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    ShermanVA's Avatar
    ShermanVA Posts: 2, Reputation: 1
    New Member

    Feb 8, 2010, 01:10 PM
    Turn off heat pumps in cold weather
    Since Heat pumps lose efficiency at lower temperatures, at what outside temp does the cost of running the heat pump (compressor, defrost cycle & ware & tare) exceed the cost of operating on backup heat? I have been told never, 30, 20, 10 deg.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert

    Feb 8, 2010, 01:47 PM
    The reason you get many different answers is the fact that heat will still be generated by a heat pump down to -20 and below since in our world there is always heat that can be extracted it seems from the air no matter how cold it is.

    The problem is the fact that sometimes the additional wear and tear on equipment is not worth the operation of a heat pump at lower temperatures. All heat pumps will have a chart as seen below available from the manufacturer or included with the machines paperwork for each different model number of unit. While this chart along with other information is used to calculate the balance point of the system (the point where a system will need to use strip/resistance heat to make up for indoor temperature loss due to the fact that the heat pump itself will not supply all the heat needed) it also can be used with other information to help calculate when it is best to turn off the heat pump and go with strait resistance heat.

    There is much more to this subject and the installer/startup tech should have adjusted the system to automatically switch over during installation. Since much more info is needed to give you an exact answer I will defer the remainder of this to your local service company who professionally installed your system.

    NOTE: The chart below is for a 5 ton/60,000 BTU unit.
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