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# Fuel Cost Calculator

The Fuel Cost Comparison Chart is an Excel spreadsheet designed for comparing the relative cost of different heating options. For comparison purposes, the common denominator being compared is "Cost Per Million BTUs delivered".

Heat is measured in BTUs – British Thermal Units. One BTU is equal to about the amount of heat from one match. All fuels have a heat value. While for some there is a range of values due to inconsistencies, for this chart I have selected a commonly accepted value. These values will work well for this purpose. For example, I have used a heat value of 1080 BTU per cubic foot for natural gas. Natural gas does vary in heat content from 950 BTU to the cubic foot to over 1100 BTU to the cubic foot. If you know the heat content of the local gas where you are, you can change the value on this Excel chart. Liquefied Propane (LP) gas has a heat content of 91,500 BTU to the gallon. #2 fuel oil is 140,000 BTU per gallon. For electricity the value is 3413 BTU per kilowatt hour (kWh) when used in resistance heat (baseboard etc.).

The spreadsheet uses the efficiency of the appliance burning the fuel times the heat content of the fuel to get the net heat content that goes into the building. It then shows how many units of fuel are needed to deliver 1 million BTU to the building (the remainder goes out the vent). Electricity when used to make heat is 100% efficient for these purposes as there are not stack losses.

By taking the number of units of a fuel needed for a certain efficiency of appliance, and multiplying that times the cost per unit yields the total cost for 1 million BTUs delivered. Again, adjust the cost per unit of fuel using your local data.

## A special note on heat pumps

Air source heat pumps do not have a fixed efficiency. The air source heat pump puts more heat in BTUs per unit of electricity consumed when the air is warmer, less when colder. All heat pumps with an ARI rating are rated at 47 F (high temp) and 17 F (low temp). In many climates some of the heat from the system also comes from the supplemental heaters.

Heat pump efficiencies are called the COP – Coefficient of Performance. The COP tells how much heat is produced as compared the heat produced using the same amount of electricity in a resistance electric heater. So the COP for electric baseboard or supplemental heaters is 1.00. An efficient air source heat pump would produce a COP of 3.5 at 47 F. This means that one kilowatt hour of electricity (kWh) would produce 3413 BTU using an electric resistance heat source, and the air source heat pump would produce 3.5 times the BTU – 11,945 – at 47 F.

Many Geothermal systems have a COP rating that averages 4 COP year round, regardless of the air temperature.

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