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Heat pump and thermostat questions

Posted by jbellemare (My Page) on
Tue, Feb 3, 09 at 18:06

I have two question and I was hoping you guys might be able to help me out.

The first question is in referance to our thermostat. It was here when we bought the house in 2007 (probably installed as a replacement by the previous owners). It is a Hunter Model #44670. It has an Span Stage setting with a 1,2 or 3 option. The manual does not really describe what the Span Stage setting is for. Does anyone have this thermostat and/or know what the Span Stage is for and what is the best setting to leave it at.

The second question is about the heat pump itself. The heat pump is a RHEEM,10 SEER, and is, IMO, not function properly. Even when it is 40 F outside it is having trouble raising the temp of the house 1 degree without resorting to the AUX heat after about 10-15 min of running. I know heat pumps are not as effective as the temperature drops outside, but should the Aux really need to kick in when the outside temp is > 35 or 40. The Aux heat is 10 KW and is killing us on the power bills. We keep the house 65-67 F so it is not like we are trying to keep the house like at an unreasonable temp. (We have had the system serviced in the last month and everything checked out, Freon levels were fine, etc.)

Thanks in advance for your help
Jim


Follow-Up Postings:

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RE: Heat pump and thermostat questions

Re: Heat Pump

You have a problem with either the heat pump itself or possibly the ductwork. A leaky return duct in an uninsulated part of the house like the attic will introduce cold air into the system. It is also possible that the air handler fan is on too high of a speed setting.

Here is temperature data for my 3-ton 14 SEER Goodman heat pump installed in '07:

Outdoor----Supply air temp
temp-------after indoor coil (based on 70F return air)

55F--------103.7F
45F--------99.1F
35F--------95F
25F--------91.6F
15F--------88.8F
5F---------84.4F

Good luck.


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RE: Heat pump and thermostat questions

Ductwork is in the floor, (the ceiling of a finished/insulated basement). Unfortunately the fan is single speed, so I can not adjust that.


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RE: Heat pump and thermostat questions

Span stage sounds like the number of degrees of difference between the actual temperature and the desired temperature that kicks the aux heat in. If it is set a 1, you will get a lot of aux heat use, especially if you set your heat back at night. If it is set a 3, you will get less.

For what it is worth, we have a similar setting with our thermostat (not a Hunter) that we keep at 4 (our max). We still get a lot of aux heat run time because we set the thermostat back at night.

Really sophisticated (and expensive) thermostats can recognize this cause and effect and tailor their aux heat calls to minimize run time.

I think you may have a correctly sized heat pump that is working properly, but you should change your span stage to 3. A properly sized heat pump will take a fair amount of time to raise the temperature one degree when it is 40 out.

I suggest you try it and see what happens.


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Rheem Fan

Check and see if the fan speed can be changed inside the unit. Our Ruud (a Rheem clone) can be jumpered to run at one of two speeds.


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RE: Heat pump and thermostat questions

Ok turns out th span is th number of degrees the thermostat will allow to heat/cool abov and below the setpoit. So it is the setting of 2 better since it will not be constantly kicking on at 1, and running forever with a span for 3.

Back to my other question with aux constantly kicking in, has the heat met tge end of it is life span. Again I understand at low temp Aux is necessary but did not think it was necessary at 35-45


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RE: Heat pump and thermostat questions

You should have some way of setting the aux heat differential. If it's not the span, it must be called something else by Hunter. If it is fixed at something like one degree, I suggest buying a different thermostat.

You can wire in an outdoor thermostat to block the aux heat above certain temperatures. Some home thermostats have a provision for it. Most don't. It can also be done inside the unit if you know what you are doing.

If your aux heat is on a separate breaker or has its own disconnect, either at the main service panel or near the air handler, you can simply turn it off while the weather isn't super cold. The only bad thing about doing so is the blast of cold air you will get out of the unit during the defrost cycle.

If you can turn the aux heat off, I suggest giving it a try to see if the heat pump can maintain the indoor temperature by itself when it is 40 out. It should be able to.


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