Heat Pumps for space heating and air conditioning
Heat pumps extract heat from the outside (usually from the air, although some extract it from the ground) and pump it into a building to provide heat. They reverse that cycle to provide air conditioning. See the Building Electrification FAQ for a more detailed explanation of the science of how a heat pump works)
Heat pumps are typically 3-4 times more efficient than the highest efficiency gas furnace or an electric baseboard system. This means that they are far better for the climate and air quality than either electric baseboard or gas systems.
Operating Costs: Heat pumps cost far less to operate than electric baseboard systems. Currently, they generally cost more to operate than gas systems in most parts of the country. Gas prices, are volatile and hard to predict, but likely to rise faster than electricity as the fracking boom plays out and the cost of solar & wind continue to fall. Of course a solar electric system on your rooftop can reduce or even eliminate the operating cost for your heat pump.
Installation Costs: In new construction, a heat pump system is cheaper to install then separate gas heating and electric air conditioning systems. For adding or replacing heat only in existing buildings, a heat pump will cost more than an electric baseboard or gas system. However, an increasing number of utilities and local governments are offering rebates to reduce the installation cost of a heat pump below that of a gas system.
Most, but not all, heat pumps are “split systems.” An outside compressor unit extracts the heat and one or more inside condenser units distribute the heat or cooling. The inside units are connected to the outdoor unit by a pipe carrying refrigerant. There are a variety of types of heat pump systems that are appropriate for different situations
Replacing a central air furnace
Ducted Air Source Heat Pump (also called a “central” or “unitary” air source heat pump).
A single outdoor compressor is connected to a single indoor condenser unit that is connected to the existing house ductwork. If the ductwork goes through an unconditioned crawlspace or attic, it is important to first seal the ductwork well to avoid losses.
Replacing a radiant floor boiler
Air-to-Water Heat Pump (also called a “hydronic” air source heat pump).
A single outdoor compressor unit is connected to a single indoor condenser unit that heats the water for the radiant floor water distribution.
Outside heat pump compressor unit
Adding a small addition or new standalone space of one to three adjoining rooms (e.g. Accessory Dwelling Unit or ADU)
Mini-Split or Packaged Heat Pump:
A Mini-Split (or Single Zone) Heat Pump has one outdoor compressor connected with a refrigerant line to a single indoor condenser unit with a fan (called a “fan coil”) to distribute the heat into the space.
A Packaged Terminal (through the wall) Heat Pump has both the outdoor compressor and indoor condenser packaged together into one unit, like a small air conditioner, mounted in a cutout in an outside wall. A packaged system may be less expensive and simple to install but requires careful air sealing not to lose heat around the opening.
The indoor unit on a mini-split system requires running a refrigerant line through walls and/or above ceilings, but provides more flexibility in the location of the indoor unit.
Ceiling and wall mounted fan coil units
Through the wall packaged unit
All new construction, or replacing a wall of floor furnace, electric baseboards, or where the existing distribution system also needs replacement
Ductless Multi-Zone Air Source Heat Pump (also called a “multi-split” heat pump).
One or more outdoor compressors are connected by refrigerant pipes to multiple indoor units. These indoor units (called “fan coil units” or “heads”) blow air out to distribute the heat into the space. Each fan coil unit can be individually controlled depending on the heat (or cool) needed in each room or zone. Fan coil units may be mounted on a wall or ceiling or may be hidden behind a flush mounted register in a wall or ceiling space.
Fan coil unit that mounts flush to the ceiling
Very cold climates
Ground source heat pumps and variable speed systems (also called “variable refrigerant flow”)
(Info on these options for maximum efficiency in colder climates is coming soon)
IHow We Fully Electrified Our Very Old House, Dave Margulius DM Workshop, Dec 30, 2021. Description of a conversion of a Berkeley CA residence from gas to heat pump for both space heat and water heat.