Illinois Need Advice on Compressor Size and Backup Heat Source

Discussion in 'General Discussions' started by Terry K, Dec 8, 2015.

  1. Terry K

    Terry K New Member

    We have a 2,300 sf ranch home with finished basement. We currently have a 4 ton air to air heat pump which is 23 years old and we want to replace it with a geothermal heat pump. In the winter, the heat pump does a good job of heating down to about 20 degrees. We also have electric baseboard heat in each room (each room has its own thermostat) which we turn on when the temperature drops below 20 degrees. We then shut off the heat pump.

    Here are my questions.
    1. We have gotten 4 estimates. Three of the installers recommended a 4 ton unit and one recommended a 5 ton unit. I am inclined to go with a 4 ton unit since the unit that we have seems to do a good job of heating & cooling our house. Obviously a 5 ton unit would cost more to install and probably more to operate . Would there be any reason that I would want to go with a 5 ton unit rather than a 4 ton unit?
    2. I have told the installers that I don't want electric backup heat in our unit as we plan to use the baseboard as the backup. This was fine with 3 of them, however the 4th one (the same one who wanted to put in a 5 ton unit) recommended keeping the electric backup. He said that the unit would work more efficiently since the ghp would run as long as necessary before the backup would kick in. Does this sound logical?
  2. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Even if the backup heat element kicks in, the geo units still provides the majority of the heat and will keep running. The electric backup heat is relatively cheap to install, and gets automatically turned on by the same thermostat. It is impossible to tell over the internet what is a good size for you. What kind of unit are planning to install. Model?
    Maybe sometimes you want to get rid of the older baseboards.
    Anyway, you need something like heating capacity of the air source heat pump at 20F, or other data, to make a good call on your heatpump size.
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    A typical air source heat pump delivers approximately nominal tonnage at 47*F and loses half its capacity at 17*F. That the current air source unit works well down to 20*F suggests that load is 2-ish tons at that temperature. Missing from the info supplied so far is Terry's location and winter design temperature.

    If winter design temp is 10*F or higher a 3 ton system with a modicum of backup strip heat might suffice.

    No sizing decision should be made without a careful ACCA Man J load calc.
  4. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Gotta know the load or it is all guess work.

    Where in Il?

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