The demand for heat pump installation is at an all-time high this summer as the cost of traditional heating sources, fuel oil in particular, has soared. And for that reason, the state of Vermont is offering rebates, via installation contractors, for several types of heat pump installations.
It might be difficult to find a contractor to complete an installation before the heating season sets in. Like many sectors of the economy, high demand has met with supply chain slowdowns and staffing shortages, especially where experience and technological expertise are a factor.
How Heat Pumps Work
The leading virtue of heat pumps is that both heating and cooling functions are provided through a compressor located outside the building. In winter, for heating, outside air is drawn through the compressor, which extracts heat. In summer, the system operates in reverse, extracting heat from inside the building. Electricity is required to operate heat pump systems, which can be provided by solar panels.
Heat pump technology and its various applications have evolved considerably in recent years. The simplest and least expensive systems extract heat from the air, even at quite cold temperatures. Contemporary technology will extract heat from the air with ambient temperatures as low as –13 F, which makes it functional for all but the coldest days in a Vermont winter. And for that reason, Efficiency Vermont recommends retaining – or installing – a source of backup heat.
In summary, the system options include:
Ductless Heat Pumps, which are also called “mini-splits.” These systems are wall-mounted air source units designed to serve a single interior room/space. A home with an “open space” design can more readily be heated with these wall-mounted units than a building with multiple small rooms.
Air-to-Water Heat Pumps are best suited for buildings using new or existing heating systems in which hot water is piped to baseboard “radiant” units that release heat into the rooms.
Centrally Ducted Heat Pumps are an option, particularly for homes that currently have a “forced air” furnace with a system of ducts distributing heat to the rooms of the house. Although ductwork can be readily incorporated in new construction, retrofitting ductwork into an existing building involves structural and cosmetic renovation and repair.
Ground Source Heat Pumps are the most efficient and most expensive heat pump installations. They can be designed to extract heat from either groundwater or the ground itself. In either case, the installation of the equipment requires considerable excavation or well-drilling.
Air-to-Water Heat Pumps work best in combination with radiant heating, meaning the heat is piped through the building and can be used in both residential and commercial buildings to provide heating, cooling, and hot water supply. Efficiency Vermont notes that design and installation of these systems require a trained contractor.
Centrally Ducted Heat Pumps can be added to buildings that have an efficient furnace and ductwork in place. With this installation a building will typically need supplemental heat on subzero days, Efficiency Vermont notes.
Commercial Water-Source Systems have three variations. The first combines a cooling tower, a boiler, and water-source heat pumps. A second combines a heat pump with a fossil fuel system that will alternate between the two for efficiency. The third, called “variable refrigerant flow” (VFR) is a system of many multi-split units that can heat or cool at the same time if needed. Note that a VFR may require a separate back-up heat source during very cold, sub-zero days.
Because heat pumps function differently than the heating sources we are accustomed to, Efficiency Vermont has a section explaining the differences: efficiencyvermont.com/blog/how-to/who-knew-8-ways-not-to-use-a-heat-pump.
Air systems in particular require at least seasonal cleaning and filter replacement to maintain efficiency.
Efficiency Vermont’s website (efficiencyvermont.com) is a tool for figuring out what system is appropriate and efficient for each type of building, whether a residence or a commercial property. Note that effective insulation and air sealing of a building is an important first step for successful reliance on heat pumps.