Good for you for considering the carbon footprint issues. It also helps if it makes economic sense to convert. As I understand it, your heating and cooling systems are up for replacement so you have to spend something just to keep warm/cool. It’s like building your first house, you aren’t investing for payback, you need a place to live. So the question comes down to what you can afford now and are you looking for short or long term costs of operation.
I used a very conservative .35 percent number from the governments website (it assumes a system makes 2.85 BTUs of heat for every 1 BTU of electric energy put in) but can tell you that my system runs very close to .20 percent (it makes 5 BTUs of heat for every 1 BTU of electricity put in, or 500% efficiency). That is measured performance using full instrumentation of the system, not theoretical or sales brochure numbers. When first installed in 2011, we were paying $3.23 per gallon propane and $0.14 per KWH for electricity. It payed for itself in six years (with the government tax credit taken into account). Anything that pays for itself in 10 years or less is a good investment in my mind since it is providing about 6% or better annual return. Our system uses radiant floor heating, pex tubing installed in a concrete slab in the basement and first floor (with tile). That allows us to run the system very efficiently. During the heating season, we only pump the water temperature in our holding tank up to 95 degree. This water is then circulated through the floor. Radiant floor heating is very nice on a cold winter day, you can walk around in your bare feet on a tile floor. However, if you don’t have radiant heating, you will need to pump the temperature up to a higher level. An air coil (in a ducted forced air system) would work much better at 120 degrees or higher, same for baseboard heating. The higher you need to pump up the temp, the lower the efficiency of the system (think of rolling a rock up hill, the high you need to go, the more energy you need to put into it) That is why I suggested you talk to your system salesman. Some are just selling stuff and some are able to give you a detailed estimate and options to improve performance. Geothermal was new and somewhat controversial before we installed our system so I spoke with the engineer in NH who pioneered the concept and he gave me some info that showed me how to optimize.
There are now other options to geothermal however that might be more attractive. Maine is the oldest state in the nation, per capita wise, and most people have a very short time perspective (they can’t see investing for the next 10 years because they likely won’t be here that long, I’m in my very late 60’s so but still think a ten year payback is worth going after because I’m planning to live to 100!). Split mini system heat pumps are very big now in Maine if you can believe it. I had one installed in a small guest house last fall and it provided heat all winter, even down to -15 degrees at less cost than we had been paying for oil and electricity. They are a much lower upfront capital investment, especially since you don’t need the geothermal well or ground loops. They are very efficient and provide both heating and cooling in one system.
Finally, if you are paying $.19 for electricity, you should very seriously look at some solar panels. It will depend on your state’s utility regulations but with net metering, solar panels in Maine (not known for being very sunny) can pay for themselves in 10 years or less. I have a 19.6KW solar system that I installed in three phases to cut down on the initial investment (paid for the system outright versus financing) and we now have no electric bills (except the monthly connection charge of $12 for the rest of my natural life and likely the same for my son when he gets the house). Our house is all electric. All we need to buy now is beer and tacos, healthcare, and college for the grandkids.
Finally, whatever decision you make takes some research on systems, State and Federal regulatory and tax issues, a little prognostication on future energy costs, what is cheaper for you versus better for the nation and the world, and faith in your decision making.
What ever you decide, take care and good luck.
From the great state of Maine to the great state of Iowa