Additional Considerations When Choosing a Heat Pump For Space Heating
HPWHs are a different form of water heating technology that still achieves abundant hot water when needed. However, it is important to understand some of these differences.
Sizing
Heating a full tank of water using a heat pump can take longer than with a conventional water heater (1). It is therefore important to consider the system, size and first hour rating when choosing a HPWH. ... If the demand for hot water is concentrated at certain times of the day, a larger water tank may be needed to ensure adequate hot water supply. Many HPWHs are hybrid: they can use a conventional, and less efficient, heating element to supplement hot water generation during times of peak demand. The first hour rating indicates the volume of hot water the system can generate in an hour (usually in gallons per hour)(2). .
Locating Equipment
Because a HPWH extracts heat from the surrounding air, it must be located in a warm area with adequate airflow. EnergyStar recommends installing it in a room with 1000 cu ft of space (roughly 12 ft x 12 ft and 7 ft high or 3.5 m x 3.5 m and 2.3 m high)(3).
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A basement or large utility room may be ideal. Alternatively, a heat pump can be ducted to draw air and/or vent to a larger space. In warmer climates, where temperatures remain above freezing, HPWHs are often placed or vented outside or in garages.
HPWHs will also cool and dehumidify the surrounding air because they draw heat from the home. This can be an advantage in the hot and humid summer months but it does increase the energy needed to heat the home in winter. This extra cooling effect is localised, and HPWHs are generally not located in living spaces where warmer temperatures are maintained(4). The dehumidifying effect is a co-benefit of water condensing from the air on the cold heat pump coils, but is often insufficient to replace a conventional dehumidifier. A condensate drain or pump is also required with HPWHs to remove this water. These systems contain an air filter that must be replaced or cleaned periodically.
Electrical Needs
HPWHs generally require 240V 30amp service and a dedicated circuit, although 120V 15A models are available.
Noise
HPWHs make about as much noise as a refrigerator but you are unlikely to notice unless the water heater is located close to a living space.
Choosing a Contractor
It is important to seek out installers that are well informed about heat pumps and have experience installing the type of system you are interested in. The HRAI (Heating, Refrigeration and Air Conditioning Institute of Canada) has a qualified contractor locator and all manufacturers have lists of qualified contractors on their websites.
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The HVAC (Heating Ventilation and Air Conditioning) industry has been slow to adopt and promote ASHPs and HPWHs. Some heating system professionals may be misinformed about the performance of heat pumps, unaware of the existence of HPWHs, or just wary of trying something different. The industry is accustomed to replacing like with like and representatives may be hesitant to risk their reputation promoting alternatives that they have less experience with. Ask around to find reputable installers that are knowledgeable, and it is always advisable to seek several quotes.
Heat pump water heaters are available from some home renovation outlets for direct purchase. Some homeowners have chosen to install their own system. Most installations do not require any specialised skills or tools, although DIY installation may affect the warranty and a certified electrician may be required to upgrade the circuits and outlet.
Availability and Installation Time
Heat pump water heaters are less common than conventional water heaters and there may be delays in receiving and installing the equipment. It is therefore recommended to do your research in advance and talk to an installer about how much time your current system has left and what work can be done in advance.
Environmental Impacts of Refrigerants
Most current HPWHs currently use R-410a, a refrigerant with a low ozone depleting potential but high global warming potential (global warming potential of 2088 (5)). This refrigerant is gradually being phased out in accordance with the Kigali Agreement (6). Although relatively small volumes of refrigerant are used in heat pump systems and they are well sealed in, a loss of performance or a system lockout could indicate a refrigerant leak and should be investigated promptly. Refrigerants with low ozone depleting potential and low global warming potential are coming on the market soon.
(2) Energy.gov (n.d.). Sizing a new water heater. Retrieved from https://www.energy.gov/energysaver/water-heating/sizing-new-water-heater
(3) Energy Star. (n.d.). Considerations – Heat pump water heaters (HPWHs). Retrieved from https://www.energystar.gov/products/water_heaters/high_efficiency_electric_storage_water_heaters/considerations
(4) Bpa.gov/energy efficiency. (n.d.). Impact of heat pump water heaters on space conditioning energy use and comfort. Retrieved from https://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-Reports-Archives/Pages/Impact-of-Heat-Pump-Water-Heaters-on-Space-Conditioning-Energy-Use-and-Comfort-.aspx
(5) Rajendran, R. (2011). Refrigerants update. [webinar]. Emerson Climate Technologies Inc. Retrieved from https://www.epa.gov/sites/production/files/documents/RefrigerantUpdates.pdf
(6) Polonara, Fabio & Kuijpers, Lambert & Peixoto, Roberto. (2017). Potential impacts of the Montreal Protocol Kigali Amendment to the choice of refrigerant alternatives. International Journal of Heat and Technology. 35. S1-S8. https://www.researchgate.net/publication/320038190_Potential_impacts_of_the_Montreal_Protocol_Kigali_Amendment_to_the_choice_of_refrigerant_alternatives
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