Can open-web floor truss space be used instead of ductwork for heating/cooling?
![](https://secure.gravatar.com/avatar/b74bd475f5cbccd8b50bfdc41e420740?s=52&d=https%3A%2F%2Fimages.greenbuildingadvisor.com%2Fapp%2Favatars%2F200x200%2Fm.png&r=g)
I have a already built 3-story 3,800 s.f. colonial Garrison outside of Boston, MA. When we built the home in the late ’80s I figured to save money on duct work by not putting in whole house AC. I might have saved then, but I’m going to have to pay now that we are putting in a new HVAC system to replace the oil baseboard heat and window AC.
The house has open-web floor trusses and am wondering if it is even possible to use the open spaces between floors for air distribution? The perimeter of all the trusses have been sealed with 3″ closed cell foam, 1″ foam board on the outside, and a house wrap, so the space between the floors is tight.
My knowledge of HVAC systems does not go far beyond cool air falls and hot air rises. Just hoping that floor and ceiling vents combined with open web floor trusses could offset some of the $12K that I just got quoted for ductwork.
Thanks,
Mark
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb1.png)
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb2.png)
Replies
It's certainly possible. Search the web for "under-floor air distribution". I've never heard of it being done in residential wood-framed construction, though.
John,
Thanks. I do a search for those words combined with residential and anything else I can think of.
Mark
Mark,
I disagree with John Semmelhack. According to the 2009 International Residential Code, section M1601.5, "Under-floor plenums shall be prohibited in new structures." Moreover, according to section M1601.1.1, "Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions: 1. These cavities or spaces shall not be used as a plenum for supply air."
As Martin said, you can not use the truss cavities as plenums, but if you have the space, you can run ducts in between the webs. In my projects, I only specify dedicated chases for main supply trunk lines and in-between web spaces for all branches. The complete duct system is metal, with some minor 5' max. flex duct ends with appropriate elbows, for noise reduction.
Martin - I didn't mean to imply that it was code-compliant or that I was recommending it...just that it was POSSIBLE, and was done in other situations...