Domestic Hot Water Heating
It is important to know in advance the factors to consider when replacing your hot water tank. Water heating uses about 20 per cent of the total energy in residential and most small commercial buildings.Hot water heaters have a normal life span of 10 to 15 years and are often replaced in emergency situations when energy efficiency is not a top priority. Researching before an emergency happens can be very useful.
In Alberta, virtually all hot water heaters consist of a storage tank heated with natural gas, ignited by a pilot light that burns continuously. The two most important energy use factors are proper sizing and efficiency. Sizing requirements depend on hot water demand, which is directly reliant on the number of users and the recovery rate of the heater being considered. A 180-litre tank will usually meet the needs of a medium to large home with four people.
Although the size of the storage tank is important, the peak hour demand capacity, referred to as the first-hour rating (FHR), is even more important. The FHR is the amount of hot water a storage water heater can supply in one hour. Generally, a heater with a higher FHR will have a bigger burner that enables it to meet the peak demand with a smaller storage tank.
The best indicator of a heater's efficiency is its Energy Factor (EF), which is the ratio of the energy delivered to the water compared to the total energy consumed. The higher the EF, the more efficient the water heater will be. Gas heaters typically have an EF between 0.5 and 0.6, with some high efficiency models around 0.8. Product literature from manufacturers usually gives an EF rating.
The Energy Factor takes into account:
- recovery efficiency – how efficiently the heat from the energy source is transferred to the water,
- standby losses – a percentage of heat lost per hour from the stored water compared to the heat content of the water; and
- cycling losses – the loss of heat as water circulates through the water heater tank and inlet and outlet pipes.
Energy efficient storage tank water heaters can perform as much as 40 per cent better than conventional models. An energy efficient model will typically have one or more of the following features:
- an extra tank insulation for better heat retention (standby loss)
- a better heat exchanger to transfer more heat from the energy source to the water
- factory installed heat traps that allow water to flow into the tank, but prevent unwanted flow of hot water out of the tank
- electronic ignition that saves energy by eliminating the need for a continuous pilot light
- a flue damper that closes to reduce heat loss through the flue vent during standby
- powered flue vent control
- condensing heat exchangers that greatly improve the overall efficiency
Instantaneous Hot Water Heaters
An alternative to storage tank systems are demand or instantaneous water heaters that eliminate the storage tank by heating water directly when hot water is required. The energy consumption of these units is usually lower since standby losses are eliminated.Instantaneous water heaters can be a good choice if water requirements are easily coordinated because there are limits in the volume that can be supplied at a given time and temperature. Electronic ignition models also save energy over those using a continuously burning pilot light.
Energy Efficient Tip
- Install pipe insulation on hot water pipes leading out of the hot water heater to decrease heat loss.
Please note: water piping within six-inches of a gas appliance vent should not be insulated to avoid a fire hazard. See picture below:
Staff at Alberta Municipal Affairs Safety Services will be happy to answer any of your questions about safely insulating hot water pipes. Call them toll free at 1-866-421-6929
Alberta Government Domestic Hot Water Rebate
All Albertans who participate in the federal government's ecoENERGY Retrofit Program and replace their domestic hot water system with a qualifying model on or after January 1, 2009 are eligible for a rebate. Visit Climate Change Central's website for more information on the Domestic Hot Water rebate.
