Keep the gas oven for cooking and the vents open

It is cold, the heating bill frightens you, and two tips turn up that sound like plain sense. Turn the oven on and leave its door open to warm the kitchen. Shut the heating vents in the rooms nobody uses, so the heat goes where you are. Both are handed around as ways to save money. The first can poison you. The second can cost more than it saves.

Do not leave a gas oven on to warm your home: it can fill the rooms with carbon monoxide, a poison gas you cannot see or smell. Keep the heating vents open, and put a carbon monoxide alarm with a battery near where you sleep.

Why the oven for warmth is not the oven for dinner

The objection arrives fast, and some people raise it: people cook with gas every day, so what changes when the oven is on for warmth? Three things change.

The time changes. A dinner takes an hour or so. Heating runs all evening and often into the night, when you are asleep. The flame changes too. An oven holds its temperature by turning its burner on and off; with the door open it never gets there, so the burner keeps firing the whole time. A gas flame that does not burn cleanly makes carbon monoxide, and that is the danger people name. The people who answered the objection add that kitchens need ventilation precisely because gas cooking makes this gas, and that heating stretches the exposure far past the length of a meal. Some people note that the rules differ from place to place, and that some places do not require a hood vented to the outdoors even over a gas stove.

Some people warn about exactly this. Carbon monoxide gives no warning you can sense. Its early signs — headache, dizziness, feeling sick, weakness, sleepiness, confusion — are easy to take for flu or tiredness, and one person stresses how subtle and confusing they can be until it is too late; another, that some people are affected faster than others. The US CDC names who is more likely to get sick from it: babies, older people, and people with heart disease, anaemia or breathing problems. One person says emergency-room nurses see these poisonings in winter in poorer northern areas. One person names who ends up doing it: students on a tight budget, and households whose electricity comes and goes. They have a reason. The reason does not change what the gas does.

One person argues the risk is overstated, because a gas oven burns at roughly the rate of several stove-top burners together and people run those for dinner. The others answer with the hours and the flame that never stops; the night, when the person breathing it is asleep, is the CDC’s point. The CDC’s own line is short — never heat your house with a gas oven — and the US Fire Administration says the same about any oven.

What the oven can give you safely

Once the oven is switched off, its burner is out, and it stops making carbon monoxide. So the warmth left over after you cook is yours to keep. Two points make this simpler than it sounds. The heat stays in the house whether you open the door or not; opening it only lets the heat out sooner. And it is less than it feels. Some people explain that the heat spreads into so much air that the room barely warms, and one adds that a good part of it soaks into the walls and cupboards around the oven; how much you notice depends on how well your home holds heat. If you do open the door, keep small children and pets well back while it cools — a US fire-safety standards body asks for a three-foot “kid-free zone” around space heaters, and an open hot oven is one. One way to make more of it: cook the slow dishes, a roast or a braise, on the coldest evenings, so heat you were making anyway warms the kitchen.

An electric oven makes no carbon monoxide. One person points out that it turns electricity into heat as completely as any electric heater does. But it is built to heat a small closed box, and it sits in one corner of one room. One person warns that running an oven at full heat for long stretches can damage its parts, and another that using it for heat shortens its life. The US Fire Administration still says never use an oven to heat your home; with an electric one, the danger is fire. The warmth left after dinner, yes. The oven as a heater, no.

Gas cooking also puts other fumes into the air, even when the flame looks clean, some people say. The US Environmental Protection Agency’s advice matches theirs: use an exhaust fan over a gas stove, vented to the outdoors. The catch is in that last word. Some people describe hoods that send the air into the attic, the basement, a bathroom, or straight back into the kitchen. A hood that only filters the air and blows it back into the room does not take fumes out of the house. Check where yours goes before you count on it. How to tell is not covered here, so the fitting instructions, or whoever installed it, are the place to ask. Where there is no outside vent, open a window while you cook. One person says ducting a recirculating hood to the outside is a job worth doing for someone who cooks a lot; this page gives no price for it.

Shutting vents can cost more than it saves

This tip sounds even more sensible. If nobody uses the back bedroom, why heat it? Some people say it does not work, and the reason is in the ducts.

A forced-air system — a furnace that blows warm air through ducts to vents in the floors or walls — is built to move a set amount of air through the whole house. Shut some vents and the air does not simply go to the open rooms instead. The pressure in the ducts rises, and more of the warm air leaks out through the joints and gaps in the ductwork, into the attic or the crawlspace if that is where the ducts run. One person adds that the pressure can open small tears at the duct joints. A 2003 study at Lawrence Berkeley National Laboratory in the US modelled this for California houses with their ducts outside the living space, and found that closing vents raised energy use rather than cutting it: the extra leaking cost more than heating fewer rooms saved. One person adds that the cold room does not stay separate, because its inside walls chill the rooms around it; another, that the furnace can end up running on and off without ever reaching the temperature you set.

The cold room carries costs of its own. Some people warn that water pipes running through a shut-off room, especially one over a garage, can freeze and burst. One person says the weaker airflow lets condensation gather inside the ducts, which feeds mould and, over time, rot.

Then the part that ties the vents back to the oven. Less air across the furnace’s heat exchanger — the metal chamber that keeps the flame’s exhaust apart from the air you breathe — makes it run hotter. A furnace has a high-limit switch that cuts the burner when it gets too hot, and the Berkeley study warned that furnaces may end up running on that switch once more than about 60% of the vents are closed. The some people warn that this can crack the heat exchanger, and a cracked one can leak carbon monoxide into the air the furnace blows around the house. Heating firms say the same in their own guidance, and put it down to the metal overheating again and again; this page found no public safety body that states it. That is the far end of the risk, not what happens the first night you shut one vent. It is also why the carbon monoxide alarm belongs in the house either way.

