ensure this happens. In the cases that combustion appliances are unvented (they vent into the living space), there are specific directions for additional ventilation needs (like opening a window).
Venting can be a wild card due to its relationship to both the weather and the physical configuration, time of year, time of day, connection with other appliances, connection with the house, and so on. All of these relationships can have a dramatic effect on the draft of an appliance. The fundamental principle is that hot air rises. We can thus figure out how much area in the vent is needed to get all the combustion products out of the building. These rules may not always result in successful venting in actual buildings. Only testing can provide an indication of the operation.


The operations of the appliance can be broken down into two components: those defined primarily by the internal controls of the unit and those dictated by the occupant. We have found many units where the appliance is not able to operate correctly and that just happened to keep the unit from being a major liability to health and safety. Changing any portion of the operation may affect safety. This includes adjusting the distribution, air tightness of the unit, ductwork, load/insulation, not to mention touching the unit itself. The client’s operation of the unit can also affect safety.

Luck (Or Lack of)

Luck is the final card. It is the random combination of the first four factors and other things that affect the building. Simple things like unclogging a dryer vent, fixing a bath fan, repairing ducts, or insulating walls, can change the operating patterns of the combustion devices.

How it Happens

In addition to the five basic components, we have seen significant patterns in the creation of CO.
Very few HVAC installers have the equipment necessary to ensure a safe installation of a combustion appliance is completed. Many units create CO because of improper setup and testing. Problems with gas pressure, orifice size, and improper venting are the most common.


Remodeling a building often involves adding walls and changing the combustion air location and source availability. At Sun Power we have seen new house designs which virtually ensure that the combustion air source will be eliminated. In addition to limiting the combustion air, remodeling typically increases the pollution in the area of the combustion devices (for instance installing a dryer in a small room with the furnace).

Deterioration and Proper Installation

Long-term deterioration of an appliance is not a common factor leading to CO production. However, deterioration is a common problem with units that were marginally installed: vents with long horizontal runs may have just met standards when they were installed but are prone to rust out over time. Venting into an unlined chimney can lead to problems (erosion of the chimney can eventually lead to leaks). Dirt from a crawlspace can fall down and block the combustion air hoes in a water heater. Even crawlspace furnaces stay fairly trouble-free unless major contaminants are introduced into the area. Dryers and water are the chief causes, but rust and lint are good at blocking everything.
CO can be drastically reduced in the home if the units are installed correctly in a dedicated area which is not connected to the living space. This requires a room for the combustion appliances that is vented with outside combustion air (or sealed combustion units) and has sealed ductwork.
-Rob deKieffer

Symptoms and Management of CO Poisoning

Common Symptoms
Making a diagnosis of CO poisoning is crucial, as acute high level CO poisoning can be fatal in just a few minutes. The symptoms are usually multiple, many are non-specific, and some are vague. They can involve many of the body systems. Please be aware that the symptom list below is not complete and that they often do not follow this rank ordering at presentation. Moreover, many of the more severe symptoms (eg. below ataxia) are only seen with acute high level CO exposure.

Symptoms in Order of Increasing Severity of CO Poisoning

  • Headache
  • Dizziness on exertion
  • Fatigue, weakness
  • Palpitations
  • Nausea, vomiting
  • Dyspnea on exertion
  • Cutaneous vessel dilation
  • Mental Confusion, difficulty with thinking
  • Fine manual dexterity abnormal
  • Tachycardia
  • Visual disturbances
  • Hallucinations, confusion
  • Ataxia
  • Retinal hemorrhages
  • Syncope, collapse
  • Tachypnea (increased ventilation), further tachycardia
  • Lactic acidosis
  • Hypothermia
  • Cheyne Stokes ventilation
  • Coma, convulsions
  • Hypotension
  • Cardiac and ventilatory depression
  • Cardiorespiratory failure (death)

Making the Diagnosis

Making a diagnosis of CO poisoning is crucial, since the condition can be fatal in just a few minutes. The symptoms are widely varied, many are non-specific, and can involve many body systems.
Victims often believe, or are led to believe, that they are have the “flu”, gastroenteritis, etc. CO poisoning is very often misdiagnosed clinically as:
  • Psychiatric illness
  • Migraine
  • Stroke
  • Drunkeness
  • Heart disease
  • Food poisoning

