About Your House
The presence of carbon monoxide (CO) in our homes is
dangerous. So, how can you protect your family from carbon
monoxide? How do you choose the right CO detector for your
home? The first step is to make sure that carbon monoxide
never enters your home. The second step is to install at least
one CO detector in your home.
This About Your House answers often-asked questions
about carbon monoxide to help you make the right decision to
make your home safe.
What Is Carbon Monoxide?
Carbon monoxide (CO) is a colourless and odourless gas. It
is not explosive. Because you can't see, taste or smell it, it
can affect you or your family before you even know it's there.
Even at low levels of exposure, carbon monoxide can cause
serious health problems. CO is harmful because it will rapidly
accumulate in the blood, depleting the ability of blood to
carry oxygen. ( Exposure Guidelines for Residential Indoor Air
Quality, Health Canada, 1989).
Where Does Carbon Monoxide Come From?
Carbon monoxide is a common by-product of the combustion
(burning) of fossil fuels. Most fuel-burning equipment
(natural gas, propane and oil), if properly installed and
maintained, produces little CO. The by-products of combustion
are usually safely vented to the outside. However, if anything
disrupts the venting process (such as a bird's nest in the
chimney) or results in a shortage of oxygen to the burner, CO
production can quickly rise to dangerous levels.
The burning of wood, kerosene, coal and charcoal produce
CO. Gasoline engines produce CO. CO production is at a maximum
during the startup of a cold engine. Starting, then idling,
your car or gas mower in the garage can be dangerous.The fumes
that contain CO can enter a home through connecting walls or
doorways and can quickly rise to dangerous levels.
How can I eliminate sources of CO in my home?
The most important step you can take to eliminate the
possibility of CO poisoning is to ensure that CO never has an
opportunity to enter your home. This is your first line of
defence. Review this list to minimize the risk of CO in your
- Have a qualified technician inspect and clean
fuel-burning appliances yearly, before the cold weather sets
in, to ensure they are in good working order.
- Have a qualified technician inspect chimneys and vents
yearly for cracks, blockages (e.g., bird's nests, twigs, old
mortar), corrosion or holes.
- Check fireplaces for closed or blocked flues.
- Check with a qualified technician before enclosing
heating and hot water equipment in a smaller room, to ensure
there is adequate air for proper combustion.
- If you have a powerful kitchen exhaust fan or downdraft
cooktop, have a qualified technician check that its
operation does not pull fumes back down the chimney.
- Never use propane or natural gas stove tops or ovens to
heat your home.
- Never start a vehicle in a closed garage; open the
garage doors first. Pull the car out immediately onto the
driveway, then close the garage door to prevent exhaust
fumes from being drawn into the house.
- Do not use a remote automobile starter when the car is
in the garage; even if the garage doors are open carbon
monoxide will seep into the house.
- Never operate propane, natural gas or charcoal barbecue
grills indoors or in an attached garage.
- Avoid the use of a kerosene space heater indoors or in a
garage. If its use is unavoidable provide combustion air by
opening a window while operating. Refuel outside after the
unit has cooled.
- Never run a lawnmower, snowblower, or any
gasoline-powered tool such as a whipper-snipper or pressure
washer inside a garage or house.
- The use of fossil fuels for refrigeration, cooking,
heat, and light inside tents, trailers, and motorhomes can
be very dangerous. Be sure that all equipment is properly
vented to the outside and use electric or battery-powered
equipment where possible.
- Regularly clean the clothes dryer ductwork and outside
vent cover for blockages such as lint, snow, or overgrown
- Reduce or eliminate the use of fondue heaters indoors.
- If you live close to a road with heavy traffic, outdoor
carbon monoxide levels can affect your indoor air quality,
especially during rush hour. Such levels should not set off
a CO alarm, but slightly elevated CO levels might be
observable on some types of CO detectors with a digital
Carbon Monoxide detectors: Is one really
If you take the actions above, you greatly reduce your risk
of CO poisoning. But unanticipated dangerous incidents may
still occur despite your best efforts to avoid CO. The
installation of at least one CO detector in your home is a
good safety precaution and in some municipalities it is the
law. A detector might be your second line of defence, but it
is necessary. You should have one in your home today.
|How does a CO detector
There are three basic types of CO
sensors metal oxide, biomimetic and electrochemical.
