Aux. heat set point

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Old 11-18-08, 07:57 PM
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Aux. heat set point

I have a 5-ton Goodman heat pump with a piggy back propane furnace for auxillary heat. The outside temp sensor is currently set at 37* for the gas furnace to operate. Can I operate my heat pump at lower outside temps and still receive adequate heat. Also, during defrost cycle the gas furnace does not operate and I get cold air for around 2 minutes. Is that cycle to short to operate the gas unit and if so can the fan be set so it does not operate during defrost.
 
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Old 11-18-08, 08:39 PM
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>>Can I operate my heat pump at lower outside temps and still receive adequate heat.

There are too many variables to give you a yes or no answer, but its easy to figure out. Does it heat adequately at 37F? If yes try 35F, if yes again try 33 and so on. You will eventually reach a point where the heat pump has to run non stop to keep up with the heat loss from your house. That is the balance point of your heat pump for your house. I would back off a couple of degrees from whatever that is because when it is windy outside that balance point will be higher. Note that this is the functional balance point. For The economical balance point you need to calculate how many BTUs you get per KW of electricity from the heat pump at a particular temperature VS how many BTUs you get from gas (minus efficiency losses) per gallon of propane.

>>Also, during defrost cycle the gas furnace does not operate and I get cold air for around 2 minutes. Is that cycle to short to operate the gas unit

Hmm, interesting question because my aux propane heat worked exactly that way (came on during defrost) and it was nice when it worked BUT when my heat pump defrosted quickly (it has temp sensors so the defrost time varies) my furnace would not make it through its startup sequence; 1st power vent, 2nd ignition, 3rd fan on. When this happened the logic board in the furnace would get confused and lock out the gas heat until it was reset manually. So you could try it, but keep the above in mind.

>>can the fan be set so it does not operate during defrost.

Yes, but you don't want to do that. The heat pump needs to steal some heat from the house in order to defrost itself. If you turn off the fan it won't get the heat it needs. Personally I'm living with the cold air right now. I'm considering installing a timer relay so I can run the furnace during defrost without risking the problematic short cycle but unfortunately its not at the top of the to do list right now.

-Doug
 
 

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