# Use airtight crawl space for cold air return??



## John (Jan 19, 2005)

I am planning on building a 28x36 spec house. It will be a single story, simple design with a crawl space, and all of the perimeter walls will be Logix insulated concrete forms from the footer to the roof top plate. I will have a vapor barrier on the ground in the crawl space. I will have a 1.5 ton heat pump to heat and cool the house. 

The crawl space is going to be conditioned, not vented to the outside. This meets local code. Now my question is this: Instead of running a cold air return trunk line, just open up the wall sections in the appropriate areas to the crawl space like as if you were going to put a boot on them, and pull air from the crawl space from a single main boot that accesses the crawl space. For the supply air, run a trunk line and connect to registers as required. This would help reduce the cost of the heating and cooling system, and I think would work. Of couse, any hole in the floor would function as a cold air return so you would have to control that, but overall i think it would work. What do you think? Hairbrained or good idea?


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## HVAC Doc (Apr 1, 2004)

John said:


> I am planning on building a 28x36 spec house. It will be a single story, simple design with a crawl space, and all of the perimeter walls will be Logix insulated concrete forms from the footer to the roof top plate. I will have a vapor barrier on the ground in the crawl space. I will have a 1.5 ton heat pump to heat and cool the house.
> 
> The crawl space is going to be conditioned, not vented to the outside. This meets local code. Now my question is this: Instead of running a cold air return trunk line, just open up the wall sections in the appropriate areas to the crawl space like as if you were going to put a boot on them, and pull air from the crawl space from a single main boot that accesses the crawl space. For the supply air, run a trunk line and connect to registers as required. This would help reduce the cost of the heating and cooling system, and I think would work. Of couse, any hole in the floor would function as a cold air return so you would have to control that, but overall i think it would work. What do you think? Hairbrained or good idea?


Check your local codes first. Here, we cannot pull return out of a crawl space no matter how tightly "sealed" it is.


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## John (Jan 19, 2005)

HVAC Doc said:


> Check your local codes first. Here, we cannot pull return out of a crawl space no matter how tightly "sealed" it is.


Does this mean in your area you cant even do one return from the crawl space to meet conditioned crawl space guidelines? That would be a shame because based on what I have seen conditioned crawl spaces are the way to go.


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## HVAC Doc (Apr 1, 2004)

Good luck finding a conditioned crawl space in these parts. According to the UMC (which is our code we follow), return air can only be obtained from an approved interior location. Yes a crawlspace is "inside" so to speak but it gets knocked out of consideration by 2 other parts 1. An unsanitary location and 2. Most are areas with less than 25% of the total area served by the supply air system.


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