There are clues that signal the likelihood of CO poisoning:

  • If everyone in the family suddenly becomes ill with some of the above symptoms.
  • If the victim is in a situation where he or she may be exposed to high CO levels.
  • If symptoms are relieved when the victim moves to a different location / into fresh air.
As a noted emergency room physician has said, “the standard of care for carbon monoxide poisoning may well be misdiagnosis

Table of Commonly Seen Symptoms

The following is a list of symptoms which have been applied mainly to acute CO poisoning. Many sources suggest they can be closely related to blood COHb level. Please note that in practice, severity of symptoms DO NOT correlate well with COHb level. Thus, any conclusions about COHb from symptoms, or vice versa, should be drawn with the greatest caution!
  • No obvious symptoms
  • Decreased tolerance for exercise in persons with existing pulmonary disease
  • Decreased angina threshold
  • Decreased threshold for visual stimuli
  • Headaches
  • Dizziness
  • Confusion
  • Decreased visual acuity
  • Severe headache
  • Nausea
  • Dizziness
  • Increased respiration
  • Irritability
  • Impaired judgement
  • Visual disturbance
  • Vomiting
  • Decreased awareness
  • Cardiac irregularities
  • Muscle weakness
  • Fainting
  • Convulsions
  • Paralysis
  • Coma
  • Usually death in a few minutes
70% -and up
  • Immediately fatal

Lesions Resulting From CO Poisoning

Acute- Cerebral edema and hemorrhages
Chronic- Necrotic lesions in basal ganglia and demyelination
Acute- Myocardial necrosis 
Chronic- Myocardial infarcts
Primary- Pulmonary edema 
Secondary- Aspiration pneumonia in comatose patients
Lobar necrosis with chronic repeated exposure
Parenchymatous degeneration leading to necrosis
Intramuscular hemorrhages, swelling, and rhabdomyolysis
Marrow hypertrophy in chronic CO-hypoxia
Erythema, blisters, and gangrene

A Classification of Carbon Monoxide Poisoning Based on Clinical Features

Clinical Degree of IntoxicationSymptoms
I – MildHeadache, vomiting, tachycardia, no disturbances of consciousness
II – ModerateDisturbances or loss of consciousness without other neurological symptoms, tachycardia, nocioceptive reflexes still intact
III – SevereLoss of consciousness, intense muscular tonus, pathological neurological symptoms, tachycardia and tachypnea, circulatory and respiratory disturbances not observed
IV – Very SevereLoss of consciousness, clinical signs of central nervous system damage, circulatory and respiratory disturbances
Comment: Many many different classifications of severity of CO poisoning are in existence. Just as COHb level does not correlate well with short-term symptomatology or with the longterm effects, the symptoms and effects of CO poisoning do not fit easily into discrete classes as the above suggests. This table is presented as just one possible approach to classification of the effects of CO poisoning, but not necessarily one embraced by the website writer.

Diagnostic Tests that may be Useful in CO Poisoning

  • Carboxyhemoglobin Saturation
  • other Arterial blood gases and pH
  • Complete blood count
  • Serum glucose and lactic acid concentration
  • Serum electrolytes, and urea nitrogen and creatinine concentrations
  • Urine analysis
  • Electrocardiogram and echocardiogram
  • Chest X-ray
  • Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities
  • Serum aspartate and alanine transferase (SGOT, SGPT) activities
  • Serum myoglobin concentration
  • Neuropsychologic screening test
  • Drug screening
  • Electroencephalogram.
  • Cerebral computed tomography
Note: With the exception of neuropsychologic evaluation, most of the above tests are usually only of value in acute, higher-level CO poisoning. In such instances, the first eight tests should be done as quickly as possible after presentation.

What to Do About CO Poisoning

In the early days of mining, caged canaries were hung in the tunnels. The birds, being so small, were especially susceptible to poisonous gases because of their high metabolism and ventilation rate. If the bird died, it was an alarm telling the miners get out of the mine. Now electronic CO detectors are available for the home.
It is best to avoid exposure to sources of CO
  • Make sure fuel-burning equipment is working correctly and is properly exhausted. This includes furnaces, hot water heaters, and propane and gasoline powered vehicles used indoors.
  • Stop smoking.
  • Don’t leave your car running in the garage, especially if it is attached to your house. It could poison you in the car, and CO could get into the house and afflict others.
  • If you are in heavy traffic, keep your windows rolled up. This is especially true if you are caught in traffic in an enclosed space like a tunnel.

