Ok but why a heat mat instead of a heater? It's always cool in my basement grow room so I have a heater with a thermostat to kick in when the temp drops. The cement floor is always chilly so the pots sit on inch thick insulation slabs so the soil doesn't chill too much and the warmer the soil the more active the bio-herd is.
I can't see the heat mat hurting anything but it just seemed a little of an odd way to warm the plants.