ESFR Temp and Obstruction for Gas Unit Heaters?

9/11/2025

We are running into a lot of gas unit heaters in warehouses with ESFR protection.

Two issues have come up:

(1) NFPA 13 2019 Table 9.4.2.5(a) clearly shows the high temperature zones around (horizontal discharge) heaters. Given there are no high temp ESFRs, we have told contractors they can install the heaters 7' below the sprinkler deflector.

The GCs do not like this and claim they have not had this issue with other ESFR installs (not ours).

(2) The heaters are large enough to be obstructions to ESFR sprinkler discharge. We must install a sprinkler underneath, but the same issue with the temperature rating comes up.

We have considered somehow adding an additional "barrier" around the bottom of the heater, so that the ESFR sprinkler is 2'-0 below the heater (but directly under the barrier).

This is also not a welcome idea by the GC.

We also do not have an actual example of this approach. Is there information we are missing here?

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6 Comments

Danefre

9/11/2025 08:22:43 am

Sorry don't have anything to contribute but we have ran into this issue before and ended up getting an allowance to install intermediate temp.

Maybe some kind of monitored high temp sensor for a peace of mind?

Curious to hear from others.

Brett

9/11/2025 08:55:01 am

For your first point, they just need to move the heaters down. ESFR sprinklers come with the drawback that you essentially have to build that building around the sprinkler system and this part of that drawback.

For your second point, I would see if your AHJ is open to allowing the new supplemental sprinkler rules in the 2025 edition of NFPA 13. That would open up the option of using high temperature standard spray sprinklers below obstructions.

Michelle

9/11/2025 12:28:26 pm

Brett,
Following section 14.2.10.3.5.1 > 9.5.5.3.3 > 9.5.5.3.3.3 > 19.5 >28.2.4.7.4.3 seems to be the way to go. I believe K11.2 or K14 storage sprinklers are viable high temp options. Would you calculate the single sprinkler under the obstruction per 28.2.4.7.4.3 (B) or would you calculate the 11 ESFRs + 1 high temp spk at the required overhead minimum pressure?

9/11/2025 01:28:30 pm

Honestly it wouldn't even be worth calculating since supplemental sprinklers are not supposed to be calculated in conjunction with the ceiling sprinklers per 28.2.4.7.4.1. If you do want to calculate the one sprinkler then it would be in accordance with 20.16.4.

Anthony

9/12/2025 08:21:27 am

I want to eco what Brett said here. you HAVE to build around the ESFR system. Early engagement with the building owner/GC is critical in having a successful project.

Jack G

9/15/2025 05:35:07 pm

Most of NFPA ESFR rules/ data come from factory mutual.
So I just follow fm— nice explanations and pictures for what you are describing. I went thru this with Chubb on a big safety manufacturing plant in Pennsylvania.

ESFR Temp and Obstruction for Gas Unit Heaters?

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