Maine is making headlines nationally by taking steps to stop burning diesel fuel (called “#2 heating oil” to avoid the tax levied on diesel intended for on-road use) with no pollution controls in our basements to heat our homes. We are also making headlines by installing huge amounts of solar power, which works very well in our surprisingly sunny state. Super-efficient cold-climate electric heat pumps are the new technology that makes it possible to make the transition from fossil fuel to sunshine to heat homes everywhere in the world (even in places with real winters, like Maine). If you’re already enjoying heat pumps, great work! And if you haven’t yet tried them, the economic and environmental benefits are getting more compelling all the time.

Two That Matter Most

To know how well you are meeting your need for heat without wasting energy or creating unnecessary pollution, these two indicators matter most:

  1. How much fuel you burn.

  2. How much electricity you use.

Heating 302

Space heating with heat pumps

Heat and cool spaces with electric heat pumps.

Equipment and Materials

  • Electric heat pump space heater

Steps

  1. Decide which spaces you’d like to heat and cool.

  2. Decide whether to install non-ducted mini-split heat pump space heaters or a ducted whole-home heat pump system.

  3. Evaluate and improve air sealing and insulation.

  4. Perform an energy-flow analysis to determine the space heating and cooling power and placements required to satisfy your needs.

  5. Determine the electrical power requirements for the equipment you plan to install.

  6. Upgrade your electrical service and panel, if necessary.

  7. Purchase and install the heat pump equipment.

Discussion

Heat pumps are three to four times more energy efficient than burning fuel for heat. They use electricity to compress and circulate refrigerant through heat exchangers. This pumps heat from a source, such as outdoor air, to indoor air, or vice versa.

In cooling mode, a heat pump system works like any other air conditioner: absorbing heat from indoor air and releasing heat to outdoor air. In heating mode, a reversing valve sends refrigerant flowing the other way so the system absorbs heat from outdoor air and releases heat to indoor air.

See past editions of One Step This Week for more about heat pumps and related technology. Search our archive to see all the topics we’ve covered.

Heat pumps are a sustainable way to heat and cool buildings because the electricity to power them can come from sunlight, wind, or water. Many people are adding heat pumps for air conditioning and dehumidifying and then enjoying the benefits of convenient and affordable electric heating as a bonus.

Ductless heat pumps are especially easy to install. A common type is called a “mini-split” because it is split into a piece of equipment outside and a piece inside. A lineset containing refrigerant tubes, electrical wires, and communication wires connects the two.

If a home already has ducting for central air conditioning and a fuel-burning furnace, it might be easy to upgrade to an all-electric heat pump system. Some writers refer to air conditioners as “broken” heat pumps. Heat pumps are simply “better” air conditioners with valves that can reverse the flow of refrigerants. Upgrading to a heat pump “fixes” the equipment so it can provide cooling and heating. Then, the fuel-burning part of the old system can be decommissioned.

A fuel-burning heating system that circulates hot water instead of blowing air can be upgraded to an air-to-water heat pump, but these systems are less common than air-to-air heat pumps. Water-to-water heat pumps, which are also known as ground-source heat pumps, can also be installed. Since they absorb heat from groundwater, they are also known as ground-source heat pumps.

Before installing any type of heating or cooling system, it makes sense to check the building's air sealing and insulation. Weatherstripping around doors and windows can eliminate drafts and lower energy bills.

Best practice for determining the location and size of heat pump equipment to install is to do an energy-flow analysis of the space to be heated and cooled. The Manual J Residential Load Calculation published by the Air Conditioning Contractors of America is the industry-standard method. Once you know the cooling and heating power required, you can specify the equipment to provide it. The two most important ratings to know are the heating output, which tells you how powerful the system is, and the coefficient of performance (COP), which tells you how efficient it is. Another way efficiency is rated is by heating seasonal performance factor (HSPF): the higher, the better.

Heat pumps can provide all the heating power required unless a building is poorly built. Since heat pumps take longer to deliver heat and go through defrost cycles, during which heat output is reduced, contractors often recommend that customers keep a fuel-burning heating system in their homes as a “backup.” Keeping a fuel-burning furnace in the home makes life easier for contractors: they can install whatever size heat pump they have in the shop without doing a load calculation and know that the fuel-burning system will compensate for a poorly designed or poorly installed heat pump system.

