Do you allow the TPR to discharge into the WH pan?

[Michael R. Boyett]

Chuck's right, the 2006 IRC (not sure of other versions) states:

P2801.5 Required pan. Where water heaters or hot water storage
tanks are installed in locations where leakage of the tanks
or connections will cause damage, the tank or water heater
shall be installed in a galvanized steel pan having a minimum
thickness of 24 gage (0.016 inch) (0.4 mm) or other pans for
such use. Listed pans shall comply with CSA LC3.

Where leaks from a water heater or storage tank or the
associated connections will cause damage to the
structure, the tank must be installed in a drain pan. The
pan must be constructed of galvanized steel or other
material intended for such use. Where listed pans are
used they must conform to the requirements of CSA
LC3. Such a pan is intended to catch water from a
leaking tank, a leaking connection to the tank or condensate
from the tank. The relief valve discharge piping
is prohibited from terminating into such pan (see
Commentary Figure P2801.5). A 3/4-inch-diameter
(19.1 mm) pan drain is not capable of carrying the
pressurized discharge of the relief valve at full flow.
See Section P2803.6.1.

And the diagram shows:

[Ben J. Gromicko]

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[William J. Decker]

I see this all the time, and I call it out.

There is a problem here with understanding the concept, even for plumbers.

The TPR valve is NOT a water drainage device, although many people, including plumbers, think it is. It is a STEAM drainage device. When those things let loose, what comes out is not water, it is live steam. The reason for the pipe is to have the steam discharge spray on the floor or some other place where it will not hit human beings.

If the pipe "drains" into the pan, it will splash up and scald a person. The amount and flow rate of the discharge is also more than the pan can handle.

Hope this helps;

[Michael Larson]

Originally Posted by wdecker

I see this all the time, and I call it out.

There is a problem here with understanding the concept, even for plumbers.

The TPR valve is NOT a water drainage device, although many people, including plumbers, think it is. It is a STEAM drainage device. When those things let loose, what comes out is not water, it is live steam. The reason for the pipe is to have the steam discharge spray on the floor or some other place where it will not hit human beings.

If the pipe "drains" into the pan, it will splash up and scald a person. The amount and flow rate of the discharge is also more than the pan can handle.

Hope this helps;

Here we go again.

Please explain to us how 210 deg. water is steam.

[William J. Decker]

Originally Posted by mlarson

Here we go again.

Please explain to us how 210 deg. water is steam.

Under pressure. 210 degrees, under pressure, and then it hits normal pressure and flashes to steam.

Hope this helps;

[Michael Larson]

Originally Posted by wdecker

Under pressure. 210 degrees, under pressure, and then it hits normal pressure and flashes to steam.

Hope this helps;

Not at normal pressures with no head space.

[Bruce A. King]

For those that consider the 3/4 drain pipe improper, would you like it if it had a 1" drain pipe off the water heater safety pan?

[Rick Maday]

Originally Posted by wdecker

I see this all the time, and I call it out.

There is a problem here with understanding the concept, even for plumbers.

The TPR valve is NOT a water drainage device, although many people, including plumbers, think it is. It is a STEAM drainage device. When those things let loose, what comes out is not water, it is live steam. The reason for the pipe is to have the steam discharge spray on the floor or some other place where it will not hit human beings.

If the pipe "drains" into the pan, it will splash up and scald a person. The amount and flow rate of the discharge is also more than the pan can handle.

Hope this helps;

Seems the pan would be irrelevant when steam comes out.

[Rick Maday]

http://www.ilga.gov/commission/jcar/...00I12300R.html

Originally Posted by IL plumbing code

Relief Discharge Outlet.

1) A relief discharge outlet shall be indirectly connected to waste. The discharge pipe from the relief valve shall not be located so as to create a safety hazard or to discharge in such a way as to cause damage to the building or its contents. The relief valve shall not discharge through a wall into the outside atmosphere or where there is a possibility of freezing.

2) No reduced coupling, valve or any other restriction shall be installed in the discharge line of any relief valve that would impede the flow of discharge. The discharge line shall be installed from the relief valve to within 6 inches of the floor or receptor and the end of such line shall not be threaded.

3) Any piping used for discharge from the relief valve shall be of metallic material and conform with the requirements of Appendix A, Table A (Approved Materials for Water Distribution Pipe) for potable water piping and shall drain continuously downward to the outlet.

4) The discharge piping shall discharge indirectly into a floor drain, hub drain, service sink, sump or a trapped and vented P-trap which is located in the same room as the water heater. (See Sections 890.1010 and 890.1050(a), (b) and (c).) The trap must have a deep seal to protect against evaporation or shall be fed by means of a priming device designed and installed for that purpose. (The use of a light grade oil in the trap will retard evaporation.)

[Brian E. Kelly]

Originally Posted by rmaday

Seems the pan would be irrelevant when steam comes out.

Very unlikely comming out af a WATER heater, now a boiler is a different story.

[ccurrins]

Steam or water?


How it Works:
Water boils at 212° F when at sea level or under 14.7 psi of pressure, however, the boiling point increases when under pressure, which allows the water to superheat beyond 212° F. Typical residential water pressure ranges between 40 and 80 psi and at 50 psi, the water can reach 300° F.


Superheated water (now significantly above 212°F) would immediately return to atmospheric pressure (the boiling point of water is 212°F) and flash into steam, causing a sudden increase in volume and release of energy.


If the water in a water heater reaches a temperature of 210°F (before superheating occurs) or the water pressure exceeds 150 psi, the TPR valve will open and release the overheated water. This will allow cold water to enter, lowering the temperature of the water in the tank and consequently the water pressure. The valve will remain open as long as the temperature or pressure exceeds the preset limit.


If the TPR is functioning correctly it will discharge water. If it malfunctions and waits until the water has converted to steam you'll probably have an airborne water heater.

[Michael Larson]

If the TPR is functioning correctly it will discharge water. If it malfunctions and waits until the water has converted to steam you'll probably have an airborne water heater.

Exactly Chris,

Thank you for finding that.

[Jonathan T. Hittle]

This is a Code question that depends on your local plumbing code. Here it is acceptable. You must be able to see the air gap so that you know that there is a problem. Also many manufactures suggests that you test your TPRV yearly but we all know that they will stick on!

[Joe Funderburk, CMI]

What about this setup, from today's inspection. How is this different from going directly to the pan???

[Chuck Evans]

Originally Posted by jfunderburk

What about this setup, from today's inspection. How is this different from going directly to the pan???


Attachment 29022 Attachment 29023

That is also a defect as it is not piped separately - write it up