/ Field knowledge · IMC 309
Portable heaters are not the heating system.
Interior spaces intended for human occupancy have to be able to hold 68°F at 3 feet above the floor on the design heating day. A portable space heater is not the compliance strategy.
Educational 2024 International Mechanical Code (IMC) 309 from Daily Code Talk. Confirm the adopted edition. Distinct from load calculations (IMC 312) and equipment location (IMC 303). This is not a heat-loss run.
- The space has to be capable of 68°F (20°C) at a point 3 feet (914 mm) above the floor on the design heating day. Active or passive heating can satisfy that — plug-in heaters cannot.
- The usual exception: spaces whose primary purpose is not human comfort, and Group F (factory), H (high-hazard), S (storage), and U (utility) occupancies. Do not apply the exception just because the room is “normally empty.” Confirm occupancy and intended use.
- Converted storage, a warehouse office carved out of a rack aisle, and a tenant back room that is now occupied all trigger heating even when the old use did not.
On the set: identify which rooms are heated, which claim the exception, and how the heating system meets the design day. If heat is omitted, state the occupancy-group exception in one sentence on the mechanical cover sheet — not “per code.”
Portable heaters are not the heating system
The comment lands when the architectural program shows occupancy and the mechanical schedule shows no heat. Shell, storage, and back-of-house are the rooms that get missed. The 68°F figure is model-code education from Daily Code Talk — confirm the adopted edition.
Source: Daily Code Talk — IMC 309 · loads: IMC 312 · tool: Does this room need heat? · location: IMC 303.
What to send
Occupancy and intended use by room, whether heat is shown, and whether this is a conversion of storage / warehouse / shell into occupied space.
If the room is occupied and the set shows no heat
Send the architectural program and the mechanical schedule. Masterbuild will say whether 309 even applies — or the occupancy exception is already the answer.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. The 68°F / 3-foot figures are 2024 IMC 309 education from Daily Code Talk — not a heat-loss calculation. This page is not legal advice.