Thread: Crawlspace heated by furnace. No sub ventilation. No supply ducts. Floor registers.

This is the second time I have seen this...house was built on a concrete block foundation with no sub ventilation. Vapor barrier covers entire crawlspace and perimeter walls. Downdraft furnace blows air directly in to and heats crawlspace using no supply ducts. A small amount of warm air rises up in to living spaces through floor registers. Has anyone ever seen anything like this before? I can't imagine this being an acceptable practice. thks.

Google some of Joe Lstiburek's work on conditioned crawl spaces. He covers it in great detail.

Originally Posted by Jim Robinson

Google some of Joe Lstiburek's work on conditioned crawl spaces. He covers it in great detail.

very interesting...thank you very much!

I saw that one time in a house with an electric furnace. I told my client the duct work was missing.
The crawlspace walls were not insulated, but it was nice and cozy down there.

That type of system is known as "crawlspace plenum system". It's funny, my very first home was built this way. Had a cheap electric furnace that blew directly into crawlspace, no insulation at perimeter of foundation. Needless to say it was not very efficient.

The potential concerns with this type of system are radon gas entering living space from crawlspace. Poor indoor air quality. High energy costs.

A good system will have insulation installed at perimeter of foundation and joist band. Vapor barrier installed very well, covering all exposed soil. Disposable register vent filters at each vent.

With the right equipment and design these types of systems can perform very well and be efficient. I have seen geothermal heat pump systems installed this way and work very well.

Originally Posted by Trent Tarter

That type of system is known as "crawlspace plenum system". It's funny, my very first home was built this way. Had a cheap electric furnace that blew directly into crawlspace, no insulation at perimeter of foundation. Needless to say it was not very efficient.

The potential concerns with this type of system are radon gas entering living space from crawlspace. Poor indoor air quality. High energy costs.

A good system will have insulation installed at perimeter of foundation and joist band. Vapor barrier installed very well, covering all exposed soil. Disposable register vent filters at each vent.

With the right equipment and design these types of systems can perform very well and be efficient. I have seen geothermal heat pump systems installed this way and work very well.

We probably see about equal amounts of these being in similar states (Oregon/Washington). I probably see on every year or two. Most I've come across has pea gravel on the floor and no vapor barrier. I saw one once that had a concrete floor and only about 6" of clearance so there was no getting in.... except for the rats and mice. What a disaster.... they buyer walked on the house which was otherwise a really nice place. I'd liken it to building a car with only a small 2" opening around the edges of the hood. You could look inside and see a couple things but there's no fixing anything.

Plenum houses with reasonably sized crawl spaces are not a terrible design but I'd probably opt against it if it were my place. With most I see it wouldn't be that hard to just install some ductwork & a vapor barrier and ventilate the crawl space.