Heat pump water heaters: how they work and where they fit
A heat pump water heater moves heat from the surrounding air into the tank, so it uses less electricity than a conventional electric tank for the same hot water. It works best in a space with enough air volume and mild temperatures, and it also cools and dehumidifies that room.
How does a heat pump water heater work?
It is a small heat pump mounted on top of, or built into, a storage tank. A fan pulls in room air, a refrigerant loop extracts heat from it, and the compressor delivers that heat into the water. Most models also have electric elements as backup for high demand, and a mode selector so you can choose heat-pump-only, hybrid or electric.
Because it moves heat instead of generating it, it can deliver more than one unit of heat per unit of electricity. A coefficient of performance of 2 to 3 is often cited for the heat pump mode, but real figures depend on the room temperature.
What space and conditions does it need?
- Enough open air volume around the unit, per the manufacturer's stated minimum. A small closet may be too tight unless ducted.
- Room temperature in the range the manufacturer specifies. A very cold unheated space cuts performance.
- A floor drain or a condensate line, since the unit removes moisture.
- Headroom for the taller body and access to the air filter.
- A suitable electrical circuit, which may differ from the old tank's.
Noise is similar to a dehumidifier, so avoid placing it next to a bedroom.
How is the savings logic worked out?
Take a home using, say, 3,000 kWh a year with a standard electric tank. A unit delivering a seasonal COP of 2.5 would use roughly 1,200 kWh for the same hot water. At an assumed $0.15 per kWh, that is a saving of about $270 a year. These are illustrative numbers, not a forecast; your usage, rates and room temperature decide the outcome.
If the tank is currently gas-fired, the comparison is harder, because gas is usually much cheaper per kWh than electricity. The same arithmetic used in heat pump versus furnace applies, and a heat pump water heater may not save money against gas.
What are the side effects in a Canadian winter?
A heat pump water heater takes heat from the room, so in a basement it adds a small load to the home heating system in winter. It also cools and dries the space, which can be welcome in summer. In winter the effect is that the main heating system, whether a furnace or a cold climate heat pump, makes up some of the lost heat. Most of the saving still holds, but it is smaller than the tank's electrical figures suggest.
How does it compare with solar hot water?
A solar water heating system uses collectors on the roof and a storage tank, and it can supply a large part of summer hot water without much electricity. The two can work together, with the heat pump as the backup. The basics of that approach are in the solar water heater guide, and the Drake Landing garage-roof collectors, shown on the solar collection page, took the idea to a district scale for space heating. Check the current rebates before purchase, because water heaters are sometimes included.
What should you look for when buying one?
Read the sound rating, the stated operating temperature range, the first-hour delivery and the warranty on the compressor and tank. Check for a mode that lets you run the electric elements only during a vacation or a fault, and a simple filter access. Look for compatibility with time-of-use rates if your utility has them, since a unit that heats mostly at off-peak hours can cut the bill further.
Installation needs a plumber and, often, an electrician. The room it goes in matters as much as the model, so measure first. Also consider whether you want a bigger tank, since a heat pump unit recovers more slowly than an element on high. Annual upkeep is similar to the heat pump maintenance checklist, with an added tank flush.
Quick answers
Do heat pump water heaters work in a cold basement?
They work, but efficiency falls as the room gets colder. Many are designed for a certain air temperature range, so check the manufacturer's limits and consider the heat the unit pulls from the room.
How much can a heat pump water heater save?
Against a standard electric tank it can cut water-heating electricity substantially, often by half or more under favourable conditions. Against gas the saving is small or negative, depending on rates.
Do they need a lot of maintenance?
Not much. Clean the air filter, flush or inspect the tank as the manufacturer advises, and keep the condensate drain clear.