I'm thinking about installing geothermal at my house. I've been using this spreadsheet to look at costs of different fuels:

My current system is forced air propane and I pay $3 a gallon for propane and 12 cents for electric. So propane shows about $35.58 per million btu and geo @ COP of 4.6 shows $7.90 per million btu. So geothermal would be 4.5 times cheaper. My question is, this spreadsheet doesn't take into account the electricity use of the furnace fan (single speed fan, %92 efficient furnace.) I'm thinking that fan costs me $10 a month to run. So do you factor that in? I mean, that's only probably $50 a year but it's a small factor to consider?

What do you guys think about that spreadsheet from EIA? I know I use at least 700 gallons of propane, so that's about 64 million btus so I should see about $1800 savings per year in heat costs alone, not even including the hot water and a/c savings. Is my logic correct? Is there something I'm missing and maybe I can't rely on that spreadsheet? I have some contractors doing heat/loss calcs , giving me estimates this week.

2400 sq foot home, tight, Allentown, PA.