Heated Slab – Recirculate air?
user-132743
| Posted in Energy, Heating & Insulation on
I am building a new house with in slab heating. I have cathedral ceilings and a hrv. I had intended to use my HRV to draw the stratified air from the cathedral ceiling using a recirculating system on the hrv. My contractor tells me this is unnecessary because the slab will hold the heat. I understand the principals of heating with a slab, but would like a second opinion on the value of the recirculation.
thanks
Replies
actual recirc might be ok, but ceiling fans, for example, are counterproductive if you are using radiant floor. the draft affect they induce reduces your comfort.
stratification is much less with radiant. but it does exist: if doing this does not induce a noticeable draft in the space, that's definitely better than a ceiling fan.
that said.. you're taking your hottest air and blowing it outside, albeit with some recovery efficiency, you're still maximizing your loss. the upward pull of the air at that point may even increase your upward heat movement and increase heat loss overall, compared to just leaving at your presumably well insulated ceiling.
it would be an interesting experiment, but unless I were an experimenter I'd probably skip it.
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Funny you should mention 'stratification' and radiant heat in the same sentence.
The one place I lived that had radiant heat (hot water piping in the cement slab floor) had ordinary 8 ft. ceilings. I noticed a few things about it.
The first was the complete lack of drafts, even from the cheap single pane windows.
The second was that I was quite comfortable with the thermostat at a much lower setting than usual. The reason was simple: stratification, but not as you would expect.
That is, the thermostat (set at 5 ft. off the floor) might read "65," but my head (maybe 36" off the floor when sitting in the sofa) was quite comfortable, anf my feet were positively toasty. In short, there was stratification with the warmest parts being closest to the floor.
Now, it's also possible that this was caused by inadequate insulation, with the heat being lost faster than it rose. All I know is that any attempt to move the air about would have reduced my comfort.
It sounds like you assume you will have stratification ... which you will not likely have. Your motivation should be ventilation ... and then if you want HRV, then do it, but don't go out of your way to destratify when you won't likely have much.