How to Check for Carbon Monoxide at Your Home

April 24, 2021

Did you know that there will be over 40,000 cases of CO poisoning in the US in 2018? Did you now that CO may be responsible for 50% of all fatal poisonings? In this article you’ll learn how to prevent this silent killer from invading your home.

Several hundred people will die this coming year, killed in their homes by an invisible, silent assassin. Thousands more will have their health damaged, perhaps seriously. The cause of all of this human carnage is carbon monoxide, an invisible, odorless gas.

Now I don’t mean to scare you, but this is truly scary stuff. When I first began researching this topic, the more I learned, the more I found myself worrying about whether my home’s furnace or water heater — two totally forgettable appliances that we tend to think of only as comfort providers — could instead kill me and my family. I’ve now taken steps to ensure that it won’t happen, and you need to do the same.

Am I being overly cautious? I don’t think so. Carbon monoxide is not a minor problem. It accounts for half the fatal poisonings in the United States each year, which, depending on the set of statistics you choose to use, means a minimum of 200 to as many as 1,500 deaths per year. A recent Canadian study of 1,000 homes found that three-quarters had some carbon monoxide buildup, 10 percent of them at health-threatening levels. Yet dangerous as it is, few homeowners know about carbon monoxide or how easy it is to guard their homes against its deadly intrusion.

Carbon monoxide risks are everywhere inside your house. Common clues are fallen soot from a wood stove, chimney, or furnace. The most common causes are disconnected vent pipes on water heater, leaking chimney pipe from wood stove, cooking appliances used for heating purposes, clogged chimney or a blocked chimney opening, portable kerosene heaters, barbecue grill used indoors, vehicles running inside a garage during extended periods of time, adding extra insulation without checking to see if extra ventilation is needed, and an airtight energy-efficient house (window film, caulking, weatherstripping)

Carbon monoxide detectors

Looking like every-day smoke detectors, these electronic units have audible alarms to warn you of carbon monoxide. The Ultralert (on left) is a combination smoke/carbon monoxide/natural gas detector requiring 120-volt power. The CoStar (on right) detects only carbon monoxide and uses a nine-volt battery for power.
Place two of the Air Check sensors near the draft hood of the furnace and water heater. The third sensor is used to double-check any sign of backdrafting.

The left photo has a combination smoke-carbon monoxide detector on the left and carbon monoxide-only detector in the right, and the right photo has several air check sensors to be placed near a furnace or a water heater

Regular checks of the chemical detector spot of this Quantum Eye carbon monoxide detector are necessary to warn you of problems. When the spot changes color, the carbon monoxide level is too high. These detectors last for one year and then must be replaced.

Why it kills

This gas is deadly because of its extreme attraction to hemoglobin, the main component of red blood cells. Its affinity for hemoglobin is 245 times greater than oxygen’s. Carbon monoxide is absorbed by the body only by breathing, the same way we get oxygen.

Hemoglobin combines with oxygen in our lungs, carrying the oxygen throughout our bodies, releasing it to the tissues as needed. But when carbon monoxide is present. it replaces the oxygen. In high enough concentrations, it can kill in minutes.

One of the reasons carbon monoxide poisoning claims so many victims is that its physical symptoms are frequently misdiagnosed by doctors as the flu or whatever bug is going around. It’s no coincidence that most carbon monoxide poisonings occur during the winter, the prime time for colds and flu.

Carbon monoxide sources

Carbon monoxide (the chemical symbol is C0) is a by-product of incomplete combustion. Colorless and odorless, it gives no warning of its presence.

It’s impossible to avoid some exposure to carbon monoxide. Your body even produces minute quantities.

Carbon monoxide sources are everywhere.

They include such obvious ones as automobile exhaust fumes, furnaces, the kitchen stove, the water heater, your fireplace, charcoal grills, even your lawn mower.

And such unexpected sources as the vapors of some sources as the vapors of some solvents, such as methylene chloride in some paint strippers.

You can’t avoid breathing some carbon monoxide, but as long as the level in the blood is below 2%, there’s no cause for concern.

