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Beautiful Duct System in a Beautiful Crawl Space! Was I Dreaming?

Crawl Space Duct System Moisture Mold Nasty Iaq

I’ve seen a lot of nasty crawl spaces. I’ve squirmed through their squalor and squeezed through their narrow confines. Possums, snakes, spiders, and camel crickets have kept me company in the dank, musty underworlds that so many people live above. Moldy joist fur (furry joist mold? joisty mold fur?) doesn’t faze me. (That’s not to say I haven’t had nightmarish experiences.)

Here in the Southeastern US, the standard way to build a crawl space is to vent it to the outdoors. As we all know, though, vented crawl spaces and the psychrometric chart don’t get along so well in a humid climate. Yeah, yeah. I know the psychrometric chart is really like a honey badger and doesn’t care about a stinkin’ crawl space. But you and I both know that in its heart of hearts, the psychrometric chart is really on our side. Right?

I’ve also seen a lot of horrible duct systems. The day I spent going on calls with Moncrief Heating & Air Conditioning recently gave me five more pieces of evidence in the indictment of duct installers. The standard duct system in homes is crap.

The world is NOT flat

Just as Christopher Columbus didn’t sail off the edge of a flat Earth, home builders are now building houses on top of crawl spaces that aren’t vented to the outside. Even better, they’re occasionally putting really nice duct systems in there. Case in point, one of the homes I visited in Nashville, Tennessee last week.

Beautiful duct system in a beautiful crawl space
Beautiful duct system in a beautiful crawl space

Beautiful! Clean, white plastic to keep the moisture out and make the place seem brighter. A trunk-and-branch duct system that will actually move the air as it should. It has to because this house is getting air flow measurements and commissioning as part of the ENERGY STAR Version 3 certification. Of course, it had its flaws (a bypass duct for zoning, for example), but overall, this system was 8027.2% better than other duct systems.

crawl space encapsulated duct system supply air nashville 440

Since the crawl space is air-sealed to the outside, the air down there is conditioned from the HVAC system. About halfway down the supply trunkline is this little supply vent blowing conditioned air into the crawl space. It felt wonderful when we entered on that hot, muggy afternoon last week!

Woodland Street Partners is building the house, Maynard Select is the HVAC contractor, and E3 Innovate is doing the HERS rating and ENERGY STAR certification. Great work, folks!

My crawl space dream

I haven’t seen numbers on how many new homes are encapsulating crawl spaces like this, but I know it’s a growing trend. In humid climates, vented crawl spaces don’t make sense. In every climate, crappy ducts don’t make sense. It’s nice to see that some home builders are getting that and doing things the right way.

Drinking nice wine in Joe Lstiburek's encapsulated crawl space at Building Science Summer Camp
Drinking nice wine in Joe Lstiburek’s encapsulated crawl space at Building Science Summer Camp

My dream is that conditioned crawl spaces will become the trendy new place to host parties. Some of the best wine I’ve ever had, as a matter of fact, was at a couple of parties in Joe Lstiburek’s crawl space at Building Science Summer Camp. Hey, this could be such a big thing that even architects and interior designers will want to get in on the fun!


Related Articles

Vented Crawl Spaces and the Psychrometric Chart Are Not Friends

I Don’t Need No Stinkin’ Building Science Summer Camp!

Release the Kraken! — The Ductopus Is Bad for Air Conditioning


I just made this number up, in case you’re wondering. A lot of the numbers you see in articles on the Interwebs are made up or otherwise meaningless but the authors won’t tell you that. In fact, I read a study that said 81% of all statistics are made up.

This Post Has 13 Comments

  1. Wise words, 
    Wise words, 
    In europe I see an exact analogue in wet heating and cooling systems. 
    Hot water dumping via a shunt pump direct into return water header. 
    Ok for hydraulics, or boiler back-end protection – but switch off when done – else its a disaster for efficiency.

  2. WONDERFUL POST! I wish we
    WONDERFUL POST! I wish we could afford to make EVERY CRAWL SPACE remodel like this. Realtors have dreams too!

  3. Keith, This is a WONDERFUL
    Keith, This is a WONDERFUL idea. Now is the time to find POSITIVE EXAMPLES. PROBLEM NOW: Good examples done by contractors are hard to find. Once we find them we need to multiple him or her.

  4. Thanks for the article,
    Thanks for the article, Allison. I lived in Houston for 20 years, so I get your pain. Even here in Colorado, though (read, “bug-free,” mostly), crawls are a mess and almost always a big part of peoples’ comfort issues. I love it when I can help a client make those better. And less creepy. 

  5. James F.:
    James F.: I don’t know enough about hydronics and how it’s done here to say whether that kind of bypass is a problem on this side of the pond.  
    Dixie W.: I’m with you on that! 
    Keith H.: Done! I should have had them in there from the beginning, so thank you for pointing out that omission. 
    Melissa B.: Ah, Houston. I was born there and lived my first 10 years in that humid, muggy, moist city. That’s why I can appreciate how cool and dry the summers are here in the Atlanta area.  

  6. This is why I sometimes
    This is why I sometimes regret not doing much new construction work:-) No one ever calls and says “Please come and let me pay you to see how well my house is built”. 
    I’m glad to see that there may be an end to those damp nasty places so that the tyvek suit can stay in the van and I won’t be pulling cobwebs out of my beard.

  7. I had the opportunity to
    I had the opportunity to learn from Dr. Joe yesterday and the seminar was in his home directly above the crawl space pictured. Lots of good information and seeing it put into practice is even better. I’ve only seen a couple of these well done crawl spaces out of the multitude that I have crawled through.

  8. Great crawl space for a party
    Great crawl space for a party as long as it is for non smokers.

  9. Great post. I sealed my
    Great post. I sealed my crawlspace years ago. Not as nice as this one! Don’t have an inch of flex! 
    Now, fish the project and solve the ridiculous and soon to be non code everywhere(already in CA)bypass ducts and dump zones in zoned systems. (VIDEO) 

  10. Allison, great article! We
    Allison, great article! We sealed over 1800 crawl spaces in North Carolina last year and it never ceases to amaze me the difference that it can make! Keep up the good work!

  11. My crawl space abuts a
    My crawl space abuts a partial cellar and gas fired hot air furnace and water heater. Would sealing off the out side affect the air supply to this equipment?

  12. G. Ameno 

    G. Ameno 
    You can still seal your crawl space but you will need to have a combustion fan installed for the gas appliances. They are commonly called fan in a can and provides make up air for gas appliances installed in sealed spaces for combustion safety! Roland

  13. Currently in process of
    Currently in process of building our house, I’ve googled and read various “how to” info on “conditioned”, “closed”, and “encapsulated” crawl spaces. I’ve read supply air of 1 cfm per 30 to 50 sq. ft. of crawl space. I would like to know how the cfm was calculated on this project and the square footage of crawl space. How was the duct opening size determined? Was the cfm requirement for space entered into the design of HVAC system? What determined location of the supply duct, just close to center of space? We have 2380 sq. ft. of crawl space and my thinking is that we need more than one supply opening to distribute air more efficiently but more importantly is determining duct opening size or sizes.

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