How does a heat pump work?

A heat pump is a heating and cooling device that moves heat from one place to another instead of creating it. In summer, a heat pump pulls heat out of your home and moves it outside, working as an air conditioner. In winter, the same equipment reverses direction and pulls heat out of the outdoor air (even sub-zero air contains usable heat) and moves it inside. Because moving heat takes less energy than producing it, a heat pump can deliver 2 to 3 units of heat for every 1 unit of electricity consumed.

At A.J. LeBlanc Heating, we install and service heat pumps across southern NH. Here is what is actually happening inside the equipment.

The basic principle: refrigerants and pressure

A heat pump uses a closed loop of refrigerant (a specially engineered chemical, typically R-410A on older systems, R-32 or R-454B on newer ones) that changes state between liquid and gas as it absorbs and releases heat. The cycle has four main components:

1. Compressor: compresses the refrigerant gas, which raises its temperature.
2. Condenser coil: the hot, pressurized refrigerant releases its heat to the surrounding air (or water) and condenses back to a liquid.
3. Expansion valve: the liquid refrigerant passes through a restriction that lowers its pressure and temperature dramatically.
4. Evaporator coil: the cold, low-pressure refrigerant absorbs heat from the surrounding air (or water) and evaporates back to a gas.

The compressor then pulls the gas back in and the cycle repeats.

The reversing valve makes it work both ways

The trick that turns a standard AC into a heat pump is a reversing valve. By switching the direction the refrigerant flows, the outdoor coil and indoor coil swap roles:

• Cooling mode: indoor coil absorbs heat from your home; outdoor coil releases that heat outside.
• Heating mode: outdoor coil absorbs heat from the outdoor air; indoor coil releases that heat into your home.

The same hardware, just running in different directions.

Yes, even cold outdoor air contains usable heat

This is the part that catches most people the first time. To a refrigerant operating at very low pressure (and therefore very low temperature, like minus 30°F), outdoor air at minus 5°F is still warmer and will give up heat to the refrigerant. The compressor then raises that heat to a useful indoor delivery temperature.

Modern cold-climate heat pumps (CCHP) are engineered specifically for this. Variable-speed inverter compressors, enhanced vapor injection, and improved refrigerants extend useful capacity well below zero. Manufacturers like Mitsubishi (Hyper-Heat), Bosch (IDS), Fujitsu (XLTH), Daikin, and LG all make CCHP units rated for NH winter conditions.

Why heat pumps are so efficient

The efficiency advantage comes from physics. A traditional electric resistance heater can produce at best 1 unit of heat per 1 unit of electricity (a coefficient of performance, or COP, of 1.0). A modern cold-climate heat pump achieves:

• COP of 3.0 or higher at 47°F outdoor
• COP of roughly 2.0 to 2.5 at 17°F outdoor
• COP of roughly 1.5 to 2.0 at 0°F outdoor
• Continued heat delivery (at lower COP) at outdoor temperatures down to minus 13°F and below

Compared to electric resistance, a heat pump uses less than half the electricity for the same heat output during most of the heating season. Compared to fossil fuels, the cost-per-BTU often comes out lower, especially in NH where electricity rates are competitive against oil and propane.

Where heat pumps fit in NH

Central heat pumps

An outdoor condenser paired with an indoor air handler (or a furnace, in a dual-fuel configuration), distributing conditioned air through existing ductwork. Best fit for homes that already have central AC and want to convert from a fossil-fuel furnace.

Ductless mini splits

An outdoor unit paired with one or more indoor heads mounted on walls, ceilings, floors, or concealed in the ceiling. No ductwork required, which makes mini splits the most popular heat pump option for older NH homes with hydronic heat.

Dual-fuel (hybrid) systems

A heat pump paired with a backup gas, propane, or oil furnace. The heat pump handles most of the heating season at high efficiency; the backup takes over on the coldest days. Typically produces the lowest year-round operating cost in NH.

Maintenance basics

Heat pumps need annual professional service to maintain efficiency and warranty coverage. A typical visit includes:

• Cleaning the indoor and outdoor coils
• Checking refrigerant charge
• Verifying electrical connections, capacitor health, and reversing valve operation
• Inspecting defrost controls
• Replacing or cleaning filters

Homeowner tasks: keep the outdoor unit clear of leaves and snow, maintain 18 to 24 inches of clearance around it, change indoor filters on schedule.

Schedule a heat pump consultation

If you are considering a heat pump for your NH home, whether as a full replacement, a dual-fuel pairing, or supplemental cooling and heat in specific rooms, contact A.J. LeBlanc Heating. Serving New Hampshire families since 1928.

Frequently Asked Questions

How efficient is a heat pump compared to electric resistance heat?

A modern heat pump can deliver 2 to 3 units of heat for every 1 unit of electricity consumed. Electric resistance delivers exactly 1 unit per 1 unit. The heat pump uses less than half the electricity for the same heat output during most of the heating season.

Do heat pumps work below zero in New Hampshire?

Yes. Cold-climate heat pumps are rated to deliver useful heating down to outdoor temperatures of minus 13°F and lower. Capacity does drop as outdoor temperatures fall, which is why most NH installations include a backup heat source.

Does a heat pump cool too?

Yes. The same equipment provides cooling in summer and heating in winter. A heat pump is essentially an air conditioner with a reversing valve.

How long does a heat pump last?

Modern heat pumps typically last 12 to 15 years with proper maintenance. The outdoor unit takes more weather abuse than a comparable AC condenser, so annual service matters more.

What is the difference between a central heat pump and a mini split?

A central heat pump uses ductwork to distribute conditioned air through the home. A ductless mini split delivers air directly from one or more wall, ceiling, or floor-mounted indoor units. Mini splits are zoned by design; central systems serve the whole home.