Can a Furnace Be In A Closed Room?

Half-walls generally surround the furnaces to keep them hidden due to aesthetic reasons. The furnaces remain safe with proper airflow to get enough ventilation. But will they be safe if kept in a closed room? 

You cannot keep the furnace in a completely closed room. So, there must be ventilation arrangements for airflow and combustion air from the other rooms or through the grills in the floors and walls. Else, the furnace will overheat and fail to release the toxic substances.

A sealed room is unsafe for furnace units as there are several safety and health reasons behind it which we will share in this article. This guide will share the dangers of installing a furnace in a closed room and room tips for the furnace.

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Can I keep the furnace in a closed room?

Generally, the furnace is surrounded by some partitions or half-walls to keep them hidden for aesthetic reasons. 

Letting them stay hidden will allow you to maintain the aesthetic look of your house. 

These enclosures, like the partitions or half-walls, allow the furnace enough airflow.

Adequate airflow will allow enough ventilation and combustion air to reach the furnace from different rooms of your house or through the grills. 

Keeping the furnace in a completely closed or sealed room will not allow the furnace to work properly. 

The unit will struggle to release warm air over the house by using too much energy. 

Below are some common results of keeping the furnace in a closed room:


When a furnace does not have proper ventilation, the unit gets overheated. 

It fails to spread the warm hot air all over the rooms and, thus, keeps struggling to do it. 

Over time, the unit can get heated up too much, leading to several fire accidents. 

Besides, the constant struggle to warm up the room uses too much energy, increasing the electricity bill. 

So, ventilation and airflow are important. 

Carbon monoxide

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Keeping furnaces in rooms without ventilation can create a huge build-up of carbon monoxide. 

The gas is deadly and will spread to other rooms if the furnace room lacks ventilation. 

You won’t be able to know it while inhaling it as the gas is very odorless. 

Inhaling this gas can deteriorate your health, and you will start having several health issues. 

According to the Uniform Building Code, a partially enclosed room with a direct-vent furnace will need at least 50 cubic feet of space for every 1,000 BTUs (British Thermal Units) of fuel input. 

BTU is more widely used in northern America than in Britain despite the name. 

The furnace room should have a combustion air opening through which at least 1 square inch of fuel should be incoming for every 3,000 BTUs. 

The opening must be around 12 inches from the ceiling, and it should be vented outside the house. 

If you have a fan-assisted or gravity air-type furnace, you must have two openings in the room, 1 square inch per 1,000 BTUs of fuel input. 

One should be installed 12 inches from the floor and one 12 inches from the ceiling.

Gas build-up

Besides carbon monoxide, the furnace needs to release the toxic gas fumes out of the house, and ventilation is vital here. 

If you place the furnace in a closed room, the harmful and deadly fumes will get mixed into the air of your house. 

You cannot smell them, so you will unknowingly inhale them and deteriorate your health. 

If the fumes accumulate in the closed room over time, they will become explosive before you can detect them by their smell. 

That can further blow up the door of the furnace room.

How can I operate the furnace safely without vents?

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You can operate the furnaces without vents in two ways. 

You can use sealed combustion furnaces

These factory-equipped furnaces draw outdoor air into the furnace and expel it through the flue. 

The indoor air is not used here; thus, the vents do not have to compete with the used stove or bathroom exhaust vents.

Another way is by using the Hoyme Damper. It has a sensor that opens a motorized damper whenever the furnace needs air for combustion. 

The damper automatically closes up when the furnace has taken up enough air. 

Can I put the furnace in a closet?

Space is an important factor when it comes to installing a furnace in a room. 

Many units are installed in attics and garages as these areas have enough space, and you can easily fit the units in one corner. 

But if you have a crawlspace, finding the right location for a furnace is quite tough. 

Installing a furnace in a closet is weird, especially when you speak of enough space. 

Some people do not recommend installing the furnace in the closet, especially if the closet is attached to your living room. 

The closet is quite a closed area, but it can also hide the furnace and maintain the aesthetic of your house.

However, you can install a furnace in the closet if you have enough room around the furnace. 

The furnace needs at least 30 inches of clearance in its surroundings. 

If you cannot shift the furnace to any appropriate place, you must install vents in the closet for good air circulation.

It would be best to consider certain factors:

Venting a closet

Arranging ventilations in the closet is quite easy to do. 

The furnaces have supply and exhaust vents installed in the unit. 

Based on the building codes, you need a double pipe system or a single pipe with a double inner layer. 

The exhaust size will depend on your furnace size. 

The size of the closet will not interfere with anything here. 

It would be best to have venting for the furnace in the closet. 

But if you extend the pipes to the roof or outside the wall house, don’t worry about the furnace. 

Space and heat are more important issues than ventilation for closet furnaces. 


When installing the furnace in the closet, ensure the door is large enough, especially for the widest part of the unit. 

If you have any other appliances in the closet, remove them before installation. 

Move out the appliances without disturbing the furnace if the installation is already done. 

Enough space will allow the adults and technicians to do the maintenance and repair jobs without problems and easily access the control panels. 

Remove flammable materials

If the furnace cannot release the hot air but cannot spread it throughout the room, it can overheat itself and lead to fire hazards.

It is when ventilation and airflow are important for the furnace and the closet. 

The heat needs to escape out of the closet, provided there is enough space in the closet. 

Do not install the furnace in the storage closet, as there won’t be enough room. 

Remove all the flammable materials, including the insulation, from the closet.

It will also give enough space to the furnace. 

Venting without pipes

Venting can be a great concern if you want to install the furnace without any piping to reach the outside air.

