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  1. #1

    Help - not sure I understand thermostat for Heat Pump

    I recently bought a house with a dual heating system and have been having issues with heat pump. HVAC guy came out to help today and he was trying to explain that you want your heat and cool within 3 degrees of each other. Not sure I understand why. If I have my cool on 74 and my heat on 55 my assumption is that my heat pump would come on when the temp is above 74 to cool and that my heater would not come on until the temp dropped below 55. What am I missing?

  2. #2
    Join Date
    Dec 2012
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    You should ask the mods to move you to AOP. I bet youd get allot more response.

  3. #3

    Help - I don't understand thermostat for Heat Pump

    I recently bought a house with a dual heating system and have been having issues with heat pump. HVAC guy came out to help today and he was trying to explain that you want your heat and cool within 3 degrees of each other. Not sure I understand why. If I have my cool on 74 and my heat on 55 my assumption is that my heat pump would come on when the temp is above 74 to cool and that my heater would not come on until the temp dropped below 55. What am I missing?

  4. #4
    Join Date
    Dec 2007
    Posts
    4,685
    You are not missing anything, your statement is correct.

    I am not sure what he meant, as it could have been a few things.

    Many thermostats do NOT allow your heat and cool to be any CLOSER than 3. For example 75 and 72.

    Also, with a heat pump you want to keep a constant temperature setting in the winter. This keeps the secondary heat source from running, which presumably is more expensive.

    As for cooling, it can be similar to heat mode. You want to keep it comfortable. If it gets uncomfortable there is a good possibility that it will not be able to bring down the temp/humidity.
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  5. #5
    Join Date
    Oct 2010
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    Anderson, South Carolina, United States
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    If the stat has the auto changeover feature enabled, meaning you don't have to manually flip a switch or press a button on the stat to switch the system from heat to cool, then there has to be a 3* difference in your heating set point vs your cooling set point. Example, if you Set your heat for 68 the cool setting has to be at least 71, it can't be 68,69,or 70. This is so the unit doesn't switch from heat back to cool back to heat and so on every time the set temp is reached with the other mode. I personally don't like auto changeover because it confuses my customers therefore I just disable it in the installer set up.

  6. #6
    Join Date
    Jan 2004
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    Lancaster PA
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    67,875
    Quote Originally Posted by jtrammel View Post
    If the stat has the auto changeover feature enabled, meaning you don't have to manually flip a switch or press a button on the stat to switch the system from heat to cool, then there has to be a 3* difference in your heating set point vs your cooling set point. Example, if you Set your heat for 68 the cool setting has to be at least 71, it can't be 68,69,or 70. This is so the unit doesn't switch from heat back to cool back to heat and so on every time the set temp is reached with the other mode. I personally don't like auto changeover because it confuses my customers therefore I just disable it in the installer set up.
    3 Min difference. but it can be greater 3 degrees if you want.
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  7. #7
    Join Date
    Oct 2003
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    Minnesota
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    Well, much depends on the exact HP you have, whether or not you have auxiliary electric heat strips, exactly which thermostat, construction of you home, and where you live geographically. Plus a few other factors I could list.

    But, generally ...

    Heat pumps tend to "recover" slowly. That is, if the space temperature drops below heating set point, or goes above cooling set point ... a typical home style HP will run a bit longer than a conventional system to bring the temperature back within desired range. Most particularly in heating mode if you live in a colder environment, or in cooling mode if you live in a hotter environment.

    One of the reasons many elect to just skip set back or set up schemes when they have heat pumps.

    For instance, I live in a cold environment and have a conventional gas fired furnace. I can do a night time 5 degree set back and my system will "recover" from that to normal heating set point in about an hour. A typical residential HP in this area might take 3 to 4 hours. And may need to cut in aux electric heat strips to get there.

    So, perhaps the fellow had in mind some settings that'd cause your heat pump to never let space temp wander too far one way or the other? I don't know, just guessing here as I don't have much specific info about your situation to go on.

    Knowing no more about your specific installation, environment, etc ... my own thoughts are that 55 and 74 degree set points should be fine as long as you're okay with the space temperatures being allowed to vary by that much. AND aren't expecting to have a 55 degree "setback" temperature during unoccupied times that can switch to a 68 degree occupied set point ... in any kind of a hurry ... without using some sort of aux heating to help the heat pump get there.

    However, as said, I don't know all the facts about your specific installation. Did you ask the service guy?
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  9. #9
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    Threads merged. Please don't make duplicate threads, thank you.
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