Where is Hose Allowance for Combined System?

4/30/2026

When hose allowance is added to the sprinkler demand on a Class III Standpipe/Sprinkler wet riser, where on the system are the inside and outside flow and pressure allowances input when calculating the system?

NFPA 13 Chapter 19 states that the allowances are not required when calculating a combined system, which appears to contradict NFPA 14 requirements to include them.

In my case, the sprinkler demand is for OH2 (ceiling higher than 40 ft), resulting in a sprinkler demand plus hose allowance that is greater than the standpipe demand.

If I don’t include hose allowance in the sprinkler calculation as per Chapter 19, this combined system is not equivalent and robust as two independent systems. Any thoughts?

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3 Comments

Glenn Berger

4/30/2026 08:22:03 am

The NFPA 13 calculations requires adding its version of hose allowance into the system at various points at the discretion of the system designer/engineer.

The NFPA 14 calcs have their own rules for where flow must be included.

You are not required to combine the NFPA 13 and the NFPA 14 calculations. Depending on your system arrangement, NFPA 14 will dictate the size of your risers in a combined system.

Michael Tapuska

4/30/2026 10:56:41 am

In my case NFPA 13 is a more onerous flow requirement than NFPA 14.

Dan Wilder

4/30/2026 08:55:01 am

So NFPA 13 - 2022

19.1.6.2 - Outside hose is added and the connection to a city main or a fire hydrant, whichever is closer.

19.1.6.3.1 - No inside hose allowance is required within a fully sprinklered building.

Hose allowance is still required, where you put the allowance is the defining change in the sections above.

NFPA 14 - 2024 Edition

10.6.1.3
The wording says "...the water supply..." so while you're not needing to calculate inside hose with the sprinkler system, either the flow test results and/or the fire pump need to accommodate the higher of the two requirements (standpipe or sprinkler demand). By proving the individual calcs within 13 & 14, you're proving the water supply and the intent of this section is to direct the designer to calculate the worst case first

From LiNK insights: In most cases, the standpipe system demand will be much greater than the sprinkler demand. Therefore, the standpipe system demand should be calculated first to establish the appropriate size of the feed main piping and stationary fire pump.

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Where is Hose Allowance for Combined System?

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