Heat Pump vs Furnace: Which Fits a New Mexico Home?

A gas furnace burns fuel and pushes the heat through ducts. Its efficiency rating is AFUE, the share of the fuel's energy that becomes usable heat in the home.

A heat pump moves heat rather than making it. It pulls heat from outdoor air, even cold air, and delivers it indoors, then reverses in summer to cool the house. Its ratings are HSPF2 for heating and SEER2 for cooling. The DOE minimum for split heat pumps nationwide is 14.3 SEER2 and 7.5 HSPF2.

That reverse trick matters here. If your AC is also aging, one heat pump can replace both jobs.

It does not rule one out, but it sets the equipment you should choose. NCEI engineering data for Albuquerque (1967 to 1996) lists a 99 percent heating design temperature of 19°F and 99.6 percent of 15°F. Albuquerque also averages about 113 freezing nights a year.

Higher ground runs colder. Edgewood sits around 6,600 feet in the East Mountains, and we would not borrow Albuquerque's design number for a house there. Use a design temperature for the actual location.

For cold weather, look at the ENERGY STAR cold-climate designation. To earn it, a heat pump must meet a coefficient of performance of at least 1.75 at 5°F, and hold at least 70 percent of its 47°F heating capacity at 5°F. Those are minimums for a label, not a promise for any one machine.

The sizing step should use real data. PNNL's Building America guide says equipment should not be selected on nameplate capacity. Use the manufacturer's extended performance tables to see output at your design temperature, then find the balance point, which is the lowest outdoor temperature at which the unit alone covers the house. Below that, something else has to help.

Run the numbers with your own bills, because rates and fuels vary across the state. Metro homes are generally on PNM and New Mexico Gas Company. Many East Mountain and Estancia Valley homes run propane, and electric service there often comes from a co-op such as Central New Mexico Electric, so confirm yours.

ENERGY STAR says switching from electric resistance, propane or oil heat to a heat pump can lower bills. Natural gas is less clear, and a written comparison using your own rates beats any general claim, ours included.

You can run that comparison yourself in a few minutes. Take the price per unit from a winter bill and turn it into the cost of one million BTU of delivered heat, using EIA's conversion factors of 100,000 BTU per therm, about 91,500 per gallon of propane and 3,412 per kilowatt-hour.

Write AFUE as a decimal, so 0.95 for 95 percent. COP is the heat delivered per unit of electricity, and it falls as the outdoor temperature drops, so run the math at a typical winter temperature and again at your design temperature. Leave out fixed monthly charges unless you would actually drop that service.

• Start with the fuel you have. Propane homes usually have the strongest case for a heat pump.
• Do not replace a good furnace to chase efficiency. Add a heat pump when the AC dies, and let the furnace back it up.
• Inspect ducts first. A heat pump needs airflow, and old ducts may fall short.
• Size from Manual J, using the real location, not a nearby city.
• Ask for numbers at your elevation. That goes for both heat pump installation and furnace replacement, since a gas furnace installation has to follow the manufacturer's high-altitude instructions.

Lean toward a heat pump on propane or electric heat, or when the AC is due at the same time. Lean toward a furnace with sound gas service and a healthy existing AC. Choose dual fuel when you want the efficient option most of the year and a burner for the deep cold. Ask for both written options, and base the choice on your house.