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Re: Minimum distace of return form furnace
OK, so bear with me as I try to parse the application of this to the most typical inspection in my area: 2 story single family home with a full basement connected to the first floor by a stairway with a door at the top.
"Outdoor and return air for a forced-air heating or cooling system shall not be taken from... 3. A room or space, the volume of which is less than 25 percent of the entire volume served by such system. Where connected by a permanent opening having an area sized in accordance with ACCA Manual D, adjoining rooms or spaces shall be considered as a single room or space for the purpose of determining the volume of such rooms or spaces."
Looks like the basement has to be considered separately from "adjoining areas or spaces" (the first and second floors)" as the door is not a "permanent opening". The attic is not conditioned space, and thus not served by the system. In my area the typical basement ceilings in older homes are around 6 '6", and the typical ceiling elsewhere is around 8', so the basement volume is around 28% of the volume served, and the 10' rule does not apply under (3) above.
"- 3... Exception:The minimum volume requirement shall not apply where the amount of return air taken from a room or space is less than or equal to the amount of supply air delivered to such room or space."
If I'm reading this correctly, you could have a return cut into a duct adjacent to a draft hood as long as you had supply registers in the basement providing a greater amount of air at the far ends of the basement, even if the basement is less than 25% of the total volume, which lead us to:
"from... 4. A closet, bathroom, toilet room, kitchen, garage, mechanical room, furnace room or other dwelling unit. "
The entire basement serves as the "furnace room", but... is this intended to apply in such situations, or rather to something like an enclosed utility closet within a basement or other "unconfined space"?
"From ... A room or space containing a fuel-burning appliance where such room or space serves as the sole source of return air."
Typically, there will be return air ducted from rooms above, so this would not seem to apply either...
So, assuming that the basement is 25% or more of total volume, what prohibits someone from putting a big honking return grill in the return plenum at the furnace?
Or even assuming it's smaller, what prohibits someone from putting a smaller return opening there if the supply to the basement is greater than the return volume at the grill?
Am I missing something here?
Last edited by Michael Thomas : 01-09-2008 at 08:21 AM.
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