Plumber's Licensing Exam: Water Heaters

The purpose of this guide may seem straightforward and you might even think you can skip it. After all, you install and service water heaters all the time. However, don’t be too quick to take this topic for granted. Water heater installation and safety guidelines are very strict, so these rules are absolutely worth reviewing.

Objectives
- Identify proper locations to install water heaters
- Explain water temperature control, how it’s done, and the ranges allowed
- State general installation requirements, including piping, valves, and drain pans
- Discuss safe installations, including siphon prevention, shutdown requirements, and relief valves

Key Terms:
aquastat
BTU
dielectric unions
domestic hot water
grade
indirect waste
natural gas
plenum
propane gas
thermostat
vacuum relief valve

Real-Life Situation: Ace Plumbing Company received a service call at 3:30 p.m. The 30-gallon natural gas water heater at the Springfield Little League concession stand is leaking. The concession operator has turned off the water supply and the gas supply to the heater. You have the job ticket to replace this water heater tomorrow morning. The heater is in a closet behind a louvered door in the same room where the volunteers work. The vent is B-vent. The permit has been paid for and posted. You must be sure the new heater is properly installed. What do you have to look for?
Quite often, small volunteer organizations will take advantage of the skills, or at least the willingness to help, of their members. Every dollar saved is, well, a dollar saved. Or is it? Harry, the guy who mowed the Springfield baseball field enough years to go through two John Deere riding mowers and about 97 weed whackers, installed the water heater in the concession stand with a little help from his friend Freddie. Freddie said he “knew about” this kind of stuff since he worked at the hardware store.
Now it’s your turn to replace the water heater, and you are a professional. Your license, reputation, and, most importantly, your ego are at stake.
 

Location
Both plumbing codes are quite specific about issues related to where water heaters can be installed. In this section, we explore this aspect of the codes.
 

Accessibility
Every water heater must be installed so that all parts that could need inspection or service are accessible. Accessibility means that you do not need to remove any part of the permanent structure to get to all parts of the water heater. For example, there might be a panel or door that covers access to the water heater; it would need to be removable without doing any damage to the building and easily replaced after inspection. These instructions seem a little vague, and leave a whole lot of room for interpretation. Thankfully, you will have the installation instructions that come with the new water heater. Read them! (Refer to IPC 501.4, 502.3; UPC 509.4)
The installation manual is considered to be a part of the plumbing code. You must strictly follow the instructions included with the water heater. The good thing about the instructions is that they take care of just about any code issue you might have. Consequently, you should have the instructions available when the inspector examines your installation, especially if the heater is unusual in some way or if it involves new technology. Vent terminals that terminate through an outside wall of a building shall be located not less than 10 feet horizontally from an operable opening (e.g., window) in an adjacent building. This shall not apply to operable openings that are not less than 2 feet below or 25 feet above the elevation of the vent terminals.
Sometimes a water heater will be installed in an attic because of lack of space in the structure. Access takes on a whole new meaning in attics. There now must be a passageway large enough to allow the removal of the water heater, and that space cannot be smaller than 30 inches high and 22 inches wide, and no longer than 20 feet (Figure below). Where the water heater stands, there must be a platform in front of the heater that is at least 30 inches by 30 inches, enough room to allow a serviceperson to work safely on the heater. And these are really only minimum requirements. Imagine dragging or pushing a water heater along in a passageway for 20 feet that is only 30 inches high and 22 inches wide! At least it is also required that the passageway have continuous solid flooring so you won’t have to worry about falling through. The UPC has added additional enforcement requirements to the manufacturer’s requirements to provide clearances and accessibility to serviceable components within gas utilization appliances.

Figure: A Narrow Passageway for Water Heater Access
 

Room as a Plenum
In large commercial buildings, such as warehouses, a room with large air-handling equipment can be used as a plenum. If a water heater is fired by any solid, liquid, or gas type of fuel, it cannot be installed in this room. If a heater of this type were installed in a room used as a plenum, the products of combustion could be distributed throughout the building if a negative pressure is created in the combustion chamber. That pretty much leaves only electric water heaters as options for a room used as a plenum. (Refer to IPC 502.2)
Both the installer and the inspector are now required to ensure makeup air is provided for fire-burning appliances in order that the products of combustion are not distributed through the building.

Garages
Any part of a water heater that can be a source of ignition must be installed at least 18 inches above floor level. The water heater stand in
the figure below is 18 inches high and is designed to support a water heater at a height that will always meet this provision of the code. This is to prevent starting a fire or explosion due to flammable gasses or fumes from products used in a garage. Gasoline fumes are a major concern in garages. (Refer to UPC 508.14)

Figure: Water Heater Support Stand (Photo courtesy of Watts)
 

Temperature Control
Let’s start with some really basic information. Some of this may seem obvious, but we don’t want to overlook anything. Every hot water supply system must have some kind of temperature control, which is adjustable from a low setting to whatever maximum temperature is allowed for the purpose of the system. Therefore, an on-off switch, a hand-controlled valve to mix cold water with hot water, or any other kind of manual control is not allowed. The temperature control must be fully automatic and require no human supervision. (Refer to IPC 501.8)

Type of Control
A typical natural gas or propane gas water heater will have a gas control thermostat. An automatic valve that controls the gas flow is controlled by a probe that monitors the temperature of the water in the tank.
An electric water heater is controlled by one or two thermostats that sense the tank temperature through conduction, by being in contact with the surface of the tank.
The control for an oil-fired water heater is another probe-type control called an aquastat.

