How is the Manual J calculation performed?
The calculation is performed in Amply, an iPad application listed by ACCA as Powered by Manual J.
Before the visit. Address lookup pre-loads the property record: square footage, year built, construction type, and the climate data for the nearest weather station. From year built and climate zone, the software assigns starting values for insulation, window performance, and air leakage, drawn from a national housing dataset.
On site. Each room is scanned with the device's LiDAR and camera. The scan measures room dimensions, windows, and doors and builds a three-dimensional model of the structure. The device compass records each room's orientation. Elevation is set from the device and verified at high altitude.
Verification. Assigned values hold unless verification says otherwise. Three verification sources. Visual inspection: window glass and frames, NFRC labels where present, visible insulation, duct routing and insulation. Records: chiefly the property record and the construction assumptions Amply infers from the year built; occasionally documents kept at the property, such as prior reports or original building plans, both uncommon. Occupant reports: accounts from the owner or occupants of how the building performs (comfort, rooms that run hot or cold, equipment run time, draftiness) and of changes made since construction (added insulation, renovations, window replacement). The assigned values assume that standard building practice for the build year was followed; a report of draftiness suggests the actual air leakage may differ from what the build year predicts. Measuring the building's airtightness requires a blower-door test, which reports leakage at a standard test pressure; that test is outside the scope of this service.
Result. Loads recalculate as inputs change. The report exports as a PDF in five sections: overview of loads and assumptions, room-by-room summaries, exposure diversity curves, the three-dimensional model, and the detailed inputs. Data collection typically takes 60 to 90 minutes, depending on the size of the building and the number of rooms.
Last reviewed 2026-09-06. Accurate to the best of our knowledge as of that date. Rules change — that's why the date is there.