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Community and Q&A

Control a heat pump with a wall thermostat?

Philip Gibbs | Posted in Mechanicals on

I have recently installed an airsource heat pump in my vacation house in central Vermont. It works great, and mostly replaces the electric baseboard heating.

My concern is that the unit can only be controlled by a hand held remote, and only goes down to 60 degrees. We normally leave the house at 45 when we are away. It seems to me I am wasting a lot of energy now, perhaps using even more than the baseboards at 45.

I have an idea on how to fix this, but I’m not sure it’s a good idea. The unit is 240 volt. Could I just turn it on and off with a regular wall thermostat? In other words, when the room reaches temp, cut the power to the unit. When it cools off, restore power. Is this okay or would it be bad for the sysytem to be frequently turned off and on this way?

Thanks.

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Replies

  1. Brian P | | #1

    I don't know if your plan is a good idea from an energy efficiency perspective, hopefully others can weigh in on that.

    Is this a Mitsubishi model? We just had a "Wireless Remote Controller and Receiver Kit" (MHK1) installed. It's integrated with our wireless router and we can control the heat pump from an online portal or phone app. This includes a notification area that you can set to email you when the temp reaches certain points.

  2. User avatar
    Dana Dorsett | | #2

    Regular wall thermostats are typically rated for switching minute amounts of current at 24VAC, not powering a heat pump.

    Some LINE VOLTATGE thermostats used for electric baseboards may have sufficient contact and amperage ratings to use in-line with the heat pump power, but that should be assessed very carefully.

  3. Philip Gibbs | | #3

    Thanks Dana and Brian. It is not a Mitsubishi; it's a Canadian brand, Caribout, do-it-yourself, but made in China. I wish it di have the option for remote control.

    I was thinking of a line voltage thermostat. I know they come big enough to handle the load (15 amps, IIRC), but am worried about the electronics and the compressor. Would they like being turnmoed on and off this way?

  4. User avatar
    Dana Dorsett | | #4

    As long as the run cycles are reasonably long, and the off-times are also reasonably long most equipment won't be harmed by during the power on & off. Some reciprocating compressors can't re-start quickly if it's only off for a few seconds (sometime several tens of seconds), but scroll compressors with ECM motor drives should manage no matter how short the off-cycle.

  5. Charlie Sullivan | | #5

    You won't hurt it but you might loose efficiency by cycling it vs. having it run more continuously at lower power.

    If you can figure out where its temperature sensor is and put a little tiny heater near it, you could fool it into thinking it's 60 in the room when it's really 45.

    But even if you cycle it and its COP drops, it will be better than an electric baseboard heater.

  6. Alex Bubier | | #6

    Hey Brian,

    Can you detail your set up? I am trying to automate my home set up at much as possible. I have two zones for my heat pumps- both connected to MHK1s.

    Thanks!

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