Chapter 13 – Inspecting Water HeatersWater Heater

We will continue our inspection with the water heater.

This chapter exceeds the primary purpose of this content and the eBook. Even though there will be little you can do to rectify problems with the water heater, it is the intent of this project to inform you on what the home inspection report will reveal.

Inside the hallowed corridors of the home inspection industry, the water heater is commonly referred to as a “Target Rich Environment.” This means there are several things that can go wrong with a water heater installation. An improperly installed water heater can spill toxic fumes, start a fire, damage your home by leaking water or even destroy a building.

Destroy a building?

Here is a little known fact.  A 30 gallon water heater with 50 pounds of water pressure where water boils at 297.7 degrees Fahrenheit will liberate 2,021,900 foot pounds (two million) of energy when the water is exposed to atmospheric pressure.  If it has been a long time since your high school science class let me put it this way.  A pound of nitroglycerine will liberate over 2,000,000 foot-pounds of energy.  Hey, that’s a lot of boom.  That’s a thousand tons.  One kiloton.

We downloaded an excellent video that shows how a 12-gallon electric water heater acts under a little pressure from  As you watch the video of this 12 gallon water heater, consider what your 40 gallon water heater is capable of.

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Let’s have a long talk about water heaters…

The water heater location could be in the garage on a platform or in a hall closet.  In mountain cabins or homes constructed on hillsides, the water heater might be under the building in the crawl space.  We have found them in attics, bedrooms, and laundry closets, exterior closets and even under kitchen sinks (these are usually rectangular in shape, to fit in the base cabinetry).

We have inspected homes with multiple water heaters.

Residential water heater capacity may vary from 30 gallons to 75 gallons.

We are seeing more on-demand type systems which are relatively small in comparison to the Tankless Water Heaterusual water heater tank.  Such systems may look like an over grown metal backpack with copper plumbing attached.  They do not have a water tank but heat the water as it passes through the unit.  This eliminates the extra expense of maintaining a tank full of hot water when it is not needed.

A gas fired water heater located in a garage or in a room that shares the garage floor should be elevated on a sturdy platform so the burner flame is at least 18 inches above the floor.

Gasoline fumes emitted from our vehicles are heavier than air and will collect near the floor.  The reason for this requirement is to prevent any flammable fumes in the garage from being ignited by the water heater.

Electric water heaters or gas fired water heaters with a sealed combustion chamber generally do not have to be elevated.

A gas fired water heater should never be installed in a bedroom, bathroom, clothes closet or a closet that opens into a bedroom or bathroom.  Some jurisdictions allow electric or sealed combustion chamber type water heaters in these locations.  Did you watch that video yet?  Think about it…

The water heater should be rigidly secured in place with special heavy-duty 16 to 24 gauge metal straps or braces to keep it from moving in an earthquake.  You can check with a local plumber to determine if strapping is required in your area.  Your Realtor will also know.

A flexible gas supply line should be installed between the rigid gas pipe and water heater regulator.  There should be a gas shut off valve present.  The flex pipe provides for movement in the event of an earthquake.

Flexible water supply lines are recommended as they are less likely to break in an earthquake.  Some plumber’s feel rigid water pipe plumbing provides greater security.  I’m not a licensed plumbing contractor so I can’t provide you with a specific answer on this issue.

There should be a dielectric connection between dissimilar piping metals to prevent corrosion of the plumbing fittings.  Copper and galvanized pipe are not good friends.  Brass fittings are the most common union between the piping and tank.

There should be a shut off valve installed in the cold-water inlet pipe.

All water heaters should be equipped with temperature and pressure relief valves (TPR) to prevent a malfunctioning TPR Valvewater heater from overheating and exploding.  The TPR valve is designed to release steam pressure in the event the temperature regulator fails.  Watch the video above and see what happens when a TPR valve gets plugged on a water heater that has lost temperature control.

The TPR valve should be located at the top or at the side of the water heater within the top six inches of the tank.  This valve should have a drainpipe that extends to the exterior of the building although some jurisdictions allow this pipe to drain on the garage floor.  The drainpipe should be within 6 to 24 inches from the floor or ground.

The drainpipe is necessary to control where potentially scalding hot water goes in the event there is a discharge.

A leaking TPR valve is not common but the discharge pipe should terminate where you will easily notice drips or water.  Leaking TPR valves should be replaced with a properly rated replacement.

The pipe that extends from the TPR valve should be made of hard drawn copper, CPVC, polybutylene or steel.  Regular PVC pipe is not adequate.  CPVC is rated for higher temperatures.

(CPVC – chlorinated polyvinyl chloride)
(PVC – polyvinyl chloride)
(Polybutylene – A type of plastic pipe, often gray in color, used in domestic water supply systems. Some polybutylene plumbing systems have been recalled due to a history of leaks and failure.)

The pipe for the TPR valve should have the same diameter as the valve.  The typical valve is ¾” so the pipe should be ¾” as well.  There should not be more than four elbows in the pipe.  There should not be any threads at the terminating point of the pipe.  People just love to hook things up to other things that are threaded, LIKE A CAP! I recently saw a TPR valve discharge pipe attached to 100’ water hose.  You really need to watch that video!

