Condensing Boiler Vs Geothermal Heat Pump - Cheap Heat Surprise
While a geothermal heat pump's 350% efficiency far outstrips that of a 95% efficient condensing boiler, higher efficiency ratings don't always mean lower heating costs.Many a home owner on the look out for something new to replace an old, inefficient heating system probably knows a thing or two about the exceptional efficiency of geothermal heat pumps. But few people are aware of the new 95% efficient condensing boilers fueled by natural gas.
While a geothermal heat pump's 350% efficiency far outstrips that of a 95% efficient condensing boiler, higher efficiency ratings don't always mean lower heating costs.
It's only when the cost of fuel is factored in can you determine the actual cost of heating for each system. In the example below the cost to produce 100,000 Btu will be used to compare the systems.
Since a geothermal heat pump runs on electricity measured in kilowatt hours (kWh), and a condensing boiler is fueled by natural gas measured in therms, it's necessary to convert kWh of electricity into "therms" to make an accurate comparison.
One therm of gas produces 100,000 Btu so we need to know how many kWh of electricity it would take to produce 100,000 Btu. Since one kWh = 3,413 Btu it would require 29.3 kWh to produce 100,000 Btu, or one "therm" of electricity.
Here in New England electricity goes for $0.143 per kWh. So a "therm" of electricity would cost $4.19 (29.3 x $0.143). A therm of natural gas, according to National Grid, retails for $0.78.
The next step is to apply each appliance's efficiency to its respective fuel price. But it's not as simple as multiplying the fuel price by the percentage of efficiency (95% or 350%). Instead you would use the coefficient of each percentage as a constant to keep the comparison apples to apples.
The condensing boiler efficiency is 95% therefore the coefficient is 1/.95 or 1.05
The geothermal heat pump efficiency is 350% so the coefficient would be 1/3.50 or .29
Finally, the efficiency coefficient is multiplied by the cost per therm of fuel for each system to determine which one produces 100,000 Btu of heat for the least amount of money.
Geothermal Heat Pump: .29 x $4.19 = $1.22 per 100,000 Btu
Condensing Boiler: 1.05 x $0.78 = $0.82 per 100,000 Btu
The surprising results show that even though a geothermal heat pump is 3½ times more efficient than a condensing boiler the heat it produces is 49% more expensive.
This paradox is brought about by recent low natural gas prices and the high cost of electricity in New England.
Depending on where you live, utility rates will vary from the ones used in this example but it should be simple enough to substitute local rates for the ones here to make your own comparisons.
Find out which condensing boilers contractors love at Best High Efficiency Condensing Boilers.