In this video, Ask This Old House building technology expert Ross Trethewey explains everything you need to know about heat pumps.
Heat pumps work by finding and moving heat in and out of a building. A heat pump will take heat from within the home during the summer and let it dissipate outside, allowing the air conditioning system to work more efficiently. In the winter, a heat pump can scavenge heat from the outdoors (even in temperatures as low as zero degrees) and pump it into the home for comfort. The only requirement? Enough electricity to run the compressors.
Heat pumps are becoming more and more advanced, but there are four basic types: water to water, water to air, air to air, and air to water.
Water to Water heat pumps require geothermal drilling, which means drilling into the earth to tap into its heat. The water travels below the surface, comes back up, and travels through a heat exchanger. In the heat exchanger, the source water heats the load water. The load side water then travels through the heating system just as it would a force hot water system.
Water to air systems require geothermal drilling to source the heat in the earth’s surface. The heat pump can move the heat through a coil in a duct. When air blows across that coil, it heats up, just as it would with a furnace.
Air to Air In an air to air system, the heat pump sources heat from the air on the load side, which is then transferred to a refrigerant. This refrigerant then travels through a coil inside the ductwork, where load side air blows across it, similar to a furnace. These are the most common heat pumps.
An air to water system sources heat from the air on the source side and transfers it to a refrigerant. This refrigerant then cycles through a heat exchanger where it can heat the load side water to be pumped through the house. Once in the house, this water can serve several purposes. It can be pumped to a zone manifold for hydronic heat, cycled through a heat exchanger for domestic hot water, or even pumped through a coil to supply a ducted system. In the summer, this system can remove heat from the home, cool the refrigerant, and supply the home with cooling. There are a ton of advantages to this system over the others. First, no drilling is required. Second, you get the efficiency of hydronics. In some cases, homeowners relying on older heating systems can expect to save thousands of dollars each year on heating costs, as well.
Where to find it? Ross explored four different types of heat pump systems: water-to-air, water-to-water, air-to-air, and air-to-water. These heat pumps can usually be sourced through a local HVAC technician or sales representative. The air-to-water heat pump that Ross saw being installed in upstate New York was an Advantage Air-to-Water Heat Pump manufactured by Enertech [https://enertechusa.com/advantage-air…]. John Siegenthaler helped explain the installation in more detail.
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