Hot water heater pressure relief valve extension pipe code

504.6 Requirements for discharge piping.

The discharge piping serving a pressure relief valve, temperature relief valve or combination thereof shall:

1.   Not be directly connected to the drainage system.

2.   Discharge through an air gap located in the same room as the water heater.

3.   Not be smaller than the diameter of the outlet of the valve served and shall discharge full size to the air gap.

4.   Serve a single relief device and shall not connect to piping serving any other relief device or equipment.

5.   Discharge in a manner that does not cause personal injury or structural damage.

6.   Discharge to a termination point that is readily observable by the building occupants.

8.   Be installed so as to flow by gravity.

9.   Not terminate more than 6 inches (152 mm) above the floor or waste receptor.

10.   Not have a threaded connection at the end of such piping.

11.   Not have valves or tee fittings.

12.   Be constructed of those materials listed in Section 605.4 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.

Consequently, Code Section 3303.3[i] dictates that a TPR valve must discharge once the pressure inside the tank reaches 150 psi (pounds per square inch).  Code Section 3303.4[ii] specifies that the TPR valve must be installed within the top 6 inches of the water heater tank in order to enable the valve to discharge at a temperature of no greater than 210�F.  As a result, any discharge piping must be rated to withstand at least 210�F to prevent melting and blockage of the TPR valve when discharged.    

Common Violations in the Field

As we have seen, the presence of a functioning Temperature/Pressure Relief (TPR) Valve on a water heater is extremely important.  However, there are other factors to consider in ensuring the protection of property and people who may be standing near the water heater when the valve actually discharges.  Namely, where does the scalding water or steam go once the valve is allowed to discharge? 

The following are the more common discharge piping violations we observe in the field:

1)  Improperly-Sized Discharge Pipe

Code Section 3303.6.1.[i] requires that the TPR valve is fitted with a discharge pipe that provides the same size opening as the valve outlet itself.   Figure 2 (right) shows a TPR Valve that has been fitted with a discharge pipe that is smaller than the size of the valve outlet.  This is a common defect that is strictly prohibited because smaller discharge pipes restrict the flow of the pressurized water released by the valve. This creates a dangerous bottleneck, building-up even more pressure at the point of discharge that can cause the tank to explode.  Personal injury (or death) and property damage may result.

Hot water heater pressure relief valve extension pipe code

2)  Missing Discharge Pipe

In many instances, the discharge pipe required in Section 3303.6.1.[i] was never installed at all.  This normally occurs during replacement or initial installation of the water heater.

Figure 3 (right), shows a missing TPR discharge pipe.  This creates a dangerous condition whereby the TPR valve will spray scalding steam or scalding hot water onto anyone (or anything) that happens to be near the water heater when discharge occurs. 

When you consider that the TPR valve discharges water at 210� F., serious injury or property damage will result.

Hot water heater pressure relief valve extension pipe code

Figure 3 - Missing TPR Valve discharge pipe
 

3)  Improper Termination of the Discharge Pipe Ideally, the TPR valve discharge pipe will be vented to the outside of the building where the scalding water or steam can be discharged without posing a threat to people or property.   However, in many installations direct piping to the outside is not possible or is deemed to be too costly to provide.

Accordingly, Code Section 3303.6.1[i] does allow for the discharge pipe to terminate inside a receptacle (or spill pan) as long as an air gap is provided between the end of the discharge pipe and the top rim of the spill pan itself without creating a hazard or potential cause of damage.

This is clearly not the case in Figure 4 (right). Here we see the copper discharge pipe runs down the right hand side of the water heater tank to terminate into a metal spill pan below.  However, the problem lies in the fact that the end of this discharge pipe terminates below the upper rim of a shallow spill pan.

This installation of the discharge pipe poses several potential dangers. 

First, the discharge pipe may be able to siphon any liquid that may accumulate inside the pan. This is due to the fact that the end of the discharge pipe terminates below the top rim of the receptacle itself. Once siphoning occurs, the liquid (be it dirty water, household chemicals, oil, etc.) will be drawn back into the water heater tank, thereby contaminating the household drinking water supply.

Hot water heater pressure relief valve extension pipe code

While this occurrence is admittedly unlikely due to the fact that the TPR valve would have to fail (stay open) while a simultaneous drop in line pressure would create a siphon, the mechanical potential does exist for this contamination to occur.  Thus the air gap provision in the building code.

