By Lee Consavage

I was recently asked to recommend a “green” heating system for a new 2,200 square foot home to be built in York, Maine (very southern Maine). The home will be very well insulated and tight, requiring an air exchanger unit. The green system would be used in place of a fuel oil boiler system (cost about $10,000).

I used the energy calculation program RET Screen (www.RETScreen.net) to determine the energy production and cost to install a geothermal heat pump system. The RET Screen results recommended a 3-ton highly efficient heat pump (Heating COP = 4, Cooling COP = 5.5) be used to heat & cool the home.

The heat pump uses electricity to operate. RET Screen indicated the 3-ton heat pump would require 2,900 kilowatt-hours per year to provide space heating for the home at a total cost of $441 (14 cents per kilowatt-hour).
The heat pump would deliver 298 therms per year to heat the home.

One gallon of fuel oil provides 1.4 therms of energy at 100% efficiency. If the gallon of oil were burned in an 80% efficient oil boiler, then only 1.12 therms of energy can be extracted from each gallon of oil. A total of 266 gallons of oil would be required to deliver the same amount of energy as the heat pump would deliver. If oil costs $3.20 per gallon (which it does now), then the cost of oil to provided the same amount of heat as the heat pump would be $851.

The new homeowner would therefore save 50% on his home heating costs each year if he installed a heat pump.

This 50% savings is impressive. What’s even more impressive though is the 65% savings realized when using a geothermal heat pump for cooling the home when compared with the cost to operate an air conditioning unit. This makes sense since a typical air conditioning unit is using outside hot air (85 degrees F for example) and conditioning that air temperature to below 75 degrees F. This process takes a lot of electricity. In this example, the homeowner could save up to $1,869 per year in cooling costs.

A geothermal heat pump is using 50 degree F water from the ground to cool the same room down to 75 degrees F, a much easier feat requiring a lot less energy.

Minimum cost of a geothermal heat pump system and all other interior work to install the heat pump system is 3 tons x $5,000/ton = $15,000.

The cost to drill the well and all other exterior work to install the heat pump is: 3 tons x $2,000/ton = $6,000.

Payback is $15,000/$2,280 = 6.6 years (Assume well cost is equal to your usual cost for a well)

If we subtract the cost the homeowner would have paid for an oil burner, then the payback is less than 3 years.