I put the yellow colored ones, in both "pump houses" after Dad and I added more 2" foam board insulation, to each pump house = I figured the heat lamps didn't need to be ON constantly, like earlier years, with more insulation and better air sealing.

They seem to be working = cold days and night = ON, when I check; and some warmer winter days, the heat lamp was OFF= we have mercury thermometers, in each little building, to verify.

A local store, sold the yellow ones, so that is what I purchased. (I only had one temp rating to choose from(what store had in stock); but I see this white ones, you can choose different ratings)

http://www.amazon.com/Easy-Heat-EH-38-Thermostatically-Controlled/dp/B0000DGA8P/ref=pd_sim_lg_4?ie=UTF8&refRID=1G0QN8B0GYFN9W1YXGEJ

http://www.amazon.com/Farm-Innovators-TC-3-Thermostatically-Controlled/dp/B0006U2HD2/ref=pd_sim_lg_2?ie=UTF8&refRID=101QAD9DV74JAP2FA8CN