Why Not Hard Pipe Sprinkler Drain to Sewer?

8/6/2020

I'm interested in hard piping the sprinkler system drain down pipe into the 6" sewer via a closed system.

My inspector can't tell me why I can't and says I need to build a 4" stand pipe with a wet trap. This will use a lot of water throughout the years just to keep the trap wet and will only be used once a year.

Why can't I hard pipe the drain into waste and avoid the air gap with a wet trap?

I would welcome any comments from anyone.

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11 Comments

Jonathan Sullivan

8/6/2020 10:25:53 am

The plumbing code won't allow a direct connection to the drain. This is another layer of backflow prevention.

This type of discharge is an indirect waste and requires an air gap or air break depending on how it is classified, ie potable or non-potable.

This must discharge into a waste receptor (floor drain, sump, mop sink, etc) that has a wet trap.

You then have two options to protect the trap as it won't be used often, either a trap seal or a trap primer.

See IPC 802 for indirect waste requirements and 1002.4.1 for trap seal protection.

Don't forget you also need fixture venting.

Matt Cornell

8/6/2020 10:57:30 am

Mr. Sullivan is absolutely correct. If you are wanting to conserve water the mechanical seal is best. Take a look at the Sure Seal by Rectorseal SS2009V

Jonathan Sullivan

8/6/2020 11:16:54 am

Thanks Matt. I too prefer an seal, less moving parts. Just make sure it's ASSE 1072 conforming.

And if permitted a bit of mineral oil.

Brian Gerdwagen FPE

8/6/2020 11:00:07 am

There are two problems I have encountered:
1 - Local water company wants the sprinkler to drain to storm since the water is unmetered and they do not get revenue to pay for the cost of treating it.
2 - Local water company cares about the environment and wants to treat the water instead of dumping it in the storm water flow, so it needs to go to sanitary.

Either option should have an airgap so that pressure does not build up and sprinkler water flows out of the air vents elsewhere in the building. I would never use a wet trap. If a trap is used, a mechanical trap seal would be my recommendation.

Glenn S Berger

8/6/2020 11:46:41 am

Agree with Mr. Sullivan, having the air gap also gives you visual indication that the system is draining. I do not recommend discharging over a flat floor drain, provide funnel drain connection and locate where tripping can be minimized.

Sue

8/6/2020 02:38:31 pm

Where I work, the only places you can discharge a fire sprinkler system is into a landscaped area, an approved bio-swale with erosion protection or to sanitary with the approval of the Sanitary agency. We are no longer allowed to flow directly to storm because of the issues of pollution. When going into the sanitary system it has to be with an air gap or a wet trap. The flow of the fire sprinkler system must be taken into consideration when using an air gap because they can splash all over the room.

Jonathan Sullivan

8/7/2020 06:51:17 am

Sue - what jurisdiction is this? What specific pollution issues are encountered here? Is the sanitary system also overwhelmed?

Mike

8/7/2020 09:41:09 am

Wet traps stop sewer vapors from entering the building.

Have never seen a hard piped drain before in the manner you describe.

TBO designing a drain connection is really out of your scope as a fire sprinkler technician. This would be the mechanical or plumbing engineers responsiblility.

Brad K

8/7/2020 10:39:29 am

System drain connection are the sprinkler design responsibility as pertains to NFPA 13-8.16.2.4...and on.
Also 8.16.2.6.1 (2010-16) prohibits this connection specifically.
see also 8.16.2.6.2

Things to consider for system drains:
-Main drain tests and inspector tests can be overwhelming for some plumbing due to pressures and flows involved.
-Visual confirmation of drain water is typically preferred for system testing and service.

Chris link

6/18/2024 05:38:05 am

Choosing not to hard pipe the sprinkler drain to the sewer makes a lot of sense. While it might seem like a convenient solution, it could pose significant environmental and regulatory challenges down the line. By opting for a more sustainable approach, such as directing the sprinkler drain to an appropriate drainage system or a separate holding tank, you're not only adhering to environmental guidelines but also ensuring long-term compliance and efficiency. It's great to see proactive decisions being made in fire safety that consider broader environmental impacts

Sean

10/16/2025 10:11:13 am

NFPA 13 (2016 edition), Section 8.16.2.6.1:
"Direct interconnections shall not be made between sprinkler drains and sewers."
Appendix 8.16.2.6.1: "Where possible, the main sprinkler riser drain should discharge outside the building at a point free from the possibility of causing water damage. Where it is not possible to discharge outside the building wall, the drain should be piped to a sump, which in turn should discharge by gravity or be pumped to a wastewater drain or sewer."
8.16.2.6.2 "The drain discharge shall conform to any health or water department regulations."

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Why Not Hard Pipe Sprinkler Drain to Sewer?

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