 &lt;/td&gt; &lt;td width="115"&gt;&lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;p class="MsoBodyText2"&gt;&lt;font face="Arial" size="2"&gt;&lt;span style="mso-bidi-font-size:10.0pt"&gt;Secondly, and even more likely, is the risk of personal injury when this TPR valve discharges.&lt;span style="mso-spacerun:yes;mso-bidi-font-size:10.0pt"&gt;&amp;nbsp; &lt;/span&gt;This is because the discharge pipe terminates into a spill pan that cannot safely catch the flow of water or steam during discharge.&lt;span style="mso-spacerun:yes;mso-bidi-font-size:10.0pt"&gt;&amp;nbsp; &lt;/span&gt;When you consider that the TPR valve discharges at 150 psi, which is five times greater than the force of your garden hose, the scalding water can strike the bottom of the shallow pan and spray out in all directions.&lt;/span&gt;&lt;/font&gt;&lt;/p&gt; &lt;font face="Arial" size="2"&gt;&lt;span style="mso-bidi-font-size:10.0pt;mso-fareast-font-family:Times New Roman;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA"&gt;Therefore, a deeper spill pan receptacle with adequate circumference would be advisable over the shallower, tightly-fitting spill pans commonly observed in the field.&lt;/span&gt;&lt;/font&gt;&lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td width="274" height="21" valign="top"&gt; &lt;/td&gt; &lt;td width="251" height="21" valign="top"&gt;&lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td width="274" valign="top"&gt; &lt;p class="MsoBodyText2"&gt;&lt;font face="Arial" size="2"&gt;&lt;span style="mso-bidi-font-size:10.0pt"&gt;&lt;b&gt;Figure 5 (right)&lt;/b&gt;, shows a spill pan that tightly fits the base of a water heater. Unfortunately, such an installation accomplishes little in the way of catching water or steam from the TPR safety discharge valve, rendering the spill pan useless.&lt;/span&gt;&lt;/font&gt;&lt;/p&gt; &lt;font face="Arial" size="2"&gt;&lt;span style="mso-bidi-font-size:10.0pt;mso-fareast-font-family:Times New Roman;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA"&gt;Spill pan installations depicted in this photograph are common in condominiums and some residential homes where space is a premium.&lt;/span&gt;&lt;/font&gt;&lt;/td&gt; &lt;td width="251" valign="top"&gt; &lt;p align="center"&gt;&lt;a target="_blank" href="http://www.myguardian.com/code/tpr/Fig5_SpillPan.jpg"&gt;&lt;img border="0" src="http://www.myguardian.com/code/tpr/Fig5_SpillPan_small.jpg" alt="Fig5_SpillPan.jpg (249239 bytes)" width="174" height="158"&gt;&lt;/a&gt;&lt;/p&gt; &lt;/td&gt;&lt;/tr&gt;&lt;/center&gt; &lt;div align="left"&gt; &lt;table border="0" cellpadding="0" cellspacing="0" width="223"&gt; &lt;tr&gt; &lt;td width="36"&gt;&lt;/td&gt; &lt;td width="183"&gt;&lt;font face="Arial" size="2"&gt;&lt;span style="mso-bidi-font-size:10.0pt"&gt;&lt;b&gt;Figure 5 - Inadequate Water Heater Spill Pan Sizing&lt;/b&gt;&lt;/span&gt;&lt;/font&gt;&lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td width="36"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="183"&gt;&lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;/div&gt; &lt;center&gt; &lt;tr&gt; &lt;td width="525" height="171" valign="top" colspan="2"&gt; &lt;p class="MsoBodyText2"&gt;&lt;script type="text/javascript"&gt;&lt;!-- google_ad_client = "pub-8687664898799764"; /* TPR Article, 468x60, Banner */ google_ad_slot = "0642714041"; google_ad_width = 468; google_ad_height = 60; //--&gt; <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js">

Summary

As we have seen, the Temperature/Pressure Relief (TPR) Valve serves an extremely important function – ensuring the safe and proper operation of the water heater.  As professional home and commercial property inspectors, we frequently observe the code violations discussed in this article and encourage property owners and inspection professionals to take the time and effort to identify and correct them. 

Consequently, the conditions presented in this article should be corrected immediately by a qualified and licensed contractor.

Please Contact Us

If you have any questions, comments or suggestions regarding the information presented in this article, or if you would like to schedule an inspection of your property to identify these and other common property defects, please feel free to contact us directly:

Guardian Inspection & Information Services

E-mail

World Wide Web

www.myguardian.com

Telephone

321.639.2743

Facsimile

321.636.6377

Address

Guardian Inspection & Information Services
113 Tropic Place
Rockledge, FL 32955

End Notes
[1] International One- and Two-Family Dwelling Code™ 1998, Copyright � 2000 by International Code Council, Inc. Published in cooperation with: Building Officials and Code Administrators International, Inc., International conference of Building Officials and Southern Building Code Congress International, Inc., Incorporated the provisions of the 1995 edition of the CABO One and Two Family Dwelling Code Promulgated by the council of American Building Officials (CABO).

NOTICE:  The information presented in this article is intended for educational purposes only.  It is not intended to identify or predict all the potential defects or conditions that may exist and be considered for a complete analysis of a given property. 

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Hot water heater pressure relief valve extension pipe code

What is code for water heater pressure relief valve?

504.4 Relief valve. All storage water heaters operating above atmospheric pressure shall be provided with an approved, self-closing (levered) pressure relief valve and temperature relief valve or combination thereof. The relief valve shall conform to ANSI Z21. 22.

Can a TPR valve pipe go up?

TPR Valve Discharge Tube Piped "UP": the drain line must never be piped upwards in any of its course. The hazard is that the drain can become blocked or that a small drip, representing an unsafe condition at the T&P valve, may be hidden as the water simply accumulates in the bend of the trap or upwards piped section.

Can you use PVC for water heater pressure relief valve?

be constructed of an approved material, such as CPVC, copper, polyethylene, galvanized steel, polypropylene, or stainless steel. PVC and other non-approved plastics should not be used since they can easily melt. not be smaller than the diameter of the outlet of the valve it serves (usually no smaller than 3/4").

What is a water heater extension pipe?

That pipe is an extension designed to discharge hot water when temps or pressure build. Pipe extensions should be terminated within 6″ of the floor. If they're too high, water will splash; if they're too close to the ground, water will splash.