Heat Pumps & Electrification

An air conditioner that can run in both directions. A reversing valve flips the refrigerant circuit, so in summer it carries heat out of the house and in winter it carries heat in from outdoor air. Because it moves energy instead of burning fuel, it delivers several units of heat for every unit of electricity it draws — which is the whole reason the retrofit is worth doing.

Run the heat and go outside. If the outdoor unit is running while the house is heating, it is a heat pump; a gas or oil system leaves that unit silent all winter. Two more tells: the thermostat has an emergency heat or aux heat setting, which only exists on heat pumps, and the air from the registers feels warm rather than hot. In the basement, a heat pump air handler has no gas line, no flue and no burner compartment.

Cold air still contains heat, and refrigerant boiling at a much lower temperature will absorb it. The compressor raises that energy to a useful temperature and the indoor coil releases it. As it gets colder outside there is less to harvest, so capacity tapers along a curve — which is why sizing is done at the winter design temperature. Frost builds on the outdoor coil as it works, so the unit periodically reverses for a few minutes to melt it clear, then returns to heating.

Four real ones. Supply air is cooler than furnace air, so it feels different even when the room is at temperature. Capacity falls as the outdoor temperature does, so an undersized system leans on expensive electric backup. The outdoor unit has to run through winter, including defrost cycles that make noise and steam. And a retrofit sometimes needs electrical panel work the old gas system never required. None of these is a reason to avoid one — they are reasons to have it sized and configured properly.

Almost never by choice. Emergency heat locks out the compressor and runs electric resistance strips alone, the most expensive way a house can be heated. It is there for a genuine failure — a compressor that will not start, a bad reversing valve, ice that will not clear. If the house is simply slow to warm on a cold day, leave the thermostat in normal heat, let the system stage the backup itself, and call us.

Twelve to fifteen years is the usual working life, a little less than a gas furnace because the equipment runs in both seasons instead of one. What extends it is annual service on both modes, clear space around the outdoor unit, and a charge that was correct on day one. What shortens it is a compressor short-cycling against restricted ductwork, which is a duct problem wearing an equipment problem’s clothes.

From the yard, almost identical to an air conditioning condenser: a metal box with a fan, a coil around the outside, and two insulated copper lines running into the house. The differences are small. It sits on a raised stand rather than flat on a pad, so meltwater from defrost can drain away, and it has a reversing valve — a brass cylinder with a solenoid on it — visible among the pipework inside the cabinet.

It usually comes down to what is already in the basement. A house with a failed condenser and a young gas furnace is the classic dual-fuel candidate: add the heat pump, keep the furnace for the coldest stretch. A house with no gas service, an oil tank you want gone, or an addition with no ductwork is a straight heat pump job. A house where both systems are at end of life gets the full comparison in the table above, run against your own heat loss numbers rather than a rule of thumb.