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Old 09-01-2010, 03:56 PM   #1
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Switching to gas furnace?


Currently I have heat pump. Last winter, I had horrendous electricity bill. So, now I wonder if I can save some money by switching to gas furnace. Is it easy to add a gas furnace to HVAC with a heat pump?

I called the gas utility company, they didn't give me their price, citing it various month by month. I checked on line, and find the number of less than $5 per mmbtu. Granted that that number may not apply to my area, I still used it to do some basic calculation. I assume the efficiency of heat pump is 300% in the winter, and assume that the efficiency of gas furnace is 80%. Now I'm paying 11 cents for electricity. Since 1kwh = 3600000 J, and 1 mmbtu is about 1Gj, it looks to me that I can save about 60%. And I also suppose that 300% efficiency may be an over estimate, so the actual saving may be even more.

Does my calculation sound reasonable?

I checked the price of a 3 ton gas furnace. I can find one with rather high efficiency at a little over $1000. So, as long as the installation is not prohibitively expensive, it looks like it worth it to install one.

Or will it be easier and cheaper if I just replace the electric compressor with a gas compressor?


Last edited by deerhunter; 09-01-2010 at 04:14 PM.
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Old 09-01-2010, 04:13 PM   #2
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Switching to gas furnace?


Last winter was brutal for everyone. How old is the current system that you have?

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Old 09-01-2010, 04:24 PM   #3
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Switching to gas furnace?


Not old.

I know it may sound silly to change a rather new system. But last winter, my friends who live in the same neighborhood had very low gas bill, and they turned their thermalstat at about 75 degree. Mine was at 62 the whole day because I simply couldn't afford to turn it up high. Still I paid much more than they did. I figure if I spend about $2000, and can live comfortably at 75 degree and spend about the same money as last winter, that's acceptable.



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Last winter was brutal for everyone. How old is the current system that you have?
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Old 09-01-2010, 05:31 PM   #4
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Switching to gas furnace?


75 is way too warm, unless you keep the doors and windows open, then it really does not matter what temp. Have the Heat Pump checked out, due to it may not have been running properly. Did you compare your bills for the same period from prior years? Degree days were colder this past Winter, which caused for higher bills. Same for this past Summer.

I looked back at bills from two years ago for the same period, and they were in line with this past Winter. We of course do not have a Heat Pump, only a Hi-efficient furnace. Now, you can run the Heat Pump with the NG Furnace as back up for Aux, especially if you have an all Electric home, and the local POCO is brutal to everyone.

Compare your bills to the other neighbors that also have Heat Pumps, and also check your local POCO website to see if they are able to let you see how you compare to others.
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Old 09-01-2010, 05:38 PM   #5
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Switching to gas furnace?


I compared the bill of the same period. I think the temp you set should matter. The higher the temp, the faster the heat loss. Also, when the temp difference is big, the efficiency of heat pump will reduce.

Moreover, regardless of the temp I set, if my earlier calculation is reasonable, then the saving by adding a gas furnace is significant. Now the gas is really cheap.

By the way, what about gas powered compressor? Is it possible to replace the compressor in my electric heat pump with a gas powered one?
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Old 09-01-2010, 05:53 PM   #6
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Switching to gas furnace?


All heat pumps use electric compressors, no such thing as a gas compressor. Nat Gas fired engines for industrial generators and compressors, yes. I would get the freon level etc checked. If it is low the heat pump loses output but still consumes lots of electricity to run the compressor. There is a balance point temp at which to go to backup elements. Beenthere or Marty know a lot more about setting them and how to determine that setting. Hang in there.
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Old 09-01-2010, 06:07 PM   #7
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Switching to gas furnace?


Could be that something is wired wrong with the heat pump.

But, lots of people use gas hat and a heat pump. Your heat pump is not 300% efficient when its below 40 outside.
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Old 09-01-2010, 08:47 PM   #8
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Switching to gas furnace?


High bills are not coming from the heat pump since it's using less then 3 KW an hour to run, mine's 2.1. Those toaster elements in your electric back up heater are spinning the meter at an incredible rate. First off get the heat pump serviced so it's running at its best. Change the filter often.

Remove any outdoor temp lock out. Lots of folks put a sensor on a heat pump and lock it out if the temp is below 30 and that's flat out wrong
with electric back up. Even with a gas back up I don't like them since the thermostat will kick on the gas when the HP can't keep up.

Don't use a set back thermostat. Two degrees is all it takes for most of them to start the back up heat into operation which costs you 2-5 times as much as the heat pump, depending on outdoor temp.

Try those before you change to a gas furnace. To answer the question yes you can change to gas but it will be expensive. Your air handler contains the coil so will need a new one along with the furnace. Will need vents for the furnace ran along with gas lines and electrical so plan on more then what you thought a furnace cost.


Last edited by Marty S.; 09-01-2010 at 08:53 PM.
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