While Chapter 5 of the Uniform Plumbing Code is titled “Water Heaters,” it also addresses combustion air, chimneys, different types of gas vent materials, exhaust gas venting, etc.

In the 2000 edition of the UPC, Chapter 5 was 9 pages with 3 sizing tables. The same chapter in the 2015 printing has 25 pages of text and 26 pages of sizing tables.

What happened to cause the number of pages to increase by 560%? Was there some change in the law of physics for natural gas and water heater exhaust vents? Was there some danger that had been ignored or overlooked in the code development process?

Actually what happened is not so nefarious. IAPMO and the NFPA worked together to bring their two code documents in closer alignment with part of the substantiation being submitted by “Ted” Lemoff of NFPA International: “This proposal is to correlate the UPC and NFPA 54 requirements. The UPC requirements are replaced extracting text from the NFPA 54 which results in more complete coverage of the subject in the UPC.”

If you reviewed the 2003 UPC you would find almost the entire chapter was affected, but not without hours of private discussion and wrangling on the conference floor prior to being printed. So, that’s what happened to chapter 5.

Something that really surprises those new to the Uniform Pluming Code is that with few exceptions, if you are installing new material on a property, that work is required to be permitted and inspected. Referring to the 2015 UPC Section 502: It shall be unlawful for a person to install, remove, or replace or cause to be installed, removed, or replaced a water heater without first obtaining a permit from the Authority Having Jurisdiction to do so.

The requirements are there but enforcement is sometime lacking. Of course, if no one knows a permit is required, and in my experience most property owners and many “plumbers” don’t, why would they make application for one? As a result, water heaters are sold, most are probably installed incorrectly (see image for one example) and no one knows about it until there is some unpleasantness.

Before the 2003 UPC, the idea of a gas burning water heater in a bedroom or bathroom was anathema; the only exception was a direct vent water heater where the combustion air came from outside the space. Note: besides obtaining combustion air from outside the building, direct vent appliances are equipped with a sealed combustion chamber. That means there is no contact between the air required for combustion, the exhaust gases, including CO2, and the occupied space. Another way we used to say it is, “So you won’t wake up DEAD.”

With the publication of the 2003 UPC all that changed. Well, sort of. Installation of non-direct vent heaters is now allowed in closets located in bedrooms and bathrooms as long as a whole laundry list of requirements are met. For more details, see Section 504.1 of the 2015 UPC.

With an understanding that a garage may house more than internal combustion powered automobiles (lawnmower, gas can, motorcycles, paint cans, etc.) at one time, water heaters generating a glow, spark, or flame capable of igniting flammable vapors, when located in a garage, were required to have their pilots, burners, or heating elements and switches located not less than 18 inches above the floor level. Note: The UPC has never required a water heater stand to be 18 inches high. At it’s essence, the section required any water heater component (i.e. pilot, burners or heating elements and switches) which have the ability to ignite flammable vapors be not less than 18 inches above the floor to reduce the opportunity of that scenario. Notice that without actually listing it, electric water heaters with their heating elements and switches were included.

Similar requirements are still present (Section 507.12 and following), however it now includes any appliance with similar ignition potential. References to elements and switches have been removed and replaced with “potential of ignition of the flammable vapors”. Using the more inclusive term, “any appliance” now covers water heaters (tank or tankless), clothes dryers, washing machines, space heating equipment and any other appliance that has the potential to ignite any flammable vapor unless the appliance is listed as flammable vapor ignition resistant. While writing this I began to wonder if you could make the case that a circulating pump less than 18 inches above the floor, though perhaps not considered an appliance, should be included.

You should also check out the requirements for a water heater drainage pan Section 507.5 and know that Section 608.5 prohibits the discharge from a T & P valve into a water heater drainage pan.

Section 509.6.2.1 The exhaust gas vent pipe from a water heater or any appliance shall not terminate less than five feet in vertical height above the draft hood or flue collar. And in Section 509.6.2.5 the vent shall terminate with a listed cap or roof assembly.

Section 509.6.3 is a section you should really understand — that vents (type B or L) are required to rise in a vertical direction with any offsets not exceeding 45°, (I see no limitations on the number of 45° offsets). However, you may have one (only one) offset not more than 60°.  By definition a 60° offset from the vertical is considered as horizontal.

To clearly see that in your mind, you must understand the UPC meaning of vertical and offset. The code definition of vertical is a pipe or fitting that is installed in a true vertical position or that makes an angle of not more than 45° with true vertical.

The definition for an offset is a combination of elbows or bends that change the direction of a pipe and then returns it into a line parallel with the first direction. It ALWAYS requires at least two fittings. Using one fitting is a change of direction, not an offset.

There are several sections that allow multiple gas exhaust vents to combine. However there are varying requirements on the why and how. You may see the language “the effective area of the common vent connector or vent manifold and junction fittings shall be not less than the area of the larger vent connector plus 50% of the areas of smaller flue collar outlets.” What many people see is the word “diameter” instead of “area.” As such, if they were combining two 4” pipes, they size the common vent pipe at 6”
(4 + 2) when it should be five inches (12.664 in2 + 6.2832 in2 = 18.9472 in2). Area of a 5-inch pipe is 19.635 in2. The area of 6-inch pipe is 28.274 in2.

Will it pass inspection? Yes, but it is larger than required.

Also consider a gravity vent relies on adequate heat to lift the exhaust gasses upward. When the vent pipe is oversized it will likely take longer to heat up.


"This article was originally posted on ww.reevesjournal.com."