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Electric Heat Costs
For most homes space heating represents the single largest consumer of energy each year. If you have an oil furnace, figuring out how much energy goes into space heating is easy; all you have to know is how much fuel oil you use and the efficiency of your furnace. If you have electric heat, figuring out exactly how much of any bill goes to heat can present a difficult challenge. However, you can calculate a pretty good approximate answer. All you need is copies of your last year's City Light bills and a pencil and paper. Using a hand held calculator might make the arithmetic a bit easier to do.
First locate the kWh usage recorded on each bill. You'll find it in the Detailed Billing Information section. Next add up the kWh usage for the past year. Then find the bill with the lowest kWh usage. This is almost always a summertime bill. We will make two assumptions about the consumption recorded on that bill. First, it contains no electric heat usage. That means it represents your home's electric consumption for everything except heat. Second, we will assume that this level of non-heat consumption is constant year round.
Now multiply the kWh usage from the low bill by six (multiply by 12 if you receive a light bill every month instead of every other month). Subtract the product from the annual total you calculated. The remainder represents the approximate number of kWh your household uses for space heating.
Here is more technical information about comparing heating fuels from the Office of Efficiency and Renewable Energy.
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Annual Fuel Cost Comparisons
For 12,000 kWh (or equivalent) per year
in delivered heat
Prices effective as of 1/07
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Heating Systems
and their
Efficiency Ratings
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Associated
costs
(converted to therms)
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| Heating System |
Efficiency Rating |
Per Therm |
Per Year |
Central Oil
$3.49 per gallon
|
60% AFUE |
$4.15 |
$1,701 |
| 80% AFUE |
$3.12 |
$1,276 |
Central Gas
$1.08 per therm
|
60% AFUE |
$1.81 |
$740 |
| 80% AFUE |
$1.36 |
$555 |
| 90% AFUE |
$1.21 |
$493 |
| 95% AFUE |
$1.14 |
$467 |
Central Electric
$0.0793 per kWh
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100% AFUE* |
$2.32 |
$952 |
Zone Electric
$0.0793 per kWh
|
100% AFUE* |
$2.32 |
$952 |
| Heat Pump |
8.0 HSPF |
$.99 |
$405 |
| 8.5 HSPF |
$0.93 |
$381 |
Terms:
AFUE - Annual Fuel Utilization Efficiency: how much usable heat is delivered from the system. Gas and oil systems are not 100% efficient because some of the heat goes up the chimney along with fumes, smoke and particulates.
*AFUE does not reflect distribution losses such as what is lost when heat has to travel through ducts or pipes before it enters a living space. That is why the chart shows no difference of efficiencies between central and zone electric systems.
HSPF - Heating Season Performance Factor: used to rate the heating efficiency of heat pumps. To qualify for an Energy Star rating, the heat pump must have a minimum HSPF of 8.0. (NOTE: SEER or the Seasonal Energy Efficiency Rating measures the cooling efficiency of heat pumps.)
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For more information from Seattle City Light on home heating, please e-mail rescons.scl@seattle.gov or call 206.684.3800.
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