The T87F Universal Thermostat provides temperature control for 24 to 30 VAC residential heating, cooling or heating-cooling systems. For heating systems, the T87F mounts on the wallplate provided. For cooling only, or heating-cooling, order the 137421A (198170A if textured designer model) Heating-Cooling Wallplate with remote switching, or the Q539 Sub base, which provides switching at the thermostat location. The SPDT switch makes one set of contacts on a temperature fall to operate the heating system. The other set of contacts make on a temperature rise to operate the cooling system when the T87F is used to control cooling.