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Heat Pump efficiency with outdoor temperature?

I have a relatively new (2 years) air-to-air heat pump in an old house (1928) .

How do I determine at what outside temperature I turn the heat pump off and turn on the propane heaters in the house? I do not want to energize the supplemental electric resistance heat in the heat pump due to its high cost.

Is there a moderate winter temperature range in which it would be wise to run both the heat pump and the propane heat? The propane heaters are a faux woodstove in the living room with variable flame, and non-vented wall units with built in thermostatic control (on-off) in other rooms.



  • SWEI
    SWEI Member Posts: 7,356
    The manufacturer should have a series of tables with entering and leaving temperatures for both sides of the pump. Those will give you a COP, which you can divide your electricity cost by to get a 'net' cost for one kW of heat output. The temperature at which that price equals the cost of your backup heat source is where you want to changeover.
  • John Mills_5
    John Mills_5 Member Posts: 935
    In most cases, especially with oil or LP backup, I'd say as cold as the heat pump will heat the house, let it run. Unless you have extremely high electric rates, the modern heat pump will blow away the expensive fuels. Mine is set to 20 but I keep the house cold. For customers I tend to do 30 to 35 and don't have complaints.
  • Spence
    Spence Member Posts: 316
    You need to plot your heating load on a balance point chart, along with the capacities of your HP at 47/17 degrees from the maker. This will give you the ODT at which the HP needs help from your LPG furnace. Then you can set the operation at restricted or unrestricted mode to give you the best comfort and economy.

    I have charts if you need one.
  • unclejohn
    unclejohn Member Posts: 1,778
    Does Spence ever read the full post?
  • Spence
    Spence Member Posts: 316
    I don't understand. What does your comment mean? The question was about the best ODT at which to use the HP, the LP heaters, or both.