Thread: TPR discharge line

I can't find this anywhere. I find code requirements but none that mention what is the maximum length of a water heater TPR discharge line. It seems to me that if the line was too long the TPR could not discharge properly. I appreciate any advice.
This is IRC code:

IRC 2803.6.1 / UPC 608.5

Requirements for discharge pipe. The discharge piping serving a pressure relief valve, temperature-relief valve or combination valve shall:
1. Not be directly connector the 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 to the floor, to an indirect waste receptor or to the outdoors. Where discharing to the outdoors in areas subject to freezing, discharge piping shall be first piped to an indirect waste receptor through an air gap located in a conditioned area.
6. Discharge in a manner that does not cause personal injury or structural damage.
7. Discharge to a termination point that is readily observable by the building occupants.
8. Not be trapped.
9. Be installed to flow by gravity
10. Not terminate more that 6 inches above the floor or waste receptor.
11. Not have a threaded connection at the end of the piping.
12. Not have valves or tee fittings.
13. Be constructed of those materials listed in section P2904.5 or material tested, rated, and approved for such use in accordance with ASME a1132.2.4.1.

9. Be installed to flow by gravity

Originally Posted by Billy Stephens

9. Be installed to flow by gravity

That still doesn't address maximum length. I know a lot of this is common sense but I saw an exceptionally long line at my inspection yesterday. I would say it was 30 feet. I did not meet #7. Discharge to a termination point that is readily observable by the building occupants. But I am curious if this (max length) is specifically addressed anywhere.

Originally Posted by Tom Rees

That still doesn't address maximum length. I know a lot of this is common sense but I saw an exceptionally long line at my inspection yesterday. I would say it was 30 feet. I did not meet #7. Discharge to a termination point that is readily observable by the building occupants. But I am curious if this (max length) is specifically addressed anywhere.

If a drain is installed to flow by gravity it would not matter how long it is.
* I'm not aware of any max length.

Originally Posted by Tom Rees

I can't find this anywhere. I find code requirements but none that mention what is the maximum length of a water heater TPR discharge line. It seems to me that if the line was too long the TPR could not discharge properly. I appreciate any advice.
This is IRC code:

IRC 2803.6.1 / UPC 608.5

Requirements for discharge pipe. The discharge piping serving a pressure relief valve, temperature-relief valve or combination valve shall:
1. Not be directly connector the 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 to the floor, to an indirect waste receptor or to the outdoors. Where discharing to the outdoors in areas subject to freezing, discharge piping shall be first piped to an indirect waste receptor through an air gap located in a conditioned area.
6. Discharge in a manner that does not cause personal injury or structural damage.
7. Discharge to a termination point that is readily observable by the building occupants.
8. Not be trapped.
9. Be installed to flow by gravity
10. Not terminate more that 6 inches above the floor or waste receptor.
11. Not have a threaded connection at the end of the piping.
12. Not have valves or tee fittings.
13. Be constructed of those materials listed in section P2904.5 or material tested, rated, and approved for such use in accordance with ASME a1132.2.4.1.

I would say that you are correct. At some point line length could be a factor. At what point I could not say. My guess is that 30 feet may still be ok, but I would report this as a potential hazard.

Originally Posted by Mark Reinmiller

I would say that you are correct. At some point line length could be a factor. At what point I could not say. My guess is that 30 feet may still be ok, but I would report this as a potential hazard.

Length of the discharge is not an issue.
Does not seem to be a code violation.
Why do you (or Tom) think it would be a hazard?

It was 30' away but still in the same room?
2. Discharge through an air gap located in the same room as the water heater.

There was quite a few reasons it was installed wrong which I wrote up, it just got me thinking if there was a maximum length. My reasoning is this: If the line was so long that it became difficult for the TPR to discharge as it was designed.

Originally Posted by Tom Rees

There was quite a few reasons it was installed wrong which I wrote up, it just got me thinking if there was a maximum length. My reasoning is this: If the line was so long that it became difficult for the TPR to discharge as it was designed.

