Most residential dwellings have a tank-type water heater which consists of a cylindrical free-standing tank with plumbing supply and outlet lines at the top of the unit. The most common heat sources for tank water heaters are electricity or gas (either propane or natural gas).
An electric water heater will have a large electrical conduit attached from the dwelling’s main electrical power source (main circuit breaker panel).
A fuel-type or “gas fired” unit will have a large vent duct at the top and a fuel source line close to the bottom of the unit.
A tank water heater not only heats water but stores it until it is needed. This is why all tank water heaters are fitted with insulation material that helps maintain the water at a high temperature between heating cycles.
Tank Water Heater Operation
At the top of all tank water heaters there are the water supply and delivery lines. The supply pipe routes cold water to the bottom of the tank through a Dip Tube. A Delivery Pipe takes water from the top of the unit and delivers it to whatever plumbing fixtures need it such as clothes washers and faucets.
All tank water heaters are equipped with a safety device known as a T&P Valve (temperature-and-pressure relief valve). This valve is designed to open if either the temperature of the water or the pressure inside the tank exceeds a safe limit.
The T&P valve of a tank water heater is required to be plumbed to expel high-pressure, hot water the exterior of the building or dwelling if the water heater unit is installed on the same floor level as the living area of the home, or if it is installed in the attic space.
If the tank unit is installed below the main floor level of a home (as in the lower floor
area of a garage, it may be plumbed to expel to a drain pan installed below the tank unit.
Tank Water Heater Construction
Most tanks are made of steel with an interior glass lining to help prevent internal corrosion. All tanks also have an Anode Rod designed to control corrosion.
The anode rod essentially protects the tank by corroding in place of the steel. Because the rod is designed to corrode, it will eventually wear out and need to be replaced. It’s a good idea to check the anode rod once a year, and replace it if necessary.
At the bottom of every tank is a drain for emptying the tank. There is also valve on the supply pipe (usually at the top of the unit) which allows the ability to shut down the hot- water plumbing without affecting the cold-water supply to the home.
Electric Water Heaters
A typical electric unit is wired to a 220-volt circuit. To heat the water, current passes through heating elements—usually two, one at the middle of the tank and one at the bottom, via a thermostat (a switch that senses water temperature). When the temperature of the water drops below a preset value, the switch closes to allow current flow and opens again when the temperature reaches its preset limit. Most thermostats have a dial for setting the maximum water temperature.
Fuel-Fired Water Heaters
Gas water heaters have an internal burner that is fed fuel through a control valve and a thermostat switch. This burner is usually situated so that the tank is heated by the flame from the burner. Exhaust gases are vented either through a hollow core at the center of the tank or around the tank sides.
Because fuel-type water heaters use actual flames to heat the water in the tank, the unit experiences a higher degree of material wear and degradation when operating. The life expectancy of a gas-type water heater is usually less than an electric unit.
The capacity of the tank, and the rate at which water is heated, affect the supply of hot water at the plumbing fixtures.
The speed at which a unit heats water is called its recovery rate. This figure indicates the amount of
water in gallons that can be heated to 100 degrees F in 1 hour. When water is drawn from the tank faster than it is being heated (as during a 45 minute College Student shower…), the temperature of the water will drop. This is commonly known as “Running out of hot water”.
Typically, heaters with low recovery rates have a high tank capacity. Although it takes longer to heat the water, there’s more of it for intermittent use. Electric units fall into this category. Conversely, a fuel-fired heater with a high recovery rate needn’t have as large of a large tank, because it can heat the water faster. In general, electric models have the lowest recovery rate, and gas units have the highest.
Tankless water heaters are becoming more and more common due to their energy efficiency and virtually unlimited supply of hot water. They are available in both electric and fuel-fired (gas) varieties. Because tankless heaters only heat water as it’s used, no energy is required to maintain water at a specific temperature for long periods of time like the tank-type units.
Tankless Unit Principle of Operation
The tankless system uses a heat exchanger to heat the water. The heat exchanger aids in transferring the heat from the gas burner (gas heater) or electric coils (electric heater) to the incoming cold water.
When a hot water tap is opened, incoming cold water passes through the heat exchanger. The heat exchanger heats water according to the specified temperature and hot water is supplied back to the tap via the hot water piping system.
There is flow sensor or flow switch which detects the water flow and turns on the system to heat the water.
Regardless of the type of unit installed, a basic understanding of the principles of water heater operation is helpful when advising clients during the real estate or insurance transaction process.