Fumes from gas fired water heaters must be carried outdoors by a vent piping system.  The Divertorbottom portion of this vent, called the draft diverter, is typically located at the top of the water heater.  The diverter and vent piping can get very hot.  Do not store any items on or near the water heater.

Some venting systems use double wall “Type B” vents that extend through the roof.  Type B vents require one inch clearance to combustible materials, single wall vent pipes need at least six inches clearance.  Penetration in the firewall issues often occur around the vent pipes for the water heater where they pass through the ceiling.

Exhaust gasses from a gas fired appliance that leak into a habitable space is hazardous.  Flue gas spillage can occur if the vent is obstructed, damaged or improperly installed. Installing carbon monoxide detectors near all gas fired appliances is a good safety measure.

Gas fired water heaters require a source of fresh air to provide oxygen to the flame.  A water heater in a closet, or a confined space such as a laundry room, requires ducts or openings to the outside to assure an adequate air supply.  Exhaust fans in laundry rooms can also cause flue gas spillage and an insufficient supply of oxygen can cause the water heater to produce carbon monoxide.Direct Vent

A venting system called “direct vent” serves two functions in a short, single structure.  The air for combustion is drawn in from the outdoors and exhaust gases are released through a specially constructed vent pipe unit.  The vent is a large flue pipe coming off the water heater that penetrates through an exterior wall and has a large defusing bonnet at the exterior of the building.

Moisture is a by-product of natural gas combustion.  It will cause rusting at the piping near the draft diverter on top of the water heater or at the firebox opening at the bottom.

Almost all water heaters eventually fail and leak.  Water flowing from a leaky water heater can cause substantial damage especially if it happens while you are away for a few days.  New water heaters are usually required to have a catch pan and drain when installed in areas where leakage could cause damage.

Be sure the water in your heater is not hot enough that it could scald you, a child, or anyone unable to move quickly out of the way.  The preferred temperature is 120 degrees Fahrenheit.

The location of the water heater will have to comply with different code requirements.  Different types of water heaters have to comply with different installation specification.  A local plumbing contractor will know these codes and specifications.

The most important thing to remember about a water heater is that the manufacturer’s specifications for installation supersede building codes.

Water heater tanks are required to have seismic strapping.  National building codes require two straps but some jurisdictions may not be as stringent.  Water heater straps should be properly secured to the wall or some rigid structure with proper bracing as required.

Check the water heater for leaks or signs of prior leaks at all of the plumbing joints or valves.

Rust or corrosion around the top or bottom joints of the tank might indicate the tank is leaking.

If the water heater tank is under the building in the crawl space it should be installed on a concrete pad.  It should NOT BE BELOW GRADE LEVEL.  Gas molecules should not be trapped in a pit under the appliance.  If a pit was necessary for an installation the pit must be properly vented.

Electrical water heaters should be properly wired and the wiring should be in conduit for protection.

Slow recovery time of hot water in an electric water heater could indicate that one of the two heating elements has failed.  Slow recovery in any water heater could indicate a damaged dip tube.  A dip tube is installed at the cold-water inlet of the water heater.  The tube extends to the bottom of the tank and prevents cold water entering the tank from mixing with the heated water that is exiting at the top of the tank.

Propane or natural gas water heaters located under the building that are not Direct-Vent should have vent piping sloping upward at one-quarter inch per foot to the outside of the building.  Make sure there are no leaks in the vent pipe from corrosion.  Holes caused by corrosion are a source of gas spillage and carbon monoxide poisoning.

Exterior venting should not terminate under a deck, eave of the roof or within 4’ of a window or exterior doorway.

Soot at the access covers of the combustion chamber is a result of a flame rollout.  Flame rollout occurs when there is a condition of negative pressure in the area of the burner and venting arrangements. This is also known as backdrafting.  Flame rollout can create serious fire hazards if flammable materials are stored too close to the water heater.

Negative pressure can be created by forced air heating system pressure differentials, clothes dryers, ventilation fans, range hoods, and house stack effect.  The “stack effect” occurs when the flow of naturally rising warm air creates a positive pressure area at the top of a building and a negative pressure area at the bottom of a building.  The negative, or low pressure will be “back filled” with air drawn from cracks and holes in the floors, walls and any openings to the exterior, including the combustion chamber of a water heater.

Backdraft interactions are more common than we would like to think. Preventing them may be quite difficult and requires trained personnel to diagnose and resolve. When in doubt as to the safety of a particular installation, an induced draft or sealed combustion gas water heater replacement may be the wise choice.  The energy savings from a higher quality, safer appliance offsets the initial expense.

Another issue is a rotten egg smell from the hot water tap.  This smell is derived from hydrogen sulfide gas dissolved in the water.  Concentrations as little as 1 ppm (parts per million) can produce this odor.  The smell is the result of four factors all of which must be present for the odor to develop:

  1. There must be a high concentration of sulfate in the raw water;
  2. There must be little or no dissolved oxygen in the water;
  3. There must be sulfate-reducing bacteria in the water heater (this bacteria is nontoxic to humans and originates in the water source);
  4. There must be an excess of active hydrogen in the tank. This hydrogen can be created as a result of the cathodic action of some anode rods in glass-lined water heaters.

