Other Kinds of Heat Pumps
If your home doesn't have air ducts to distribute heat, don't fear. You could potentially use a special kind of heat pump called a mini-split heat pump. The cutest of all heat pumps, it connects an outdoor air-source unit to multiple indoor units. These indoor units connect to water heat or space heaters. These ductless mini-split systems are useful for retrofitting a home with a heat pump system because their locations outside and inside the home are flexible. Another plus is that the installation only requires a 3-inch (7.6 centimeter) conduit to come through the wall, which is pretty unobtrusive. They're also versatile. The indoor air handlers can be installed in walls, ceilings or on the floor, and they're small to boot.
And who can forget the reverse cycle chiller (RCC) heat pump? Instead of heating and cooling air, this bad boy heats and cools water, and can operate efficiently in below freezing temperatures. In an RCC system, the heat pump connects to an insulated water tank that it either heats or cools. Then, a fan and coil system pump heated or cooled air away from the tank and through the ductwork to one or more heating zones. An RCC system can also pump hot water through a radiant floor heating system, so when those bare feet are comfy on a toasty tile floor this winter, you can thank your RCC.
In a typical air-source heat pump, there's the need for a backup burner to supply temporary heat when the system switches into reverse to defrost the coils. This backup burner prevents the system from blowing cold air through the registers while the coils defrost, which is key if your goal is to stay warm. Some might say that the RCC system is superior in that it uses the hot water from the tank to defrost the coils, so no backup burner is needed. This also means the system never blows cold air when it shouldn't, and the result is that you stay nice and warm.
A new type of heat pump showing promise for extreme climates is the Cold Climate heat pump, which operates efficiently at extremely low temperatures -- even below 0 degrees Fahrenheit (-18 degrees Celsius). The Cold Climate heat pump detects the minimum amount of energy needed to provide the desired level of heating or cooling and adjusts its output up or down, so it never wastes energy. It's an extremely green alternative, but is still in its early stages of implementation because of delays in funding, which slowed research. In 2011, Canada invested $4 million in Cold Climate heat system development.
The All-Climate heat pump is yet another new kind of pump, which can operate in temperatures as cold as -30 degrees Fahrenheit (-34 degrees Celsius) and can increase efficiency by up to 60 percent over a standard heat pump [source: EERE]. The All-Climate heat pump is designed primarily for heating, though, and won't work efficiently in climates where the heat pump would be in cooling mode most of the time.
Even special heat pumps have limitations. Read on to learn about the pros and cons of heat pumps, and what you need to know before buying one.