Small Mechanical Closet a Plenum/Small Space?

4/8/2025

Question regarding a mechanical closet and/or plenum. We have what I'll call a mechanical closet because it houses an electric AC/heating unit for an apartment using NFPA 13.

The sprinkler designer/contractor is calling it a plenum/small space and is omitting sprinklers. The plans do not show any sprinkler coverage.

Is this closet a plenum or small enough space to omit sprinkler protection? Is there code justification for this?

Thanks in advance.

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8 Comments

Pete H

4/8/2025 06:36:51 am

You're in 13 and you have mechanical equipment in the mechanical closet (it's an accessible space with mechanical equipment).

I'm leaning on: You have to protect it.

I can't verify if that specific HVAC unit is fuel-fired or not, but that would only make me say "you have to protect it more."

Dan Wilder

4/8/2025 07:58:56 am

This would really need to be seen on a floorplan with clarification on if this is a fuel fired piece of equipment of not (looks to be all electric but to confirm), size of the door access, and construction type around the unit.

The unit itself (assuming a non-fuel fired unit), when placed in an attic of non-combustible construction would not trigger the need for sprinklers. The fact it's ground level only changes the access to be easier, thus the ability of storage could occur within the unit space. If the plenum is of "tight" construction as to not allow storage around the unit and the access is only for a filter change out and electrical service panel access, I could see a good argument to omit sprinklers. This all assumes that the wall construction is non-combustible as well.

Also, if the ductwork out of the unit completely takes up the space above the unit as to not allow a sprinkler could be used as another possible reason to omit protection.

Glenn Berger

4/8/2025 08:18:55 am

Not enough information provided to render to proper response.

In addition to the comments made by others:

What is the size of this mechanical closet?

Is there any other equipment provided in this space?

Jesse

4/8/2025 08:30:06 am

Full 13 design has me leaning to protect the space. Isd this eequipment combustion fuel fired or electric?

Jack G

4/8/2025 10:31:56 am

From the label, it appears the appliance is a heat pump. It has a compressor and blower motor. It’s 200-230 volt single phase.
The amps distress me a little bit.
I d like to look at the size of the wire hooked up to it. It indicates I believe when I blow up the pic 14.6 to 16.2 amps.
When determining the wire size it’s always you determine the breaker size. It’s 1.25 times the amps for the breaker size . In this case
14.6 x 1.25 is 18.25 or a 20 amp breaker and a 12-3 wire.
For 16.2 amps x 1.25 is 20.2 which by code should be a 10-3 wire ( exceeds 20 so go to next size )
NFPA 13 system indicate the space should be protected with sprinklers. I ve seen reports In my 55 years in fire protection where fires in electric supplied appliances had fires start in hot water heaters, heat appliances At connections, blower motors , capacitors ( for start up— usually installed instead of a soft starter switch like we d do on an air compressor) My neighbors house had a big fire in his home at the hot water heater while he was taking a shower alone in his house. Ended up undersized wire. And this stuff does get by inspectors.,
I question the wire size as to expect the documents to show a 12-3 wire size which is maxed out for the breaker size. That plus the distance the wire has to run could cause high heat, the breaker tripping a lot under high load, and if the owner locks the breaker in ( little wires attached to the breaker)in on that hot summer day….an electrical fire. I would not be as concerned with 10-3 wire for an electrical fire but the wire size is important in this case and “ go cheap “ is the option usually followed, but as I stated a full NFPA 13 system would require it to be protected.
Thank you for providing the appliances electrical
Label.

Michael Ruda

4/8/2025 10:38:56 am

Ultimately that decision would be up to the Authority Having Jurisdiction.

Todd E Wyatt

4/8/2025 11:34:30 pm

If the scoping Code (e.g. IBC-2024) requires an automatic sprinkler system (ASPS ... see 903.2 Where Required) based on the building's Occupancy Classification (see 903.2.1 - 903.2.10), or per Specific Building Areas and Hazards (see 903.2.11), or during construction (see 903.2.12), then ASPS protection is required "throughout".

