Tempiture Setting for Furnace in WInter

Live in a townhouse condo (middle unit)in Ohio. Will be gone for the duration of the coming winter. Plan to shut off the water and drain the water from the pipes. Have no plants in home
How low can I set the thermostat on the heat pump furnace? When I go away for the weekend in the past, I would set it at about 60. Now since it is for an extended time, and with the price of fuel up, I would like to set it lower. I am inclined to set it at 50.
What do you guys think?
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Set it as low as you can go. I have a building that is set at 40 (hard to find T'stats that go that low) and never had a freeze up of water lines in it.
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Hi Les, hope you are having a nice day
On 14-Oct-04 At About 12:46:23, Les wrote to All Subject: Tempiture Setting for Furnace in WInter
L> Live in a townhouse condo (middle unit)in Ohio. Will be gone for the L> duration of the coming winter. Plan to shut off the water and drain L> the water from the pipes. Have no plants in home
L> How low can I set the thermostat on the heat pump furnace? When I go L> away for the weekend in the past, I would set it at about 60. Now L> since it is for an extended time, and with the price of fuel up, I L> would like to set it lower. I am inclined to set it at 50.
A heat pump thermostat should never be set lower than 60 degrees when in heat mode. any lower and you risk compressor damage.
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heat
Turn it clear off ???
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The lowest I am able to reduce the thermostat is 45 degrees; any idea why a heat pump may require higher than 60?
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Hi Les, hope you are having a nice day
On 18-Oct-04 At About 08:30:13, Les wrote to All Subject: Re: Tempiture Setting for Furnace in WInter
L> The lowest I am able to reduce the thermostat is 45 degrees; any idea L> why a heat pump may require higher than 60?
It is due to the High side pressure. it is just the same as running the A/C in any temperature lower than 60 degrees outside. the head pressure runs too low and causes liquid to return to the compressor which causes excessive compressor wear or even damage.
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HvacTech2;
Could you explain the rational for not setting it lower than 60. I have a ground source HP with incoming water temp at 50 degrees. If I set thermostat at 55 in heat mode, I don't see why there would be any damage. Likewise if set at 45 degrees. Furnace would just run long enough to arrive at set temp and then stop until next call for heating. I'm not an expert. Just trying to learn. Also I set mine at 50 degrees when I go on long winter vacation, Thanks

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Hi Treetops, hope you are having a nice day
On 15-Oct-04 At About 00:52:43, Treetops wrote to All Subject: Re: Tempiture Setting for Furnace in WInter
T> HvacTech2;
T> Could you explain the rational for not setting it lower than 60. I T> have a ground source HP with incoming water temp at 50 degrees. If I T> = set thermostat at 55 in heat mode, I don't see why there would be T> any = damage. Likewise if set at 45 degrees. Furnace would just run T> long enough to = arrive at set temp and then stop until next call T> for heating. I'm not an expert. Just trying to learn. Also I set T> mine at 50 degrees = when I go on long winter vacation, Thanks
it is due to the high pressure side of the unit. if you have an air to air a/c unit it is the same thing. you cannot use it when the outdoor temp is lower than 60 degrees. if you do yiou risk slugging the compressor with liquid refrigerant.
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Ran my HP down to 20 degrees all last winter before gas furnace kicked in with no ill effects. Explain more in detail why you can not set it below 60 when leaving home. First year with HP and just trying to figure out best way to use it. Thanks
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Thanks for reply. I think I understand the issue in cooling mode; the cooler air (less than 60 degrees) in the house will not transfer enough heat to the low side and so the return to compressor could be liquid instead of vapor. And compressor doesn't like liquid input. In heat mode, if air at condenser is < 60 degrees, the high side input vapor may not become fully liquid. However I don't see how this is a problem as the evaporator changes the low side refrigerant to a vapor anyway. So compressor still sees low side vapor. Now I am a way out of my depth!! Maybe you could explain the issue, in heat mode, in a little more depth? Just surprised at the no-no of running less than 60 degrees as I have not seen this as a caution in the operating instructions and have done it many times over 8 years without problem. Also does this limitation differ from unit to unit? Thanks again!

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