heat pump/gas furnace or AC/gas furnace

Chazbo54August 9, 2011

Indianapolis, IN. 2200 s.f. tri-level home. Replacing a 10 yr old 3 ton AC unit (SEER 10)and a 40 yr old gas furnace. So in this area do heat pump/gas furnace combos make sense? Some installers are saying yes, others say no, that indiana weather changes too much and heat pumps need 32 F to make more sense than using A/C.

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What is your electric rate and cost of gas?

    Bookmark   August 9, 2011 at 6:54PM
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Heat pumps don't work for heating very well north of the Mason-Dixon line. When the temp gets below about 32 degrees the auxillary electric coil heater generally kicks in. The exception to this is when using geothermal means to heat or cool the exchanger. In those conditions the system thinks it's always 65 degrees outside.

    Bookmark   August 9, 2011 at 10:57PM
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I think the heat-pump paired with a gas furnace is the way to go.
Why? because the heatpump shouldn't cost much more than the regular A/C and for this extra cost you have an entirely extra alternative to heat your house.

I'm much farther north of you and I have a 15 seer heatpump with a 90% gas furnace. My electricity isn't cheap but its not outrageous either (12 cents per KW total) I run the heatpump down to 35 degrees fahrenheit. The heatpump is cheaper to run and more comfy down to this temperature for me. And by the way, the heatpump heat doesn't dry out the air. Typically the longer runs of the heatpump do a nice job of evenly heating rooms and eliminate cold spots.

If natural gas were to get expensive I could run the heatpump down even lower and it could still keep up. In my situation the heatpump can maintain 68 in my house down to 20 degrees outside. I will admit when the heatpump runs constant like this its not quite as comfy though.

Other things depend also like why well insulated or leaky your house is.
Generally leaky, less insulated homes don't work as well with a heatpump.

You want the highest efficiency single stage heatpump, your gas furnace providing the backup is cheaper than having electric resistance heat and is a good option to have for the colder days.

    Bookmark   August 10, 2011 at 7:36AM
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Thanks for the information. I am leaning toward a heat pump because I do like the idea of a backup heating system. I expect the gas furnace to supply most of the heat during the 'real' winter months. My biggest question now is, are heat pumps a lot less efficient at cooling in the summer? My 3 ton (10 SEER) unit has been able to keep up, but would I need to get a bigger unit if I use a heat pump? If so, how much bigger?

Also, are some brands much better than others or should I be most concerned with SEER ratings/tonnage and furnace efficiency?

TIA, Charlie

    Bookmark   August 10, 2011 at 9:56PM
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a heatpump is the exact same in the summer time as your regular a/c.

I like the heatpumps that have demand defrost. Not all brands do.

Brands that do are York/Coleman/Luxaire, Trane/American-STD, Rheem/Rudd, and maybe Lennox but I"m not sure.

I"m very happy with York products. Their offbrand Coleman and Luxaire models are feature rich and don't cost a fortune. Mine is very quiet.

A highest eff. single stage will save alot of money over your old 10 seer. Highest efficiency single stage is about 15 seeer 9.0 hspf.

    Bookmark   August 11, 2011 at 8:32AM
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A 3-ton heat pump is the same cooling capacity as a 3-ton AC unit. going from 10SEER to 14SEER should decrease you electric bill by perhaps 20%.

    Bookmark   August 11, 2011 at 3:55PM
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Thanks for the info. Ok, so I look at the advice of 5 experts and they all differ. At least I'll have information on which to base a decision. I figure the more information I gather, the better chance of a good decision, so it's more research time.

Thanks all,


    Bookmark   August 12, 2011 at 4:25PM
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The DOE has worksheets that can help you calculate the relative cost of heating and cooling with different systems using your current energy costs. Of course you need to predict the relative costs over the next decade or two to really tell what is best. How is your crystal ball working?

I would like to clear up a couple of common misconceptions. One type of heat does not dry a house in the winter any more than another. Leaky house envelopes dry houses. Heat by flame of some sort might dry a house more because they draw more outside air in if there is not a source of outside combustion air. That would be the only mechanism.

There is nothing special about heat pumps in poorly-insulated, leaky homes. No heat or air conditioning source works as well in that situation as well as they do in tighter, well-insulated homes.

    Bookmark   August 12, 2011 at 7:19PM
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I also recommend that you contact your local electric utility (or go to their website) and find out if there are any special rate programs offered for putting in a new system with a heat pump.

Some have special rates, some have a 1-time rebate. If there is something like this offered in your area, then you will want to make sure the system and installer you use will qualify you for the program if it makes sense.

    Bookmark   August 13, 2011 at 7:50AM
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I don't follow the comment about having a "back up" heating system. If you have a power failure, then neither the heat pump or furnace can operate. On the other hand, I have never seen an interruption of the supply of natural gas except in the one case where the supply line outside was ruptured. Everyone in the house had to evacuate. Having a back up did not matter in that case.

    Bookmark   August 15, 2011 at 2:23PM
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Mike_home the backup is because your heat pump can not heat your house in all conditions so at 35 degrees the heat pump can not heat the house and needs a backup system to perform heating of the house at 34 degrees and below?

Chazbo if you have a fair amount of weather in the 35-70 degree range then the heat pump is the way to go, they are much better than an AC. I live in portland oregon and we occasionaly get to the 20s and a heat pump is the ideal HVAC system for me(with a gas furnace backup)

    Bookmark   August 15, 2011 at 4:52PM
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By backup I was meaning that if gas prices were to jump to the point where electric heat was the more economical, I'd already have it and could just switch. Having said that, I believe I'd have enough weather where a heat pump makes enough contribution to pay for itself over an air conditioner.

    Bookmark   August 16, 2011 at 5:43AM
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