A fuel-burning generator is one option if you have an all-electric heating system and are concerned about what happens during a grid power outage. Whole-home battery backup systems are another option; they are still relatively more expensive than a fuel-burning generator, but batteries can be recharged from solar modules every sunny day. Solar and battery backup systems can be designed to operate as long as wanted. It’s even becoming relatively easy to be completely energy independent, running heat pumps from solar power without buying any grid power or burning any fossil fuel.

All but the smallest heat pump space heaters will require dedicated 240-volt electrical circuits. Another thing to know about heat pumps sold in 2024 is that a wide variety of refrigerants are in use, many of which have high greenhouse-warming potential and will be banned. More sustainable refrigerants and solid-state refrigeration, which uses solid materials instead of refrigerant gas, are active areas of research.

Definitions

  • Air-source heat pump: any heat pump (including refrigerators, air conditioners, and mini-splits) that absorbs and releases heat from air

  • Coefficient of Performance (COP): output power per input power

  • Condensate: water that condenses from air during the operation of a heat pump

  • Ducted systems: heating systems that use fans to blow heated or cooled air through ducts to distribute it throughout a building

  • Greenhouse gas warming potential: the potential of a gas to persist in the atmosphere and absorb radiation, thereby warming the surface of the Earth; carbon dioxide has a greenhouse gas warming potential of 1

  • Ground-source heat pump: a heat pump that has a loop buried in the ground to absorb or release heat

  • Heat pump: a system that uses electricity to pump refrigerant in a loop through a heat exchanger to move heat from one place to another

  • Heating Seasonal Performance Factor (HSPF): ratio of heating capacity (measured in British Thermal Units per hour) to electricity consumption (measured in joules per second)

  • Space heater: equipment that heats air to provide comfortable indoor temperatures in cold weather

  • Refrigerant: a substance which can be depressurized to absorb heat and pressurized to release heat

  • Split system (e.g., “mini-split”): one part of the system is located outside, while the other is located inside, with a lineset connecting the two

  • Vapor-compression: the standard refrigeration technology that compresses a refrigerant gas to pump heat between locations

Troubleshooting

  1. You aren’t sure if heat pumps alone will provide enough heat

    1. Ask your installer to conduct a Manual J load calculation

  2. You don’t have a good place to put the indoor “heads” of heat pumps

    1. Consider an air-to-water system so you can distribute heat through a hydronic system

    2. Consider a central system with ducting

  3. You don’t have enough space for additional circuits in your electrical panel

    1. Add a sub-panel or upgrade your main panel; tax credits and other incentives may be available to help pay for the cost

    2. Upgrade your lighting to LED and consolidate lighting circuits to free up space for heat pump circuits

  4. You’ve installed heat pumps, but they aren’t keeping you warm

    1. Check air sealing and insulation levels

    2. Make sure you’re “setting and forgetting” your units; they are slow and steady

    3. Have someone redo the Manual J load calculation to make sure sufficient heating power was installed

    4. Have the heat pumps inspected and cleaned well; make sure you don’t have a refrigerant leak or a dirty heat exchanger

    5. Consider adding another heating unit or upgrading the power of a central heat pump system

  5. Your fuel-burning heating system keeps coming on even though you have heat pumps installed

    1. Set the heat pump thermostat higher; leave them on all the time

    2. Set the fuel-burning system thermostat lower

Strategies and Goals

  • Community

    • Demonstrate best practices

      • Inspire people in your community to use heat pumps

  • Energy

    • Increase energy efficiency

      • Heat space more efficiently

    • Electrify

      • Use electricity for heating and cooling

Milestones

  • Decrease fuel consumption

    • Measure: Fuel and utility bills

    • Method: Records

    • Time Period: Year

  • Decrease energy consumption

    • Measure: Fuel and utility bills

    • Method: Records

    • Time Period: Year

Limitations

  • Requires money to purchase a heat pump space heater.

  • It may require upgrading the electrical service or panel.

  • Non-ducted systems may not distribute heat well, especially in buildings with many separate rooms.

  • Some units still use refrigerants that are harmful to the environment.

  • Coordinating thermostat controls can be difficult.

Opportunities

  • Insulating 101 - Sealing and Insulating Attics and Basements

    • Decrease heating and cooling load

    • Get more value per dollar invested in heat pumps

  • Powering 201 - Using Solar Electricity

    • Increase reliability of electricity

    • Decrease pollution from electricity

References

Keywords

space heating, heat pumps, electrification, efficiency