Good analysis so far. Comments below:
I know this is an older thread but I thought I would chime in here.
I'm building a new house this summer and as an engineer I like to analyze things.
A load calculation to determine how much heat the house needs is a good starting point.
If you want to roughly determine the impact of different design options (heating, windows, insulation), try a energy modelling program. A good free one is Hot 2000 - produced by natural resources Canada.
The type of heating system has an impact not only of the capital cost of the equipment, but ductwork too...
Heatpumps need significantly more airflow to deliver the same amount of BTUs.
Geothermal needs around 400 CFM (that's cubic feet per minute) per ton or 12,000 BTUs/hr of heat. (the same goes for a/c units, geothermal or not)
Modern furnaces only need 222 CFM give or take per 12 000 BTU/hr of heat.
Heat gain is always much lower than heat loss in our climate, so generally a duct system designed for a furnace these days should be adequate for a/c but not necessarily a heatpump sized for heating.
For example a home with a design heat loss of 40 000 BTUs @ -20C could easily get by with a 2 ton (24000 btu/hr) a/c.
If you get a geothermal system, be sure it has a two stage compressor -> otherwise it will be oversized for cooling (to the point of not dehumidifying properly) or undersized for heating. (necessitating the use of expensive supplemental heat)
I understand that geothermal you can realize COPs in the 4 range, and NG furnaces are about 96% efficient, which in effect means that the cost of the fuel (electricity) has to be (4/.96) or 4.17 times more expensive (or less) to be more economical to run.
When it comes to environmental impact - along with cost, the efficiency of the power plant has to be taken into consideration.
A COP of 4 might sounds good, but goethermal may only offer a marginal improvement over a 95% efficient gas furnace, because the typical nuclear/coal/gas power plant is only 30-45% efficient. (note: some of the new gas plants are better -> in the 50-60% range)
No one knows what kind of power generation mix ontario will have over the life of the house, but the province has built a lot of gas fired plants. Coal appears to be going away and all of the nuclear plants will have to be refurbished or replaced in the next 20 years.
I then normalized the cost per therm of electricity and natural gas, using my December gas and electricity bills, to see if electricity was 4.17 times more expensive(or less) which would justify the pursuit of a geothermal system.
The price of nat gas is pretty much guaranteed to increase over the next 20 years, since - adjusted for inflation, it's pretty much as cheap as it ever has been over the last 30 years.
The cost of electricity will probably increase for at least the next 5 years since mcguinty has locked the province into a lot of renewable energy contacts. (many of which are for capacity which hasn't even come online yet) After that, who knows?
For electricity, my December bill, including all BS charges (delivery, debt retirement charge, HST, etc) averaged 17.12 cents/kWh. With a conversion rate of 29.30 kWh/therm, electricity costs ~5.02 dollars/therm.
17 cents /kwh seems a little high - did the subtract the fixed monthly charge and include the ceb. (a subsidy - 10% off all charges)
For natural gas, my December, including all BS charges averaged 21.26 cents/m^3. With the conversion rate of 2.83 m^3/therm for natural gas, the cost per therm (in dollars) is 0.602.
Therefore 5.02 dollars/therm(electricity) / 0.602 dollars/therm(natural gas) is 8.336, which means that for the rates I have documented above, electricity is 8.336 times more expensive/therm than natural gas. That means the COP of a geothermal system has to be 8.336 times higher than the natural gas fueled system for the cost of operation to be equivalent.
I have not seen a geothermal system with a COP higher than 6.
Therefore for the price of energy in my region, there is no business case for geothermal heating, as 8.336 > 4.16.
One thing to remember is that the COP only applies when the geothermal heatpump can heat the house by itself in extreme cold. Heatpumps (even geothermal) are often installed with supplemental heat strips, which only have a cop of 1.
There is still some analysis that needs to be done to see if the cost of cooling with geothermal is significantly cheaper than a, say 15 SEER A/C unit to offset the increased cost of heating. Again, this cost would have to be offset from the increased initial cost of geothermal.
Modern air to air a/c units have an effective cop of 3+.
15 BTUs/watt (that's what seer is) = a cop of 4.4.
However, SEER isn't very representative of performance in very hot weather. It's pretty much a seasonal rating which includes outdoor temps at which the average person wouldn't use cooling to begin with.
A/Cs carry an EER rating which is BTU/watt at 95F indoor/80F outdoor.
A 15 seer a/c has a EER rating of 12 give or take 0.5 -> COP of 3.5
But if you're going from a strictly environmental stance, the geothermal system is more efficient in its use of energy, but its not cheaper.
BTW I'm in the Hamilton, ON area.
WARNING: The HVAC information I provide is not based on field experience and DOES NOT constitute professional advice.