Warm air furnace installation clearances & fire clearances:

What are the required clearance distances around a heating furnace: here we provide a table of recommended working space and fire clearances for gas fired heating furnaces.

This article series answers just about any question about forced air or warm air furnace central heating system troubleshooting, inspection, diagnosis, and repairs in residential buildings and homes.

Warm Air Furnace Clearance Distances

Here we describe typical and code-cited fire safety clearance distances for gas fueled furnaces and then for oil-fired furnaces. Some model or adopted codes such as the Minnesota Fire Code 603.5.3 Heating Appliance Clearance to Combustible Materials make no distinction between the fuel the heater uses:

603.5.3.1 Gas or Fuel-Oil Heaters

A minimum of 18 inches (457 mm) shall be maintained between gas or fuel-oil heat-producing appliances and combustible materials.

While other furnace clearance distance requirements vary depending on the furnace fuel and, of course, the manufacturer's installation instructions for the specific oil- or gas- furnace brand and model.

Article Contents

• GAS FURNACE CLEARANCE DISTANCES
• OIL FURNACE CLEARANCE DISTANCES

Gas Furnace Clearance Distances

There are several gas or oil fired heating furnace clearance distance types:

1. Clearance from combustibles - ranging from 0" to 18" to 36" (typically) depending on the fuel type (electric, gas, oil).
2. Working space or clearance distances - that may allow 0 on 1-3 sides but always requires working space at least at the front, or at front + rear if access to a blower or filter are at the unit rear side.
   
   Typically for gas furnaces there must be a minimum of 24" front accessibility to the furnace, and any access door or panel must have enough clearance space to permit removal of the largest component in the equipment.
3. Direct vent terminal clearance distances: distance from the exhaust vent at the exterior wall to building features such as gas meter outlet, windows, doors, balconies, building corners, clearance over a driveway or paved sidewalk.
   
   These range from 0" to 7 ft. - this set of distances is surely not what your maintenance guys were discussing regarding your clothes dryer. Details are
   
   at GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES
4. Flue vent connector clearance distances: distance from the flue vent connector of "flue pipe" to combustibles
   
   For gas furnaces see
   
   FLUE VENT CONNECTOR FIRE CLEARANCE: GAS FIRED EQUIPMENT
5. Chimney clearances: for heaters vented into a metal or masonry chimney, clearance distances around the chimney and chimney top including chimney top to roof.
6. Location related clearances: for heaters installed in a garage or in another location subject to hazards of gas accumulation at floor level or subject to impact by a vehicle, protection and elevation above the floor are required.

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Notes & References for the table above:

1. AMERICAN STANDARD GAS FURNACE INSTALLATION MANUAL [PDF] (2008), American Standard Heating & Air Conditioning, A341624P07, Upflow / Horizontal gas furnaces, Downflow / Horizontal gas furnaces, Models CUX1B040A9241A CUX1B060A9361A CUX1B080A9421A CUX1C100A9481A CUX1D100A9601A CUX1D120A9601A CDX1B040A9241A CDX1B060A9361A CDX1B080A9421A CDX1C100A9481A CDX1D120A9601A Pub. No. 41-5016-07

2. Any access door or panel must permit removal of the largest component in the heater at that location

3. Combustion air requirements: COMBUSTION AIR DEFECTS

4. Allow space above supply plenum or above the furnace to add a cooling coil including installation work space if not installed at time of furnace installation

5. Garage installations:

Furnaces installed in a garage must place burners & ignition source no less than 18" above the floor & furnace must be protected from physical damage from vehicles

6. Attic installations:

A horizontal gas furnace installation in an attic should be on a service platform large enough to allow for proper clearances on all sides and service access to the front of the furnace (see manufacturer's I&O manual).

Line contact is only permissible between lines formed by intersections of the top and two sides of the furnace casing and building joists, studs, or framing.

7. Attic installations, suspended:

The horizontal furnace may also be suspended from the joists using 3/8" all-thread rods with pieces of angle iron underneath the furnace to form a hanging rack at both ends and the midpoint. The rods need to be of sufficient length to allow for proper clearances from combustible materials. The angle iron needs to be at least 32" in length to allow for access to service panels.