The scoping Code includes select rooms/areas/spaces where the ASPS is exempted (see 903.3.1.1.1 Exempt Locations) but this "mechanical closet" is not specifically listed.

If this equipment is located in an "attic" and the building is protected by a NFPA 13R ASPS, there are some exemptions (903.3.1.2.3) that may be applicable. Otherwise, a NFPA 13 ASPS is limited to those exemptions listed in 903.3.1.1.1.

Todd E Wyatt

4/8/2025 11:35:45 pm

REFERENCES
IBC-2024
Chapter 9 Fire Protection and Life Safety Systems
Section 903 Automatic Sprinkler Systems
903.3.1 Standards
903.3.1.1 NFPA 13 Sprinkler Systems
903.3.1.1.1 EXEMPT LOCATIONS
Automatic sprinklers shall not be required in the following rooms or areas where such rooms or areas are protected with an approved automatic fire detection system in accordance with Section 907.2 that will respond to visible or invisible particles of combustion. Sprinklers shall not be omitted from a room merely because it is damp, of fire-resistance-rated construction or contains ELECTRICAL EQUIPMENT.
1. A room or space where sprinklers constitute a serious life or fire hazard because of the nature of the contents, where approved by the fire code official.
2. Generator and transformer rooms separated from the remainder of the building by walls and floor/ceiling or roof/ceiling assemblies having a fire-resistance rating of not less than 2 hours.
3. ROOMS OR AREAS THAT ARE OF NONCOMBUSTIBLE CONSTRUCTION WITH WHOLLY NONCOMBUSTIBLE CONTENTS.
4. Fire service access elevator machine rooms and machinery spaces.
5. Machine rooms, machinery spaces, control rooms and control spaces associated with occupant evacuation elevators designed in accordance with Section 3008.
903.3.1.1.2 Bathrooms
903.3.1.1.3 Lithium-Ion or Lithium Metal Batteries

903.3.1.2 NFPA 13R Sprinkler Systems
903.3.1.2.3 Attics
Attic protection shall be provided as follows:
1. Attics that are used or intended for living purposes or storage shall be protected by an automatic sprinkler system.
2. Where fuel-fired equipment is installed in an unsprinklered attic, not fewer than one quick-response intermediate temperature sprinkler shall be installed above the equipment.
3. Where located in a building of Type III, Type IV or Type V construction designed in accordance with Section 510.2 or 510.4, attics not required by Item 1 to have sprinklers shall comply with one of the following if the roof assembly is located more than 55 feet (16 764 mm) above the lowest level of fire department vehicle access needed to meet the provisions in Section 503.
3.1. Provide automatic sprinkler system protection.
3.2. Construct the attic using noncombustible materials.
3.3. Construct the attic using fire-retardant-treated wood complying with Section 2303.2.
3.4. Fill the attic with noncombustible insulation.
4. The height of the roof assembly shall be determined by measuring the distance from the lowest required fire vehicle access road surface adjacent to the building to the eave of the highest pitched roof, the intersection of the highest roof to the exterior wall, or the top of the highest parapet, whichever yields the greatest distance. For the purpose of this measurement, required fire vehicle access roads shall include only those roads that are necessary for compliance with Section 503 of the International Fire Code.
Group R-4, Condition 2 occupancy attics not required by Item 1 to have sprinklers shall comply with one of the following:
4.1. Provide automatic sprinkler system protection.
4.2. Provide a heat detection system throughout the attic that is arranged to activate the building fire alarm system.
4.3. Construct the attic using noncombustible materials.
4.4. Construct the attic using fire-retardant-treated wood complying with Section 2303.2.
4.5. Fill the attic with noncombustible insulation.

Small Mechanical Closet a Plenum/Small Space?

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