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AC + gas furnace vs, Heat Pump + furnace

Posted by Mike2345 (My Page) on
Wed, Aug 24, 11 at 20:06

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?

Follow-Up Postings:

RE: AC + gas furnace vs, Heat Pump + furnace

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.

RE: AC + gas furnace vs, Heat Pump + furnace

$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.

RE: AC + gas furnace vs, Heat Pump + furnace

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.

RE: AC + gas furnace vs, Heat Pump + furnace

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.

RE: AC + gas furnace vs, Heat Pump + furnace

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.

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