Reddit reviews Frost King, Black HC24A Automatic Electric Heat Cable Kits, 24ft x 120V x 7 Watts/ft, 24 Feet
We found 1 Reddit comments about Frost King, Black HC24A Automatic Electric Heat Cable Kits, 24ft x 120V x 7 Watts/ft, 24 Feet. Here are the top ones, ranked by their Reddit score.
24Ft x 120V x 7W/ft.Keeps water flowing down to (-40) degrees FFor metal and plastic water pipesEasy to install
You could wrap your pipes (or lag your pipes), or string some heat tape around them for when it's really cold out.
http://www.amazon.com/dp/B000BPG5XA?psc=1
Are they heat or just water? Is it the whole underside of the house?
I think with the unheated nature and the concrete you should be careful with the moisture issue. But like busstopvip says foam board might be best. You can cut and tape it easily. I don't know how you'd put fiberglass up on concrete unless you put some beams up which would be maybe a bit more work then is necessary.
Or maybe switch them to PEX?