8. Crawl space installations:

The furnace may be placed horizontally in a crawl space on a pad or other noncombustible material which will raise the unit for sufficient protection from moisture.

9. Condensate drain elevation space:

A horizontal furnace in a crawl space must also be elevated approximately 4-6 inches to allow clearance for the condensate drain to exit the cabinet in the horizontal position.

10. Condensing furnace venting:

American Gas Association has certified the design of condensing furnaces for a minimum of 0" clearance from combustible materials with a single wall plastic vent pipe.

See DIRECT VENTS / SIDE WALL VENTS for a complete table of recommended clearance distances from a direct vent gas appliance terminal to other building components or features.

See also CONDENSING BOILERS/FURNACES

11. Masonry flue or shared flue venting:

Where the system is routed to the outdoors through an existing masonry chimney containing flue products from another gas appliance, or where required by local codes, then 3" venting of Type 29-4C stainless steel must be used in place of PVC material.

These furnaces have been classified as CATEGORY IV furnaces in accordance with the latest edition of ANSI Z21.47 • CAN/CGA- 2.3 Standards. Category IV furnaces operate with positive vent pressure and with a vent gas temperature less than 140° F above the dewpoint. These conditions require special venting systems, which must be gas tight and water tight.

99. WALL-MOUNTED FURNACES - separate clearance distance requirements are given for wall-mount heating furnaces

Watch out: the Gas Furnace Installation Manual for your specific furnace brand and model will give additional specific clearance requirements. To find the manual for your gas furnace

see MANUALS & PARTS GUIDES - HVAC

Elevate Furnace Ignition Source & Protect from Impact

Appliances having an ignition source shall be elevated such that the source of ignition is not less than 18 inches (457 mm) above the floor in garages.

For the purpose of this section, rooms or spaces that are not part of the living space of a dwelling unit and that communicate with a private garage through openings shall be considered to be part of the garage.

See details at ELEVATE OIL or GAS BURNER 18" ABOVE GARAGE FLOOR - IRC Requirement

Also,

Appliances shall not be installed in a location subject to vehicle damage except where protected by approved barriers.

See details at PROTECTION BOLLARDS for MECHANICAL EQUIPMENT

Original source of the text and illustration above:

• Stevens WA, COMMONLY USED RESIDENTIAL BUILDING CODES, IRC 2009, [PDF] retrieved 2019/05/08 original source: co.stevens.wa.us/landservices/documents/MECHANICALSECTION.pdf

Oil Furnace Clearance Distances

Standard Oil Furnace Clearances

Standard clearances are mandatory minimum clearances from heated surfaces of the furnace to combustible materials to assure protection from fire hazard during furnace operation.

(Refer to the Standard for the Installation of Oil-Burning Equipment, NFPA 31-2001, for definitions of combustible and non-combustible material

s.) Accessibility clearances, which are typically greater, may exceed fire protection clearances.

Therefore, consider providing at least 24 inches of clearance from the front (and the rear, for lowboy furnaces) of the furnace to obstructions and surfaces for adequate service and maintenance access . - (Trane 2009)

Oil Furnace Fire Clearances

Minnesota Fire Code 603.5.3 Heating Appliance Clearance to Combustible Materials:

603.5.3.1 Gas or Fuel-Oil Heaters

A minimum of 18 inches (457 mm) shall be maintained between gas or fuel-oil heat-producing appliances and combustible materials.

