Anyone know of a thermal switch that will close the circuit at 25*F ???

I need to insulate and air tight my pump house my 3/8" pressure switch line just froze (barely - took 10min to thaw with propane heater) it's 20*F. I`m going to insulate it, make it air tight (as can be), put up some walls (OSB), and put in an overhead heat lamp. I want to rig the heat lamp to a thermal switch to kick on at 25*F and probably turn off at 27*, or maybe on at 23 off at 27... not too sure yet what kind of temps it will maintain once I get it insulated.

Ideas ???

The well house is about 7'x7' so it's not huge, and has 8' walls, and open ceiling (which I will close to form a mini-1' tall attic space.