AC + gas furnace vs, Heat Pump + furnace

12 years ago

I live in west central Indiana. I'm replacing the 18 year old 80% gas furnace with a 95% Bryant. I will also replace the 18-year-old single stage 10 SEER A/C unit, but am not sure whether to replace it with another A/C unit (3-ton 17 SEER) or a heat pump (3-ton 16 SEER, 9.0 HSPF)

The heat pump is about $600 more than the AC unit.

I get that the heat pump may save money (electricity being less than natural gas, though I don't know how to figure comparative costs) and will make the furnace last longer. But it seems that (1) the pump, with a slightly lower SEER would cost a little more than the A/C to cool, and (2) since the A/C and pump both cost over twice what the furnace costs, it would be smarter to use the furnace more and make the A/C last longer.

I'm also not sure how cost-efficient the pump would be at temperatures lower than 40.

So I'm tending toward the A/C unit.

This is my first foray into the world of HVAC replacement. Any suggestions?

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Comments (5)

david_cary
12 years ago
You need to post your rates.

I would guess I save about $300 a year with a dual fuel setup. I live in a warmer area but you would think that the savings would be about the same, you just would have a much higher gas bill. Mine was $100 for all of last year. The breakeven point for me is more like 28 degrees.
neohioheatpump
12 years ago
$600 is a pretty reasonable upgrade cost. You will gain alot of flexibility with this configuration. Going from 17seer to 16seer is barely noticable is efficiency. I wouldn't let that concern you.

What is your electric rate? heatpump heat is typically very cheap when above 40 degrees. I recommend upgrading to a heatpump if the upgrade isn't expensive in most situations unless the home is very leaky/badly insulated or very expensive electricity (approaching 20 cents per KW.

If natural gas gets expensive again atleast you have some options. I like the heatpump heat during milder cold days. Its heat isn't hot, so it runs longer and evenly heats the house. I run my heatpump down to 30 or 35 then let the natural gas take over. I switch to natural gas (my emergency) when snowing or sleeting alot.

My electric rate is 12 cents per KW total.
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You should definitely be pricing with just heat pump. I live in NC which probably is a bit colder in the winter. We get down to the teens but only 15 nights a year maybe. Our winter average low is about 30. Under 10 degrees is definitely a news story. I have 5000 sq ft. I'm looking at my NG bill of $30. I have dual fuel and seer 16 heat pumps. Last winter was very cold and I spent about $700 with $200 being gas. This winter is going to be $120 in gas. My electric rates are similar to yours without the first 1000 discount. What is my point? Your gas usage will likely be $100 a year. Even if that were replaced with all heating strips, you'd be saving $200 a year or so. Since it would probable be 80% heat pump still, the dual fuel is only saving you $40 a year. So a $2500 furnace to save $40 a year seems a little crazy (on dollars alone). Turns out for me, it is probably worth it but only marginally so. I have a 90% (which you should be able to do as mine is basement with horizontal PVC exhaust). It probably saves $60-$70 on an average year. Probably cost $2000 (new house - I can't remember). What is that a 30 year payback (or never if you count interest or NG rates increase)? You do get some flexibility and you can setback at will with dual fuel. That is worth something.
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I'm leaning towards just heat pump with heat strips. That should be fine for your area. If you plan on keeping it that warm in the house as you say in your OP, I would get the Bosch Inverter heat pump as it produces heat clear down to about 5-6 degrees ambient and very efficient at what it does. Then use the strip heat as you need it. I don't know that you'll find a contractor though for this for a new construction job as Bosch just recently came to the Houston market a few months ago. The distributor network for Bosch is in it's infancy... so there are pros and cons for choosing this brand. For what it does / how it does it --- it's a game changer for my market. (Katy, Texas area) As a comparison --- an average run of the mill single speed heat pump will probably struggle once temps drop into the 20's for any significant amount of time. They are efficient when compared to strip heat (utility bill cost wise) but there are higher limitations with those. I've gotten email notifications from my electric provider that they are estimating my next electric bill at less than $50 for November. This may wind up being my lowest electric bill ever for my power rate of 12 cents per KWH. With that said, I keep it quite chilly during the winter and my house is all electric (no gas at all). I shut it off at night and really just use it to take the chill out of the house in the morning. If it gets really cold here, I will probably just heat the main part of the house over night --- as I have it attached to a 4 zone duct system. (This is to explain the how and why my electric bill is so low -- design of the HVAC system is a big part of it.)
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weedmeister
12 years ago
the other thing you will need for a 'hybrid' system is a thermostat with an outdoor temperature sensor. With that, you can adjust when the gas furnace comes on and the HP shuts off. Usually these temperatures overlap a bit so that there is a range where both can come on at the same time. You then adjust these temperatures based on comfort and price.
mike_home
12 years ago
Usually the life a furnace is longer than the life of the AC condenser. Upgrading the AC to a heat pump will shorten the life of the condenser. You are doing the right thing by factoring this into your overall operating costs.

Post the model numbers of the Bryant equipment. It may influence some opinions.

In my opinion natural gas rates will remain low for the forseeable future. The US has an over abundant supply.
Mike2345
Original Author
12 years ago
All units are Bryant

Furnace = 355BAV
A/C = 127A
Heat Pump = 226A

Had to order today to take advantage of rebate offer that ends 8/31. Never could figure out how to estimate the cost of running the heat pump vs. the gas furnace and couldn't locate any on-line calculators/spreadsheets that would help. Figured I'd save a bunch with new 95% furnace over the old sigle-stage 80%, and the new 17 SEER a/c over the old single-stage 10. It's small house (1450 sf) and well insulated, and I didn't know if I'd squeeze enough additional savings with a heat pump to justify the extra initial cost of the pump plus whatever extra cost would be involved in replacing it sooner because of running it much more. When in doubt, play conservatively (at least where money is involved), so I went for the a/c unit. Wish I'd discovered this website a month earlier. Thanks to all those who responded.

AC + gas furnace vs, Heat Pump + furnace

Comments (5)

david_cary

neohioheatpump

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AC + gas furnace vs, Heat Pump + furnace

Comments (5)

david_cary

neohioheatpump

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Mike2345Original Author

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