We’ve experienced price increases in all aspects of our daily lives from groceries to fuel and everything in between.
Here in Massachusetts, National Grid will be raising the cost of electricity by approximately 64%. This raise is because the bulk of our electricity is generated from natural gas, which has dramatically increased in cost.
Fuel oil also drastically increased in price last year and has maintained a high price even throughout the summer. Many experts predict that fuel oil costs will be as high or higher than last winter.
What does all this mean for the average homeowner and what can be done about it?
How a Heat Pump Works
To answer the previous questions let’s first get familiar with what a heat pump is and how the variable efficiency of heat pumps effects operating costs.
A heat pump is a mechanical device that forces heat to move the way it doesn’t want to go – that is, from cold to hot.
Heat pumps don’t create heat, they move heat from the colder space to the warmer space.
Refrigerators, air conditioners and mini-split systems are all heat pumps in that they move heat from the colder space into the warmer space.
In the winter, a heat pump moves heat from the colder outdoor space into your warmer home. The larger the temperature difference, the more work the heat pump has to perform to move the heat. That is why heat pumps have a variable efficiency that changes with outdoor temperature.
The warmer it is outside, the less work the system performs to move heat inside to warm your home.
We refer to that variable efficiency as the coefficient of performance (COP.)
An electric resistance heaters’ COP is always 1. That is, you put 1,000 Watts of power into your heater and you get 1,000 Watts out. Heat pumps also have a COP and they are always higher than 1. For example, we’ll take the case of a Mitsubishi mini-split system, the only brand of mini-splits we install.
|Outdoor Temperature (F)||COP|
As shown in the table above, a Mitsubishi heat pump is always at least twice the efficiency of an electric resistance heater (-5 F) and gets even better as the outdoor temperature rises.
When it is over 50 F outdoors, a Mitsubishi heat pump is more than four times the efficiency of an electric resistance heater.
Heat Pump Heating Cost Comparison
Now let’s discuss how this matters when heating your home.
We use the table below to illustrate how much money it will cost to produce a certain quantity of heat, in this case, 1 million BTU’s.
Each line represents the cost of generating 1 million BTU’s of heat using a different fuel source or heat pump as a different COP.
|Fuel Source||Unit Measure||Cost||Cost per Million BTU’s|
|Electric Resistance||kW Hour||$ 0.39||$ 115.32|
|Oil||Gallon||$ 5.50||$ 57.77|
|Propane||Gallon||$ 5.50||$ 77.84|
|Natural Gas||Therm||$ 2.42||$ 29.20|
|Heat Pump COP 2 (-5 F)||kW Hour||$ 0.39||$ 57.66|
|Heat Pump COP 3 (35 F)||kW Hour||$ 0.39||$ 38.44|
|Heat Pump COP 4 (50 F)||kW Hour||$ 0.24||$ 17.58|
As you can see, a Mitsubishi heat pump operating at a COP of 2 (-5 F) will produce 1 million BTU’s for roughly $58 at the new National Grid rates, which is nearly the same price as oil at $5.50 / gallon and an 85% burner.
Here in Massachusetts, it doesn’t get to -5 F very often, so your heat pump will be operating at a COP between 2 and 3 most of the winter. That means that the same 1 million BTU’s will cost between $58 and $38 dollars to produce for most of the winter.
In the shoulder months, fall and spring, the heat pumps will operate with a COP greater than 3 and the cost of producing 1 million BTU’s is even lower. That is what makes heat pumps such a great system for heating AND cooling your home.
At their worst performance on a bitterly cold day, a heat pump will operate for roughly the same cost as your oil burner and any day that is warmer than -5 F, the heat pump will cost less to operate than an oil system using oil at $5.50 a gallon AND the heat pump provides air conditioning in the warmer months.