The first question would be how fast would the internal pressure of the tank have to rise to exceed the capabilities of the TPR to relieve the pressure at maximum discharge volume.

Then a second question would be the friction over the distance that would restrict the flow as to increase discharge pressure.

From the Watts web site "WARNING: To avoid water damage or scalding due to valve operation, discharge line must be connected to valve outlet and run to a safe place of disposal. Discharge line must be as short as possible and be the same size as the valve discharge connection throughout its entire length. Discharge line must pitch downward from the valve and terminate at least 6" (152mm) above a drain where any discharge will be clearly visible. The discharge line shall terminate plain, not threaded. Discharge line material must conform to local plumbing codes or ASME requirements. Excessive length over 30' (9.14m), or use of more than four elbows or reducing discharge line size will cause a restriction and reduce the discharge capacity of the valve."

same reply from...

Hi Barry:

The statement that “anything over 30 feet of pipe, or more than 4 elbows, will restrict the capacity of the relief valve”, is a long-held engineering policy. We would be reluctant to qualify this regardless of pipe size or type.


Thanks,

CASH ACME

Technical Support

Division of the Reliance Worldwide Corporation

2400 Trade Drive S.W.

Cullman, AL 35055

Phone: (256)775-8179

in this instance plumber said increasing the size of discharge pipe would allow for over 40' and 7-90s so did ahj

The restrictions as to length and number of bends is in the standard for the TPRV and a part of the listed instructions and warnings for same pertaining to the discharge of same. Unlike Minnie Pearl's Hats' price tags, or matress tags, the Warning tags on TPR Valves are not supposed to be removed! Dated by the installer and left in place for the occupant, service personel, etc.

Keep in mind the special discharge ends at the airgap/airbreak/exposure to atmosphere where equilibrium to atmosphere, release of energy (temperature & pressure) occurs. Thenceforth (following exposure to atmosphere/reduction of energy) it is DRAINAGE, although slightly special in the rules which may apply (such as location and visibility (to an alert, caring, responsibile occupant, etc.).

Thanks guys. I knew there had to be some restriction on length. I should have gone to the manufacturers site instead of code to begin with. I noticed the code I referenced does not address the elbows either. My next inspection I will get my glasses out and actually read the tag. Here is link to Watts: Temperature and Pressure (T&P) relief valves - Support - Water Safety & Flow Control -Watts

I do not see a restriction on length
Watts has information saying that excessive length over 30' reduces discharge capacity.
Note: Excessive= More than is necessary.
So another way to say it is:
More than is necessary length over 30' reduces discharge capacity.

Watts did not say, Length is restricted to not more than 30'

Watts information says to discharge "at least 6" above a drain".
However the codes says
" 10. Not terminate more than 6 inches (152 mm) abovethe floor or waste receptor"
Watts says, 6" or MORE, but the code says, 6" or LESS
Which one do you go by?


Cash Acme said " We would be reluctant to qualify this regardless of pipe size or type."
Reluctant to qualify, is not the same as saying, it's not allowed.

BTW
I'm sure Mr Watson knows this, I think he just mis-typed.
The pipe must discharge through an AIR GAP, not an AIR BREAK.
I only mention this because it may confuse someone.

Originally Posted by Garry Sorrells

The first question would be how fast would the internal pressure of the tank have to rise to exceed the capabilities of the TPR to relieve the pressure at maximum discharge volume.

Then a second question would be the friction over the distance that would restrict the flow as to increase discharge pressure.

Great thread, good discussions.

Just to add a little, if a 3/4" line were to flow say 10 GPM which is a lot for that size of line, the pressure required would be ~18 PSI over 100 LF. If a P and T were rated at 150 PSI the 18 lb drop would not affect the discharge all that much.

Just some hypothetical mind droppings.

I think the important points to convey to the client are:

1) This is a device to defuse a bomb inside your house.

2) You want to be absolutely sure the pipe is not blocked or restricted. Keep it where you can see it.

3) Any moisture coming from the end of the pipe is wrong, get it fixed.

4) If you can't see the end of the pipe, you will not know if moisture is coming out of it.