Best Of

I'm not sure what happened with the original post from @RenovationWontEnd. It would be interesting to hear how his project turned out, both the heated slab and his upstairs with stapled up PEX between the joists.

Thanks @Jamie Hall, we will use area rugs where needed. I expect we'll have a few thicker cushioning mats in the kitchen. No additional floor covering is planned unless we end up hating the polished concrete.

The floor is not perfect but the minimal cracking we have is acceptable. We talked about control joints and placed the PEX low enough to saw cut them. After getting a quote to cut and fill the 4' x 4' decorative grid we wanted we decided to take a chance and omit them. Most of the resulting cracks are too small to easily fill and not very noticeable. There are no cracks in the open floor areas, they are all off the corner of doors where the concrete was not able to shrink without cracking. Some will be covered by door mats while the worst are in the garage and mechanical room where it's not a big deal if they are visible. We skipped the fiber mesh to avoid possible issues when polishing the concrete. The biggest negative came from twigs and softer material in the concrete which caused flaws in the polished surface but even that isn't a big problem for us. I'm not sure how that could have been avoided with our local batch plant.

The interior slab shrank up to 1/4" away from the ICF wall on two edges and that movement probably prevented cracking in the middle of the floor around the columns. The thermally broken thresholds for exterior doors seem to be effective when combined with adjacent PEX loops but the rebar across the break probably contributed to the cracking there.

The upstairs areas will be heated with Jaga low-temp panel radiators on a separate ODR circuit. This seemed like a much simpler approach than PEX in between the floor joists and TRVs offer independent control in each room with a single water temperature. The total heat load averages about 5 BTU/sq-ft at the design temp of 8F so the combination of radiant slab and radiators should work with relatively low water temperatures. So far there is no drywall or interior insulation and the entire space stays at 65F with about 85-90F water holding the slab around 70-72F. Keeping 800 gallons of heat storage charged to run the floor only requires one firing per day of the Froling boiler. This should improve once the ERV is operating to reduce infiltration losses. So far I'm very pleased with how well the system is working and especially the power consumption since we're off grid with minimal winter sun for power.