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Heat Pump Electric Backup Heating Basics. There are different types of electric heating available in homes. Probably the most common use for electric heat other than portable electric heating units is electric heat strips. Electric heat strips used for backup heat in heat pumps. Sizing the electric heat strips for heat pump backup heating applications will depend on many different variables.
These variables include the size of the space to be heated and the insulation values of the whole structure. It also includes doors and windows. Additionally, it includes the geographical location of the dwelling, along with many other factors. Backup heat for heat pumps is essential for the defrost cycle.
Heat Pump Electric Backup Heating
Typically, air-source heat pumps are more common in southern climate regions where the temperatures in the winter are mild. When the temperature outdoors drops below 38 degrees Fahrenheit, the outside heat pump units start lagging behind. That is a lag on-demand to heat the structure.
Therefore, a backup source of heat is needed to provide heating when the temperature outside drops below this temperature. If you have an air source heat pump, you likely use electric backup heating.
Heat Pump Electric Backup Heating - Staging Electric Heat Strips for Heat Pump Back-up Heat
As the temperature outside falls the ability of the outside heat pump condensing unit to provide declines. A heat pump condenser absorbs heat from the outside air and moves this heat indoors. Even though the temperature outside is 40 or 45 degrees Fahrenheit, there is still heat present in the air. However, as the temperature drops, the mechanical process used to move this heat to the indoors declines. For this reason, it becomes necessary to provide backup heat for the structure. That is sometimes done in stages to minimize energy usage.
Proper Control | Heat Pump Electric Backup Heating
When a heat pump system with backup heat strips is properly controlled, only the amount of energy necessary to provide heat for the demand is utilized. This is down with a heat pump thermostat. As the temperature outside drops and the outside unit loses its ability to provide heat, the thermostat ambient temperature reading drops. But, the unit cannot keep up with demand, and the temperature in the structure drops.
Depending on the thermostat, staging set points, or the settings of the stage set points (in some heat pump thermostats the temperature set point for staging is manually set on installation. These are usually top of the line digital heat pump thermostats.).
A heat pump system with two stages of heat will have temperature set point differentials of 2 to 4 degrees Fahrenheit. These degree differentials initiate staging of the heat strips. If the temperature drops below 2 to 4 degrees Fahrenheit of the manual setpoint stage, one will turn on.
Stage one will provide backup heat for the system. A temperature drop of 2 to 4 degrees Fahrenheit further below the manual setpoint adjustment, then the second stage of electric heat strips will engage. That provides additional heat above the first stage for the structure.
Electric Heat Strips and Heat Pump Condenser Defrost | Heat Pump Electric Backup Heating
Every air to air heat pump system needs a defrost cycle to defrost the coils of frost and ice. The heat pump condenser almost always operates below the dew point when in the heating mode. When the heat pump condenser is operating below the dew point, moisture in the air will cause frost or ice to build up. The frost or ice build-up happens on the outside heat pump condenser unit.
Therefore, it is necessary to defrost the heat pump condenser coils on a periodic basis to prevent blockage of the heat pump condenser coils from ice and frost build-up. A defrost timer control board controls that (printed circuit board).
Lastly, the outside heat pump condenser unit will change from the heating cycle to the cooling cycle. In the cooling cycle, the heat pump condenser unit will begin to heat up so that the ice and frost will defrost. When this happens, cold air can be introduced into the structure and needs to be countered.
The defrost timer control board, when it calls for the heat pump condenser unit to go into the defrost mode, will also engage the electric heat strips to counter the cold air produced by the heat pump condenser when it goes into defrost mode.
Conclusion | Heat Pump Electric Backup Heating
The video below is about a hybrid heat pump system. A hybrid heat pump system uses a gas furnace backup heat rather than electric heat strips. Don’t forget to share our page on social media with the handy buttons located below the video. Thanks!!
Heat Pump Electric Backup Heating
Technical Resource: Refrigeration and Air Conditioning Technology
I live in SW Texas Hill Country. My current AC system with Propane Furnace has gone out. I was hoping to replace it with a Heat Pump. Will I need to purchase an electric furnace to heat on those days that the Heat Pump can’t handle the below freezing whether? We do get a few days between November – February where it goes below freezing here.
I’ve researched and it seems that most HVAC companies who sell Heat Pumps suggest that the heat pumps be combined with backup furnaces, but usually they only sell gas furnaces. Some sites suggest that some current high end heat pumps don’t need backup furnaces. So somewhat confusing. Please advise.
A dual fuel heat pump is typically a gas furnace and a heat pump. The gas furnace serves as the air handler and the gas is only used in defrost mode or when it is very cold and the heat pump itself cannot keep up (rare where you live). Dual fuel heat pumps are more expensive on upfront installation costs but more efficient than electric backup heat.
I have a gas furnace that dose not heat the new adldtion as well as the original house. Probably mid 60″s when below freezing. I live in NJ. Will the heat pump in an ac be enough to bring it up to 70 degrees without the heat strips going on?
Probably not. Looks like the system is undersized for the new addition. You need to either upgrade the existing or add another system to the addition.
what size and type of ASHP would you recommend for a small timber frame highly insulated dwelling with ground floor underfloor heating of 44m2 and upper floor of 30m2 having two radiators.
the typical average daytime winter temperature is +5 and night time – 3 and summer + 15 down to + 10 overnight.
You would have to do a manual J load calculation. There are some software versions available online.
What would it cost to put a back up on a heat pump?
it would be nearly impossible to answer your question without looking at what you have now. First I would check your breaker box to make sure there is capacity for a new circuit. Then running the proper sized wire from the breaker to the air handler. Then make sure you have the proper duct work to meet code. The best thing you can do is call an HVAC Contractor that will give you a free estimate. I always recommend getting 3 different estimates from different companies before agreeing to the work.