Each is discussed in the chart below. Note that while
there may be performance differences between these
technologies, all detectors are tested and approved for
their operation.The retail cost of a detector will
generally relate to the number of features included and
its warranty conditions.
||Metal Oxide Semi-conductor (MOS)
|How does it work?
||The original technology for detecting CO. Heated tin
oxide reacts with CO to determine the levels of the
toxic gas. Must connect to house power.
||Gel-coated discs darken in the presence of
Colour change sounds an alarm.
|Chemical reaction with CO creates an electrical
current, setting off an alarm.|
||No need to remember to check batteries as the unit
Battery backup is available for up to 20
|- Less expensive technology.
- Can be battery
|- Highly sensitive and accurate readings at all CO
- Most units come with a continuous digital
readout and a memory feature that allows you to check
past CO levels.
- Fast reset time.
- Most units
sound an alert when sensor needs
There are performance differences between these detector
types. However, changes to the CO standards should soon result
in all detectors, regardless of detector type, having to
undergo extensive testing. All will be certified to operate
under different environments (various chemical exposures,
different relative humidities, etc.) satisfactorily if they
meet the standards.
What features should I look for when purchasing a CO
Most CO detectors are designed to give an alarm when CO
levels reach a high-level in a short time. However, health
agencies advise that long term, low-level exposure are also of
concern, especially for the unborn and young children, the
elderly and those with a history of heart or respiratory
problems (Health Canada, 1989). Detectors that can display
both high and low levels are more expensive but they do
provide greater accuracy and more information.
Here are some features to consider when purchasing a CO
- Look for a detector that is listed with the Underwriters
Laboratories of Canada (ULC) to the Canadian Gas Association
(CGA) or Canadian Standards Association (CSA) standard.The
logos of both testing agencies will be on the product.
- Choose a detector with a memory if you want to monitor
long term low-level exposure and short term, high-level
exposure. Even though product standards do not allow
manufacturers to display low levels of CO, these units
monitor and store this information. Peak levels, no matter
what the level of concentration, can be viewed by pressing a
- Battery-operated units allow detector placement in the
most convenient location. However, any battery-operated
device requires the user's diligence in replacing worn-out
- Do not connect plug-in units to an electrical outlet
that is controlled by a wall switch.
- No detectors will operate properly forever. Replace them
at least every five years, unless the manufacturer specifies
a shorter or longer life. Eventually, manufacturers may be
required to print expiry dates on their CO detectors.This
will ensure that you are purchasing an up-to-date product
with a full sensor life.
Where Do I Put A CO Detector?
Most manufacturers specify where you should locate their CO
detector. In general, the best place to put the detector is
where you will hear it while sleeping. CO is roughly the same
weight as air and distributes evenly throughout a room, so a
detector can be placed at any height in any location, as long
as its alarm can be heard. Additional units could be installed
in several other locations around the home, such as a child's
bedroom; check the list below before installing.
To avoid both damage to the unit and to reduce false
alarms, do not install CO detectors:
- in unheated basements, attics or garages
- in areas of high humidity
- where they will be exposed to chemical solvents or
cleaners, including hair spray, deodorant sprays, etc.
- near vents, flues or chimneys
- within 2 metres (6 ft.) of heating and cooking
- near forced-or unforced-air ventilation openings
- within 2 metres (6 ft.) of corners or areas where
natural air circulation is low
- where they can be damaged, such as an outlet in a high
- where directly exposed to the weather.
What do I do if I hear the CO detector alarm?
Do not ignore the CO detector's alarm if it sounds.Treat
each alarm as serious and respond accordingly.
CO detectors are designed to sound an alarm before a
healthy adult would feel any symptoms. Infants, the elderly
and those with respiratory and heart conditions are at
particular risk and may react to even low levels of CO
poisoning (Health Canada, 1989).
Response To An Obvious Source Of CO
If your detector sounds an alarm and you have an obvious
source of CO, such as an unvented kerosene heater:
- evacuate the house, including pets and do a head count
- if anyone is suffering from flu-like symptoms, call 911
- remove or turn off the source
- ventilate the house
- reset the alarm
- do not re-occupy the house until the alarm ceases
- take steps to avoid this situation in the future.
