The emergency heat setting switch on a heat pump thermostat confuses many people. Bottom line is this: emergency heat is simply a switch that turns on electric heaters that are installed in your unit to supply heat in an emergency only. And it will cost you tons when your electric bill comes in!
A heat pump installed where the temperature can drop below 35 degrees need a supplemental heating source. Most often this is electric resistance heating – at the indoor unit. Sometimes this heat would be gas, oil or even hot water but normally it is electric. It is also called second stage or back up heating.
If your system needs this heat, it will call for it automatically. The primary heat pump will call for supplemental heat only when it has to have it to meet the thermostat setting.
Emergency heat is just that – emergency heat! If you are freezing inside and you go outside to check your heat pump and it is a frozen block of ice… or if a tree has fallen on it and it OOC (out of commission) then turn on your emergency heat and call us for help!
Of course you would want to periodically check your outside unit in the winter just as you should be doing in the summer to make sure all is OK with it.
Emergency heat is more expensive. Unless you have gas or oil heat as backup heat (it would more than likely be your primary heat source!) then your emergency heat is electrical. Electrical resistance heating is the physical action of electrical current being forced through metal that resists the current so it takes a lot of electrical current to make it work.
If you have a light on your thermostat it means someone has set the thermostat to emergency heating. Sometimes the heat will come on just because you have moved the thermostat too much too quickly. If you have just started your heat, and there is a large temperature difference, lower your thermostat gradually to allow your heater to work properly and not kick in the emergency heat.
Now you know what the emergency heat setting is on your thermostat and why you should try not to use it!