March 2015

What’s a Heat Pump?


John M. Onstad


Since the beginning of civilization, people have heated their homes by burning things: wood, coal, peat and, more recently, fuel oil, kerosene, natural gas and propane.

These fuels heat effectively and cheaply because a lot of energy in the form of BTUs (British thermal units) is stored in a relatively small volume. A cord (4 ft. x 4 ft. x 8 ft.) of piñón wood contains about 22 million BTUs, a gallon of liquefied propane about 90,000 BTUs, and a cubic foot of compressed natural gas about 1,000 BTUs. At 75 percent efficiency in a wood stove, a cord of piñón will heat a 1,500-square-foot, well-insulated home for about a month, if you don’t mind hauling and splitting wood, tending the fire all day and dealing with the smoke and ashes, not to mention waking to a cold home at 6 a.m. And, as cozy and comfortable as a wood fire is, if we all heated our homes that way, the air would be considerably dirtier. Further, all of the above energy sources produce the greenhouse gas carbon dioxide (CO2) as well as other pollutants.

So let’s discuss a home-heating device that doesn’t burn anything: a hear pump. A heat pump is a refrigeration machine that extracts plentiful heat from the atmosphere, even when it’s bitterly cold outside, and uses this heat to warm your home. Heat pumps also can extract heat from the earth, underground aquifers, lakes or ponds.

Seem far-fetched? It did to me several years ago when I first began to investigate this technology.

Consider the freezer compartment of your home refrigerator, where the temperature is about –10° F. If you open the freezer door to load your groceries and then close it, the temperature might rise to 0° F. The compressor turns on and reduces the temperature from 0° F to –10° F. and blows warm air on your feet. This is a good example of how a heat pump works, extracting BTUs from a frigid environment and producing usable heat as a byproduct.

I have stated that a heat pump doesn’t burn anything, which is technically correct. But it is powered by electricity from a power company (like PNM), which burns something like coal or natural gas to produce electricity.

Here’s where the “magic” of a heat pump comes into play: it utilizes energy to make considerably more energy than it consumes. That is, for every kilowatt-hour (kWh) of electricity purchased from the power company—or produced by your photovoltaic (PV) system—a heat pump will extract 3 to 4 kWh of energy from the outside air during the winter months (1 kWh of electricity equals 3,415 BTUs).

If you research heat pumps on the Internet, you’ll read numerous comments that tell you heat pumps don’t work when it’s cold outside. Don’t believe them! That was true 30 years ago. I’ve installed a couple dozen in the Santa Fe area, and they heated just fine when the mercury dipped to -20 ° F in 2011, and that’s without any form of back-up heat.

So, what are the benefits of heat-pump technology to you as a homeowner?

  1. A heat pump heats in the winter and cools in the summer.
  2. Because a heat pump extracts energy from winter ambient air, it’s a renewable energy source like PV solar, thermal solar and wind power. It will comfortably heat your home at 2 a.m. in January.
  3. If you’re currently heating with propane or electricity, it can reduce your heating bill by up to 75 percent.
  4. A heat pump can be an affordable heating and cooling system to install in a small zone such as a converted garage, sunroom, bonus room or addition, as well as your whole house.
  5. It can provide heating and cooling for a home with a failed radiant-heating system, as well as cooling for a home with radiant heating.
  6. Last but not least, a heat pump can make chilled water for radiant-floor cooling, a surprisingly affordable way to air-condition your home.


John M. Onstad is the owner and general manager of Hubbell Electro-Mechanical. His company has designed, installed and repaired heating and cooling systems in the Santa Fe area since 1980. 505.471.4221,



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