Learn More ... Domestic Hot Water Heaters


Some of the questions your property insurance company is likely to ask you pertain to how the domestic hot water in your home is being heated.Their concern arises out of frequent claims that occur when domestic water heaters fail.These failures often result in significant damage when a water heating system leaks, discharging its content into the living spaces of the home.

More damage can occur when a temperature and pressure relief valve fails.This valve activates when the thermostat in the water heating systems fails to shut down the active heating of the water when it reaches the set desired temperature (usually between 120° and 140°F).The water will continue to actively heat and the system, as it moves closer to the boiling point, will build up excessive pressure.At that point the pressure relief valve will activate and discharge that excess pressure.If that safety feature fails, your system can effectively become a steam bomb.Severe damage and possible injury can occur.

So, if you have had a professional home inspection, the chances are good that the inspector included some important information in their report.The fuel source and the age will likely be noted; the risk of failure increases as the system ages (particularly true of reservoir type systems that store large volumes of water).Most tank type heaters, unless defective, will last 10 years and beyond.If much older, your insurance company may insist on its replacement.

The presence or absence of a pressure and temperature relief valve and its appropriate discharge tube will be noted.These valves should always be replaced when the water heater is replaced. And, typically, the volume of the water heater will be noted as a courtesy; helping you decide if the size is adequate to your needs.

Types of Systems

This is intended to describe the most common systems.As technology advances, new innovative systems may come into the market.

Broadly, there are two delivery systems: tankless and reservoir systems.Occasionally, there is a hybrid system that heats the water in a tankless boiler and stores a volume of that hot water in an insulated tank.The fuel source for these systems can be electricity, oil, natural gas, liquid propane, and biofuels such as wood.Supplementary means of heating the water can include solar panels and/or heat pumps.


Tankless hot water systems can be heated by all the fuel types discussed above, except wood.These boilers are usually wall-mounted and hold a small volume of water in coils inside the boiler.As soon as hot water is called for at a faucet, the water heater begins to heat more hot water as it passes through the boiler.The water is heated very quickly and is usually adequate for a moderately sized household.The main advantage of this "on demand" supply is the lack of a high volume of water being stored in a reservoir, where it can lose heat energy over time.

In homes with hydronic (hot water radiator) heating systems that heat the entire building, the same boiler that is used to heat the home may also have a domestic hot water coil installed inside the boiler's water jacket.This behaves in the same way as tankless water heaters described above, but it is usually floor-mounted and much larger than the wall-mounted units.Like the wall-mounted units, this system is usually adequate for a moderately sized household but may struggle to keep up with the demands of a larger household.

Of late, we are seeing hybrid systems where an insulated thermostatically controlled reservoir is used to store heated water.The water temperature in the reservoir is maintained by a hot water coil inside the tank which draws on the heat from the main boiler.This hybrid system is known as an indirect water heater and greatly improves the volume of domestic hot water needed for higher demand situations.It also reduces the number of times the burner needs to cycle on and off.


Reservoir (storage) systems are the most widely used in North America.The insulated tank is usually cylindrical, and in Canada it is usually (not always) located in the basement or a separate utility room off an attached garage.These systems have been with us for many decades. The water in reservoir systems is heated directly by a burner in the case of oil or gas-fired systems, or by electrical heating elements inside the reservoir if the heating fuel is electricity. They take up more space that a tankless wall-mounted system but are less expensive to install and store hot water in various volumes for immediate use.


Any of the above systems can be aided with the installation of solar panels that consists of roof-mounted panels and/or pipes that contain either water or antifreeze.Depending on weather conditions, they can present significant savings by supplying preheated water into the main system.These are somewhat expensive investments that take several years to pay for themselves in energy cost savings.However, using renewables such as solar energy can contribute to reduced greenhouse gases in the atmosphere.The following link is a good place to start learning more.Solar water heaters (nrcan.gc.ca)


This is typically an attachment to an electric reservoir type water heater.A small heat pump is installed on the top of the water heater.This heat pump extracts warmth from the surrounding air and transfers that heat to the stored water.It is less expensive to operate than resistance type heating elements.The heat pump is not sufficient to be the sole heat source in most locations in Canada during colder winter months.So, resistance type electrical elements are also present and able to supply heat when the heat pump cannot meet the demand.This link will take you to a more detailed discussion of these hybrid water heaters:Today's heat pump water heaters - Plumbing & HVAC (plumbingandhvac.ca)


All water heaters require inspection and maintenance from time-to-time.The frequency depends on some variables, such as age, volume of use, energy type used, and the quality of the water being heated.If your water has a high mineral content, maintenance will need to be more frequent.

All reservoir hot water tanks have a component known as a sacrificial anode rod (also called and anti corrosion rod). When water is heated ions are produced.These ions will corrode the metal of the tank unless there is a more easily corroded metal present.That more easily corroded metal takes the form of a magnesium or aluminum rod that corrodes instead of the water tank.When the sacrificial anode is spent (fully corroded), it needs to be replaced - to prevent the ions from corroding the water tank itself.As the water heater ages, a qualified plumber can check the condition of the anode rod and replace it if needed.This measure will extend the service life of your water heater.

Fuel-burning water heaters that use gas or oil should be inspected and maintained annually.The burner's efficiency can negatively impact your energy costs if it is operating below peak performance. The venting systems for exhaust gases is also an important component.Loose connections or blockages can result in a dangerous level of carbon monoxide (CO) in the home.This can seriously affect the health of the home's occupants, even to the point of causing death.Be sure your home is protected with strategically placed CO detectors on all bedroom levels.

During Canadian winters, some of us like to travel to a warmer climate for week or longer.Turning off your reservoir type water heater can save you money as, while you are away, it will continue to cycle on and off as the water heater sheds heat.If a prolonged power failure occurs while you are away, there is a risk that domestic water systems will freeze.This can cause devastating damage to a home.So, you may want to take some precautions.Turning off the water supply at the main pipe entrance to the home can limit the extent of flooding should a pipe burst.To go a step further, you may even want to drain the supply pipes in the home and install antifreeze in the drain traps.This should probably be done in consultation with a licenced plumber.

If you're looking for a qualified professional home inspector in your area, check out our Home Inspector Database on our website.

Author:  Brian Hutchinson, RHI-Retired

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