Popoff Drain Length?

[Linda Swearingen]

Is there a maximum on the length of drain allowed for a water heater pop-off valve? I couldn't find anything stating a distance limit on the water heater instructions, just a requirement to allow plenty of flow. There were only 2 elbows (a 90 just below the floor and one after exiting the crawl space wall) and no reduction in diameter, but no increase, either, and the run was over 30' before exiting the crawl space.

[James Duffin]

One thing I don't see mentioned in your description is the air gap in the room the heater is in. If the relief valve discharge is not in the same room as the heater there needs to be an air gap in the room before it leaves the room.


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 either on the floor into an indirect
waste receptor or outdoors.

[Brandon Whitmore]

One thing I don't see mentioned in your description is the air gap in the room the heater is in. If the relief valve discharge is not in the same room as the heater there needs to be an air gap in the room before it leaves the room.

Depends on where Linda lives. An air gap is not required in OR.

[James Duffin]

Very true....I normally include "in NC" but I forgot this time. Thanks for the clarification.

[Gunnar Alquist]

Is there a maximum on the length of drain allowed for a water heater pop-off valve? I couldn't find anything stating a distance limit on the water heater instructions, just a requirement to allow plenty of flow. There were only 2 elbows (a 90 just below the floor and one after exiting the crawl space wall) and no reduction in diameter, but no increase, either, and the run was over 30' before exiting the crawl space.

Linda,

Filling-out your profile to at least include your location can help us answer your questions better. Please do so at your earliest convenience.

I have not been able to find any specific maximum length in the IRC (2803.6.1); however, my Code Check it states 30 feet max, but refers to the manufacturer (presumably of the water heater).

[Jerry Peck]

however, my Code Check it states 30 feet max, but refers to the manufacturer (presumably of the water heater).

The T&P relief valve manufacturer, typically Watts. The maximum length is 30 feet with 4 elbows maximum.

That is even applies for states where the discharge is required to be in the same room or space as the water heater (i.e., such as a garage, the water heater could be in one corner and the T&P relief valve discharge could be at the opposite corner ... as long as the length was less than 30 feet and there were no more than 4 elbows.

Keep in mind that "elbows" is not just 90 degree elbows, but includes 45 degree elbows, this is because a change in direction like that creates a back pressure resistance to the flow of the water, and the manufacturers do not want any pressure resistance, they want open to atmosphere discharge in as short a distance as possible.

[Linda Swearingen]

Thank you to all of you. I believe I'll drop by the house and pace off the length (I can do that from outside). As it happens, I'm prohibited from quoting code here in KY, but I'm still able to note that type of problem as being a safety or fire issue. Yes, even 45's are elbows, but this one happens to have the pair of 90's.

[Jerry Peck]

I'm prohibited from quoting code here in KY,


Are you prohibited from quoting manufacturer's installation instructions? :)

[Rick Cantrell]

Are you prohibited from quoting manufacturer's installation instructions?

Good point.