Storage Tank Type Water Heaters
The most common type of water heater in Ottawa and most of Canada, uses a storage tank. Burners or elements are used to heat and store 40 or 50 gallons of hot water, ready for use at any time. When the hot water tap is turned on, water is drawn from the top of the tank and cold water enters the bottom of the tank to be heated. Storage type water heaters can be used with several fuel sources including electricity, gas or oil.
New storage type water heaters are more efficient and can can perform as much as 40 percent better than older models. Most new water heater models will have extra tank insulation to hold the heat better and reduce heat losses through the walls of the tank. This reduces the frequency that the burner of elements will need to operate to maintain the water temperature.
Many new water heater models may also include better heat exchangers to more efficiently transfer heat from the energy source to the water. Factory-installed heat traps help to allow water to flow into the tank but help prevent unwanted flow of hot water out of the tank.
Energy-efficient gas-fired storage water heaters may include additional design features, like electronic ignition, which saves energy by eliminating the need for a continuous pilot light, and powered exhaust, which virtually eliminates heat drafting through the chimney when the water heater is not in operation. Some water heater models have condensing heat exchangers, which can improve the overall efficiency by as much as 25%.
Tankless water heaters
Tankless Water Heaters are also known as demand or instantaneous water heaters. These water heaters do not have a storage tank. Tankless water heaters only heat water when there is a demand. By doing this, they minimize standby heat loss associated with water tanks. Tankless water heater come in several configurations and use, electric elements or gas burners which heat water as it flows to the tap.
Tankless water heaters are often installed to serve a specific need near the point of use, such as under a kitchen sink. Depending on overall water flow volumes and temperature rise required, they may not have the capacity to supply an entire home with hot water.
Newer gas fired tankless water heater technology is capable of supplying much more hot water to the home. These systems will include features like electronic ignition and power exhaust. Although many are more efficient than conventional tankless heaters there are some considerations.
In most cases, the gas line will require upgrading to a larger size. As well, it is important to consider the maximum temperature required in relation to the incoming water temperatures. Incoming winter water temperatures in Ottawa are 40-F meaning the tankless water heater needs to be capable of raising the water temperature by at least 80-F at the required flow volume. In some cases the Tankless water heater may need to be connected to an external storage tank to supply the flow rates required.
Integrated space/water heating systems combine heating of the home, or smaller areas with domestic hot water needs. There are a number of methods to combine these functions, depending on the amount of heating and hot water required.
In recent years it has become more common to use water heaters to serve as a source for heating the home. Although this may appear to be an attractive option, the initial cost saving may not compensate for the ongoing operating costs related to a very low seasonal efficiency. In Ottawa, there a very large home heating requirement, so any water heater sized to produce enough heat to warm a house on the coldest winter day will be grossly over sized for the primary function of heating domestic hot water resulting in significant efficiency losses. This option should be reserved for very small space heating applications and may be a good option for limited radiant floor warming, as a supplement to a primary heating system.
When High Efficiency Boiler is used, efficiencies can be as high as 98%, meaning only 2 cents of every fuel dollar is lost. These systems can employ an insulated external storage tank with a high-efficiency heat exchanger to heat the domestic hot water, an air handler that passes hot water through a coil (as in a car radiator) The hydronic air handler then blows the heat around the house in a warm air distribution system, like a conventional furnace. The same boiler can be used for radiant heating, ranging from the entire home to smaller floor warming applications aimed at improving comfort. In addition, the heating for a pool or spa, heating a garage or workshop, and even snow melting on walkways or driveways is easily added to the boiler. Many High Efficiency Boilers modulate the amount of gas used to closely match the heat requirement by the outdoor temperature and the heat required for any of the above functions. This ensures maximum efficiency, regardless of the time of year. Longer term benefits also include lower maintenance costs, as you are only dealing with one combustion appliance.
Integrated Mechanical Systems, like the NTI Matrix, combine forced air heating with a boiler, tankless hot water, as well as ventilation into one unit. The internal boiler can also be used for radiant heating or any of the other functions mentioned above.
These boiler systems are often coupled with indirect water heaters in locations that are closer to the point of use. Often in larger homes, it makes sense to have a water heater located at one end of the home, serving the kitchen and perhaps a powder room or master bedroom. Often, other bathrooms may be located further away, and it may make sense to locate another water heater there.
Indirect Water Heaters
Indirect water heaters are insulated storage tanks that incorporate a heat exchanger. water is heated indirectly, usually using a High Efficiency Hot Water boiler. Although indirect water heaters do store hot water, there is no flue-pipe, which is the largest source from which heat can escape in a standard gas water heater.
The efficiency of indirect-fired water heaters depends primarily on two factors. The effectiveness of the insulation around the tank, and the efficiency of the boiler providing the hot water.
Most indirect-fired water heaters, with a few cheaper exceptions, have two inches of polyurethane foam insulation. With this level of insulation, the standby losses of most indirect-fired tanks is around a half-degree per hour. this is considered a minor heat loss.
Today’s High Efficiency Boilers have efficiencies up to 95 percent. If the indirect-fired storage tank is located near the boiler and the supply/return piping is insulated to minimize energy-losses, the efficiency of the water heater will be close to that of the boiler.