A few months back I wrote a blog post on how air-to-air heat pumps work (Heat Pumps 101). Today I want to explain why these heat pumps can be part of our heating solution in New England.
A little history: air-to-air heat pumps have been popular south of New England for decades. When the outside air temperature doesn’t get too cold, it is not too difficult for one of these heat pumps to extract some warmth from that air…at, say 45F-50F, and compress it high enough to provide 70F air for the inside room. And, since a heat pump can work backwards, it can extract heat from inside the house and vent it to the outdoors in the summer when the occupants want air conditioning (cooling).
Only in the last few years have the manufacturers of these heat pumps increased the efficiencies of the equipment and the refrigerant to be able to extract heat from 0F degree air. In New England, where we have lots of 0F outside air, these heat pumps are now worth adding to the list of equipment that we should consider in our energy system designs.
Costs: Electricity costs vary from state to state, with most of the New England states commanding relatively high rates per kWh (kilowatt hour), approximately 12-16 cents/kWh. Compared to oil or propane, the dollars per BTU (or unit of heat), is generally higher for electricity, so we often choose to heat with a fossil fuel over electricity.
One of the most important features of a heat pump (which is run on electricity), is that as the outside temperature goes up above 0F, the amount of electricity used to produce one unit of heat becomes 1/2 or even 1/3 as much. So, when you are heating your house in the spring and fall, where the temperature hovers around 32F, you will spend less money on the electricity to run a heat pump then you would on a fossil fuel to provide the same heat. As it gets colder, the efficiency of the heat pump goes down, and you would spend less money using the fossil fuel.
So many people in New England are looking at mini-split heat pumps to offset some of their heating costs in the shoulder seasons and using fossil fuels only for the coldest part of the year.
An added benefit of using heat pumps is the ability to offset some or all of the electricity with local solar electric panels. So if you are trying to reduce or eliminate fossil fuels and you want to have more control over your own energy production, a heat pump might be a good step for you.