Our homes and our health

As it our homes didn’t already have enough sources of carbon monoxide, we tend to make the situation worse in pursuit of energy efficiency. Some houses are simply too tight for safety.

Besides being fighter thanks to more insulation, caulking, insulating window films, and weatherstripping, as thermostats have been turned down, a variety of room heaters have taken their place, or a fireplace or wood stove installed. Or maybe you’ve built an enclosure around the furnace or water heater in the process of remodeling the basement.

If you didn’t provide for adequate fresh air flow, perhaps from outside, you may have created a perfect opportunity for carbon monoxide to build up.

Clues around the home for excess CO

Even though carbon monoxide can’t be detected by your senses, sometimes, but not always, there will be other clues to its presence:

Persistently stuffy, stale or smelly air that never clears.
Very high humidity, often showing up as moisture on the windows
Soot around the outside of the fire place, furnace or chimney.
No draft in the chimney.
A hot draft from the chimney into the home.
The smell of exhaust fumes.

Health-related CO poisoning clues

Because carbon monoxide poisoning is more of a problem during the winter when heating systems are running and everyone seems to have a cold or the flu, the physical symptoms are often misdiagnosed. Some of those symptoms are:

Persistent severe headaches.
Dizziness, blurred vision.
Nausea and vomiting.
Confusion, disorientation, loss of muscle control.
Sleepiness. but never feeling rested.
Rapid heartbeat, pulse or a tightening of the chest.
An abnormal cherry color to the skin.
Chest pain (angina) when exercising.
Fainting, unconsciousness.
Feeling sick and tired at home, but fine once you leave the house.

A lot of these symptoms sound just like the last time you had the flu. don’t they? That’s what makes this such a sneaky, hard-to-identify problem. If everyone in the family seems to be experiencing the same illness to some degree (body size and health are both factors that determine when symptoms will arise) and nothing seems to help, ask your doctor to check for carbon monoxide poisoning, immediately.

Ask for a carboxyhemoglobulin level blood test. It’s the only test that will identify carbon monoxide poisoning. Other routine blood and drug tests won‘t do the job.

High levels of carbon monoxide don’t affect everyone equally Pregnant women, people with heart problems, and children are all more susceptible. Carbon monoxide also has a stronger effect at higher altitudes because the air has less oxygen in it to begin with, allowing the carbon monoxide to bind even more effectively with the hemoglobin.

The treatment for carbon monoxide poisoning is usually just fresh air and time. In severe cases, however, the patient will be placed in a chamber with oxygen under high pressure. While carbon monoxide doesn’t accumulate in your system, long-term exposure causes permanent damage to the nervous system.

What not to do

To keep carbon monoxide from becoming a problem, keep these common-sense rules in mind:

Don’t sit in a parked car with the engine running and the windows closed, or let the engine idle for long periods of time in a closed garage.
Never use a charcoal grill indoors.
Never use a kitchen stove or oven for heating purposes.
Never use an unvented gas heater indoors
Avoid extensive use of kerosene heaters — better yet don’t use them at all.
Don’t put furnaces and Water heaters in an enclosure unless you provide adequate ventilation, perhaps ducted in from outside. Your local utility can give you guidelines on what to do.
Don’t use LP gas lamps, heaters or gasoline lanterns indoors or in an RV, unless they’re vented to the outside.

What you should do

Besides knowing what not to do (above) there’s a number of steps you can take to ensure you won‘t have a problem:

