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ITD · 02-17-2013, 11:40 AM

I'm still struggling with payback numbers here. The claims I see on payback seem to talk about retrofits and include not only the system installation, but also new/better insulation, new windows and doors, which in and of itself would decrease heat use and lower costs regardless of fuel, so the payback numbers seem to exaggerate the benefit for someone who doesn't make, or need to make insulation improvements.

I found this energy use calculator, that provides up to date retail energy costs and converts them to dollars per million btus. This is a useful calculation to compare heating costs across different fuels. I'm not sure if I posted this link before, so I provided it below.

Looking at the spreadsheet, natural gas is the way to go if you want to save money. $8.99 per MMbtus Natural gas versus $10.56 per MMbtus for geothermal. The spreadsheet uses an efficiency number of 82% for the NG furnace, you can buy a 95% AFUE condensing unit that would yield a number of $7.76 per MMbtus. The geothermal number is also a little conservative, it seems 3.5 is a good representation of what is available which yields a number of $9.95 per MMbtus per the spreadsheet.

Anyway, to keep it simple, let's use the numbers in the spreadsheet and figure payback. For Natural gas versus geothermal, there is no payback, keep your gas furnace, or upgrade to a condensing super efficient model if necessary, that is the best bang for your buck.

For oil, let's assume that you use 100,000,000 btus in a season. (That should equate to a little under 1,000 gallons at 78% efficiency.) Using the numbers from the spreadsheet, for oil it would cost $36.82 per MMbtus times 100 equaling $3,682.00 per year for oil. Now for a geothermal system it would cost $10.56 per MMbtus times 100 equaling $1,056.00 for electricity, resulting in a savings of $2,626 per year.

Using this savings number and the $30,000 price bandied here as a geothermal retrofit price the payback on converting from oil to geothermal would be 11.4 years......

www.eia.gov/neic/experts/heatcalc.xls

02-17-2013, 11:40 AM	#87
ITD Senior Member Join Date: Apr 2004 Location: Moultonboro, NH Posts: 2,865 Thanks: 463 Thanked 668 Times in 367 Posts	I'm still struggling with payback numbers here. The claims I see on payback seem to talk about retrofits and include not only the system installation, but also new/better insulation, new windows and doors, which in and of itself would decrease heat use and lower costs regardless of fuel, so the payback numbers seem to exaggerate the benefit for someone who doesn't make, or need to make insulation improvements. I found this energy use calculator, that provides up to date retail energy costs and converts them to dollars per million btus. This is a useful calculation to compare heating costs across different fuels. I'm not sure if I posted this link before, so I provided it below. Looking at the spreadsheet, natural gas is the way to go if you want to save money. $8.99 per MMbtus Natural gas versus $10.56 per MMbtus for geothermal. The spreadsheet uses an efficiency number of 82% for the NG furnace, you can buy a 95% AFUE condensing unit that would yield a number of $7.76 per MMbtus. The geothermal number is also a little conservative, it seems 3.5 is a good representation of what is available which yields a number of $9.95 per MMbtus per the spreadsheet. Anyway, to keep it simple, let's use the numbers in the spreadsheet and figure payback. For Natural gas versus geothermal, there is no payback, keep your gas furnace, or upgrade to a condensing super efficient model if necessary, that is the best bang for your buck. For oil, let's assume that you use 100,000,000 btus in a season. (That should equate to a little under 1,000 gallons at 78% efficiency.) Using the numbers from the spreadsheet, for oil it would cost $36.82 per MMbtus times 100 equaling $3,682.00 per year for oil. Now for a geothermal system it would cost $10.56 per MMbtus times 100 equaling $1,056.00 for electricity, resulting in a savings of $2,626 per year. Using this savings number and the $30,000 price bandied here as a geothermal retrofit price the payback on converting from oil to geothermal would be 11.4 years...... www.eia.gov/neic/experts/heatcalc.xls