New Construction, SLAB COOLING

I’m planning a 24’ x 24’ two story studio with guest quarters, kitchenette & bath. The first floor heat will be an insulated concrete slab with PEX, boiler undetermined, maybe pellets.

Second floor will be wood construction w/o in-floor heat, probably electric baseboard which is common in the region.

This is a northern climate but, as we all know, it’s getting hotter. So, it gets into 90s F in summer. I’ve thought of two slab loops, one for hot, one for cold. Let’s just say there’s plenty of cold water handy, creek at 55F or ground water not too deep, 10-20’ probably. I could also dump the cold water back into an “open” well.

Will I have condensation on the slab when cooling? Is it an issue? If so is it easily solved with dehumidification?

  • 2
    Using toaster heat in 2023 "because it's customary" is frankly insane.
    – Ecnerwal
    Commented Nov 8, 2023 at 21:29
  • 1
    Does slab cooling even work? Slab heating works largely due to convection, which wouldn't occur with cooling.
    – isherwood
    Commented Nov 8, 2023 at 21:31
  • 1
    Solved with dehumidification will probably cancel out any savings, if not cost much more. Check into mini splits/heat pumps if wanting heating and cooling and save money.
    – crip659
    Commented Nov 8, 2023 at 21:33
  • 1
    A lot of the benefits from having air conditioning is the removal of moisture, creating lower humidity. Having a cooling loop embedded in the floor will do nothing for reducing humidity in the air since air conditioners blow the air over cold coils. So at best, you'll have cold floors, MAYBE very slightly cooler air, and a humid environment, which would lead to likely condensation on your floors. If you feel the need to leverage your creek water, look into ground source heat pumps, which would give great benefit both for heating and cooling.
    – Milwrdfan
    Commented Nov 8, 2023 at 22:02
  • Ha, nuff said, but more is welcome. Although, I have a 44 x 44 shop with an insulated heated slab, temps range from +90’s to -50’s f. And, that’s not wind chill. When the slab is warm, the air inside is warm. When the slab cools so does the air inside. Warm slab, warm air. Cool slab, cool air. No condensation here.. What’s the difference? Warm air? Warm fluid in the PEX. Cold air? Cold fluid in the PEX. Not much for stratification either in a 14’ ceiling. If there were a problem with my theory, I think a Humidex might help if not cure a problem. Heat pumps are on my list to learn more about.
    – Robert
    Commented Nov 8, 2023 at 23:12

1 Answer 1


Hint - what's the dewpoint in cooling season? is it below 55°F or above that? Dry desert you might not drip, as the dewpoint might be below 50°F all summer; where it gets hot and muggy with dewpoints in the 70s°F you'll drip like crazy.

Hint 2 The separate cooling loop should be on (or just below) the ceiling, (with a gutter under it unless the dewpoint stays below 55°F all the time you want to cool,) not in the floor. Hot air rises, cold air falls, as does cold water.

Warm floors are good for heating, cold floors are not particularly good for cooling, as the air just stratifies and is still hot, while your feet get cold.

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