Replace Old Sprinklers with Higher K-Factor?

2/12/2025

If the fire sprinklers for an entire area or building have to be replaced, such as if they are more than 50 years old, is there any problem or benefit (hydraulically) from increasing the replacement sprinklers to the next higher K-factor (e.g., K5.6 to K8.0 or K8.0 to K11.2), especially for production and storage areas?

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14 Comments

Jesse

2/12/2025 08:06:59 am

Certainly a higher K-factor can be conducive to being able to provide a higher density, but the system would need to calculated with that K-factor sprinkler. Increasing the orifice size may lead to the system being hydraulically inadequate.

Allison Olsen

2/13/2025 09:47:14 am

I think the even more straight forward answer is, if the hydraulics worked, they would be limited to increasing to a K8.0, which have the same 1/2" NPT as the K5.6.

They could not upgrade to a K11.2, which are all 3/4" NPT.

To your point this system was hydraulically designed manually using the pipe schedule method, so the calcs would need to be done. Even then, without upgrades to the sprinklers its doubtful they could meet the current NFPA 13 requirements for manufacturing and storage without upgrades to the system, so then, what's the point?

Mark Fessenden

2/16/2025 06:36:52 am

JCI (Tyco) has an 11.2 k with a 1/2 NPT.

MICHAEL BRIAN MOREY

2/12/2025 08:09:46 am

Bigger isn't always better. Every increase in K factor increases the discharge rate of the head. While it lowers the pressure required for an individual head, it could very well increase the friction loss in the pipe. If the fire isn't controlled by the first few heads you may run out of water before you reach the entire design area. You absolutely shouldn't change K factors without a proper hydraulic analysis.

Eric R

2/12/2025 08:12:50 am

Besides the logistical issue of different thread size when going from 5.6k to higher, yes there is a significant issue with doing this without understanding the hydraulic implications of the change.

System piping sized to protect a specific hazard class will very likely not properly function over the full design area if the k-factor is increased. This is due to over-discharge from the larger orifice sizes that will compound as more heads open. You will quickly reach a point that the friction loss along the branch-lines causes your head pressures to drop below what is needed to supply the required discharge density.

I'll caveat this by saying that there are also plenty of system arrangements that can benefit from a change like this, but it will always be specific to the hazard class, head pressure required for the density, and the pipe layout/sizing.

Cordell Beache

2/12/2025 08:13:17 am

The system will need to be hydraulically calculated to ensure that the pipe sizes and water supply are adequate for the new K-Factor heads. There are sprinkler heads that can be used specifically for this type of system upgrade. They have 1/2" NPT with an 8.0K factor.

james

2/12/2025 08:17:52 am

Not only is the calculation requirements an issue but you have to take into consideration the coverage area per sprinkler. The higher K-Factors may require respacing to a lower coverage area.

Glenn Berger

2/12/2025 08:19:04 am

Yes - There can be problems utilizing higher k-factors than the original design required. See previous responses.

Yes - There can be benefits with utilizing higher k-factors than the original design provided.

Sprinkler systems that are older than 50 years most likely were not hydraulically designed (calculated) as these systems were installed in the 1970s.

Now is a good time to review the entire system. including supply, and provide updated recommendations to meet current standards.

Allison Olsen

2/13/2025 09:40:56 am

They would have been hydraulically calculated by hand using the principles of the old pipe schedule method.

Dan Wilder

2/12/2025 08:23:41 am

Change out of the sprinklers with a like-for-like k-factor is all that is required, anything more would require hydraulic analysis.

If you are being asked to perform a hydraulic analysis on the existing system and a larger K-Factor works, that may be an option provided the water supply & existing system works hydraulically, or the modifications needed fall within the owner's budget.

You may run into issues with a 5.6 to 8.0 K-Factor increase due to outlet size from 1/2" to 3/4" but allowed within NFPA 13 for existing systems only. There would not be an 11.2K option with a 1/2" thread.

Storage areas, especially high-piled, has changed so much that there are often large modifications needed. The city getting a chance to go back into a building to review the existing building also has its pit falls as they can now require alarm upgrades and egress modifications, address existing construction deficiencies, require racking permits, and generally create a lot more work than just the sprinkler upgrade so prepare your owner for that.

David Kendrick

2/12/2025 08:29:18 am

With review / consultation with a FPE I’d consider response time update. Inform / consult the insurance provider as well.
50 year old heads didn’t have a response time index like later products. Orifice is the same, hydraulic remote area should still be available.
Installing quick response could help.
Internal pipe condition could be reviewed during the process as well.

Chad

2/12/2025 08:31:17 am

I’m 100% behind everyone’s answers above and I’m glad the person did ask and not just changed to a higher K factor (Or I’d like to hope they didn’t?)

Franck

2/12/2025 01:24:23 pm

If there is no need for change of density, it might be problematic to change the k-factor for all above mentioned reasons.
In all cases, if you change the k-factor, a hydraulic calculation is mandatory to validate the change.

This being said, and especially for storage occupancy, it could be good to check if it is possible to change the k-factor and, in some cases, the temperature rating.
Larger k-factor means larger droplets for the same delivered density, thus more efficient to penetrate heat plumes from storage fires.
NFPA is now requiring to adapt the k-factor to the density with storage occupancy (and it was not the case 50 years ago).
Temperature rating change can also be beneficial for EH occupancy and storage occupancy when high temperature sprinklers are used instead of ordinary temperature.
The good news? Changing the temperature rating does not change the hydraulic calculation results.

sean

2/13/2025 10:24:27 am

Yes there is an issue.
you would need to recalculate

Replace Old Sprinklers with Higher K-Factor?

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