Water Heater Types
Storage Tank Water Heaters
Tankless Water Heaters
Integrated Space/Water Heating Systems
Heat Pump Water Heaters
Solar Water Heaters
Heat Recovery Water Pre-Heaters
Storage tank water heaters are by far the most common type used in Canada. These systems heat and store water in a tank so that hot water is available to the home at any time. As hot water is drawn from the top of the tank, cold water enters the bottom of the tank and is heated. The heating source can be electricity, gas or oil.
Energy-efficient storage tank water heaters can perform as much as 40 percent better than conventional models. An energy-efficient model will typically have one or more of the following features:
Energy-efficient gas-fired storage tank water heaters may include additional design features, such as:
Oil-fired water heaters with state-of-the-art burners offer high-efficiency performance and minimal stack losses.
Also known as demand or instantaneous water heaters, these systems do not have a storage tank. They heat water only when it is needed, which avoids standby heat loss through tank walls and water pipes. The most basic units consist of either an electric element or a gas burner surrounded by flowing water.
Tankless water heaters are usually installed near the "point-of-use" to serve a specific need, such as under a kitchen sink. Depending on overall water usage, they may not have the capacity to supply an entire home with hot water. For this reason, they are often used as booster heaters to supplement another water heating system.
A relatively new tankless technology - the low mass water heater - is capable of supplying much more hot water to the home. These systems are typically gas-fired with electronic ignition and power exhaust, which means they are also more efficient than conventional tankless heaters. They can be connected to an external storage tank, if necessary.
Integrated Space/Water Heating Systems
Integrated space/water heating systems combine the household heating requirement with the household hot water needs, saving money on total system installation. A single boiler is used requiring only one combustion burner and only one vent. Often these systems employ an insulated external storage tank with a high efficiency low mass boiler to first heat the water. Then the system passes hot water through a fan coil (similar to your car's radiator) and blows the heat around the house in a warm air distribution system, similar to a conventional furnace.
For integrated systems that do not use high efficiency boilers, the initial cost saving is soon eliminated by very low seasonal efficiency. The heater is sized to produce enough heat to warm a house on the coldest winter day. However, in the spring, summer and fall when no heating is required, the same heater heats domestic hot water only. The effect is an oversized water heater that operates for several months of the year with a low heating demand and, subsequently, low efficiency.
One type of integrated system that has been around for many years, particularly in the Maritime provinces is a fuel-fired hot water boiler with a tankless coil water heater that uses a heat exchanger in the boiler to heat tap water, but without a separate storage tank. The water flows through a coil inside the boiler whenever a hot water faucet is turned on. The drawback is that this system is dramatically less efficient in warmer months when space heating is not required, as the boiler water must be kept hot all the time.
Heat pump water heaters use electricity to move heat from the air to the tank instead of generating heat directly. Residential heat pump water heaters use the same technology as your refrigerator, but it operates in a reverse order. The inside of the tank captures heat instead of rejecting it. You can save even more energy if the cold air the heat pump produces is used to supplement your air conditioning needs. A heat pump water heater can easily cut the lifetime operating cost in half compared to conventional electric water heaters. Despite their high initial cost, heat pump water heaters can be more cost-effective than conventional electric storage tank heaters, especially in warm to moderate-cold climates. Their potential drawback is that heat pump water heaters loose efficiency below -8° Celsius. Whether this makes them cost-comparable to an efficient fuel-fired heater depends on your local cost of electricity versus natural gas or oil.
Air-Source Heat Pump Water Heaters:
There are several different designs of air-source heat pump water heaters available on the market. All use heat from the house as the basis for the heat "pumping" and thus can actually increase the heating load for the house, even though they may reduce the specific cost of heating the hot water. The add-on heat pump consists of a heat pump that is attached to an existing electric storage tank water heater. A small pump circulates water from the tank through to the heat pump. The integral heat pump is built into the water storage tank and eliminates the need for a pump to circulate the water. A special class of the add-on heat pump that works best in fairly airtight houses is the return-air or exhaust-air heat pump. This type of heat pump water heater is located in the return air duct of the home's heating and cooling system.
Ground-Source Heat Pump:
A ground-source heat pump uses the earth or ground water or both as sources of heat in the winter, and as the "sink" for heat removed from the home in the summer. For this reason, ground-source heat pump systems have come to be known as earth-energy systems. The ground-source heat pump with a hot water desuperheater has proven effective as a minimum, water pre-heater in colder Canadian climates. It is often not practical for an existing house because it requires that the yard be excavated, but it is more practical and may be of interest when building a new home.
Solar water heaters use the sun's energy to heat water. Passive solar systems pre-heat water in a solar collector and then transfer it by line pressure to a conventional storage tank water heater powered by electricity, gas or oil. Active solar systems, on the other hand, use pumps and controls to move the heated water from the collector to the storage tank. In areas where the temperature drops below freezing, the fluid in the collectors is usually a form of antifreeze, which is then run through a heat exchanger to heat the household water.
Solar systems can supply up to 50 percent of the energy needed to heat water for an average household (depending on climate conditions and water use). Since energy from the sun is free, solar water heaters can significantly reduce a household's water heating costs - savings that in turn can offset the higher purchase and installation costs of a solar system.
Heat Recovery Water Pre-Heaters
These systems use waste heat recovered from air or water to pre-heat cold water before it is sent to a conventional storage tank water heater. Due to their high purchase and installation costs and additional space requirements, heat recovery water pre-heaters are generally not cost-effective in Canada for single family dwellings. However, research is continuing on this technology, with very promising results.
Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency