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  1. #1
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
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    207

    Lowest Thermostat setting for heat pump

    We are in Canada, and go away for a couple of months during the winter. In past, we had just electric baseboard heating, but we now have a central Mitsubishi Zuba heat pump.

    Outdoor temperatures are in the 10-30F range in February and 20-38F range in March.

    Heat pump has no heating strips, but we still have BB heaters.

    Our questions is - How far can we safely turn the heat pump down? And would that be better than using the baseboard heaters at their minimum setting (41-45F).

    One other question - Our heat pump came with an installation manual only. No owners manual. Only owners manual was just the thermostat and it is generic. Do other makes provide an owner's manual that might provide answers to questions like the minimum recommended temperature setting?

  2. #2
    Join Date
    Jan 2004
    Location
    PA
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    68,793
    50 is generally the lowest manufacturers allow.
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  3. #3
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
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    207
    Quote Originally Posted by beenthere View Post
    50 is generally the lowest manufacturers allow.
    Thanks. I had sent an email out this evening to Mitsubishi and amazingly they answered right away. They said that recommended lo setting was 17C (63F).

    That seems high, and would mean that we would be better off to shut the unit down and use some of our electric baseboard heaters which we have in past set to 5-7C (41-45F).

    Is it OK if we shut down the heat pump for two months by turning off the power to it at the breaker panel? I think installation manual says to turn on and warm up for 12hrs before restarting, so we would do that when we returned.

  4. #4
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    Something sounds wrong there... You can't use the heat pump below 63 degrees? What would be the point of having a heat pump then? You dont need any heat when it is 64 degrees outside...

    I have a 4 ton coleman heat pump for my home and it does just fine all the way down to the low teens here in NC without going to the strips...

    Hopefully I am misunderstanding what you guys are saying here, cause if you cant use that heat pump below 63 degrees then it is basically an AC, not a HP.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  5. #5
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,224
    I think he means 63 indoor temp.

  6. #6
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,793
    No harm in shutting it off, as long as you remember to turn the power on for 12 to 24 hours before using it again.
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  7. #7
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by HVACTechNC View Post
    Something sounds wrong there... You can't use the heat pump below 63 degrees? What would be the point of having a heat pump then? You dont need any heat when it is 64 degrees outside...

    I have a 4 ton coleman heat pump for my home and it does just fine all the way down to the low teens here in NC without going to the strips...

    Hopefully I am misunderstanding what you guys are saying here, cause if you cant use that heat pump below 63 degrees then it is basically an AC, not a HP.


    63 degree indoor temperature with a heat pump will cause long defrosts and can lead to incomplete defrost.

  8. #8
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
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    207
    Quote Originally Posted by chuckcrj View Post
    I think he means 63 indoor temp.
    Yup - You can't SET the outdoor temperature

  9. #9
    Join Date
    Aug 2011
    Location
    Kingston, Ontario
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    207
    Quote Originally Posted by beenthere View Post
    No harm in shutting it off, as long as you remember to turn the power on for 12 to 24 hours before using it again.
    OK thanks - My dealer says it doesn't draw much if power is left on, but I don't know just how much "not much" is! But similar "Mr. Slim" outdoor unit only uses 39 watts for crankcase heater.

    If I turn it off, I would definitely let it heat back up for 24hrs.

  10. #10
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,618
    I'd still leave the heat pump turned on because it will use about 1/2 the electriciy of the baseboard heaters. Just leave the BB heaters set at their lowest setting and the heat pump above that. Without back up heat, the heat pump will only heat down so low, and the BB heaters will give you freeze protection. As for setting of HP stat? Me? I'd probably not go below 60 or so because you are using the indoor heat to defrost it as you have no strips inside it for defrost. If you set the HP too low, then it'll never get thru the defrost cycle without putting the house down into the BB heater temp setting range. Just have a neighbor see what kind of temp. the house maintains from time to time while you are gone. They can adjust from that.

  11. #11
    Join Date
    Mar 2009
    Location
    Several Miles from Sane
    Posts
    1,472
    Have you considered winterizing the home for that 2 months. I suspect that the cost to do so would be completely offset by the electrical savings for the same period.

    I know several people with mountain homes that do that every winter (when they go to Arizona for 3 month) and it costs under 200 bucks to have the Plumbing Contractor do it for them. They save 3 times that amount in electric and propane cost. Just sayin .

    As whaoo said leave the HP on but turn the thermostat "Off" so it doesn't run. That way you don't have to remember the "on for 24 hours" thing when you return.
    If sense were so common everyone would have it !

    All opinions expressed are my own. Any advice provided is based on personal experience, generally accepted fact or publicly available information. As such, it is worth exactly what you paid for it, not a penny more not a penny less !!

  12. #12
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,618
    David, don't worry about your HP settings, as you have a built in back up heat source. These folks are using their baseboard electric heaters as back up heat on the heat pump as their heat pump does not have back up strips. During defrost the heat pump uses the back up heat system to keep the home comfortable, but if this is not a built in source then turning the HP to a very low temperature setting will cool the home down until baseboard units kick on and increase the defrost cycle length quite a bit.

  13. #13
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by DavidPJ View Post
    I also am questioning the lowest indoor temperature for a vacation home with heat pumps. In my case, the HPs are Trane XL14i's. Do these HPs as well as others always have a maximum time that the defrost cycle can run? Or, might there be something inside these HPs that always ensure the complete defrost cycle is run and coils defrosted regardless of the time it takes?

    I've been setting 2 of our XL14i thermostats down to 40-50 degrees in the winter with some home winterization as well. No problems so far. Winter outside night low temps are in the 16-35 degree range.
    Most manufactures have a maximum 10 minute built into the defrost board.

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