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