We are heating our house during the day with a wood stove on one end and a pellet stove on the other. We also have an oil fired hot air furnace in the basement. The pellet stove will burn through the night but the wood stove is small & will not and so the furnace comes on often at night. Our oil co. installed a vent & thermostat (at my request) in the basement to keep it from getting too cold, but the thermostat can't be set below 50 degrees. The furnace comes on more often than seems needed because it is keeping the basement at 50. I kind of doubt the basement would get cold enough to freeze the pipes except in extremely cold weather, so I'd like to get a thermostat that will go dow to 40 or 45 degrees. Does this seem reasonable, and if so can you suggest where I could buy one?

If the thermostat in question is a mechanical/mercury type, you could try changing the level of the mounting to skew it a few more degrees in your favor. Thermostats of this type rely on a level mounting for accuracy.

i`VE INSTalled a few cheap digital tstats that work as low as 40 degree,,,,,,check on E-Bay

Some digital tstats also allow for calibration, which you could skew to meet your needs.