Use Main Drain for Forward-Flow? What to Test?

2/11/2025

Forward Flow Test Confusion... I have an NFPA 13R system built in 2013 that doesn't have any hose connection(s) for forward flow testing. The sprinkler contractor is saying they're unable to conduct the test.

I am attempting to understand the codes around this topic and ran into several questions.

First, NFPA 25: 2020 NFPA 25 13.7.2.3 states, "Where connections do not permit verification of the forward flow test at the minimum flow rate of system demand, tests shall be conducted at the maximum flow rate possible."

Can someone please explain what this means exactly?

My second question concerns using the main drain to conduct the forward flow test if it's sized appropriately. A previous Meyer Fire blog post, "Solutions for the Overlooked Forward Flow Test," Option 4, mentioned the 2016 NFPA 13 A8.16.2.4.2, but I cannot find that section in the 2019 version.

Has this method changed somehow?

Can the sprinkler contractor use the main drain as a means to conduct the forward flow test?

If so, what else does the AHJ need to know?

Calcs to prove drain size can flow system demand? Pitot reading?

Thank you for reading and I'd love to find some clarity.

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12 Comments

Dan Wilder

2/11/2025 08:02:42 am

Couple items:

NFPA 13R in 2013 did not have a requirement for forward flow testing of a backflow, that was added in 2016

If there is no means to forward flow test the backflow, any available means to test the backflow (i.e. main drain) shall be used and recorded.

The Annex section was incorrectly removed in the 2019 rewrite and then added back for the 2022 edition.

Yes, a contractor can (use main drain) to provided the results are documented and the test procedures are generally equal (for most of my local AHJ's). Use of a stream straightener is highly recommended. Calc's may get you close to a proof for equivalency but doing the test is still required so why waste the time?

If there is a large enough issue (AHJ or Insurance is pushing back on the lack of forward flow) just propose the addition of a couple mech tee's and some hose valves within the room or add a bypass at the FDC (if accessible) and this solves all those issues. Remember, the test is only for system demand and does not include hose allowance.

Anthony

2/11/2025 08:12:17 am

I agree with Dan here. There is no cause to update a system to allow for new testing requirements. Just use the main drain to prove the system is able to achieve full flow through the drain piping.

If I was a cynic, I'd say this is a someone looking for a billable deficiency.

Joe Meyer

2/11/2025 08:14:47 am

FWIW, I can validate that this is an AHJ asking for advice on how it's proven and not a sprinkler contractor. : )

2/11/2025 09:39:59 am

A curve at the riser can always be established with the K factor on the inspector's test and the static at the riser. This works best if there is a test and drain right at the riser. all you'd have to do is read the pressure gauge while the insp test is flowing and use the K factor formula to get your flow. it's not perfect but it's a start.

Brian

2/12/2025 04:39:12 pm

Thank you for the info and just wanted to ask one follow up question. The code says if there are no available test connections, then "tests shall be conducted at the maximum flow rate possible". Does this imply that if the main drain is unable to meet system demand, then no further action is needed as it was tested at the maximum possible flow rate?

Jonathan Griffin link

2/11/2025 09:47:32 am

One can also insert a Pitot at the 2" Main Drain outfall and obtain a reading... there is a chart available that provides GPM flow from a 2" pipe, as well as software that can provide flow from the 2" piping. (The NFPA 291 formula also works here).

Good Luck!

Chad

2/11/2025 12:01:12 pm

"Where connections do not permit verification of the forward flow test at the minimum flow rate of system demand, tests shall be conducted at the maximum flow rate possible."

On a 2013 13R that is going to be the main drain, unless there are standpipes/roof hydrant. They can run hoses outside off the standpipes.

Randy Kimbro

2/11/2025 01:08:46 pm

From an AHJ perspective, the spirit of the forward flow test is to annually exercise all backflow devices/valves to their full open position and ensure the water flowing can meet the GPM for the defined system demand as listed on the hydrostatic data plate. If there is no way to flow that amount of water (we have one riser in a basement that would require 3-400 feet of hose to reach the outside), the main drain can be used as a base measurement of GPM. Whatever test method is approved by the AHJ, it should be repeated the same way annually.

Our tests always include pitot readings which we record every year.

Although NFPA 13R did not include this until 2016 as Dan mentioned, NFPA 13 included this at least from 2007. Dan was incorrect on the hose allowance. NFPA 13 (2019 and 2022)
6.10.2.5.2 The minimum flow rate tested in 6.10.2.5.1 shall be the system demand, including hose stream demand where applicable.

Bottom line from an AHJ, we want to ensure annually, that the sprinkler system can supply the engineered GPM flow in case of a fire.

2/11/2025 04:54:27 pm

The question was a 13R system installed in 2013 and there is no provision in 13R through the 2025 edition to include hose stream, it only references "system demand". I didn't want to introduce extra info that can be confusing for the OP.

2/12/2025 04:45:13 pm

I appreciate the info. So if the main drain was not able to flow the system demand, could you then require test connections be added to provide verification of the flow?

Jeff Ayers

2/12/2025 10:44:54 am

A remote head test was used on one of my projects for the forward flow test. We actually removed the head and connected to the 1 1/4" branch line

But the option we chose on the next project (6 level Multi family Type IIIA with NFPA 13) was to use the roof FHV.

It was nearly as far (remote) as the most remote head, but it was at the highest elevation, providing a more stringent test.

Flowing water through a 2 1/2" FHV on the roof proved to be a very successful test.

Jack G

2/12/2025 05:20:26 pm

If you doubt that the test and drain and piping isn’t large enough to forward flow the 13r water requirement for the system just install a space for a “ test meter) that will actually measure the flow. Then return pipe you removed. (

Use Main Drain for Forward-Flow? What to Test?

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