Plumbing & HVAC

Plumbing and HVAC sizing rests on diversity: fixtures are used intermittently, rooms do not all peak at once, and a system sized to the sum of its parts is several times larger than it needs to be. The calculators here apply that diversity where it genuinely exists and refuse to apply it where it does not — continuous demands, such as irrigation or a process load, are added at full flow.

Sizing is also a pressure and temperature problem, not only a flow one. A pipe adequate on flow can fail on velocity or on residual pressure at the highest outlet; a heater adequate in summer disappoints in February when the mains water is six degrees colder. Where a page's result depends on a seasonal or site condition, it asks for that condition rather than assuming a comfortable one.