Management of CO Poisoning – Quick Points

  • Remove victim from the site of CO exposure
  • oxygen immediately – If possible take a blood sample for COHb before this is done
  • Use endotracheal intubation in comatose patients to facilitate ventilation
  • Remove the patient to a hyperbaric facility when indicated (if at all possible)
  • Keep the patient calm and avoid physical exertion by the patient
  • Manage complications: e.g. electrolyte imbalance, brain edema, cardiac arrhythmias

Guidelines for Management

  • Remove patient from the site of CO exposure
  • Immediately administer high-flow, 100% oxygen through a tight-fitting mask
  • If possible take a blood sample for COHb before O2 is given
  • Consider endotracheal intubation to facilitate ventilation in comatose patients
  • In cases of severe poisoning, or in presence of unconsciousness or neurological signs, treat with hyperbaric oxygen
  • Keep patient calm to reduce metabolic rate and oxygen consumption and avoid physical exertion by the patient; insulate body and warm, if hypothermic
  • Look for signs of cardiovascular and neuropsychiatric dysfunction
  • Manage complications: e.g. electrolyte imbalance, cardiac arrhythmias
  • Consider supporting cardiovascular function with inotropes, anti-arrhythmics, etc.
  • Consider treating cerebral edema with hyperosmotics such as mannitol, and with steroids, to lower intracranial pressure and restore brain blood flow
  • Treat pregnant patients more aggressively, even those with moderate CO poisoning
  • Comatose patients who survive may show immediate or delayed neuropsychiatric deficits; hyperbaric oxygen therapy decreases the incidence of both types of sequelae
  • Survivors should avoid exertion for 3-6 weeks after severe poisoning

Allowable (Legal) Limits for Carbon Monoxide

Occupational Safety & Health Administration, USA (OSHA) (for industrial situations) –

Permissible Exposure Limit (PEL, by TWA) – 50 ppm, 8 hrs. 
Old PEL Standard (by TWA) – 35 ppm, 8 hrs. 
Threshold Limit Value (TLV, by TWA) – 25 ppm (29 mg/cu. m) 
(recommended by American Conference of Governmental & Industrial Hygienists ACGIH) 
Ceiling (max. value, 15 min.) – 200 ppm (229 mg/cu. m)

MI Occupational Safety & Health Administration (MIOSHA) –

PEL (Industry, by TWA) – 35 ppm, 8 hrs. (38.5 mg/cu. m) 
PEL (Construction, by TWA) – 50 ppm, 8 hrs. (55 mg/cu. m) 
Ceiling (max. value) – 200 ppm (229 mg/cu. m)

Environmental Protection Agency, USA (EPA) –

Domestic, outdoor air, all ages (TWA) – 9 ppm*, 8 hrs. 
Domestic, outdoor air, all ages (TWA) – 35 ppm, 1 hr.

World Health Organization (WHO) –

Domestic, outdoor air, all ages (TWA) – 9 ppm*, 8 hrs.

American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) –

Indoor air (leakage at a heat register) – 9 ppm

American Gas Association –

Indoor air (leakage at a heat register) – 15 pm
-TWA – Computed by making measurements at intervals over 8 hours, then adding the sums of the concentrations and the intervals, and dividing by 8 hours (480 min.). * Based on several published studies of people with coronary ischemic disease showing ECG changes during moderate exercise when breathing concentrations of CO giving 3% COHb.