Whether shut vents also wear out the fan motor is argued both ways here, and this page does not rest on it. One side says the fan labours against the extra pressure, runs hot and burns out. The other side, one retired heating technician among them, says a fan pushing against a restriction moves less air and does less work. The deciding question, in one of those exchanges, is the kind of fan and how hard the airflow is choked.

And some people push back on the whole warning. Some people describe closing vents for years without a breakdown, one of them for twenty-five. The person whose question started one conversation had done it with an oil furnace and watched their oil use fall; when others challenged it, the same person said they had not looked into it and might simply have been lucky. Someone asked the obvious question — why make vents adjustable at all, if closing them is harmful — and that conversation gave no direct answer, only the hint that systems differ, and some cope with a partly closed vent where others do not. One person says a vent should be closed only when a room gets too much air: a small room that overheats, say.

So if you do close some, stay inside the limits people and the study give. A few, never most; one person says keep at least one open on each branch of ductwork. Never in a room with water pipes, or over a garage. Watch that room for damp. And listen to the blower: one person says a clear change in its sound means it is being overworked. If you really want to heat only part of the house, one person says to have a heating technician measure the pressure in the ducts and the temperature rise across the furnace first, and another to fit proper shut-off dampers in the ductwork rather than covering floor vents. The cheaper saving is sealing the draughts at the window and door frames with foam or a sealant, which keeps heat in without straining anything. Two warnings sit beside it: one person says a house sealed too tight can grow mould and make the air worse, and another that blankets hung over windows trap moisture, so check behind them for damp.

If the heat is out and it is freezing

Here people split, and it is the one place this page does not leave the choice open. Some people say a gas oven for heat should never be done. On the other side, one person says that when there is no other heat and freezing is close, a gas oven with a window cracked beats hypothermia, and the warning against the oven, as some people put it, makes the same exception: avoid it unless it is life or death. The CDC and the US Fire Administration make no exception, and the reason is the one this page is about: a cracked window does not tell you how much carbon monoxide is in the room, and the person it poisons may be asleep.

What works instead, safest first:

• Go where it is warm, if you can. A friend, family, or a public building such as a library while it is open; there is a page about that linked below. In the US, calling 211 can point you to local help, including warming centres where your area runs them, and LIHEAP, below, helps with heating bills. In the UK, contact your energy supplier and ask about its Priority Services Register, and Citizens Advice can help with what support you are owed.
• Warm the person, not the house. What needs no power comes first: the US CDC’s advice for the cold is several loose layers of clothing with a hat and gloves, dry blankets, and warm drinks that are not alcohol. Some people offer the same kind of answer: an electric blanket, in good condition and used as its instructions say; a heated throw; and one person’s tent over the bed. The same account suggests a bag of rice heated in the microwave to warm the bed. Greater Manchester Fire and Rescue Service, a UK fire service, warns that microwaved wheat bags, the same kind of heat pack, can catch fire if overheated, reheated before they have cooled, or kept hot under bedding, and tells people not to use one as a bed warmer at all. If you use one, hold it against your body, heat it no longer than its instructions say, and let it cool fully, about two hours, before you heat it again.
• Not the barbecue, the camping stove or the generator. Each makes carbon monoxide the way the oven does: the US CDC says never to burn charcoal or use a portable gas camp stove indoors, and never to run a generator inside the home or garage, even with the doors and windows open; US emergency guidance puts a generator outdoors, at least 20 feet from windows and doors.
• An electric space heater, by the rules. The US Consumer Product Safety Commission says plug it straight into a wall socket, never into an extension cord or power strip, and keep it at least three feet from bedding, curtains and furniture; the US Fire Administration adds: off when you leave the room or go to sleep.
• A stove you already have. One person says an unused wood or pellet stove can heat the room you are in, especially where there is no gas; the wood-heat page linked below covers burning safely, and that room needs a carbon monoxide alarm of its own.
• Know the danger signs of cold. The CDC lists shivering, exhaustion, confusion, fumbling hands, memory loss, slurred speech and drowsiness in adults, and bright red, cold skin with very low energy in babies. Those need emergency help: 911 in the US, 999 in the UK, your local emergency number elsewhere.

A well-insulated house also stays warm longer when the power goes, which takes away some of the desperation behind the oven; the attic page linked below is part of the same answer. One person says never to let the heating setting drop below 55°F (about 13°C), so the pipes do not freeze.

Who this page is not for

If your home is heated by a boiler and radiators, with no air vents in the floors or walls, the vents and filter parts of this page do not apply to you; some people say so directly. The gas-oven warning does. This page does not cover how to tell whether a boiler also has an air handler that needs a filter.

If an alarm is sounding, you smell gas, or people in the home feel ill right now, this page is not the tool. The steps are at the top: get out, then call from outside.

And if you rent, whether your landlord must fit a carbon monoxide alarm depends on where you live, and this page does not cover landlords at all. In England, since 1 October 2022, a landlord must fit one in any room used for living that has a fixed appliance burning gas, oil, coal or wood — a boiler or a wood stove, say — and must repair or replace it once you report it faulty. The rule leaves out gas cookers, so a gas oven on its own does not require one. In the US, it depends on your state. Wherever you are, you can fit your own.