Ideal Sprinkler K-Factor for NFPA 13D System?

3/12/2025

For NFPA 13D and a single family home of 1,000 sq ft, what is the optimal k-factor I should be considering?

In this particular project, we don't have a city water supply but we do have a good well.

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7 Comments

Peter Howard

3/12/2025 06:30:50 am

Residential heads are typically between 4.0 and 5.8.

Somewhere in that range is probably for the best.

I do see some 7.6k residential sprinklers, but rarely.

Dan Wilder

3/12/2025 07:52:53 am

For concealed, we vary between the 4.3K & 4.9K styles.
For recessed, we use the 4.9K pendent
This is for a decent water meter size and decent pressure.

For more restrictive pressure requirements, using a 3.0K concealed/recessed pendent with more sprinklers at a smaller spacing hits the design sweet spot more often with lower flows and the lesser PSI requirements.

Sidewalls aren't utilized a lot in our area but when needed, it really depends on room spacing and ceiling types so those K-Factors tend to bounce between the 4.2K/4.4K & 5.8K.

Pat Rance

3/12/2025 08:10:04 am

I usually use a 3.0k pendent for 13D or even 13R.

Jesse

3/12/2025 08:13:13 am

It just really depends on the hydraulic characteristics of the system. Most often, we use the Tyco LF-II in K=4.9.

Gonna offer a plug for the K-Factor Selector in the Meyer Fire Tool Kit. If you're not subscribing to the Tool Kit, you really owe it to yourself. This is an invaluable tool for what we do. (You owe me 5 bucks now Joe...)

Anthony

3/12/2025 08:40:49 am

I agree with Jesse here. Calculations and layout will determine the best K factor. K factor responds to system supply not the other way around.

Jack G

3/12/2025 10:38:55 am

Since the density is a constant ( 13-r-d)
The spacing is the determining factor. Obviously 20x20 uses more end head pressure.

danefre

3/12/2025 11:39:08 am

A lot of good responses here. Keep in mind, in 13D you need to calculate UP TO 2 sprinklers within a compartment. Meaning if you have 4, you're still only calculating 2.

Essentially, you can add sprinklers to reduce the coverage area of each sprinkler and make the small K-factor sprinklers worth it.

In our market, the smaller K-factor sprinklers are not worth it because we do all our systems with pump & tank so we adjust to that. All the piping ends up as 1" anyway.

Also, different states have different water duration requirements and that could be a problem for a well supplied system.

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Ideal Sprinkler K-Factor for NFPA 13D System?

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