I am in the process of switching from radiant baseboards to in slab radiant heat. I have an open floor plan 3500sq foot split level home in northern MN. I am going to poor 3-4″ of concrete over the existing slab in the basement which is about 4+ feet below grade. Do I need to put any insulation down before pouring the slab on a slab? Also is there any issue with using 3/4″ pex? Thanks
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Definitely insulate on top of the existing slab to create an resistive barrier, and also insulate where the floor touches any exterior exposure.
A heat loss calculation for the conditioned space will determine boiler & tubing size, tubing spacing, flow rates, number of circuits, and supply water temps.
3/4" tubing is difficult to bend; you may be able to use 3/8 or 1/2" tubing. Be sure to keep your circuit lengths under 300'; we always try to limit lengths to 250' or less.
Constant circulation with outdoor reset & adjustable heating curve is our favorite operating mode with high mass radiant installs; no tstat needed.
Many traditional cold climate plumbing / heating wholesalers will provide help with radiant system design & material / equipment specs.....
What is the typical insulation for that?
2" polystyrene
Then do I just lay the pex direct on it...0r should there be space
We just did our slab in northern MN_ foolproof method:
4 mil or better (6 mil) poly with tyvek type taped seams, then lay 2" R-10 blue or green foam, tape those seams as well. 1/2" PEX A can then be stapled down to the foam in individual circuits of 250-300 running feet. If your basement is less than 1,500 sq ft, then you can do fine with one zone and five circuits. The 1/2 " PEX A is plenty and you want very gradual wide bends when laid. The last important thing is to be sure_100% sure that you have antifreeze mix that is pumped in within the conditioned water for filling the circuits....avoid the open system. O2 is the enemy for longevity. be sure to have them install an automatic air separator and a magnetic particle filter that can be flushed once a year. Califfee brand is reliable.