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Old 08-11-2010, 05:08 PM   #1
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need help with natural gas vs air source heat pump decision


My 16 year old house and heating and air system is an American Standard 2 ton 10 SEER air conditioner and an 80% efficiency natural gas furnace (attic) . I had the air conditioner charged a couple of months ago and now it is low again. I was told the leak in the outside unit can not be fixed and that I may have a leak in the coil inside as well.

At this point I am considering having it all replaced. I am looking at a 2.5 ton Trane 15 SEER and 80% furnace. Multple HVAC companies have told me I should not go above 80% with my furnace in an attic space.

My local utility provider, Kentucky Utilities provides fuel cost comparison information on their web site. Kentucky electricity mostly comes from coal power plants so the cost compared to other sources I believe is still low. Fuel cost for a high efficiency heat pump is only shown to be a little less for a 1,000,000 btu output for the high efficiency heat pump over a 78% efficient natural gas furnace. The cost for natural gas is $9.33 and the electricity $8.93.

I would hope to be able to recoup some of my cost of the new system over the next 8-10 years by getting a very efficient system. Can anyone help me justify the cost of a 15 SEER dual fual system air source heatpump/natural gas vs ddedicated air conditioner and natural gas only furnace?

A few more details...1300 sq ft ranch house on concrete slab. It has had an energy audit with a door blower and the house is said to be very tight and well insulated.

thanks in advance for any help!

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Old 08-13-2010, 02:41 AM   #2
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Originally Posted by supermaxhd View Post
My 16 year old house and heating and air system is an American Standard 2 ton 10 SEER air conditioner and an 80% efficiency natural gas furnace (attic) . I had the air conditioner charged a couple of months ago and now it is low again. I was told the leak in the outside unit can not be fixed and that I may have a leak in the coil inside as well.

At this point I am considering having it all replaced. I am looking at a 2.5 ton Trane 15 SEER and 80% furnace. Multple HVAC companies have told me I should not go above 80% with my furnace in an attic space.

My local utility provider, Kentucky Utilities provides fuel cost comparison information on their web site. Kentucky electricity mostly comes from coal power plants so the cost compared to other sources I believe is still low. Fuel cost for a high efficiency heat pump is only shown to be a little less for a 1,000,000 btu output for the high efficiency heat pump over a 78% efficient natural gas furnace. The cost for natural gas is $9.33 and the electricity $8.93.

I would hope to be able to recoup some of my cost of the new system over the next 8-10 years by getting a very efficient system. Can anyone help me justify the cost of a 15 SEER dual fual system air source heatpump/natural gas vs ddedicated air conditioner and natural gas only furnace?

A few more details...1300 sq ft ranch house on concrete slab. It has had an energy audit with a door blower and the house is said to be very tight and well insulated.

thanks in advance for any help!
Can you tell me the units on your gas and electric prices? Is that per 10s of therms and per 100 Kilowatt hours?

What is the price and usage on a recent gas/electric bill..


Your situation sounds similar to mine. See my thread here for some insight:
Heatpump vs Natural Gas - Energy Cost Spreadsheet

Since I did it myself and since I wanted to be "green" more than I cared about doing the cost benefit analysis I'm not sure how long it will take to pay off.. For me, the Heat pump was only 300 dollars more than the AC only solution. I had an existing 90% furnace to use as backup heat. I would never do baseboard/heating coil heating as backup but I would do a 80% with a heatpump or a 90% with a heatpump again in a heartbeat. I think it will take a while to justify the professional installation cost of the 90 vs 80 if you are going just based on cost. But I am sold on the heatpump concept. I also really like the idea of the heat coming off the furnace is only 80 degrees with the 90+ furnaces..


Last edited by zootjeff; 08-13-2010 at 02:49 AM.
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Old 08-14-2010, 08:09 AM   #3
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Can you tell me the units on your gas and electric prices? Is that per 10s of therms and per 100 Kilowatt hours?

What is the price and usage on a recent gas/electric bill..
My actual natural gas usaage over the last 12 months was 54.6 Mcf (about 561 therms if my math is correct). I am locked in to a price of $8.49 per Mcf (or about $0.83 per therm) through June 2011. Summer months my gas usage is .8 Mcf for hot water. I estimate that hot water takes 10 Mcf over the year leaving 44.6 Mcf for heating.

My actual electricity usage over the last 12 monhs is 8638 kwh. The current rate from the last bill is $0.088 per kWh (my calculation, I added in taxes and fees but not the basic service charge).

Also for heat I used a portable baseboard radiant heater in my bedroom on really cold nights (only to keep furnace from heating unused areas as much).

Lighting is CFL and I have energy efficient appliances. A rough guess of my actual electricity for air conditioning is 2250 kWh per year. (450 kWh per month for five months)

thanks for the help!

