Hi. Part of our house is on a slab and currently doesn't have enough heat. I was thinking of running some new pex heating lines underground to the addition. One issue is that I'd rather continue to use straight water in the system. So, if I insulate the pex, does it need to be below the frost line?
...is that you put your well-insulated water lines in conduit. Earth is essentially always wet and is a wonderful heat sink! The moisture, even with insulated lines, will carry off loads of heat. If you keep the lines in conduit, you'll prevent that loss and be able to get to the lines if needed. Others will have to comment on depth of burial and frost line, though if the water flow stops, it must become the same temperature as the surrounding soil in a few hours or less.