Equipment Selection (Manual S)

Manual S establishes sizing limits to prevent oversizing. Air conditioners must be sized at 95-115% of the Manual J total cooling load. Furnaces must be within 140% of the Manual J heating load. Heat pumps follow 115-125% of cooling load depending on climate region per Manual S Table 1a/1b.

Equipment that exceeds these limits is flagged with an explanation of the consequences: oversized AC units short-cycle, fail to dehumidify, and waste energy.

Search by manufacturer, equipment type (AC, heat pump, furnace, package unit), capacity range, efficiency rating (SEER2, HSPF2, AFUE), or refrigerant type. The database includes performance data from 100+ manufacturers interpolated to your project's actual design conditions.

Performance at actual conditions differs from rated capacity. A unit rated at 36,000 BTU/hr cooling at 95F outdoor may only deliver 31,000 BTU/hr at your design temperature of 105F. The database interpolates between manufacturer-published data points to show capacity at your exact conditions.

Heat pump selection adds balance point analysis and COP curves. The balance point graph plots the building load line (from zero at setpoint to peak load at design temperature) against the heat pump capacity curve.

Dual-fuel comparison mode models the economic crossover point — the outdoor temperature at which gas heating becomes cheaper than heat pump heating based on your local gas and electric utility rates.