Last edited by supermaxhd; 08-14-2010 at 08:20 AM.
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Old 08-14-2010, 06:56 PM   #4
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need help with natural gas vs air source heat pump decision


How long is your areas outdoor temps above 35F.
Above 35, you should be able to get a 3 COP from a 15 SEER heat pump. Which at your posted rates would make an 80% gas furnace $10.38 for 1,000,000 BTUs of delivered heat. And the heat pump $8.59 for 1,000,000 BTUs of delivered heat.
Which of course still hasn't figured in the additional saving on your cooling bill.

If your system qualifies for the tax credit. It makes it even less expensive up front.
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Old 08-14-2010, 07:56 PM   #5
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How long is your areas outdoor temps above 35F.
Above 35, you should be able to get a 3 COP from a 15 SEER heat pump. Which at your posted rates would make an 80% gas furnace $10.38 for 1,000,000 BTUs of delivered heat. And the heat pump $8.59 for 1,000,000 BTUs of delivered heat.
Which of course still hasn't figured in the additional saving on your cooling bill.

If your system qualifies for the tax credit. It makes it even less expensive up front.
Average temperature in January is 31 with average low of 24. Average number of days where low temperature is below freezing is 94.

I used $1100 of my $1500 tax credit on new windows last year. I can get the other $400 and it looks like Kentucky still has some money left for the cash for appliance program which is $400 for a qualifying heat pump and $300 for a qualifying furnace.

I've been getting a lot of mixed information as to whether I can put a furnace in my attic above 80% efficiency. Some say I can if I take precautions to keep it from freezing. What do you think? thanks again!
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Old 08-14-2010, 08:41 PM   #6
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You can put a high eff. furnace in an attic. Protecting from freezing is a must. Have plenty of them around here in attics and it gets -20F at times.
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Old 08-14-2010, 08:46 PM   #7
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As above. yes, you can put a 90%plus in your attic. But the installers must make provisions to protect the drain from freezing.
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Old 08-15-2010, 10:43 AM   #8
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As above. yes, you can put a 90%plus in your attic. But the installers must make provisions to protect the drain from freezing.
Don't they also make provisions to keep the exaust from freezing too? They insulated my exaust line in my garage as to prevent ice buildup. But my garage never gets below 40...
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Old 08-15-2010, 11:09 AM   #9
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Don't they also make provisions to keep the exaust from freezing too? They insulated my exaust line in my garage as to prevent ice buildup. But my garage never gets below 40...
Yep. Every installation manual I have read requires the exhaust pipe to be insulated for any portion that runs through an unconditioned space.
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Old 08-15-2010, 01:35 PM   #10
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Yep. Every installation manual I have read requires the exhaust pipe to be insulated for any portion that runs through an unconditioned space.
Don't recall seeing anything about insulating a 4 foot section in an attic.

Strange that they would want that. Since often 3 foot or more is outside uninsulated after you penetrate the roof. And they don't have you insulate that.
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Old 08-15-2010, 01:43 PM   #11
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need help with natural gas vs air source heat pump decision


Horizontal needs sloping and draining back to the furnace and insulating so it does not freezeup. I would be more concerned if the power goes off that any trapped water in the furnace or condensate trap does not expand/freeze and damage them. Or if you get a drafty cold attic.
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Old 08-15-2010, 01:48 PM   #12
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Should really be a insulated framed room built around it. Best protection you can give it.
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Old 08-15-2010, 01:58 PM   #13
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My furnace is in an uninsulated and unconditioned space. Just a roof over it which has roof vents and gable vents. It gets really not up there in the summer and outside temperature in the winter.

Last edited by supermaxhd; 08-15-2010 at 02:09 PM.
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Old 08-15-2010, 09:21 PM   #14
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It sounds like I shouldn't consider a 90% or 95% gas furnace since it will get cold. I found other lengthy discussions on attic installs where the consensus was that it is not a good idea over 80% efficiency although it does sound possible.

Can anyone confirm new Trane rebates? I was ljust listening to the Bengals game on a Cincinnati radio station and a commericial said that a $1000 Trane rebate was available on top of the $1500 tax credit. I am in Lexington KY. THANKS!
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Old 09-10-2010, 05:14 PM   #15
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My new system was installed a couple of weeks ago. I went with a Trane super efficiency XL15I heat pump and XV80 gas furnace. Installer did a nice job. The XL15I had a $200 instant rebate. Ii've applied for a $400 state appliance rebate and I will get the remainder of my $1500 tax credit in the spring. Also, I believe another $250 state tax credit.


Last edited by supermaxhd; 09-10-2010 at 05:23 PM.
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