 History of Carbon Monoxide

  • “Coal fumes lead to heavy head and death” – First mention of the lethal effects of coal fumes — Aristotle, Greece, 3rd century B.C.
  • Inhabitants of Nuceria killed by CO suffocation in the bath — Hannibal, Carthage, 247-183 B.C.
  • Coal fumes were used for suicide and execution — Cicero, Rome, 106-43 B.C.; suicide of Roman author Seneca, 65 A.D.
  • A combustible gas that burned with a bright blue flame described — Joseph Priestley, England, 1772
  • First clinical description of coal gas poisoning — Harmant, France, 1775
  • CO identified as the toxic substance in coal gas — LeBlanc, France, 1842
  • Shown that CO produces hypoxia by reversible combination with hemoglobin — Claude Bernard, France, 1857
  • Demonstration that rats survive CO poisoning when placed in oxygen at 2 atmospheres pressure — John Scott Haldane, England, 1895
  • Polar explorer Richard Byrd nearly loses life as result of chronic CO poisoning — early 20th century
  • 611 CO-related deaths occur in New York City from use of illuminating gas — 1927
  • Treatment of CO poisoning with Hyperbaric Oxygen (HBO) in experimental animals — End & Long, U.S., 1942
  • First clinical use of HBO therapy in CO poisoning — Smith & Sharp, 1960
  • International tennis star Vitas Gerulaitus loses life in CO accident involving a pool heater, September, 1994
  • Use as euthanasia agent by medical suicide advocate, Jack Kevorkian, M.D. — 1990s
Note: It has been suggested based on his writings that the famous American author, Edgar Allan Poe, was chronically poisoned by carbon monoxide, probably contained in illuminating gas. Poe died November 17, 1875, 32 years of age.
-Used with permission from the author David G. Penney, PH.D.

Where Does Carbon Monoxide (CO) Come From?

CO is Produced when:

Carbonaceous materials are burned with insufficient oxygen. Its lethal effects have been known for centuries; in ancient Rome, “coal gas” was used for executions and suicides.

Man-made sources of CO include:

  • Incomplete fuel combustion used in transport –
  • Automobile/Truck exhaust
  • Airplane exhaust
  • Smoking of cigarettes, cigars, pipes, etc.
  • Defective heating (furnace, water heater) systems
  • Defective cooking appliances
  • Industrial plant exhausts
  • Burning of solid waste
  • Detonation of explosives

Natural sources of CO also exist but they contribute very little to the overall atmospheric CO level.


  • Marsh gases
  • Forest fires
  • Volcanic gases
  • Natural gases in coal mines
  • Photo-dissociation of CO in upper atmosphere
  • Formation of CO during electrical storms


  • Endogenous CO production by land animals
  • From vegetation during seed germination
  • From marine brown algae or kelp
  • Marine hydrozoans: e.g. jellyfish

Overheated Clothes Dryers Can Cause Fires

Consumer Product Safety Alert
The U.S. Consumer Product Safety Commission estimates that there are an estimated annual 15,500 fires, 10 deaths, and 310 injuries associated with clothes dryers. Some of these fires may occur when lint builds up in the filter or in the exhaust duct. Under certain conditions, when lint blocks the flow of air, excessive heat build-up may cause a fire in some dryers. To prevent fires:
  • Clean the lint filter regularly and make sure the dryer is operating properly. Clean the filter after each load of clothes. While the dryer is operating, check the outside exhaust to make sure exhaust air is escaping normally, If it is not, look inside both ends of the duct and remove any lint. If there are signs that the dryer is hotter than normal, this may be a sign that the dryer’s temperature control thermostat needs servicing.
  • Check the exhaust duct more often if you have a plastic, flexible duct. This type of duct is more apt to trap lint than ducting without ridges.
  • Closely follow manufacturers’ instructions for new installations. Most manufacturers that get their clothes dryers approved by Underwriters Laboratories specify the use of metal exhaust duct. If metal duct is not available at the retailer where the dryer was purchased, check other locations, such as hardware or builder supply stores. If you are having the dryer installed, insist upon metal duct unless the installer has verified that the manufacturer permits the use of plastic duct.
U.S. Consumer Product Safety Commission

Dryer Fire Fact Sheet

Statistics and Implications

  • Dryer exhaust fires now surpass creosote (chimney) fires in frequency on a national level. In 1998, the most recent statistics available, the Consumer Product Safety Commission reports that over 15,600 dryer fires occurred killing 20 people, injuring 370 more and causing over $75.4 million in property damage. According to the CPSC, in most of these cases the culprit was lint getting into the machine’s heating element, sparking and fueling a fire. In response to this growing trend, many dryer manufacturers now employ a device that shuts the appliance down when airflow is obstructed. However, these safeguards are subject to wear and have been known to fail. Not surprisingly, some fire departments and insurance companies now require that dryer vents be inspected and cleaned regularly.
  • With gas dryers, there is also concern of carbon monoxide (CO) poisoning. Since lint and flue gases use the same avenue of exit from the house, a blocked vent can cause CO fumes to back up into the house. These fumes are colorless and odorless and they can be fatal. Low-level CO poisoning mimics flu symptoms (without the fever): headache, weakness, nausea, disorientation and deep fatigue. At higher levels, occupants can fall asleep, lapse into a coma and die.

