How to prevent carbon monoxide poisoning, winter’s odorless killer

When the furnace turns on, the risk increases.

When you burn something, whether it’s wood in the fire, charcoal on the grill, or gas in your garage, it emits some amount of carbon monoxide, or CO. Colorless, odorless, and tasteless, this gas is completely undetectable—and it’s responsible for up to half of all accidental poisonings in the world.

According to the CDC, carbon monoxide poisoning happens most commonly in winter, when we seal up our homes and burn extra fuel for warmth. Now that the weather has cooled, it’s time to take extra precautions. Here’s how to keep this silent killer out of your house.

How carbon monoxide kills

If you tested the air near you, you’d probably find [trace amounts of carbon monoxide] ( In fact, CO is the second most common molecule in the universe, and radio astronomers regularly use it to track clouds of interstellar gas.

But here on Earth, its concentration usually remains very low (at roughly 0.2 parts per million, or ppm, which means that for every million molecules in the ambient air, at least 0.2 of them are carbon monoxide ones), so low that the gas can’t do any harm. The problem only starts once the air you breathe reaches 35 ppm or higher. It’s key to remember that ppm is a dimensionless quality for measuring very small amounts; you can be in a warehouse with a million cubic feet of atmosphere, and if just 0.000035 percent of it consists of CO gas, you’ll be in trouble.

At this point, CO turns deadly. “Carbon monoxide attaches to the hemoglobin exactly where oxygen is supposed to attach, reducing the amount of oxygen in the blood,” says Joseph Fisher, University of Toronto professor and chief medical officer of Thornhill Medical, manufacturer of the ClearMate, a CO toxicity treatment. “Worse still, it inhibits the oxygen that did attach from leaving the blood. Thus the rest of the organs are starved of blood, asphyxiated from the inside.”

This grisly poisoning often starts with flu-like symptoms like headaches, dizziness, and nausea. In fact, most sufferers assume they have a bug. However, these signs may not appear until hours after exposure, which means people are less likely to realize it’s a problem with the air, not their immune system. After six to eight hours of 35 ppm exposure, most sufferers get a mild headache, pop an aspirin, and walk out of the house thinking they’ve solved the problem. That means the leak can build for weeks before it becomes clear that something’s wrong.

As the gas builds up in the air, symptoms become more pronounced and arrive faster. At 100 ppm, the headaches, dizziness, and nausea arrive after one to two hours. At 800 ppm, confusion sets in after two hours—if you take a nap, you might wake up unable to save yourself, if you even realize what’s happening. And with CO at 1,600 ppm, you’ll die within two hours.

Even if you survive, studies have found that you might suffer from long-term damage. For example, carbon monoxide exposure can aggravate cardiac conditions and, in rare cases, damage the liver. Other effects—including confusion, amnesia, blindness, and depression—result from brain damage.

Fisher emphasizes the neurological issue. “We say ‘time is brain’,” he says. “The longer it takes to restore oxygen delivery, the more brain cells die.”

Remove potential sources

Clearly, we have good reason to avoid CO poisoning. So how do you prevent carbon monoxide from building up?

Remember, almost without exception, anything that burns hydrocarbons or organic matter emits this gas: Potential sources include everything from your clothes dryer to your oven. To limit how much CO these machines emit, start by removing any unnecessary fuel-burning machines from your home.

For example, you might replace your fuel-based appliances and power tools with electric ones. For fuel-burners that have no convenient substitutes, such as generators, at least keep these items out of your living space. Instead, store them outdoors or in a properly-ventilated outbuilding.

In addition to storing these machines outside, you should try to avoid using them indoors. When you rev up a motor or start burning fuel, make sure to do so outside or in a well-ventilated space, such as a garage with the door completely open. While you’re at it, never leave anything with an engine unattended—for any length of time.

Keep appliances clear

You won’t be able to shut off or exile every potential source of carbon monoxide. So for furnaces, fireplaces, generators, clothes dryers, and other necessary appliances, make sure they stay in working order.

Before we start, a quick word of warning: Bear in mind that the gas in question is incredibly toxic and you shouldn’t mess around with it. No matter how handy you are, if you suspect even the possibility of a leak, call in a professional and get everyone out of the house.

In general, as appliances like furnaces and hot water heaters age, their safety systems accumulate more strain. So check your machines and consider upgrading the oldest ones. If your budget has enough room, look into an energy-efficient replacement, which will save on bills and reduce CO poisoning risk.

Whether or not you buy new appliances, you should regularly check your machines to make sure they keep working well. The onset of cold weather is a good time to do this, since many of us will be turning up the indoor heating for the first time since spring.

For your furnace, first clean or replace the filter. Then inspect the ductwork for any corrosion or damage, looking for rust and other signs of wear and tear. If your heat is currently running, place your hand on the ductwork above it; if it feels even slightly too hot to touch, that’s a sign the furnace needs repairs.

Next, check the vents. Your hot water heater, clothes dryer, and other fossil-fuel-burning appliances should have nearby outlets that let air circulate—but they can’t do so if dust and other obstructions get in the way. Start in your basement and then walk around your house, checking each vent to ensure it’s clear. You should perform this type of check more than once a year. In particular, repeat it after every snow storm, so you can clear away any snow and ice that may gum them up.

For pellet stoves and fireplaces, call in a professional to clean the chimney before the snow flies. Once you do, try to use these heat sources only occasionally. For example, consider swapping that warm firelight for a flickering LED bulb.

Appliances like ovens are harder to avoid. For these machines, only use them for their intended purpose. Although cooking with your oven might make the room warm and toasty, this appliance is not designed to heat your house, so don’t fire it up for warmth alone.

Install alarms

Since CO has no smell, taste, or color, detecting its presence early requires an alarm. These beepers come in several models, including hard-wired, battery-operated, and plug-in. You get what you pay for, so look for brand names you recognize. However, you don’t need all the bells and whistles: Some alarms offer a stock-ticker-style display to track your air quality, but unless you’re very concerned—or have an atmospheric chemistry hobby—that’s not necessary.

The one thing you should look for in your chosen device is battery backup. This holds true even if you’ve selected a plug-in or hard-wired model: A battery lets it keep working if the power goes out. Just make sure to change your alarm batteries at least every six months.

You should install at least one alarm on every floor, located where you can check it on a daily basis. Manufacturers like Nest recommend you place them roughly five feet above the floor, in part so you can easily read them. However, if you just want the alarm and not the display, you can put them on the ceiling. Just don’t place them near the oven, ceiling fans, or vents, as those may affect its ability to sample the air properly.

If you already have alarms, check their date of installation. These devices usually expire after five years, so you may need to replace them.