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Tricky Heating

I have a 1200 square foot home built in the 60's. It is a slab with 2x4's tipped on side like a frame with plywood sub floor. We have no idea how the slab was constructed as the main part of the house was originally a garage. I was just quoted $13,000 for a ductless ac/heat system, but the heat will not go where I need it. I currently have radiant heat with registers on all outside walls (even going through the kitchen cabinets and closets). My issue is I have a 9 month old daughter and this winter she will be crawling/learning to walk on freezing cold floors. I wear wool socks and slippers and still have to keep my feet off the floor during Wisconsin winters. I have tried carpeting, but it doesn't do much to make the floors warmer. I love my home and its location and my dream is to switch to radiant floor heating but my father says we have to figure out a way to insulate or I will just be paying to heat the slab. The problem is there is no way to access the slab aside from ripping up the entire sub floor. I was thinking about blown insulation which may only require small holes to get it in the spaces but there is really no way to get a vapor barrier in there. My other issue is current ceiling height is 7'6 1/2" so raising the floor with a layer of insulation, cement, radiant product more cement and tile would raise it a ridiculous amount. Has anyone else dealt with something similar? What was your solution? Help!

Re: Tricky Heating


This is a somewhat difficult topic to respond to over the internet, as it requires that you have a number of various heating installation experts do an on-site visit to your home to evaluate the situation and suggest a solution; I recommend that you consult the Yellow Pages under "Heating Contractors", and search the display ads present there to determine which contractors in your area do radiant heating installs.

Is your present radiant system electric-based, or hydronic (hot water) based?

Extending your present radiant panel install to the CEILING (ceiling radiant panels) may be a possible solution; as you may know, radiant heat is mostly infrared waves that don't give up their heat until they strike an object (much like the sun's rays don't give up their heat energy until they strike a solid object)---in YOUR case, radiant panels installed in the ceiling should give up nearly all their energy to the CARPET & FLOOR, which is what you need-----this may be an excellent way to heat your cold floors.

Click onto the site below to get a large list of radiant ceiling heating panel images & installations to learn how radiant ceiling panels work, then click onto each of the images to get a larger picture & to read the accompanied captions.


Re: Tricky Heating

See if I have this right. There is a slab, then there are 2x4 laid on their sides with a subfloor on top so that there is a 1.5" airspace between the subfloor and the slab. You would like to insulate this airspace without tearing up the whole subfloor.

Judging by your ceiling height, I would guess this subfloor was added after the house was built so the walls are not resting on it. The walls are resting on the slab, does this sound right? If so, taking up the subfloor will be relatively easy if you want to go that route.

Is the slab at grade or above grade? Most are above grade, sometimes with block walls for sides. If so, there is one thing that is pretty easy that can really warm up the floor and that is to insulate the sides of the slab. Most of the heat loss from the slab is through the exposed sides, not to the ground below.

You can go about this two ways. one is to just dig down to the footings, glue 2" thick rigid foam boards to the sides of the slab and then cover the foam with stucco or thinset cement. You may need to add some trim to the siding if the slab is then proud of the exterior walls.

A variation on this is to dig down to the footings, then continue digging down about 2 more feet, but at a 45° slant away from the foundation. Your footings should be below the frost line so this will go an additional 2' beyond that. Then you attach the foam boards as described above, but install more foam boards against the slanted sides of the ditch. Seal the edges of the foam boards, then stucco the slab part and backfill. The extra foam boards will act as a heat trap to keep the ground just below the slab warmer.

You can make this heat trap deeper, but you quickly get into a diminishing returns situation. No matter how deep you go, the ground below the slab will never be higher than about 58°F. Now if you blow a little insulation into the space below the subfloor, the slab should be warm enough to prevent condensation so you will not need a vapor barrier.

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