How Far Does A Wall Have To Be From Furnace?

Furnaces help heat up the house quickly and make it comfortable for you. Having adequate space around an enclosed house or building furnace is vital. The walls of your room should not be very close to the furnace. 

As a general rule, you must keep at least 30 inches of distance between the walls and the furnace. Otherwise, the rooms and walls may get heated up too much, preventing the room from staying comfortable. Also, remember that the service workers need easy access to the area. 

While having a furnace at your home, you need to know about the space it should have in its surroundings. If you are planning to get it, go through this article to understand the importance of adequate space around the furnace. 

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How far should the wall have to be from the furnace?

Maintaining enough distance between the furnace and the walls is very important. 

Suppose the furnace is very close to any wall or any material. 

In that case, it will obstruct the furnace from spreading heat evenly in the surrounding. 

That will overheat the furnace and can become prone to accidents.

It will be dangerous, especially if the furnace is close to combustible materials like clothes or wood. 

You must keep proper space around the furnace to avoid such accidents and heat-ups.

An unofficial distance that most people suggest maintaining for a furnace is around 30 inches. 

Keep or install a furnace 30 inches away from your nearest wall. 

If the furnace is too close to the walls, it can heat the room quickly at a great level. 

That will make the room very hot, uncomfortable, and intolerable for people staying in it. 

It is not only about maintaining distance from the wall. 

It would be best to keep 30-inch of clearance around the furnace to allow it to spread the heated air throughout the room.

Does apartment size affect the distance?

Some people suggest maintaining a distance of more than 30 inches. 

Keeping at least 2.5 feet is good enough. 

That will allow the technician to fit into the space and do their repair and maintenance jobs. 

Keeping 2.5 feet of distance clearance around the furnace would be appropriate in smaller apartments or homes. 

But, if you have a larger house, you should extend the clearance and maintain at least 4 feet distance between the furnace, the wall, and other items.

A larger room will need more ventilation and better furnace efficiency. 

What to do during the renovation?

Redesigning or renovating basements can affect the apartment size and change the distance clearance around the furnace. 

In that case, you must consult and follow the manufacturer’s instructions regarding the clearance unit. 

In some situations, you might have to change the furnace’s location depending on the redesigning project’s demands. 

Combustible materials to keep away from the furnace compulsorily:

The furnace rooms can double the size of the laundry and storage rooms. 

But you should keep certain things away from it and keep a proper distance. 

Combustible materials that must be far enough away from the furnace are:

  • Used filters
  • Rags and papers
  • Clotheslines
  • Gasoline
  • Paint and paint thinners
  • Wood scraps and sawdust
  • Cleaning or laundry products
  • Cat litter box

You must also regularly clean the furnace to prevent it from getting dirty and dusty. 

Why is proper spacing between the wall and furnace important?

Maintaining proper distance between the wall and the furnace is important because it prevents the room from getting too much hotter. 

Also, keeping space around the furnace will prevent the blocking of the heated air and increase airflow. 

Here are some importance of giving space around the furnace and furnace and wall:

Avoids fire hazards

Furnaces help in increasing the temperature of the surrounding environment. 

One risk of having a furnace is that it can burst into flames if the temperature gets too much higher. 

Furnaces using mineral fuels can increase the risk of fire accidents. 

So, keeping proper space around the furnace, especially between the wall and furnace, will reduce the heating up of the room and prevent fire hazards. 

Materials like rugs, rages, wood scraps, curtains, clotheslines, wood, etc., should be kept away from the furnace. 

Increases proper ventilation 

Leaving enough space around the furnace will improve the airflow and allow the furnace’s heat to spread evenly throughout every corner of the room. 

But, if the furnace is in a compact place, it cannot spread the warmth. 

As a result, the furnace will struggle to spread it, get too much heated up, use too much energy, and increase the bill. 

If the furnace is too hot, there can be a risk of fire hazards. 

So, space is necessary around the furnace, especially between the walls and the unit. 

Also read: Can a Furnace Be In A Closed Room?

Other required clearance distances around a heating furnace

Besides the distance between the furnace and the wall, the furnace must have specific distance clearances from every side, like the sides or top.

For example, if you have an oil furnace in the working space, you need to have clearance in its surrounding, like:

  • 24 inches in the furnace casing front
  • 3 inches around furnace casing sides and rear for Trane and other brands and models
  • 6 inches in the furnace casing sides and rear (Hallmark³)
  • 3 inches at the casing top 
  • 3 inches at any side of the supply air plenum
  • 3 inches above the supply air ducts within 6 feet of the furnace 
  • 8 inches in the front casing of the furnace to the closet door for Trane and other brands. The exception here is the lowboy rear flue model, which requires 3 inches from the front casing of the furnace to the door. The downflow/horizontal furnace will need 22 inches from the furnace to the closet door. 
  • 9 inches from the chimney connector to the flue/vent connector.      
  • 18 inches from the chimney connector to the ceiling and combustible wall
  • 18 to 24 inches in the front for service space
  • 18 to 24 inches on other sides and panels of the working area
  • 18 inches for burner and ignition above the garage floor.
  • 3 inches in the combustion air opening and nearest closed panel or door

These are some of the approved furnace clearances. The space at the front has to be around 18 to 24 inches and not less than that. 

