Comparing Heating Costs

Heating space is typically the single largest consumer of home energy — as much as 43% for the average home.  Can you save money by switching your heating fuel?Seattle City Light has compiled this table to show the relative operating costs of the heating system types most often found in Seattle. As a point of reference, the table below shows the heating costs for a home with a heat load of 41 million BTUs per year which is probably a bit higher than average for Seattle. If you’re considering changing fuels, remember that improving the weather-tightness and insulation of your home will often make your home more comfortable and be more cost-effective than changing out your heating system.

Annual Fuel Cost Comparisons

For 12,000 kWh (41,000,000 Btu) per year
in delivered heat

Prices effective as of 7/3/12

Heating Systems
and their
Efficiency Ratings


Heating System

Efficiency Rating

Per 100K Btu

Per Year

Central Oil
$3.75 per gallon (7/3/12)

60% AFUE*



80% AFUE*



Central Gas
$1.06 per therm (5/14/12)

60% AFUE*



80% AFUE*



90% AFUE*



95% AFUE*



Central Electric
$0.0987 per kWh (1/1/12)

100% AFUE*



Zone Electric
$0.0987 per kWh (1/1/12)

100% AFUE



Heat Pump
$0.0987 per kWh (1/1/12)

8.0 HSPF
(235% AFUE*)



8.2 HSPF
(241% AFUE*)



8.5 HSPF
(250% AFUE*)



(294% AFUE*)



10.75 HSPF
(316% AFUE*)



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. Heat pumps can be more than 100% efficient, because they work by extracting heat from the outside air or soil rather than burning fuel or using electrical resistance to create heat.*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. Poorly sealed or uninsulated ducts or pipes can result in large efficiency losses with any furnace.Btu – British thermal unit: The amount of energy needed to raise one pound of water one degree Fahrenheit. Furnaces and heat pumps are commonly rated in Btu/hour output.

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 (8.2 for split systems).NOTE: SEER or the Seasonal Energy Efficiency Rating measures the cooling efficiency of heat pumps.

Calculating your Heat Load
If you have electric heat, figuring out exactly how much of any bill goes to heat can present a challenge. However, you can calculate an approximate answer without too much trouble. All you need are 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.

First, locate the kilowatt hour (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, which 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, which 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. If you don’t have your last six bills, you can call an Energy Advisor at 206-684-3800 for assistance in getting the information needed for this calculation.

If you heat with gas, by looking at your past year’s gas bills you can break out the amount of gas dedicated to heating the same way that is described for electricity above. Those who heat exclusively with oil can calculate their usage fairly easily by adding up how much oil is purchased in a year. Averaging your oil purchases from the past two years may give a more accurate measurement because it will reduce the inaccuracy caused by differing amounts of oil left in the tank over the summer.

You can find more technical information about comparing heating fuels from the Office of Efficiency and Renewable Energy.

For more information from Seattle City Light on home heating, please e-mail or call 206.684.3800.

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