Does a Hydrant Fed From Building Meet Code?

3/4/2025

My jurisdiction (I am the AHJ) has had several buildings built with private hydrants supplying the sprinkler system where the main comes into the building, through the RPZ, feeds the sprinkler system/standpipes, and leaves the building and feeds the hydrant(s).

This has always seemed counterintuitive to me, at best. I feel we are "robbing Peter to pay Paul" and have wondered if this arrangement will adequately supply the sprinkler system when we (FD) pull water from the hydrant and pump it back into the FDC.

Per our state law, private hydrants have to be "protected" with a backflow.

Is this configuration code compliant, and if not, what is a solution?

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14 Comments

Pete H

3/4/2025 06:34:32 am

It really should be fed off a bypass line instead of going through the double check for a cleaner install imo.... but as long as the hydrant can calculate the required water and meets code in every other way, a private hydrant can be fed from main that goes through a building.

And it's not exactly like it's terrible it goes through the double check, as there are private hydrants in some master-metered communities.

But as long as the hydrant has the required flow and pressure and the double check and internal piping (different c factor if applicable, elbows and tees, etc.) are included in the calculations, this isn't against code as far as I know. Warning/take with a grain of salt: I'm not specifically checking the code as much as I'm thinking of existing buildings where I've seen this before when saying this response.

Dan Wilder

3/4/2025 06:59:50 am

While not common, if calc's prove it works I see no code-based opposition. Review of the max flow through the backflow to confirm sprinkler and hydrant demand does not exceed the max flow (plan on one or several increases in sizing to accommodate max flow or valves in parallel).

In this setup though, the FDC is useless as it will just feed back out to hydrant in a loop (the red arrows illustrate this well). Using Pete's idea of a bypass prior to the backflow would solve the issue or there would need to be individual connections to systems, all with their own checks, to avoid recirculation. Alternate arrangement could have the feed to the hydrant come off right after the backflow, then through a check valve, then to the rest of the system and FDC (basically switch the hydrant & FDC lines and add a check valve. If the flow switch is needed for the hydrants, that would also need to be pulled back.

Mike Morey

3/4/2025 08:14:37 am

In the cases where we've done this we've ensured that there is still a city side hydrant near the FDC and only used it for hydrants beyond the pump/riser room. Large building loops are built this way all the time at spec/shell/warehouse buildings. Biggest issues are ensuring you can provide the required site fire flow or portion there of the AHJ wants from the hydrant(s) and accounting for the hydrants connection point as your hose stream demand point in the sprinkler calc.

Joe

3/4/2025 08:38:09 am

Not normal but you would have the same issue if after the back flow device you install underground piping with hydrants spaced per you code and then somewhere you have a leadin going into the build for the sprinkler systems

As other said check the cut sheet for the backflow, and make sure you have done a good flow test on the public water line. I always try to flow two 2 1/2 or one 4 AM inch outlet to stress the systems.

Casey Milhorn

3/4/2025 08:42:27 am

What Mike M said... typically I suggest a public hydrant as the hydrant used for the pumper truck. Also what Pete said, a bypass line WITHOUT a control valve would be best in my opinion. That way you still have hydrant flow if the backflow is out of commission and valves are closed off. It appears as if you might have a decent size building and I would be concerned that you would be able to meet your fire flow demand through that backflow, not to mention the amount of pressure loss across a RPZ will be considerable. With a 6" Wilkins 375, you are maxing out it's listing at 1,500 gpm. I would imagine your fire flow demand is at least 1,500 gpm.

Glenn Berger

3/4/2025 08:55:22 am

As long as the system supply can support the maximum expected flow through sprinklers and the exterior hose connections that the layout seems acceptable.

Many thoughtful responses have been provided to this question.

Anthony

3/4/2025 09:09:01 am

this appears to be legal with an RPDA/RPZ however, the calc's will get more difficult as the hose allowance will have to be take out after the water has passed by the supply for the sprinkler system. I think this may cause over sizing on the sprinkler system you'll want the hydrants that to tee off prior to the system supply.

DJT

3/4/2025 10:19:03 am

The hydrant supply needs to be separated from the FDC. As it's shown the FD pumper will circulate water from the hydrant and pump it back through the FDC as the arrows indicate. This risks checking the incoming water supply back until the sprinkler discharge drops the system pressure, rendering the FDC/pumper useless. The two solutions are either tee off to hydrant from upstream of the FDC tee while adding another check valve between the two connections, or move the FDC to tie into each riser above their check valves. Some problems don't have code justification.

Jack G

3/4/2025 10:56:00 am

First of all I would add an fdc check to each of the sprinkler systems and a check at the end of the manifold before the tee going to the hydrants. Then I d tie the checks into one fdc.
This way you avoid a ( loop ) between the hydrants and the fdc.
Language in 24 leads you to run 6 inch to 2 hydrants and 2 sprinkler systems but 8 inch to more systems.
I ve also run supplies to “ wall hydrants “ on the opposite walls of the building with wall post indicator valve to open and connect to the wall hydrant and avoid lots of underground piping if permitted by the AHJ.

Jack G

3/4/2025 11:02:28 am

And you could add an fdc to the far side of the building ( bulk and check) to use in combination with the wall hydrants and common fdc.
I also don’t like the rpz loss on the systems no matter which configuration, but if required, what can you do ?

Jack G

3/4/2025 11:06:10 am

I would also use OS&Y Valves on each side of the rpz with the appropriate tamper switch instead of the gate valves shown.

Jack G

3/4/2025 11:13:54 am

Of course the fdc shown would not be tied in where shown but after the 5 checks added ( tied into 1 fdc , and or another on far side of the building) and I d make the fdc a storz and or 6 inch fdc, for the hydrants .

3/4/2025 12:22:12 pm

DJT is correct. The current arrangement will not work. The fire hydrant supply has to be before the tee for the FDC with a check valve in between. Otherwise, the system will not pressurize appropriately since you are recirculating the flow.

Mark Harris

3/5/2025 03:18:54 pm

Great comments. Made me think about a distribution center that could have a booster pump or pump and tank fed from city supply with FDC on the pump house and as noted the pumper truck supply for FDC would need to be a supply hydrant before the pump house. Then could have private underground loop with private hydrants and supply into building for sprinkler risers.

Don't see much anymore but used to occasionally see wall hydrant connection on back of building with a wall PIV to control water supply. Sometimes to have fire water source for rail siding, idle exterior pallet storage or maybe truck trailers. But those days were not million square foot buildings with dock doors all the way down two sides so private underground fire loop with hydrants is more common today.

Does a Hydrant Fed From Building Meet Code?

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