ACCA Manual J

The residential load calculation procedure used across the US: working out, room by room, how much heat each space loses on a winter design day and gains on a summer one, so that the equipment, the ducts and the emitters can be sized against it. It is the first link in a chain rather than an answer in itself.

Its loads are what Manual S selects equipment against and what Manual D sizes the ducts to deliver, so an error made here travels through both. Its inputs are the house as it stands: the construction, area and orientation of every wall, ceiling, floor and window, the air that leaks in, where the ducts run, and the indoor and outdoor design conditions for the place.

What it produces is a design load at those conditions, not a forecast of energy use. A season is mostly milder than the design day, and the hours spent there are what an energy estimate counts and a load calculation leaves aside.

It is where most residential oversizing is either made or prevented. A capacity read off the floor area, or copied from the unit being replaced, skips it entirely, and nothing further down the chain can recover the load that was never worked out.

Canada's National Building Code sizes a dwelling's heating to a different standard, CSA F280, at the design temperatures of its own Subsection 9.33.3 (NBC 2020, Article 9.33.5.1).

Obtained from Air Conditioning Contractors of America. What ACCA publishes

This site holds no edition list for ACCA Manual J, so a citation here names ACCA Manual J rather than a year. The publisher above has the current designation.