Types
The most popular method of heating water in American homes is the standard tank type gas water heaters. Click here for information on tankless or electric water heaters.
Gas burning units commonly burn natural gas, but can be purchased or converted to burn propane or butane also. Whoever fuel gas selected, in general gas units will heat up the tank in half the time of an electric unit for less than half of the cost.
Electric water heaters are equipped with either one or two insulated elements which extend into the tank and heat the water via radiant heat. While these units avoid the risk of flame and flammable fuel gas, they are much less efficient to operate.
Installation
When installed in a home or attic, the unit should be installed in a drain pan large enough to catch a normal leak . The drain pan should have a drain pipe to the exterior capable of handling the run off from a leaking fully opened valve. Generally these drain lines to the exterior are not linked to the TP Valve discussed below, however, there are some circumstances that allow this technique. Any unit mounted in a garage or in a room adjacent to the garage, connected by a door, must be mounted on a stand that raises the pilot light at least 18 inches above the garage parking surface. If your home is located in a seismic zone, the unit should be firmly properly braced to a structure such as the wall. Both the garage and seismic precautions are attempts to prevent common fire risks.
TP Valve
In general, any pressurized tank has some variety of pressure relief valve to prevent accidental tank eruption. Water heaters (regardless of energy source) are no different. The process of heating the water in the tank caused the pressure to increase. If the thermostat on a unit failed to turn of the burner or element, the unit could continue to cook until the interior pressure of the tank exceeds the strength of the tank weld and the unit would burst. A catastrophic failure of a 40 gallon water tank could do significant structural damage to the home. TO prevent this risk, all water heaters are equipped with Temperature and Pressure Relief Valves.
This valve is commonly refereed to as a TPR, T&P or relief valve. There are usually factory set to open when the internal tank temperature reaches 210º or 150 psi. These trigger points represent about twice the average demand temperature and water pressure in most homes and are well below the strength of the tank.
The valve should be mounted in the upper third of the tank, on the side or top. The valve is screwed into an opening provided for it and has a probe that extends into the water tank. A drain pipe extends from the valve to the exterior of the home, garage floor or basement sump, depending on region or code. The T&P and drain pan drain line should not normally share a common drain pipe, however, there are two installation techniques that allow this.
All T&P valves are equipped with a manual test lever. While manufacturers recommend occasional testing, this may not always be a good idea. If you live in a region with hard water you will experience a build up of heavy mineral sediment in your water heater tank. Chunks of sediment can lodge in the T&P when being tested and prevent it from closing. This will lead to a valve replacement.
High limit switch
When the tank gets too hot it trips the high limit switch, (a circuit breaker). The high limit switch is in the top thermostat and usually has a red button. In order to get it working again the high limit switch must be manually reset by pushing in the red button.
Anode
The sacrificial anode is a metal rod usually magnesium or aluminum which helps prevent corrosion of the metal tank. Electrolysis eats away the metal anode instead of the metal of the tank. Once the anode is gone the tank itself begins to corrode. Most manufacturers recommend replacement of anode tubes, however, in practical application, the entire water heater will fail before ht anode needs to be replaced.
Softeners can cause the anode to wear out more quickly. Bacteria can react with magnesium anodes causing hydrogen sulfide which can cause a rotten egg odor. Switching to an aluminum anode rod can help eliminate the odor problems.
Dip Tube
The dip tube is a long narrow tube that directs incoming cold water to the bottom of the tank closest to the heating element. From there, good old physics takes over. Cool water settles to the base of the unit to be heated and rise to the top to be used. Without the dip tube, or with a broken dip tube, it may seem as though you run out quickly, or you just get warm water.
Thermostat
The thermostat senses when the tank drops below a certain set-point and causes the burner to come on. When the desired set point is reached, the thermostat shuts off the burner. You might have noticed that I am writing “set point” and not “temperature”. The simple reason is that no manufacturer places actual temperature numbers on the thermostat. There are several good reasons why listing temperature is not feasible. Instead, all they provide is a knob and some ticks or letters on a short arc.
Drain Valve
The drain valve allows the tank to be emptied for periodic removal of sediment or for unit replacement. Most manufacturers recommend periodic draining of several gallons of water in order to remove sediment. Unfortunately, they all install cheap plastic drain valves. If you can, replace the cheap valve with a good quality machined metal “ball-type” valve at the time of installation. If you can not, be very careful about using or replacing the cheap plastic drain valve
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