Control Range
All tankless water heaters must be restricted to an output temperature of 140°F. A practice that is becoming more and more common is to use water heaters both to heat a building and also to provide domestic hot water. Often the space-heating portion of the system is radiant tubing. All water heaters used for both domestic hot water and for space heating must have an approved tempering valve that limits the domestic hot water temperature to 140°F.
The potential for scalding must be taken seriously. Every year people are injured and some die from scalding injuries. All people are at risk, but extra consideration must be given to children, the handicapped, and anyone who may have difficulty controlling the temperature of a bath or shower. People who would have difficulty getting out of a hot shower or bathtub face the same danger (Table below).

Installation Requirements
Primarily, this section addresses piping configurations that need to be adhered to when installing water heaters. Drain pan requirements are also discussed.

Piping Requirements
A drain valve needs to be installed at the bottom of every tank-type water heater and every hot water storage tank (Figure below). Drain valves are required to facilitate servicing or replacement of a water heater. (Refer to IPC 501.3, 503.1)
You might wonder why there needs to be a code rule requiring a valve on the cold water inlet. It’s only logical that you would want a valve on the cold inlet of a water heater, and one that’s in a handy place. But think, if there was a house that had a problem with the basement flooding occasionally, it would be better to have the water heater up on the first floor rather than in the basement where it is susceptible to water damage. If the cold water supply valve were left in the basement, it would be very inconvenient to work on this water heater; if there were a reason that the building occupant needed to shut the water off in some kind of emergency situation, he or she wouldn’t be able to tell which valve was the right one to close.

Fact: The cold water inlet to the water heater must have a valve on it, which is only for the water heater. It cannot influence the flow of cold water in any other part of the cold water supply system. The valve must be located near the water heater and on the same floor as the water heater.


Figure: Water Heater Drain Valve Location

Drain Pans
Any water heater that is installed in a location where leaking could cause damage to the property must have a drain pan installed under it (
Figure below). (Refer to IPC 504.7; UPC 508.4)

Figure: Drain Pan to Capture Leaks from a Water Heater

When tank-type water heaters leak, the problem usually starts slowly. Because the leak is small but steady, a lot of damage to the structure can occur. Evaporation hides the leak from the building inhabitants for some time while the slowly leaking water begins to soften, swell, and rot the structure. Flooring, drywall, plaster, and ceilings get ruined, making for a very expensive repair that goes well beyond the cost of the water heater replacement.
The drainpipe from a water heater pan must be a minimum of 3/4 inch in diameter and must be extended to drain into an indirect waste receptor. If the drain terminates outside the building, it must be extended to a distance not less than 6 inches and not greater than 24 inches above grade.
Most of the time, the pipe from the drain pan is run to a floor drain. Other places to lead the pipe to could be a laundry tray, service sink, or a floor sink. Do not connect the drainpipe directly to the sanitary drainage system. The pipe cannot be reduced in size over its entire length. If the most effective way to safely end this pipe is outdoors, it must be brought to a reasonable height above the ground as stated above to prevent snow, leaves, and plant growth from plugging it; at the same time, it must be low enough to not be a dripping nuisance.

Safety
Incidents involving unsafe water heaters are rare. For that reason, it might be easy to overlook safety regulations when installing a water heater. To the credit of code writers and code enforcers, safety is taken seriously and approached on a no-exception basis. All new water heaters have a new temperature and pressure relief valve shipped with them now. This was not the case even just a few years ago. Safe installations must be ensured by the plumber. The building occupants’ lives could literally be on the line: it’s up to the plumber to make sure that water heater mishaps due to unsafe installations continue to be rare.

Antisiphon Strategies
An approved means of preventing siphoning of water from a tank-type water heater or hot water storage tank must be installed. A siphon anywhere in a water distribution system could draw contaminants into the piping system. (Refer to IPC 504.1)

Real-Life Situation: OK, so far so good. The location of the water heater in the concession stand is fine. Let’s move on. The old water heater has no drain pan, but it really doesn’t need it. It is sitting on a concrete floor with a floor drain about 2 feet away. Harry and Freddie put a 3/4-inch gate valve on the cold supply pipe about 14 inches up the pipe. Looks good enough to reuse on the new installation. They even installed dielectric unions to prevent corrosion.
Tank-type water heaters that have the cold water connection at the top of the tank are equipped with a dip tube, which is a tube extending inside the tank from the cold water inlet at the top, down to a point near the bottom of the tank (Figure below). The purpose of the dip tube is to take the incoming cold water to the bottom of the tank where it can be heated, while the heated water rises to the top of the tank. Hot water tends to stay at the top to be drawn off at the hot water outlet and the cold at the bottom because cold water is denser, and therefore heavier than hot water per cubic volume. If conditions arise that could cause a siphon, the dip tube has a small hole drilled in the side of it near the top to break any siphon that may occur.

