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Old 01-08-2007, 12:26 AM   #16
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Can supply air come from a vented crawl space or even a vented attic, or does it have to come from outside the building?

I am wanting to do a very similiar type enclosure and was going to install ducting in the stud cavaties of the new furnace room with one venting from the crawl space into the furnace room (floor level) and one going from high in the furnace room to the vented attic.

Sorry for the interuption...


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Old 01-08-2007, 12:16 PM   #17
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It is actually best to bring it in from both if you have that option. This gives you the required high / low combustion air. The only thing you are not supposed to do is draw it from the living space. However as I have found out on this sight, it is apparently legal in some parts of the country to draw off the living space. Make sure to check your local mechanical codes to be sure.

Good luck
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Old 01-08-2007, 12:26 PM   #18
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Don't see that upstairs, but may be you can use those special door for the furnance room which has a lot of slots in it for air flow then you don't need to open up vent for the wall...
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Old 01-12-2007, 08:08 AM   #19
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If the adjacent "open" space is large enough (based on room volume), many codes consider it "unconfined" space, and you can use this for combustion air for the water heater (or any gas appliance), rather than having to duct from the outdoors. It is a simple calculation if you check your local code, although often the adjacent space is not large enough (code people couldn't make it THAT easy on us, could they? )

Usually, you will first have to compare the adjacent space volume to the BTUH input (gas) of the appliance, which should be on the appliance label. For every 'X' Btuhs, you will need 'Y' cubic feet of space in the adjacent area in order to consider it “unconfined” ('X' and 'Y' vary per local code). And then if you determine that the adjacent area is considered “unconfined”, then you will also have a minimum free area of vent (a wall grille, louver, hole, whatever) that you have to provide between the room with the appliance and the “unconfined” room. Many times (as some mentioned here), codes require a grille (or louver, hole, etc.) near the floor AND near the ceiling.

Check your local mechanical code – it is usually pretty straightforward.
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Old 07-31-2007, 03:01 PM   #20
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Originally Posted by amazinlittledevil View Post
Thanks everyone for the good advice.
How did you get on with the installation? I'm about to do a similar thing and found this thread. Good advice guys. Thanks!

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