Energy flow in crawl spaces

Please, I need help. What determines whether a crawl space is conditioned or unconditioned for energy purposes? Is it insulation? Vents? Piping/HVAC in it? I have not found a definition.


Easy peezy. Does it have a source of heat and/or AC? Is it inside or outside the building thermal envelope?


In order to understand what a conditioned crawl space is one needs to understand the meaning of an unconditioned or vented crawl space. As a CPI, this was part of your training. Do review it. As far as meeting certain energy standards, there are specific guidelines that must be followed and they vary with locale.

Read deep into this thread. You will see where I was “schooled” about conditioned crawlspaces.

It is all about the thermal envelope. There are also a few links in there that will shed more light.

Just to add to above comments. There is a difference between a conditioned and an encapsulated crawl space.


If I am not mistaken, a non vented crawl must be either conditioned or have a dehumidifier as well as proper vapor barrier.

Has anyone ever run across a house with a “plenum” crawl space? It’s a heavily conditioned crawl space - as in the whole thing is a heating duct. The floor of the crawl space usually has pea gravel (no vapor barrier) and it looks like the heating ducts have been removed. There’s just one bit output duct (usually near the furnace) that blasts conditioned air into the space and the heat registers just open to the crawl space and air is “forced” up through them. There are no foundation vents and it’s just an enclosed system.

I suppose this didn’t prove to be the greatest idea since they are SUPER rare. The only reason I can think to do this would be to save on heat ducts.

In 21+ years inspecting in the land of crawl spaces (Oregon) I’ve probably run across a half dozen or so.

Yes, however very ineffective for proper air flow in the habitable space.
I run across 1 or 2 a year here in Michigan and always recommend a proper duct system be installed.

It is more common in older commercial buildings where the area above the drop ceiling and below the roof structure is used for a return plenum. Worse yet for proper air flow.

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Conditioning the crawl space is the practice of pulling the conditioned air from the main area of the home down through the crawl area.


Thank you all for your help. Marcel, the articles helped a lot. Thank you