Use Fire Pump Test in Lieu of Flow Test for Calcs?

4/1/2026

Can a fire pump test report be used in place of a hydrant flow test?

For an existing building, a fire pump flow test has to be done annually. It should include all the information a hydrant flow test provides to perform a hydraulic calculation for an existing building modification.

Is there any code basis for taking this approach?

I have an AHJ that keeps pushing back on this approach for determining the water supply information.

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17 Comments

Pete H

4/1/2026 06:19:02 am

It depends on AHJ.

But in most AHJ's I have seen: yes, it is acceptable (provided the pump test is within a year).

The best code reference I can scrape up in five minutes of research is A4.2(4) and 4.2(4) and Chapter 5 of NFPA 13 (2025 Ed.)

Basically the code refers to flow test information as one of (undefined) possible "approved methods" of obtaining water supply information.

It is weird that a pump test is an approved method for 99% of AHJ's in the country and you found the 1%, but if you did find the pump characteristic information and have a hydrant flow test, you should be able to enter both into your calculation.

Dan Wilder

4/1/2026 07:47:49 am

Can it be used, yes as it is listed in Chapter 5 as an acceptable source and I to have used the info for submittals.

Is it an accurate representation of the water supply, no because there is a municipal water supply (assumed) providing flow and pressure. It will also only provide a finite GPM range based on the capacity of the fire pump and the PSI loss across that limited GPM segment. It is likely a more restrictive path and would provide a higher margin of safety however that doesn't translate as an acceptable water supply in some cases (or some people).

Glenn Berger

4/1/2026 08:09:19 am

If this was my project - A hydrant flow test and a pump test would be required.

Josh

4/1/2026 10:05:05 am

Ha, I always come to the forum posts to see "what does Glenn say?" because as an FPE, I find we speak a very similar language on most all issues, but you have more experience so there's insight in a lot of the comments.

Joe

4/1/2026 11:33:02 am

Would you also require excavation and mapping of the underground? As-builts are almost never available or accurate if they are.

In your pursuit of accuracy you are adding unknow variables.

Jose R Figueroa

4/1/2026 11:49:12 am

Joe, that's a tough requirement. I have done it occasionally during my days in Europe and Latin America. It always depended on the client or underwriter’s request for high-value or strategic occupancies. It's a pain in the neck to organize such an endeavor.

Josh

4/2/2026 09:21:25 am

this is a great point. Once NFPA 24 hits at the public, I've found the underground is rarely accurate. Aboveground being inaccurate where it can be traced visually is one thing, but the UG being who knows what is sometimes terrifying that nobody seems to know for sure!

Jesse

4/1/2026 08:11:32 am

I'm with Dan and Glenn here. It can be used, but if it were my project with my stamp on it, I would require a hydrant flow test.

Ivan Humberson

4/1/2026 08:25:06 am

IMHO, for an existing building, a flow test of a hydrant in the vicinity of the building is not as accurate as a fire pump test inside the building. The existing fire main supplying the building likely has corrosion and tuberculation that would change the hydraulic flow characteristics from what would be expected for new pipe. I maintain that, for an existing building, the only way to accurately know what the available water supply will be to the base of the sprinkler riser is to flow test the underground pipe. The fire pump flow test would be a good representation of that available supply. (Just don't forget to adjust for variations in the available supply based on the water purveyor's data.)

4/1/2026 08:59:58 am

A fire pump would have far more accurate results than a hydrant flow test in my opinion. However, as you may be aware listed gauges are not calibrated or liquid filled so unless the inspector performing the test is replacing the gauges on the fire pump suction and discharge to be liquid filled and calibrated for the test, you can argue the results may not be as accurate. The pitot gauges being used to measure the flow would likely be liquid filled calibrated gauges.

In a perfect world you would get both a fire pump and hydrant flow test, however if I could only get one, I would want the fire pump flow test since it includes the data from the water supply and the fire pump performance which can degrade over time. Also, depending on the fire pump size, 6 hose valves with playpipes measuring the flow versus two hydrant butts, I will trust the fire pump test header. Realistically if you plot the suction side pressures against the pump flows you should get something close to the hydrant test, with the exception of the friction loss from the underground piping from the road to the building. I have performed this exercise when our fire pumps are commissioned with a full fire pump flow and the results are very close. On the last couple we have commissioned, our fire pump flow test is within 1 psi of our theoretical fire pump performance + the hydrant flow test.

In fact, I would argue there is usually extra safety factor since if we use a fire pump test curve, we have to start at the fire pump discharge flange. Therefore, all hose allowance must be applied at the discharge flange, rather than at the nearest hydrant or roadway connection to underground water main.

Jose R Figueroa

4/1/2026 10:34:47 am

In my days as a field engineer, I often used the nominal pump performance curve because sometimes conducting a pump flow test isn't possible for various reasons. I always took 10% of the nominal curve as a safety margin.

Taylor Jenkins

4/1/2026 10:42:44 am

While a hydrant flow test is an accurate representation of what is available in the municipal water main, a current fire pump test is far more accurate in showing you what you actually have coming into the building. Assuming that the pump test was performed correctly with new gauges, the results will indicate any losses in the suction line from the water main to the pump suction which you can't otherwise approximate accurately.

For instance, we had an existing building with a fire pump that had not been tested recently. A flow test was performed and showed plenty of water for the design task inside the building. Then, the pump test was performed only to find out that the suction line coming in from the street was obstructed to a point that dropped the suction to the pump below 20 PSI during the test.

We now require forward-flow tests on all existing systems before performing designs. I've had three recent projects where the available flow and pressure at the riser was far less than what the flow test indicated out in the street.

Joe Meyer

4/1/2026 10:45:30 am

Even without a fire pump, I've had this happen on a project too.

Water supply at the street was fine (what we expected). Static riser pressure was fine. Main drain test was what it was (initial acceptance testing).

But once we did the forward flow, we hardly had anything. Turned out the building's supply tap was only partially made and was 80%+ obstructed.

We would have never known had we not conducted the forward flow test.

Jesse

4/1/2026 02:31:16 pm

Joe I had a similar situation in my Loss Control days surveying a furniture warehouse in Denver. Completed the survey and got the flow test. When I put it all together and calc'd the AS systems with the pump, it wasn't working. It was hydraulically inadequate. The underwriter freaked out and was going to bail on the policy. Turns out that a month or 2 before my visit, utility work had been done and the local utility left a valve closed on the public side. This made the difference between hydraulic adaquecy and not. But we wouldn't have know if we didn't get the flow test.

danefre

4/1/2026 11:29:07 am

One of the reasons we were pushed to do hydrant flow tests on pump jobs is to include the outside hose allowance. Depending on the software, there are some creative ways to include that but it's still getting called out regularly. The outside hose allowance SHOULD affect the net pump curve logically.

Jack G

4/1/2026 05:31:58 pm

Calibrated gauges are required in the 3 states around me for fire pump tests and hydrant flow tests.
Yes. Fire pump test with calibrated gauges is acceptable.
All municipalities around me require a hydrant flow test also.
So combining the 2 should be easy, except paying for the hydrant flow tests.
( hydrant flow tests can indicate open, closed valves from when the fire pump test was made due to replacement/ upgrading water lines) example— shutting down a main feeding city mains feeding pumps -freeze ups, repairs, to multiple buildings - cutting the supply to pumps , could cavitate.)
I ve made myself rules thru the years—--
Before testing the pump ( pump on ) I test the city only to ensure the pump won’t be affected. 60% of the time there is a closed city valve).

Use Fire Pump Test in Lieu of Flow Test for Calcs?

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