Figure: Dip Tube in Tank on Cold Water Inlet

Fact: All tank-type water heaters must have a pressure relief valve installed directly into the body of the tank and the relief valve must have a pressure rating of no more than 150 psi or the rated working pressure of the tank, whichever is lower. This valve must be self-closing and located in the top 6 inches of the tank.
Water heaters that have the cold water inlet at the bottom must have a vacuum relief valve installed in the cold water inlet pipe. If the drain valve is opened with both the cold water inlet and all the hot water outlets closed, a vacuum will occur that might cause some water heater tanks to collapse. The vacuum relief valve allows air to enter the tank through the cold water inlet and prevent the vacuum condition.

Shutdown
Every electric water heater must have a dedicated electrical disconnect switch in the same room with the water heater to allow for complete shutdown. All water heaters using other fuels must have a dedicated valve to shut off the fuel supply. (Refer to IPC 504.3)

Relief Valves
Quite possibly the most important item in the water heater section of the plumbing code is the section on relief valves. First, the nuts and bolts of the code. (Refer to IPC 504.4, 504.5, 504.6; UPC 505.4, 505.5)
As you most likely already know, a water heater is usually equipped with a combination temperature and pressure relief valve (T & P). The plumbing code allows for them to be separate, so they are treated separately. The IPC has now changed the code with respect to water heaters with separate storage tanks. It now specifies that both water heaters with separate storage tanks and storage water heaters must be installed with approved, self-closing (levered) pressure relief and temperature combination valve.

Fact: Tank-type water heaters must be equipped with a temperature relief valve installed directly into the body of the tank. The opening temperature cannot be set at more than 210°F. The temperature relief valve must be able to relieve at or above the BTU input rating of the water heater. This relief valve must also be self-closing.

Caution: Never reuse the old T & P valve when you change a water heater. Never plug the outlet end of a relief valve, no matter how much it is dripping. Replace it. Always check the T & P valve on a water heater to make sure it is installed correctly. Lives could be at risk.
If there were no T & P relief valve on a water heater, there could be catastrophic consequences. If the pressure in a water heater exceeded the pressure the tank could tolerate, obviously the tank would fail, expelling the water under great pressure, for a moment anyway. Personal injury is certainly a possibility, along with extensive water damage to the building.
The greater risk is if the temperature control on a water heater fails and the temperature of the water continues to climb above the boiling point. Initially, there is a very real danger of severe scalding if anyone opens a hot water faucet. A catastrophe can occur if the temperature exceeds 212°F and the system pressure climbs above the bursting pressure of the tank through expansion of the heating water. This can occur if there is a backflow preventer on the water main, giving the expanding water no place to go. Now, you have a tank of superheated water, which is water remaining in the liquid state above the boiling point because it is under pressure. Let’s say the rated working pressure of the tank is 150 psi. That means the burst pressure is at least 11/2 times the working pressure. That would be 225 psi.
At that pressure, the water has been able to remain a liquid water, but it’s now at a temperature of 397°F! Remember, water boils in your teapot at 212°F, and you can’t say that’s not hot.
At this point, the tank just can’t take it anymore, and a dangerous explosion is the likely result. Forty gallons (almost 300 cubic feet) of superheated water just turned into 480,000 cubic feet of very hot steam! This will send the water heater on the next Mars mission. There are only 200,000 cubic feet of limestone in the Empire State Building. The results can be devastating. Incredible damage and loss of life have been attributed to exploding water heaters. They have been known to go up through multiple stories in large buildings. You can check this out for yourself on the Internet. There are lots of stories and some of them can send chills up your spine.

Relief Valve Outlet
The outlet of the relief valve must be a plain-end pipe, which remains at the full diameter of the relief valve outlet. It must drain by gravity, indirectly to an indirect waste receptor, to the floor or to the outdoors.
If a relief valve were dripping outdoors in freezing weather it would soon be plugged solid with ice. Therefore, if an outlet pipe is drained to the outdoors, it must first drain into an indirect waste receptor in a heated area, and then the waste pipe can be directed outdoors. When the pipe simply drains to the floor, it must end within 6 inches of the floor.
The outlet pipe cannot be directly connected with any other relief valve piping. The relief valve outlet is never connected directly to any drainage system.

Tips
Premade water heater discharge pipes are available for purchase wherever you buy water heaters. They are inexpensive, quick and easy to install, and they meet code regulations.

Real-Life Situation: There is a 1/2-inch gas cock 8 inches away from the water heater gas connection, which serves only the water heater. There is a 3/4-inch T & P relief valve installed directly into the side of the tank about 4 inches down from the top. It has a BTU rating label that is far greater than the BTU input rating of the water heater. For the drop pipe on the outlet of the relief valve, Harry used a piece of 3/4-inch galvanized pipe, threaded on both ends and long enough to end 5 inches off the concrete floor. So how did old Harry do? Pretty good job for an amateur, but with one thing wrong—it shouldn’t have passed inspection.