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!
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 - at the indoor unit. This is an all-electric Heat Pump, but it could also 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, with "first-stage" being the Heat Pump only. Emergency Heat is when you use your supplemental heat (2nd stage) by itself, without the use of your heat pump (1st stage heat).
Different systems and thermostats have different ways of determining when the second-stage heat comes on to assist the heat pump, but it is always done automatically. The two stages will work together in the colder months, and it is not necessary to switch your thermostat to Emergency Heat. So now we know that Emergceny Heat is basically when you use your supplemental heat by itself.
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.
This Heat pump is completely frozen solid. It actually got so bad that it ruined the heat pump and it had to be replaced.
During the winter months, you should try to make it a habit of looking at your outdoor heat pump. Check for signs of excessive ice or snow build-up on or around the heat pump.
If this problem was caught sooner, it might have just needed a minor repair instead of an expensive replacement.
When switching to Emergency Heat, the red indicator light will go on. And it will stay on until you stop using the Emergency Heat. This just lets you know you are in emergency mode. On a call for heat, no signal will be sent to the outdoor Heat Pump. Only the indoor unit and the back-up heat will run. On all-electric systems, this will provide enough heat to keep you going until the Heat Pump can be fixed. Gas/Oil/Hot-water system should provide plenty of heat.
If you have an all-electric heat pump, then the answer is a definite YES! It is much more expensive to run your heat pump on Emergency Heat. And as the name implies, should only be run in an emergency until your heat pump can be repaired. Now if you have Gas or Oil heat for your backup system, then the answer isn't so clear. It depends on the cost of your fuel, the efficiency of your heating system, compared to your electric rate and so on. But it is safe to say that the price increase won't be as much as an all-electric system.
As explained earlier, the Emergency Heat light will be on if your thermostat is set to Emergency Heat. But if your thermostat is not set to emergency heat and the light is on, then that usually indicates a problem with your heat pump. For more on this issue, see: Thermostat red light flashing or stays on.
Please keep in mind that the information found on our website is provided free of charge and Hannabery HVAC does not assume any liability resulting from the information we provide. We hope this information helps, but please note that these are just rough guidelines, and not all possible situations are covered. Your HVAC system should be inspected and repaired by a trained technician.