Wall clearance for gas furnace


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Old 03-28-06, 07:35 AM
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Wall clearance for gas furnace

I'm in the process of remodeling my basement, where my natural gas-powered forced-air furnace is situated, and I need to know how much clearance I need around the furnace. For instance, is 2 feet of floor space between the exterior of the furnace and the wallboard sufficient for servicing the unit? Do I need more space at the front of the unit? The installation instructions for the unit don't give any specs on such a consideration.
 
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Old 03-28-06, 06:30 PM
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In mobile homes, gas furnaces are stuck in wooden closets with only a few inches of clearance. Yet, oddly, in apartment buildings I see furnace rooms that are concrete with steel fire doors on them. Perhaps different codes apply to multi-units.

If you have open combustion, meaning the intake to the furnace is not sealed, and there is no pvc piping lettin *IN* air to the burner area (such furnaces have 2 pvc pipes..one for intake and one for exhaust), then you have to have provisions to getting fresh air to the burners. You don't want some small boxed-in space where lots of air can't get to the furnace. Also, you don't want to run the risk of cold air return air drawing air from the burner area back into the cold air return.

If you can duct in fresh outside air through ducting with a damper on it, into the room with the furnace, I think that would be ideal, if you have the open combustion. For this 4-plex that I work on that has a furnace room with 4 furnaces in the room, they have such a duct. When one or more furnaces run, you should feel the air flying in through the duct, showing how much the burners require of (fresh) air.

But, as we all know, many homes built prior to the high efficiency closed combustion furnaces systems had no outside fresh air piped in and simply relied on size of building and air leaks/air being drawn through wall/roof vents and chimneys to get fresh air. So, you want to at least have the room not sealed...that is a given

Regarding gaining access to the furnace: In mobile homes, the only provision there is for front access. All the furnaces are walled in on 3 sides and either left open to the front or there is a fully louvred door. IF you have a/c, you want to make sure that you can gain access to the plenum (seam) to get into the A-coil to clean, or replace it, without cutting a big hole in your room.

My suggestions are just that, based on actual observed applications and knowledge of furnace systems in general. Code can require something entirely different. I know inspectors of housing want combustibles kept so many feet away from furnaces. There also might be a provision requiring fire-rated sheetrock to line the room. Stuff like that.

You might want to contact some local builders association and ask if there is someone you could talk to regarding code regarding this, for your area, where you can gain the necessary information. Or, maybe an HVAC company would tell you what you want/need to know, seeing that you aren't taking work away from them, but simply making a room for the furnace. Calling up an inspector would be my last choice, personally, as in my past experiences they start sounding like police officers and want to know all kinds of information. But that is up to you.

You could also contact the furnace manufacturer and see if they can, or will, answer questions from a homeowner. Some companies are wary of doing so for liability purposes. But, seeing you won't be tampering with the furnace, and only want to deal with clearances, you would think they would oblige.
 
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Old 03-28-06, 08:09 PM
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Thank you for your lengthy and extremely well-written answer. Your answer reinforced my commitment to never live in a mobile home. In my previous home, when I replaced the HVAC package unit I spent an extra $1000 to move the location of the HVAC and electrical disconnect so the service person could have five-sided access to the unit. How can I expect someone to properly install, maintain and repair my HVAC unit if he can't get to all sides of it?
My 1991 high-efficiency gas furnace has PVC pipe ducting for the intake, similar to your description, so I'm in pretty good shape there.
I believe I will begin by asking a factory authorized service company what they recommend for clearance, and if I can't get an answer there, I'll call the factory. After that, I'll call my city code enforcement office and ask them to research the uniform building code for specs.
 
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Old 03-30-06, 06:28 PM
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A common mistake is not allowing enough room to get the A/C coil out without kinking the lines. This problem is occurs most often when the coil is sitting across the furnace rather than paralell with it. Manufacturers don't take this into account in their installation specs.
 
 

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