Response To An Unknown Source Of CO
If your CO detector is sounding an alarm and there is no
obvious source of CO:
- evacuate the house, including pets and do a head count
- if anyone has flu-like symptoms, call 911; if there are
no health problems, call your gas utility, heating
contractor or the fire department to have your house tested
- if you live in a single family home: do not ventilate
your home, turn off fuel-burning appliances or reset your CO
detector prior to someone testing your home *
- if you live in a duplex, row house, apartment, or
otherwise attached house, do ventilate the house and turn
off fuel-burning appliances. In this case, the safety of
your neighbours is more important than trying to find the CO
- have a qualified service technician inspect and repair
all fuel-burning appliances, if they are identified as being
the CO source
- do not re-occupy the house unless those who tested the
house inform you that the danger is over.
* Many CO alarm calls have been classified as . false
alarms. because the homeowner has ventilated the home and
turned off the equipment before firemen or technicians can
measure the CO levels and find the source.
Symptoms of CO poisoning 2
Be sure that all members of your family know the symptoms
of CO poisoning:
Flu-like symptoms such as headache, running nose, sore
Drowsiness, dizziness, vomiting.The sense of disorientation
and confusion may make it difficult for some victims to make
rational decisions like leaving the home or calling for
Unconsciousness, brain damage, death
Continued low-level exposure to CO
While this may be not lead to observable symptoms, you
should still avoid such exposure.
Testing A Carbon Monoxide Detector
Most CO detectors have a test button that should be pressed
once a week to confirm that the device is in operation.
Detectors with displays can be tested with a known source of
CO such as smoke from a cigarette or incense stick. Hold the
CO source about 8-10 inches away and watch the digital display
respond to the presence of even a small amount of CO. BUT an
alarm will most likely not sound with this test.
There are CO detector test kits available, where CO
detectors are sold, that provide a vial of high level of CO
(1000 ppm) and a plastic tent to house the unit during the
test. This test only proves that your detector will sound an
alarm with a very high level of CO.
Changes In Test Standards
The standards organizations of Canada (CSA International)
and the United States (Underwriter's Laboratory or UL) have
co-ordinated the writing of CO standards and product testing.
The standards as of January 2000 prohibit showing CO levels of
less than 30 ppm on digital displays. The new standards also
require the alarm to sound at higher levels of CO than with
previous editions of the standard.The reasoning behind these
changes is to reduce calls to fire stations, utilities and
emergency response teams when the levels of CO are not
life-threatening.This change will also reduce the number of
calls to these agencies due to detector inaccuracy or the
presence of other gases. Consequently, new alarms will not
sound at CO concentrations up to 70 ppm. Note that these
concentrations are significantly in excess of the Canadian
Detectors with a digital display and a history option
can provide the true CO concentrations in a house. A low-level
display would be useful for people with existing respiratory
problems or for those who like to spot evolving problems,
rather than having to wait for the situation to become
serious. Low-level CO detection products are becoming
commercially available. They will not be certified to CSA or
UL standards, as these standards currently prohibit low level
|CO concentration in parts per million
||Normal conditions in and outside Canadian
||Maximum tolerable indoor concentration over an
||Maximum allowable concentration for continuous
exposure for healthy adults in any eight-hour
||CO detectors must not sound alarm within 30
||CO detectors must sound alarm within one to four
||CO detectors must sound alarm within 10 to 50
||Slight headache, fatigue, dizziness and nausea after
two to three hours. CO detector alarm must sound within
||CO detectors must sound alarm within four to 15
||Dizziness, nausea and convulsions within 45 minutes,
death within two to three hours.3|
||Death within one hour.3|
||Danger of death after one to three
1 Exposure Guidelines for Residential Indoor
Air Quality, Health Canada, 1989.
2 From the CSA Standard 6.19, Residential
Carbon Monoxide Detectors(January, 2000)
3 Carbon Monoxide Poisoning, Iowa State
University of Science and Technology, AEN-172
Although this information product reflects housing experts'
current knowledge, it is provided for general information
purposes only. Any reliance or action taken based on the
information, materials and techniques described are the
responsibility of the user. Readers are advised to consult
appropriate professional resources to determine what is safe
and suitable in their particular case. CMHC assumes no
responsibility for any consequence arising from use of the
information, materials and techniques described.