Home Improvement Asked on September 15, 2020
My house is built on a slab. Within the slab are “channels” which act as ducts for the HVAC system.
I assume it is partially lined with metal but based on photos from an HVAC-cleaner, it’s hard to tell how far that metal goes from the registers.
Long term, I plan on re-routing all of my HVAC outside of this slab ductwork as it is extremely dirty, probably contaminated with all kinds of mold and insects, and essentially a big mess. This house was built over 60 years ago.
In the mean-time, I am about to re-do a single room’s floor. It is currently concrete (carpet had been ripped up) but is going to be replaced by porcelain tile. This specific room is really close to the furnace (with a direct wall-vent a previous owner “cut in”) so I am not concerned about its temperature.
I want to fill in, or otherwise seal off, the slab-duct and register in this room so I can tile over it. Long term, I want to do quit using all of my in-slab ducts.
Can I simply seal off the duct at this register? Or do I need to fill the entire duct in the slab in this room? What material (concrete/cement? specific type?) should I use in either case?
Thanks!
I would remove the register and pour ready-mix concrete into the channel to seal the old "ducts" and fill up the hole in the floor. Shouldn't cost you more then $20, if that.
Answered by iLikeDirt on September 15, 2020
I see this is an older Question. But yes, you want to fill that room's entire duct for structural stability with gravel or even expanding foam. While it's been perfectly fine for this long, the heat removal could allow freezing now or later & invite cracking or collapse of that minimal section.
If you'd prefer to just keep the in-slab ducts, if cleanliness was addressed long term. Then, these can be scrubbed out (not just vacuumed) & paint sealed with a few layers of sprayed-on paint via a hose. I don't know of anyone who could do it personally, but it really should be quite quick & simple with wonderful results.
Answered by Iggy on September 15, 2020
Not sure why Community popped this up as active since it has old answers, but I think you wasted a lot of time and money unless there was some issue with the HVAC system performance you weren't disclosing. If you're concerned about debris in the ducts, just have someone clean them out. There are services that specialize in that.
Answered by topshot on September 15, 2020
when you pour concrete into slab duct you will have expansion from new cement. I would think you need to insert some expansion material to prevent cracking the floor slab. Foam may do the same thing. My slab from 1952 had dust, neighbor has leaches. Old metal pipes rust out that they used for slab ducts. local companies refuse to work on them.
Answered by mike on September 15, 2020
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