Oil furnace flue vent connector ("stack pipe" or "flue pipe" that connects the heater to the chimney) clearance requirements are given in detail separately

at FLUE VENT CONNECTOR FIRE CLEARANCE: OIL FIRED EQUIPMENT

Oil Furnace Working Space & Fire Clearances

Notes to the table above

1. Though these are approved clearances for these furnaces, space must be provided at the front (18 inches minimum, 24 inches recommended) and at the rear of the furnace for access, service, and replacement of the oil burner, air filter(s), circulating air blower, and fan motor. - (Trane 2009)
2. Trane, OIL FIRED CENTRAL FURNACE INSTALLER'S GUIDE [PDF] (2009) - Models: THV1M087A936, 948, 9V3, 9V5SA - Highboy TLF1M087A936, 948, 9V3, 9V5SA- Lowboy Front Flue TLR1M087A936, 948, 9V3, 9V5SA - Lowboy Rear Flue TDF1M087A936, 948, 9V3, 9V5SA - Downflow/ Horizontal - Trane Corp., 6200 Troup Highway, Tyler, TX 75707 USA, retrieved 2022/08/30, original source: VT Energy https://www.vtenergy.com/documents/23-r110101.pdf
3. Hallmark, HALLMARK OIL FIRED FURNACE INSTALLATION & OPERATION MANUAL [PDF] Boyertown Furnace Co. PO Box 100 Boyertown, PA 19512 610-369-1450 www.boyertownfurnace.com
4. FLUE VENT CONNECTOR FIRE CLEARANCE: OIL FIRED EQUIPMENT

Watch out: the Oil Furnace Installation Manual for your specific furnace brand and model will give additional specific clearance requirements. To find the manual for your oil-fired furnace

see MANUALS & PARTS GUIDES - HVAC

Typical Furnace or Boiler Clearance Distance Measurement Points

The illustration above appears, in various versions, in many boiler and furnace installation manuals. The minimum and most-basic fire-safety and working space clearance distance measurements are as follows:

Front view boiler or furnace clearance distance measurements

• A = clearance distance from exterior surface of the boiler's sides to any nearby wall or other obstruction (such as other equipment)

Side view boiler or furnace clearance distance measurements

• C = distance in front of the equipment to any wall, door, or other obstruction
• D = distance from the back surface of the heater to any wall or other obstruction
• E = distance from the upper surface of the flue vent connector (stackpipe) to the closest underside surface of the ceiling

Top-down view boiler or furnace clearance distance measurements

• A = distance to side walls or obstruction
• D = distance to ceiling
• E = distance from flue-vent connector (stack pipe) to wall

The actual permitted distances for each of these measurements are given in tables on this page for furnaces and for boilers

at BOILER CLEARANCE DISTANCES

You'll see that those numbers vary by heating equipment brand and model and fuel.

Solid Fuel Furnace Clearance Distances

Again using as an example the Minnesota Fire Code 603.5.3 Heating Appliance Clearance to Combustible Materials:

603.5.3.2 Solid Fuel-Burning Heaters

A minimum of 36 inches (914 mm) shall be maintained between solid fuel-burning appliances and combustible materials.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2019-07-23 by (mod) -

Anon:

The "coil" in a furnace is usually a cooling coil used when the air handler is providing both heating and COOLING to the home. If there is a cooling coil there'll also be an outdoor compressor/condenser unit.

The coil will be on the outlet or "supply" side of the air handler.

On 2019-07-23 by Anonymous

Is there a coil inside the under the floor furnace someone told me there was a in the furnace condenser is this true

On 2019-04-19 by (mod) -

It's an interesting question. Thank you. Because there are definite fire and explosion hazards you should be sure that any final design you have in mind it's approved by your local building or fire inspector.

The basic concept has more than just ventilating the area it is that you need to provide enough combustion air for the equipment in the enclosed space. I best design would bring the combustion air from Outdoors.

To avoid picking up combustible fumes the air intake to heating equipment is often required to be some height between 18in or more to 2 feet or more above the floor.

On 2019-04-19 by quinn

Hello.
Ranch home in NYS. My basement has garage door and there is lots of gasoline powered equipment stored there. Based on design of house I would like to just enclose the utilities (natural gas heater and hot water tank) vs a huge room around the equipment to minimize explosion risk from accidental gasoline leak.

At some point in past I saw some requirement (cant remember where) which suggested that there should be venting ports should be up high and low to prevent vapor pooling inside the room; if my intent is to protect against gasoline explosion wouldn't the low vent be an issue?

