The Emergency Heat switch on a Heat Pump thermostat confuses many people. The fact of the matter is that most people don't seem to understand exactly what Emergency Heat is and when they need to use it. Many people think that Heat Pumps don't work in cold weather and they are supposed to use the emergency heat whenever it gets really cold... Wrong!
What is Emergency Heat?
Simply put, all Heat Pumps in northern climates [below 35 degrees] need a supplemental heating source. Usually it is in the form of electric resistance heating. This is an all-electric Heat Pump. It can be a gas, oil, or hot-water back-up system as well. The supplemental heat is also referred to as "second-stage" or "back-up" heating, "first-stage" being the Heat Pump only. The supplemental heat is also what is used as the Emergency Heat.
Different systems have different ways of determining when the second-stage comes on to assist the heat pump but it is always done automatically. So the two stages will work together in the colder months and it is not necessary to switch your thermostat to Emergency Heat. Now we know what supplemental heat is and that it is also used for Emergency Heat.
So when do I actually use the Emergency Heat?
As the name implies, it is only used in emergency situations. It is used when there is something wrong with first-stage heating [the Heat Pump itself]. In other words, if you notice your house is cold and it isn't heating properly and you went outside and noticed that a tree fell and crushed your heat pump, that would be a good time to switch to Emergency Heat.
Or if you look at the picture below; this Heat Pump turned into a block of ice due to a malfunction. At this point, it isn't capable of providing any heat. Simply turn the thermostat to Emergency Heat and call for service.
