IMC 312 is the section that prevents equipment sizing from becoming guesswork. Heating and cooling design loads used to size systems, appliances, and equipment must come from a recognized calculation procedure.
Plain-English Summary
Use ASHRAE/ACCA Standard 183 for design loads, or an approved equivalent computation procedure using the design parameters in Chapter 3 [CE] of the IECC. The load calculation is part of the permit proof chain, not an optional design backup.
Why It Matters
Oversized equipment can create humidity, short cycling, noise, energy, and comfort problems. Undersized equipment creates comfort and owner-risk problems. The code wants a defensible load basis before equipment is selected.
Permit Proof Chain
Space use -> envelope and internal loads -> ventilation/infiltration assumptions -> design weather and IECC parameters -> load calculation method -> equipment capacity selection -> zoning/control basis -> schedule values match calculation output.
Masterbuild QA Lens
The calculation, equipment schedule, ventilation schedule, and controls narrative must tell the same story. If the schedule capacity does not trace back to the load file, the permit set invites comments and the owner inherits performance risk.
Drawing / Submittal Check
Submit or retain the load summary showing method, inputs, design conditions, space-by-space or zone loads, equipment selection, and any safety factors. Make sure the equipment schedule and model numbers match the selected capacity.
When To Escalate
Escalate unusual envelopes, large outdoor-air loads, kitchens, labs, high plug loads, humidity-sensitive occupancies, tenant changes, and existing buildings where envelope assumptions are uncertain.