Is it acceptable to have the low vent with a fan to push the air out of the room to minimize the risk. I look toward your comments.

On 2019-04-15 by (mod) -

Rose

Using the search box just above to search InspectApedia.com for "air conditioner clearance distances" finds

CLEARANCE DISTANCE, HVAC at https://inspectapedia.com/aircond/HVAC_Clearance_Distances.php - that's more complete than could answer here

On 2019-04-15 by Rose

What is the IL Code law for distance, putting an outside heating/AC unit between two residential houses? How close/far does it need to be from neighbors residential property line?

On 2019-01-22 by (mod) -

Sharon

I think you're asking about the furnace exhaust vent clearance distance from the wall termination or vent cap to other surfaces or obstructions.

That distance depends on a number of factors such as fuel (gas vs oil), and also the manufacturer's specifications.

I have never seen an Installation/Operation manual for a direct vent heater that did not include a sketch showing required clearance distances.

But if really your heater's manual (please give us the brand and model furnace so we can take a look too) omits that data,
see

GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES
at
inspectapedia.com/chimneys/Gas-Heater-Direct-Vent-Clearances.php

IMAGE LOST by older version of Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-01-22 by Sharon

Oh I forgot to mention, the furnace doesn't have any information on the outside to tell me what the distance should be :(

What is the distance that needs to be allowed from the vent pipe and the wall? Had the insurance inspector in my home and they are telling me it needs to be checked as the distance isn't enough.. Although the furnace has been there since the house was built and I have had technician in there before for regular maintenance and no mentioning of this..

On 2018-11-28 by (mod) -

Apologize George but it's difficult to diagnose the system when we can't see it and know nothing about it. In general one can cut and repair ductwork for various reasons. However the supply plenum needs to fit the situation and be able to connect to the supply ducts.

On 2018-11-27 by George smith

can I cut my warm air duct to raise the furnace off the floor

On 2018-11-27 by Anonymous

can I cut my warm air duct to raise the furnace off the floor

On 2018-10-15 by (mod) -

Mary

Warm air blowing out of heating air supply registers is not itself a fire hazard.

However if you block heating supply air you make the room cold or make it more costly to heat as well as making it heat more slowly- if at all (depending on the extent of blockage).

There could be a subtle hazard: if you block too much supply air from exiting the supply duct system you could cause overheating at the furnace heat exchanger itself. In extreme cases the fan limit control, reaching a high temperature, should then shut down the heating system.

However repeated overheating at the furnace could ultimately damage the heat exchanger. If that damage results in a crack or hole the heat exchanger could leak fatal carbon monoxide into the building air.

That scenario is possible, though unlikely.

So in sum, the main concern with furniture too close to the heating vents is blocking heat from entering the room.

Using a couch whose back parallels a wall for example, I keep the couch 8" away from the closest edge of a floor or wall heating supply or return air vent. I figure that if there is 6-8" of clearance in width by several feet in length for air movement, I'm not obstructing air flow and the room will heat (or cool).

On 2018-10-15 by Mary

I'm wondering how far furniture needs to be from the heat vents in a room for safety sake?

...

Continue reading at FIRE CLEARANCES, SINGLE WALL METAL FLUES & VENTS, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BOILER CLEARANCE DISTANCES
• CLEARANCE DISTANCE, HVAC
• CLEARANCE DISTANCES for BUILDING SYSTEMS & FEATURES - topic home
• ELEVATE OIL or GAS BURNER 18" ABOVE GARAGE FLOOR - IRC Requirement
• FIRE CLEARANCES INDOORS
• FIRE CLEARANCES, SINGLE WALL METAL FLUES & VENTS
• FURNACE CLEARANCE DISTANCES
• FURNACES, HEATING - topic home
• GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES
• OIL TANK CLEARANCE DISTANCES & LOCATIONS
• PROTECTION BOLLARDS for MECHANICAL EQUIPMENT

Suggested citation for this web page

FURNACE CLEARANCE DISTANCES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

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