In-Slab Ductwork Retrofit
Hi GBA Community – hoping for some advice on how to approach in-slab ductwork that we have on our old house.
For context, we’re in the midst of planning a larger remodel which will focus heavily on energy efficiency, bringing our 1950’s California ranch up to code and generally making things more comfortable. Half of our home has a crawlspace through which HVAC ducts run, the other half is slab-on-grade from an addition that the previous owners did in 1965. At that time they added additional HVAC ducts to the addition that run through the slab.
We’re planning to move away from a central HVAC system in favor of a multi-split system featuring a combination of a few ducted runs in the attic and some cassette units in other areas.
This leads me to my question: what should we do with the ductwork that will remain in the slab? It hasn’t had any issues with mold or moisture condensation since we’ve moved in, but of course we’re also usually either heating or cooling the home largely due to it’s poor energy efficiency.
Should we fill these ducts with something? Poured cement? Closed cell foam? Or just cover up the supply vents and add flooring over them?
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Replies
I doubt you need to fill the ductwork, but it would be a good idea to seal the openings where they meet living space. You could use rigid foam, cut smaller than the opening and sealed with canned foam, covered with plywood and flooring.