Heat Pump Technology: How a Mitsubishi System Heats and Cools Your Home
Quick answer: a heat pump system is one or more indoor units (ducted or ductless) connected by refrigerant lines to an outdoor unit. In summer the indoor coil absorbs heat from your rooms and the outdoor unit expels it; in winter the cycle reverses and the outdoor coil pulls heat from cold air and delivers it inside. A variable-capacity inverter compressor speeds up or slows down to match the exact load, and Mitsubishi's Hyper-Heating INVERTER (H2i) technology keeps full output at 5°F and operation to -13°F, or -22°F on H2i Plus, which is what makes heat pumps a primary heating system in the North Country.
The components
- Outdoor unit: compressor, outdoor coil, fan and the electronics that run the inverter. See outdoor units.
- Indoor unit(s): a coil, a fan and filters, in wall-mounted, floor-mounted, ceiling cassette, ceiling-concealed ducted or multi-position air handler form. See indoor units.
- Line set: two insulated copper refrigerant lines plus power and a condensate drain, through a three-inch wall penetration.
- Controls: handheld remote, MHK2 wall thermostat or the Mitsubishi Comfort app.
One multi-zone outdoor unit can control up to eight indoor units, each as its own comfort zone with its own setpoint. A single-zone outdoor unit pairs with exactly one indoor unit and is the most efficient match for a single room.
The refrigerant cycle, in plain terms
Refrigerant boils at a very low temperature. In cooling, liquid refrigerant evaporates inside the indoor coil, absorbing heat from room air blown across it; the gas travels outside, the compressor squeezes it to a high temperature, and the outdoor coil dumps that heat to the air. In heating, a reversing valve flips the roles: the outdoor coil becomes the evaporator and absorbs heat from outside air (there is heat energy in air even at -10°F), the compressor raises its temperature, and the indoor coil releases it into the room. Nothing is burned; electricity only runs the compressor and two fans. That is why the system delivers about three units of heat per unit of electricity across a season.
Variable-capacity inverter compressors
Older heat pumps and most furnaces are single-speed: fully on or fully off. An inverter compressor runs at whatever speed the house needs right now, from a trickle on a mild afternoon to full speed at -10°F. The benefits are concrete: steady room temperature instead of swings, lower electricity use because the system is not repeatedly starting from zero, a soft start that does not spike the electrical service, and quiet operation. Mitsubishi's indoor wall units run as low as 19 dB.
Hyper-Heating INVERTER (H2i) for extreme cold
Conventional heat pumps were built for mild climates and lost capacity quickly below freezing. Mitsubishi's H2i technology adds a flash-injection circuit that routes a portion of refrigerant back into the compressor, letting it run at high speed in very cold air without damage, plus a smart defrost that clears frost from the outdoor coil only when sensors call for it. The result: 100% of rated heating capacity at 5°F, continued operation to -13°F on standard H2i, and -22°F on H2i Plus models. Both winter and summer extremes are covered; the same equipment cools in outdoor temperatures up to 115°F. Learn more on our Hyper-Heat page and cold-climate heat pumps.
Filtration in every zone
A central furnace filters air at one spot in the basement. In a zoned heat pump system each indoor unit filters the air of the room it serves, through washable multi-stage filters that catch dust, pollen and pet dander, and many units add deodorizing or electrostatic stages. Fewer or no ducts also means no hidden duct runs collecting dust. For homes with allergies or a woodstove, that per-room filtration is a noticeable change. See air filtration.
Ducted and ductless, together
Because the indoor unit styles all connect to the same outdoor units, a system can mix them: a ducted air handler on the existing furnace ducts for the main floor, a ceiling cassette in the kitchen, a wall unit in the addition. That flexibility is why a Mitsubishi system fits an 1800s farmhouse in Crown Point and a new build in Lake Placid equally well. Newer equipment (2025 on) uses R-454B refrigerant, a lower global-warming-potential replacement for R-410A, and our technicians are certified for both.
Frequently asked questions
How does a heat pump make heat from cold air?
Air at -10°F still contains heat energy. The outdoor coil, filled with refrigerant that boils far below that temperature, absorbs it; the compressor raises the refrigerant's temperature; and the indoor coil releases the heat into the room.
What does the inverter do in a heat pump?
It varies the compressor speed continuously to match the home's heating or cooling load, instead of cycling fully on and off. That holds a steadier temperature, uses less electricity and runs quieter.
What is Hyper-Heating INVERTER?
Mitsubishi's cold-climate technology: a flash-injection refrigerant circuit and smart defrost that keep the compressor producing full rated heat at 5°F and operating to -13°F, or -22°F on H2i Plus models.
How many indoor units can one outdoor unit run?
Mitsubishi multi-zone outdoor units run from two up to eight indoor units, each controlled independently. Single-zone outdoor units pair with exactly one indoor unit.
Talk to us
Have questions about your home? Call Adirondack Heat Pumps at (518) 812-1958, stop by the showroom at 15 Montcalm Street in Ticonderoga, or request a free in-home estimate. We serve Essex County, the Lake George and Lake Champlain shores, the High Peaks and Addison County, Vermont.