Anatomy of a Dryer Fire

Dryer fires usually start beneath the dryer when the motor overheats. Overheating is caused by a build-up of lint in the duct that increases the drying time and blocks the flow of air, just like cholesterol in your arteries can build up and block the flow of blood to your heart. Naturally, any lint that has collected under the dryer will burn and the draft from the dryer will pull that fire up into the duct. Since the duct is coated or even blocked with lint, many times a house fire results. Other contributing conditions may include failure of the thermostat and limit switches in the dryer, lint inside the dryer, a missing or damaged lint screen, a crushed hose behind the dryer, or a bird’s nest or other debris blocking the vent.

Higher Risk Situations

  • Residential dryer vent lengths may not have an equivalent length greater than 25 feet. Five additional feet for each 90-degree bend must be added to the actual physical length to compute the vent’s equivalent length. This will determine the vent’s actual resistance to the airflow.
  • Homes with larger families or where dryers are used heavily are at greater risk.
  • Flexible plastic duct is no longer code-approved for clothes dryers. It is normally one of the first things burning lint will ignite, having been shown to flame in as little as 12 seconds. Lower cost and high flexibility often make it attractive to unadvised homeowners installing their own machines.
  • Flexible duct made of thin foil is not recommended for clothes dryers. It’s tendency to “kink” and stop airflow makes it dangerous to use.

Warning Signs

  • Dryer is still producing heat, but taking longer and longer to dry clothes, especially towels and jeans.
  • Clothes are damp or hotter than usual at the end of the cycle.
  • Outdoor flapper on vent hood doesn’t open when dryer is on.

Additional Benefits to Dryer Vent Cleaning

  • Allows your dryer to operate more efficiently, using less energy and saving you money.
  • Protects your dryer from excess wear and premature death.
  • Helps clothes dry faster—a time savings for busy families.
  • Reduces excess household dust and humidity
  • Helps preserve clothing, as the life of many fabrics is damaged by excessive high heat.

Inspection Frequency

Most vents need cleaning every two to three years. Some dryer vents need attention more often. If it is the first time that a dryer vent has been cleaned, having it re-checked again in a year can help to make a reasonable judgment. Determining factors include:
  • How heavily the dryer is used
  • How long the vent is and the materials used. Shorter vents usually blow better.
  • The age and type of dryer used. Full size dryers blow better than smaller stack dryers or older dryers
  • The design of the vent. Those with a lot of turns and elbows blow worse and build up more lint.

Overheated Clothes Dryers Can Cause Fires

Consumer Product Safety Alert

The U.S. Consumer Product Safety Commission estimates that there are an estimated annual 15,500 fires, 10 deaths, and 310 injuries associated with clothes dryers. Some of these fires may occur when lint builds up in the filter or in the exhaust duct. Under certain conditions, when lint blocks the flow of air, excessive heat build-up may cause a fire in some dryers. To prevent fires:
  • Clean the lint filter regularly and make sure the dryer is operating properly. Clean the filter after each load of clothes. While the dryer is operating, check the outside exhaust to make sure exhaust air is escaping normally, If it is not, look inside both ends of the duct and remove any lint. If there are signs that the dryer is hotter than normal, this may be a sign that the dryer’s temperature control thermostat needs servicing.
  • Check the exhaust duct more often if you have a plastic, flexible duct. This type of duct is more apt to trap lint than ducting without ridges.
  • Closely follow manufacturers’ instructions for new installations. Most manufacturers that get their clothes dryers approved by Underwriters Laboratories specify the use of metal exhaust duct. If metal duct is not available at the retailer where the dryer was purchased, check other locations, such as hardware or builder supply stores. If you are having the dryer installed, insist upon metal duct unless the installer has verified that the manufacturer permits the use of plastic duct.

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