High-Altitude Appliance Input Derate
The derated maximum input for a gas appliance at altitude per the NFPA 54 / IFGC high-altitude provision: from the nameplate input and installation elevation, the derate factor (default 4% per 1000 ft above 2000 ft, both editable) and the derated input, with a high-altitude-kit flag. Field orifice drilling is generally prohibited; use a listed kit and the AHJ governs.
Formula and source
steps = max(0, (elevation - threshold) / 1000); factor = max(0, 1 - (derate-per-1000ft / 100) x steps); derated input = nameplate x factor. A high-altitude-kit flag is set above the threshold.
NFPA 54 (National Fuel Gas Code) / IFGC high-altitude provision (by name, not reproduced); the derate basis is an editable convention.
Audience
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Posture
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