Check your chimney every fall (or have it done for you) for signs of blockage, such as bird’s nests.
Have your chimney cleaned annually, before the start of the heating season and especially if you frequently use a fireplace or wood-burning stove.
Have all heating appliances checked for proper function by a professional. preferably on an annual basis. The check should include a visual inspection of the furnace’s heat exchanger, all vents, fan motor and belts, and fuel shutoff switch. Your local utility company usually offers this inspection at low cost. To avoid a lengthy wait, schedule the inspection before the heating season begins.
Make sure the water heater is properly vented with no leakage (see “Can Your House Breathe?” below) .
If you've recently remodeled your home, especially with improvements that make it more energy efficient, have the Carbon Monoxide level checked by the utility company to ensure that you still have adequate ventilation.
If your furnace is enclosed, make sure it has access to enough outside combustion air. Again, your utility company can provide specific advice.
Have your family vehicles’ mufflers and tailpipes checked, replacing them if they're worn out or loose fitting.
On any appliance, learn to recognize a properly adjusted burner flame. The flame should burn crisp and blue. If it’s orange, it needs adjustment — get professional assistance.
The older the furnace, the more likely you'll have problems. If you need a new furnace, or are purchasing one for a new home, choose a “sealed combustion” model. (Note: Don't confuse this type with versions classified as “induced-draft” or “direct-vent.” They’re not the same.) All of the major manufacturers offer them. These units draw air directly into the combustion chamber from the outside. and vent the exhaust gases straight back out.
Sometimes you can retrofit your present heating system with either a power venter (gas furnaces) for about $350 to $550, or a delayed-action solenoid valve for about $200 on oil-fired furnaces. Power venters move exhaust gases directly outside through a side wall. The delayed-action solenoid stops the flow of oil until the blower goes on.
If your home is very airtight (most homes aren’t). you may want to install an air-to-air heat exchanger, also called a heat-recovery ventilator. It ensures that your home won't become depressurized, which leads to backdrafting.
If you install or have a new water heater installed for you, make sure the job was done right by doing a backdraft check afterward.
Install one of the electronic or chemical carbon monoxide detectors as cheap insurance.
Periodically, conduct a backdrafting check.

Detectors – the best defense

Even if you take all of the precautions outlined so far, there’s nothing that guarantees the furnace’s heat exchanger won’t develop a leak two minutes after the inspection. In the past that was a risk you had to run, but not anymore.

Just as smoke detectors are now common in homes and apartments, Carbon monoxide detectors, sometimes paired with a smoke detector, are now available. The accompanying photos provide help in choosing a detector that meets your needs and budget.

Least expensive but requiring a regular monitoring are the small chemical detectors. These use carbon monoxide-sensitive chemicals that change color when exposed to a certain level of the gas. Typically costing under $20, they must be replaced at least every year. Most important, you need to develop the habit of checking them regularly, looking for that telltale color change.

Electronic detectors are more expensive, but you don’t have to monitor them. Just like the smoke detectors that they resemble, their alarms will sound if a certain level of carbon monoxide is present. One model, the Ultralert, is a combination smoke, carbon monoxide, and natural gas (methane) detector. The Ultralert is slightly larger than most smoke detectors, and requires a 120-volt power source.

Can your house breathe?

Homes need to breathe because fresh air is necessary for the furnace, water heater, and stove. If there isn’t enough fresh air available inside the home, it will be pulled into the home down the furnace or fireplace chimney. This is called “backdrafting.” Backdrafting reverses the chimney’s normal siphoning effect, so all the carbon monoxide produced by the furnace and water heater stays inside the house instead of going up the chimney.

To determine if your home is receiving enough fresh air, conduct this test:

Here you can see the smoke properly going up the draft diverter

Close all doors, windows, and fireplace dampers.
Turn on all exhaust fans, such as those in the kitchen, bathrooms, attic and your clothes dryer (whether gas or electric).
Turn on all vented gas appliances, such as the furnace and water heater.
Wait 10 minutes for drafts to stabilize.
Hold a lighted wood match or incense stick below the furnace draft hood air intake (typically on one side of the furnace or an open section at ductwork near the furnace). If the smoke is pulled up toward the draft head, this indicates sufficient fresh air.
If the match flame goes out, or the incense smoke is blown away from the draft hood, backdrafting exists. Immediately call your local utility for assistance.
Repeat this test on the gas water heater.
If you have a fireplace, start a fire in it and wait until it’s well underway. Then check for backdrafting again at your furnace and gas water heater draft hoods. If it's present, you must install a duct to provide the fireplace with air from outside.

Here you can see the compolete lack of draft and the smoke staying indoors