Crawlspace plenums.. unbelievable!

I don’t know if this has been done anywhere else, but somewhere in the 60’s there were some local builders who ran the A/C and heat into the crawlspace, then just cut holes in the floor to allow the air to blow into the house. I don’t know how anyone approved this, but it just doesn’t work.
It’s crazy, but I still see some with the original units and no ductwork. Most have been updated with new units and flex duct in the crawl, but not all. They actually work OK in heat mode, but the A/C is worthless. One seller last year said their power bill in the summer was about 600-700 a month!! Here’s a pic of the A/C unit and crawl on this house. Note the plastic covering the dirt floor. I’ve seen some with leaking toilets and drain lines. Imagine blowing your household air into the crawl with that and then breathing it in! Another builder shortcut that didn’t work and was eventually done away with.

Good one Joe…:shock:

That looks like an HVAC package unit of which we have many around here. They work well, but they do require supply and return ducts!

Package units are the norm around here. This one, as numerous others around here, is blowing right into the crawl.

and how about RADON?

Joseph, Those are very popular up here as well, not only no ducts but the main plenum is always sitting the the dirt.

So the crawl space is sealed tight? Never heard of this - home owner must have got a heck of a good price on the installation?

I wouldn’t know if the homeowner got a good price or not, the builder probably pocketed the savings! :slight_smile: This hasn’t been done around here for quite some time, but a lot of these haven’t been updated so they’re still out there. What also happens is an A/C company bids on an A/C changeout with new ducts installed, but don’t cut in foundation vents.:shock:

In the original installation there were no outside vents installed. The premise was the A/C and heating provided the ventilation. But there are some A/C yoyo’s that bid a job on the cheap, and don’t cut in any vents. Presto! Instant problem.

These systems just don’t work for a couple of reasons. One is that cold air sinks, and the other is that A/C systems have to have some static pressure to move the air. With such a large plenum under the house, the pressure is very low, and there is almost no air movement. The blower wheel does what is called “freewheeling”, spinning but not pushing any air.
They work a little better in heat mode, only because the heat rises into the house. All in all, a very poor system. I wouldn’t want the A/C in my house being blown in the crawl with the dirt and leaking water pipes and (heaven forbid) a sewage leak. :shock:

Radon is not typically a problem around here, but with a sealed crawlspace all bets are off.