In such a case, your furnace should not be smaller than 50 cubic feet per 1,000 BTUs of heat the furnace will produce. 

It means you must add a basic vent to allow the new outside air to enter the closet and the furnace for combustion. 

Safety tips for a furnace room

We only visit a furnace room sometimes. 

But you should visit it if you want to confirm everything is safe. 

Some house owners make safety mistakes in the furnace room without understanding them. 

It happens because you or the technician might have forgotten something while working. 

Here are some common safety tips for a furnace room:

Allow the room for enough ventilation and maintenance.

If you have a separate room for the furnace, ensure the room has enough ventilation. 

It will help in good airflow to spread the air and also allow technicians to easily access the panel doors and fit in the space for repair and maintenance.

Whether to keep the furnace door open or closed depends on the situation. 

An open door can improve ventilation and evenly distribute the heat on the floor and rooms. 

But if you have pets or kids, you must keep the door closed, so they do not get any access to the unit. 

There are vented doors in the furnace, which allows the air to flow without depending on any other extra space. 

The furnace room should not have any paint or cat litter.

Paint is a highly combustible material. It can create fumes even at a low level of heat. 

Cat litter is another thing that you should not keep in the furnace room. 

The fumes from this litter will generate ammonia and corrode the unit’s heat exchange. 

Repairing such issues can be quite expensive. 

So, keep the paint and cat litter out of the furnace room. 

Other materials to keep away are:

  • Clotheslines
  • Papers and rags
  • Wood
  • Sawdust
  • Used filters

Check the lighting of the furnace room.

Having a proper light in the furnace is very important. 

If there is no light or it is very dim, you or the technician cannot properly access the right place or parts of the furnace. 

That can lead to accidents. 

Ensure that the room has enough light so that every corner of the room and every part of the furnace is properly visible. 

You can also keep a flashlight for the room to see in during the power outage. 

Light is the most important thing for the furnace room, especially the flashlight if there is a backup heating method.

Keep the room clean. 

Dust and debris accumulation in the room can be very unpleasant for the furnace. 

It attracts several insects and animals to make their nest. 

That can harm the furnace and disturb its smooth functioning. 

So, you need to wipe down the nests, dust, and debris from the room to keep the room neat. 

Clean the room regularly to avoid dust and debris accumulation and nest build-up in the room. 

The best floor for the furnace would be one that can be easily cleaned and is not flammable. 

You can choose vinyl over the carpet. 

Remove the old filters from the furnace.

Always keep new filters in the furnace and remove the old ones. 

Not changing the old filters will stop the furnace from smooth working, especially if the filter is too close to the furnace. 

Filters can collect enough debris and dust, especially flammable ones and increase the risk of fire hazards. 

Inspections and permissions

Suppose you are building a new house or basement. 

In that case, the building inspector will need permits for the furnace’s housing, venting, and combustion systems. 

The inspector will ensure they are safe and the building codes are followed before you own or occupy the residence. 

If you have older furnaces, a certified furnace or building inspector must check your furnace for compliance. 

If needed, the inspector will help you with the proper guidelines to work according to the code. 

Things to put and avoid in the furnace room

Certain things should not be kept in the furnace room, like the flammable materials. 

But, some materials need to stay in the furnace room for safety. 

Things to avoid keeping in the furnace room are:

  • Cardboard boxes
  • Wood and sawdust
  • Paint and cat litter
  • Other flammable liquids like gasoline, kerosene
  • Electrical devices to avoid potential fire hazards
  • Products used for cleaning
  • Rubber and plastic

You should add some things to the furnace room to remain safe. They are:

  • Fire detectors 
  • Carbon monoxide detectors
  • Fire extinguishers
  • First aid kit, in case there has been an accident
  • Emergency contact numbers to call the emergency unit during any serious accidents

Should I insulate the furnace room?

Insulating a furnace room is a great idea to help the furnace run smoothly. 

Insulating the room will improve the furnace’s efficiency and save energy costs. 

Either you can insulate it yourself or hire a professional to do it. 

Sometimes, the furnace does not run efficiently, which can be due to improper sealing of the furnace room. 

So, you have to seal it to avoid such inefficiency. 

The house owners can use rigid foam insulation, fiberglass batting, or spray foam insulation. 

Consider the airflow before using the seal. 

Final thoughts

Keeping a furnace in a closed or sealed room is a very bad idea. 

The furnace must have enough space around it, and the room must have enough ventilation and airflow to allow the combustion air to enter the unit.

Besides, the furnace expels harmful carbon monoxide and other gasses which need to be released outside. 

The build-up can explode and blow the door of the room. 

So, ventilation and airflow are compulsory.

It will also prevent overheating of the unit and allow the heat to spread throughout the house.

You can also keep the furnace in a closet if it has enough space and ventilation. 

But do not install it in a closet attached to any living space. A furnace must be away from the air you inhale. 


Can I put a furnace in the bedroom closet?

It isn’t good to install a furnace in the bedroom closet. Though you can install it in a closet, the closet should be separate from your living spaces. 

Make sure to install the furnace at a place that is always far away from the air you and your family breathe.

Does a furnace need a louvered door?

Having a louvered door in the furnace is a great way to improve the air circulation of the furnace room. 

The door supports the venting for enough combustion air to enter the furnace room. 

When the furnace pushes air into the home, it will need the same amount of air to go back to the furnace room for efficient operation. 

The louvered door also keeps your family’s health good as it helps the furnace to function properly and prevent moisture build-up, mold, and mildew. 

Reference: Furnace Science Direct, Effects of HVAC on combustion-gas transport in residential structures, HVAC System and Part of Indoor Air Quality.

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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