I'd say that is a good estimate.  Here is a spreadsheet from the US Department of Energy that can help you get closer.  It takes into account fuel costs and equipment efficiencies: www.eia.doe.gov/neic/experts/heatcalc.xls

Personally, if I were making the investment, I'd compare the cost for a higher efficiency geo unit.  A COP of 3.0 is at the low end.  Don't forget that 30% federal rebate can help justify the slightly higher cost.

Regards,
Ed

I'm a homeowner. One thing that comes to mind is that a geothermal system that is sized correctly for a house most likely won't be able to put out the same BTU's per hour as the furnace (since furnaces are typically over sized). So, if your heat loss is more than the geothermal system can produce within a given time, the auxiliary heat may come on. You have choices on what type of auxiliary heat you can choose. In NC, this may not be much of an issue since you don't typically have brutally cold winters, this winter excluded! The people quoting your install will be able to run figures for you. Auxiliary heat isn't necessarily bad thing since it can save on installation costs, it's just something that isn't figured into your post.

It's 20f at our location in VA today. As an experiment, I am keeping our system at 67 today in first stage. I'm surprised that it is maintaining temperature. Our loop and system may be a bit over sized. Typically, over sizing a system costs more to install, but since quotes vary between installers, there is a possibility it may not. Note, an over sized system may be better able to keep up with more extreme outdoor conditions, but it may cost more for the installation and running cost.

I see Ed just mentioned a higher efficiency unit.  This is a good idea, and your idea to use an average COP is good too.  I'm not sure what a good average COP would be to use in your estimate for high efficiency equipment.  Maybe 3.5?

I used an average COP of 3 to be conserative and to have a fair comparison. Thansk for the replies.

Ozark01,

Check your computation for accuracy. You need a COP of 4 to arrive at $69 electric cost, under your assumptions. With your intended COP of 3, the electric cost is about $92.

Regards,

Masoud

My thought was that I was paying for the kw's that ran the heat pump and with a COP of three that would be four units of energy with three being "free". Is that the wrong way to sya it?

Yes, that is incorrect. COP stands for Coefficient of Performance and thus is a multiplier not an addition. A COP of three means buy one get two free.

COP 3.0 is a good number for economic comparison purposes, however, you won't get COP 3 if you shortloop the system.

Ozark01,

Overall coefficient of performance for an energy system:

COP = Total Energy Output ÷ Total Energy Input. Both output and input values are measured in the same unit, like btu, kwh, calorie...

Regards,

Masoud

Thanks guys!

New costs for heating my house (see earlier posts for formulas, type of house, etc.)
Month Feb (01/28-02/24)
Heating degree days: 1011
If I had oil still (previous system that I removed), I would have used 170 gallons
Cost of those 170 gallons: $503 (2.94/gal in this area)
Cost to heat home with Geo (total elec bill - base cost with no heating/cooling) = $125
Saved: $378

Upcoming goals as the weather warms up (although here in the northeast, I don't think we remember what spring is):
Spray foam to seal around the perimeter of the house in the basement (sill plates, etc.)
Insulate all basement ceilings above unheated spaces or insulate basement walls/floor (min R-19)
Have duct work issues resolved (see other posts of mine)

Been trying to think about how the costs compare to a standard heat pump. I've never had one in this particular house, but in comparing to my previous house, I note the following:
In 2008, my previous house (1200 sq feet, built 1982, twin) had an air-to-air heat pump, and in Feb of 08 cost $60 to heat the house.
In 2010, my current house (2100 sq feet, built 1959, single-family) has a geothermal, and in Feb of '10, cost $125 to heat the house.
The number of heating degree days in Feb 08 and Feb 10 were about equal.
I know, twice as big house, much older, but should I be surprised that it cost twice the electricity to heat the new home, with a system that's supposedly much more efficient? Is my current house that much worse at retaining heat?
Sure, compared to oil, geo is cheaper for this home, but I'm surprised at basically $4/day to heat the house. I've always heard it should be about $1 - $2 per day.

I wonder if the shared wall in the twin contributed greatly toward insulation value (since it was not exposed to the outside). Also, no windows on that wall either (unless the neighbors were very friendly). 

Common wall would make a substantial difference - it is up against conditioned space and has no windows.

Did I miss something - Stu wrote "new" house was constructed in 1959???

LOL, it's true. I think I said my new house was 1959. I meant, my previous house was built in '82 and my present house (new to me!) is an older home, 1959 cape. I didn't take a TARDIS back to the other one or anything like that.

A WHO fan!

Yep. He's got a huge vaulted ceiling in the TARDIS. What kind of heating system do you think he uses? With all the grates on the floor, perhaps it's some sort of forced air system, or perhaps the roundels are radiant? If each one had its own proximity thermostat, that could really keep a time capsule comfortable. My guess is that it's not geothermal.

I was OK with the NYC Asian Escorts as a brief welcome dalliance from later winter concerns of loop temps, aux heat etc, but ads for bike parts are right out!

Time for you to no longer darken our door!

Don't misunderestimate the importance of bike parts to GREEN Asian Escorts.

Anyhoo, there's nothin' worse than an escort with a huge ...uh, carbon footprint.

...just sayin'

Looby

I actually have some questions about the performance of my Asian Escort.

My mother in law just came over last night to our house. She keeps her house at 68, says it feels cold all the time, has gas for heat. Her house is a townhouse, 2 shared walls (she's in the middle), smaller house than ours, newer construction, newer windows, etc.

Her bill last month for gas and electric combined: $540!

My house, bigger, a lot older, kept at 71 (she commented how warm it felt), geothermal, last month: $230! Then my wife said, come in the summer and enjoy the air conditioning too. Her reply, "It does air conditioning TOO????"

I'd subsidize my mother-in-law's heating bills if it kept her from coming over.