With these factors present the hydrogen and sulfur combine to form the hydrogen sulfide gas that gives off the rotten egg odor.  Active use of the water heater will reduce the problem.  An idle water heater (while you are on vacation) allows the accumulation of this hydrogen sulfide gas.

Smelly water can easily be eliminated or reduced by chlorination of the hot water system (both the water heater and all hot water lines) and by replacing a glass-lined water heater anode rod with one of a less active material.

Only glass-lined water heaters are equipped with anodes, therefore, chlorination of the system may be the only treatment necessary for some water heaters.

If you hear a bubbling sound when the water heater fires up it is most likely the result of mineral buildup in the bottom of the tank.  This is common in older water heaters.

A.O. Smith Water Products Co., a nationally known manufacturer of water heaters, publishes a series of technical bulletins. These bulletins may be found at

A.O. Smith’s Technical Bulletin 13, titled “Mineral Build-Up,” offers a detailed discussion about the symptoms, cause and cure of a “rumbling” water heater.

All furnace and water heater manufactures as well as the National Fuel Gas Code (see section 8.5.7 of NFPA 54/ANS Dripleg GraphicZ223.1) require that sediment traps be installed on the gas fuel supply line as close to the supply inlet as possible.  The sediment trap is also known as a “drip leg.”  A drip leg is installed to prevent foreign material in the gas pipe from getting into the appliance and causing problems such as gas leaks and regulator failure.  The installation instructions also require that the gas change direction of flow by 90 degrees.

In my region of the country there is no code requiring that a drip leg be installed and guess what, there doesn’t need to be because the manufacturer’s installation instructions supersede code.  Many times the drip leg is missing or improperly installed.

I got into a rather tense “discussion” with a homeowner one time about this issue.  While going through the inspection report with the buyer, I commented that the water heater drip leg was improperly installed.  The owner became a bit irate and wanted me to show him what was wrong.  We went into his garage and I explained the problem.  A drip leg was present but the pipes were not installed in a way that allowed the flow of gas to make the 90 degree change in direction.

He said, “You’re not a building contractor, not a plumbing contractor, not an HVAC contractor and not a “real” building inspector.  My son works for the company that built this house and they are a reputable
nationwide corporation.  What gives you the authority to say this is wrong?  The county didn’t even call it out.”

I was prepared to show him why.  I said, “Sir, you are absolutely correct.  I am not a building contractor, not a plumbing contractor, not an HVAC contractor and I am not a county building inspector either.  I am sure your son is a fine person and the company he works for is well known for its excellent reputation.  However, this device is still improperly installed.”

“County inspectors look for code violations.  This drip leg does not fall under a code so is not checked by a county official.  What we are dealing with is a manufacturer’s requirement.  You can see in this installation manual taped to the side of your water heater exactly what is required.  Even though I am not one of the professionals you mentioned, I can read and this manual says it needs to be installed this way.”

He was very apologetic and said he was going to call his son and let him know about this mistake.  He left me alone the rest of the time I was there.  By the way, he was a building appraiser and a very nice man after all.

There are other devices that can heat water including hydronic boilers, coal and fuel oil boilers, wood fired boilers and probably others.  I have only encountered tank and tankless water heaters and a few hydronic boilers.  The hydronic hot water heater equipment I have encountered was usually integrated with radiant heating for baseboard or in-floor systems.  We will touch on these in the HVAC chapter.

Except for the water tank itself, the “backpack” tankless water heaters have many of the same considerations regarding venting, air supply and plumbing as a tank type water heater.

If you have a device that is not the typical tank type water heater the information covered will provide a basis from which to observe your system.  I recommend that you have a qualified tradesman inspect it if you observe anything out of the ordinary.

Here is one of my “over and over again” notes.  Your goal is to eliminate this kind of note…

Note:  No gas line drip leg could be identified (see photos).  Further information could be obtained from the appliance manufacturer’s installation manual.Water Pressure Regulator

In most cases, there was no drip leg installed.

One item of importance I seemed to have missed was the importance of the water pressure to the building.   Maximum pressure to is recommended at or below 80 lbs. to help prevent leaks and ruptures of plumbing lines and fixtures.  The pressure can be adjusted with a pressure regulator installed somewhere after the primary shut off valve.  A licensed Plumbing Contractor can install this device if not present.


The information provided above represents a small portion of the material related to water heater installation.  Provisions for exhaust venting and combustion air supply sources are extensive and beyond the scope of this report.

Water heater installations and replacements require a permit and should only be done by a competent plumbing contractor.

Things you can probably do yourself are wire brush the corrosion off the plumbing nipples, clean around the appliance and maybe even install a proper TPR pipe.  Much more than that is not recommended.  Have your water heater inspected if you see any conditions similar to those in the eBook Photo Gallery.

I have included several images from the eBook here.


An additional 32 images with descriptive captions are available in the 27 Dollar Home Inspections eBook.

Click here to move on to
Chapter 14 – Inspecting HVAC Systems