Also read: What Kind Of Door Do I Need For A Furnace Room?

What are the best places to install a furnace?

The location of the furnace determines the distance around the furnace, especially between the wall and the unit. 

Knowing the best areas would help you find the right location more easily and get your furnace sufficient space around. 

Poor location of the furnace or any HVAC system will cause issues, especially if they are too close to the wall or any other substance. 

The walls can get too warm or too cold, making the room uncomfortable. 

Besides, keeping the unit near any combustible materials can be dangerous. 

Additionally, insufficient space won’t give the technician enough space for repair. 

Here are some best places to install a furnace in the house:

Central area

Placing a furnace at a central location in your house supports an even distribution of heat in every corner.

It will also help prevent the need to invest in ducting and reduce unnecessary energy consumption. 

So, you can save money here. 

Some people install it directly at the center of the house. 

That can obstruct the traffic or create other obstacles based on the structure of your apartment. 

Easily accessible spots

The location does affect the distance between the furnace and the wall. 

Along with the distance clearance, you should keep in mind its accessibility. 

You must ensure that the adults and technicians can easily access the furnace, but it must be out of the children’s reach.

So, considering these things, a good place for the furnace would be in the attic or crawlspace. 

The furnace will be out of the children’s sight, and you will only know and easily access it. 

Though an attic is a good place for the furnace, you must reconsider it. 

You have to work cut out during the maintenance activities. 

Besides, putting the unit in the attic means the furnace will have to work harder to spread the warmth around your house and increase energy consumption. 

Find areas with good airflow.

If your furnace is bigger, it will need open space for proper airflow. 

The warmth will only reach every house corner if the airflow is good. 

You need to ensure that the furnace’s surrounding area has enough space for adequate airflow. 

If you have a small apartment, have electric furnaces for enough airflow as they have smaller designs. 

You can also use oil or gas-fueled furnaces for larger areas like the basement. Hire a professional to install the new furnace. 

Energy efficiency

The location of the furnace will affect its energy efficiency of the furnace. 

Place the furnace close to the energy source or anywhere in the room if the cables are too long. 

The furnaces need ventilation despite having a fuel source to prevent overheating or breaking. 

Radiant furnaces work by heating the objects around the furnaces, which get transferred into the air evenly. 

But, if there are not enough objects within the perimeter of the furnace, the heat won’t be able to spread around properly. 

The furnace will struggle and consume more energy to spread heat and increase your bill without any good results. 

So, radiant furnaces are not congested areas. 

If you have one, consider placing it in areas surrounding certain objects to heat the room. 

At the same time, you must take care of enough airflow.

What are the building requirements for furnace rooms?

Various areas have their building codes.

One important requirement of a building, while including furnace rooms, is to maintain the distance between the walls and the furnace. 

It has to be at least 30 inches. It should not decrease but can increase based on the apartment size. 

Here are the other guidelines you must follow while having furnace rooms in the house:

Furnace room ventilation

The proper ventilation system is very important for the intake of air. 

That will allow enough combustion and exhaust to eliminate carbon monoxide and other toxic materials. 

It protects the house members from fire and chemical exposure. 

Your furnace must have one vent on the floor and another on the ceiling. Both vents should be at least 12 square inches. 

Ceiling and wall requirements 

Do not ever seal the furnace room without proper ventilation. 

Use materials like brick and concrete while building walls around the furnace. 

It will give good protection and insulation.

Furnace system energy needs

The furnace must have a proper, efficient rating determined by the AFUE or Annual Fuel Utilization Efficiency rating. 

In most states, the rating requirements are around 80%.

Final thoughts

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Generally, you must put the furnace at least 30 inches away from the wall. 

It will prevent the wall from excessive heating and keep the room warm and comfortable. 

However, the distance may vary based on the apartment size. 

Around 3.5 feet distance between the wall and the furnace is enough for a small apartment. 

On the contrary, you should maintain at least 4 feet distance between the wall and the unit.

That is not enough, as you must also keep space on every side of the furnace. 

The minimum distance should be 30 inches, but it can change. 

Having enough space around the furnace will keep the furnace from overheating and fire accidents and allow the air to pass through every corner of the house without consuming too much energy. 

However, some furnaces do best in congested areas. 

So, keep only a little space around such furnaces. 

Otherwise, the heated air cannot spread properly.


Should I give ventilation space in the furnace closet?

 The furnace must have its supply and exhaust vents. 

If your building code allows, you must install a single or dual pipe system with a double inner layer. 

Also, leave some space for cool air that can get into the exteriors of the furnace. 

The ventilation space will stop the furnace from overheating. 

How much clearance should be left in front of the furnace?

You should leave at least 18 to 24 inches, 30 inches being the best option. 

However, you can leave more space if you can afford it.

However, if the heater needs compact areas to spread the heat evenly, you should leave only a little space. 

Leave enough for easy access in front of the panel doors so the technician can reach for repairs.

What should I do if there are space constraints?

Optimize the space of your room to create enough space around the furnace. 

First, plan the room’s structure and interior design, arrange everything, and make enough space for your furnace. 

For exhaust issues, solve them with piping and ductwork. 

Installing the piping to the furnace to collect the fumes, flames, and bad gasses. 

You can use a dual pipe system for one pipe to expel the exhaust, and another will take in the air. 

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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