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Personal: Residential

Water Usage and Sizing

Whether you're buying or leasing a new water heater, you don't want to install a system that is bigger or smaller than you need:

  • Installing a tank that is larger than necessary will end up costing you money because you will be heating more water than your household needs, even during peak periods. And you'll waste more energy as this water loses heat through the tank walls and water pipes and has to be re-heated.
  • Installing a system that is too small could lead to "rationing" of shower time or expose you to the shocking experience of a cold shower!

Estimate your household's peak hot water demand

The peak demand usually occurs during showering. There should still be some hot water left in the storage tank after three people have showered (over a 40-minute period) or rinsed their hands and faces at a sink. If you use a low-flow showerhead, these hot water requirements can be met by a water heater with a first hour rating (FHR) of 270 litres (60 gallons). FHR is a measurement of how much hot water the heater can supply during a busy hour.

Determine the right tank size for your home's circumstances.

But don't confuse tank size with your home's daily hot water consumption. Selecting a small water heater tank with a high FHR should result in good performance during the busiest time of the day while minimizing cycling and standby losses when hot water is not in high demand. The table below provides some guidelines on what size tank you will need, based on typical recovery rates.

Hot Water Use Family Size (people) Electric Tank Size Gas Tank Size Oil Tank Size
Vacation Cottage
– no dishwasher
– no clothes washer
Up to 2 135 litres (30 gallons) 90 litres (20 gallons) 90 litres (20 gallons)
Small/Medium Family Home
– 1 bathroom
– no dishwasher
– clothes washer
2 180 litres (40 gallons) 135 litres (30 gallons) 135 litres (30 gallons)
Medium Family Home
– 1.5 bathrooms
– dishwasher
– clothes washer
3 225 litres (50 gallons) 180 litres (40 gallons) 135 litres (30 gallons)
Medium/Large Family Home
– 2 bathrooms
– dishwasher
– heavy-duty clothes washer
4 290 litres (65 gallons) 180 litres (40 gallons) 180 litres (40 gallons)
Large Family Home
– 2 or more bathrooms
– heavy-duty dishwasher
– heavy-duty clothes washer
5 360 litres (80 gallons) 225 litres (50 gallons) 225 litres (50 gallons)
Large Family Home
– same as above with whirlpool baths
6 540 litres (120 gallons) 340 litres (75 gallons) 340 litres (75 gallons)

Check the Energy Factor

Once you've determined the capacity and size of water heater you need and selected an energy source, check the energy factor (EF) of different models to identify the most efficient heater that meets your needs.

Select a water heater with the highest EF. This information is found in the manufacturer's product specifications brochure or on the manufacturer's Web site. The EF measures the efficiency of the water heater by comparing the energy supplied in heated water to the total daily energy consumption of the water heater. The EF is determined by the manufacturer and is based on a standardized test procedure. Under Canada's Energy Efficiency Regulations water heaters sold in Canada must achieve a minimum EF, which is based on the size of the storage tank. You will probably find that the larger the storage tank, the lower the EF, especially in sizes above 65 gallons.

The range in efficiency ratings within a certain tank size is accomplished through a variety of design features and quality of manufacture. In many cases, the higher efficiency units are usually more expensive, and perhaps carry a longer warranty protection.

The bottom line is, the lower the EF, the higher the operating costs.