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av-geek 06-22-2012 07:15 AM

gas furnace efficiency, hybrid heat pump, and payback times
I just recently moved into an older home with an old, but functioning HVAC system (If you remember that post about a month ago with that old Sears compressor in it!) My original plan was to upgrade the air conditioner with a high-efficiency heat pump of 16-18 SEER by just replacing the A-coil, and keep the oil furnace for backup heat, since the oil furnace is only about 15 years old and works great.

Well, I have been getting to know the neighbors around here, and lo and behold, there's gas lines in the neighborhood:) I called the gas company, and they said they would connect up a gas line to the house for free if I install a gas furnace :) This changes everything since natural gas prices are MUCH cheaper than oil! I am now thinking about 3 options here and want some opinions on this:

First option is to replace the entire system with a high efficiency heat pump with electric strips for backup. This looks like the cheapest route, but may cost more in electricity, and is possibly low on the comfort factor.

Second option is a straight air conditioner on top of a gas furnace. Both being high efficiency models, This could give a high comfort factor in the winter, but I am up in the air on how much more expensive the operating costs are, because I don't know how much gas I would be using.

Last option is similar, but instead of an air conditioner, is a heat pump. I imagine heat pumps are not that much more expensive than a straight air conditioner, since they just add a reversing valve to the system. This could spread the heating costs over both the electric and gas bills. This I think would provide reasonable comfort since the gas furnace would operate in the coldest temps, and also run when the thermostat is cranked up several notches.

The house is a 2200 square foot brick tri-level built in the sixties, and it is very well insulated surprisingly. My wife and I are cold natured people. Our old house had a heat pump that kept the utility bills low, but didn't do much for comfortable heat. I want to move towards a fossil-fuel source of heat, but if the price is significantly more to use a gas furnace over a heat pump, I may kick that option aside, especially if the newer heat pumps put out warm air. Both of us grew up in homes heated by gas, and we like the temps about 72 when we are home. (we also like to turn back the heat to 65 or below when we are not home, and at night and think a fossil-fuel system could boost the temps much quicker when we want it)

gregzoll 06-22-2012 07:46 AM

With a heat pump, you do not want to roll it back that far, and until you get it installed and get used to it, you do not know yet if 72 is going to be too warm. During the peak of the Summer, we set our thermostat for 69 at night, 72 during the day. As for Winter though, we set it at 69 when home, 62 when in bed.

Now of course, if we had a heat pump, vs A/C, I would probably use different settings. As for your setup, depending on utility prices, go with the best option, with the highest payback. If both electric & nat. gas suppliers give rebates for the heat pump, and you are also saving to have gas ran, go for it. Now of course, if you have the space and willing to put the money into a geo-thermal unit, that would be even more cost effective, but with the longest term for payback.

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