Intake in crawlspace

I was in a crawlspace today ICF walls, vapor barrier, and poured concrete on top of barrier. I’ve never seen a conditioned crawlspace. Would you consider this a conditioned crawlspace? I found no vents in foundation, no air exchange, other than the furnace intake. I couldn’t find any sort of open exhaust duct as I thought that was part of a conditioned crawlspace. I did see signs of moisture in the crawlspace as the bolts that were attaching the rim board to the foundation were rusty. It was 40 degrees outside but warm in the crawlspace, I was hot!

Do you mean the sill plate?

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Yes sorry it’s been a long week. My brain is working half speed right now.

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No, I wouldn’t consider it a conditioned crawlspace.

From Google:

What is a conditioned crawl space?

A conditioned crawl space is hermetically sealed from outdoor air and its conditioning is a part of the house HVAC system. Conditioned crawl space includes a ground completely covered with a vapor barrier, with the barrier’s seams and junctions as well.

How does a conditioned crawl space work?

It does this by allowing conditioned air from your home to flow through it in a sealed space , which then vents the used air to the outside of your house. Think of it as a mini basement under your home.


I hope this helps you, Cory.


Okay that’s helpful thanks Larry. Why would there be an air intake for the furnace piped into the crawlspace? There was no other pipes anywhere nearby that may have come off. As far as I can tell it came that way when the house is built and I can’t figure out why.

There are so many cracks, gaps, places for air to enter the crawlspace that the furnace can get some or all of its makeup air from the crawlspace. It is not a well sealed conditioned crawlspace, Cory.

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Larry I always appreciate your shared knowledge thanks.

Just to verify even though there’s the concrete slab and no foundation vents at all, this is okay?

Cory, In pic. 1 it looks like there may be some wood rot going on in there? did you pick on that?

Yes i did/ Thanks for checking. I think its discolored from the moisture. of it sat out and was exposed to elements for a while.

I don’t know Cory, It sure looks like advanced rot from the pic. not picking on you it looks like rot in the pic. I would recheck that.

If it was my crawlspace, I would remove the batt insulation from between the floor joists and caulk and seal the perimeter block and rim joist and any other place air could get in. Then I would tightly insulate the perimeter of the crawlspace, with rigid Polyisocyanurate 2" thick and make sure the floor was sealed 6" to 8" up the walls and tight to the bottom of the columns.(We don’t want to rot out the bottom of the wood columns, if the are wood.) And also put enough registers and return air down into the crawlspace to make it part of the building envelope. Which means the make up air vent would need to come from the attic or somewhere else.

Regarding reporting, I would narrate that the crawlspace was very hot, humid with some rot starting and refer if out to an insulation contractor that understands sealed crawlspaces.

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No. I see no actual “rot” whatsoever.

It does look like rot but the OP that was there said:

It is difficult at times to see rot in a picture or even visually in person. When I see something questionable I do a gentle “ice-pick” test.

Zackty, Joe, Zackty! :grin:

Some jurisdictions require a fresh air inlet for gas fired appliances in crawlspaces and basements and have for some time. That is more than likely what you are seeing.
My house was built in 2000 and has a 6" duct that runs from the attic space over the front porch and ends about 12" above the floor very near the furnace and water heater. Fresh air supply for the lower efficiency appliances that were installed when the house was built.

Just one thought: What is your radon level in the house?

Is an electric furnace.

The radon level is very low here.