Reuben's Home Inspection Blog


Four Common Water Heater Installation Defects

Gas water heaters are a lot like decks, in the sense that most handymen feel qualified to install one.  Thanks to these handymen, I find more installation defects on these two items than just about any other component in the home, and today I'm going to share my list of the most common gas water heater installation defects.

Improper Discharge Pipe

If the water heater were to malfunction and the burner just kept heating the tank, the water heater tank could would eventually rupture, turning the water heater in to a missile.  Mythbusters did a great re-creation of this - click here to see quick video of it.

To prevent this from happening, a valve is installed on the water heater which is set to go off at 150 psi, or 210 degrees Fahrenheit.  This valve is called the temperature and pressure relief valve.  To prevent this valve from shooting scalding hot water or steam in to someone's face, the Minnesota State Plumbing Code (Section 4715.2210) requires a discharge pipe to be attached to this valve.  A few requirements for this pipe are as follows:

  • Must be full sized.  This almost always means it must be a 3/4" pipe.  Bushing at TPRV
  • Must terminate within 18" of the floor (6" for the rest of the country - we're special here in Minnesota).Short Discharge Pipe
  • Must not be threaded or capped at the end.  If it were threaded at the end and the valve started leaking, some dope might screw a cap on the end, thus disabling it.
  • In some jurisdictions, such as Minneapolis, only metal is allowed.

This seems like a really easy thing to get right, but experience has told me that it definitely isn't.

Improper Gas Piping

The installation requirements for the gas piping that leads to water heaters is the same as that for just about any other gas appliance, but again, I find the most problems at water heaters.

  • There must be an approved gas valve installed within three feet of the water heater.
  • There must be a way to disconnect the gas piping to the water heater after the valve.  This could be through the use of an appliance connector or a union.
  • There must be a sediment trap installed just before the water heater.

Improper Water Piping

  • The water supply pipes must be at least 3/4".
  • Only metal pipes are allowed within the first 18" of the tank.
  • There must be a shutoff valve installed on the cold water supply pipe that feeds the water heater.  Note:  a common myth among home inspectors is that there should never be a valve on the hot water side... but this is perfectly acceptable.
  • Flexible water supply connectors are prohibited in Minnesota.  Water Supply Connector

Improper Venting

  • The vent connector must have three screws at every joint.
  • For a single-wall vent, six inches of clearance must be maintained to any combustible surface, such as wood or drywall.  For a double-wall vent (B-vent), the clearance can be reduced down to one inch.  Vent Clearances
  • The vent must pitch upwards with a minimum slope of 1/4" per foot. This is a minimum requirement - just following this requirement does not mean the water heater will draft properly, but it's a start.Backpitched Vent
  • For a powervent water heater, the manufacturer's installation instructions must be followed: they all use the diagram below for the vent termination location.  Powervent WH Terminal

That wraps up my list of the most common installation defects.  This is by no means an all-inclusive list of the requirements for a water heater installation, but it probably covers 95% of the installation defects that I find during home inspections in the Twin Cities.  For Minneapolis Truth In Housing evaluations, any installation that is three years old or less must be completely up to code; failure to follow any of these requirements would require repair.


Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 7 commentsReuben Saltzman • May 06 2010 06:09AM


Thank you for sharing, this is very thorough. On my way to re-blog to my readers.

Posted by Catherine Chaudemanche - Edison & Central NJ, Full Time, Informed and Involved- Results Driven (Metuchen Keller Williams Elite Realty / Middlesex County, NJ) almost 9 years ago

Reuben - thank you for sharing this informative post. No way would I tackle a water heater install but now I know what to llok for. Great post!

Posted by Tom Priester, Paradise Sharks (Paradise Sharks ) almost 9 years ago

Excellent post Reuben, thank you.

Posted by Katherine Fornale, SFR, GRI (REMAX REALTY 9) almost 9 years ago

Hi Reuben, what does Minnesota have against the flexible connectors?  Out here I rarely see one without them.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 9 years ago

Catherine - thank you for the re-blog.

Tom - there's a lot that can go wrong, isn't there?

Katherine - thanks for reading.

Charles - you got me, I really don't know.  I've heard that it has something to do with the thickness of the metal in the connector - it doesn't meet our rigid standards.  Personally, I think it has more to do with a strong plumbers union...

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 9 years ago

Quite interesting to see the difference between our California requirements and your Minnesota requirements. For example, we don't use sediment traps out here on the gas line, and the plumbers would have a fit if there were a water valve on the hot water line. Not to mention that I'd have a lot of Clients calling me and wanting me to pay for the visit by the plumber.

Posted by Not a real person almost 9 years ago

Ray - no kidding about the hot water valve?  Is that part of your plumbing code, or just a generally accepted practice?  What's the reasoning?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 9 years ago