HRV Sizing Calculator

This calculator sizes a heat recovery ventilator (HRV) by computing required ventilation two different ways and taking whichever is larger. Method 1 scales with Building Volume and Air Changes per Hour (Building Volume x Air Changes ÷ 60); Method 2 is a simplified stand-in for ASHRAE 62.2's residential whole-building ventilation formula, which combines a per-occupant rate (7.5 CFM per person, used directly here) with a smaller area-based term keyed to conditioned floor area and bedroom count -- this calculator approximates that area term from Building Volume rather than asking for floor area and bedroom count directly, so treat Method 2's result as an ASHRAE-62.2-style estimate, not a code-compliance calculation. Method 2 scales with Occupants. At the default inputs (16,000 cu ft, 0.35 ACH, 4 occupants), the volume-based method wins at 93 CFM versus the occupant-based method's 50 CFM, so Building Volume and Air Changes per Hour drive Required Ventilation in that regime -- Occupants has no effect until it's raised enough to flip which method is larger; at 50 occupants (same building volume), the occupant-based method takes over and Required Ventilation jumps to 395 CFM. Recommended HRV Size is picked from a stepped list of standard unit sizes (70, 100, 150, 200, 250, 300, 400 CFM) rather than a continuous value, so it only changes when Required Ventilation crosses one of those thresholds -- a 10% increase in Building Volume from the default is enough to push Required Ventilation from 93 to about 103 CFM, crossing the 100 CFM boundary and bumping Recommended HRV Size from 100 to 150.

Heat Recovered and Est. Annual Savings depend on the temperature difference between Indoor and Design Outdoor Temp along with Sensible Efficiency, independent of which sizing method is active. Recommended HRV Size tops out at the largest standard unit, 400 CFM; if Required Ventilation exceeds that (very large buildings or high occupant counts), Exceeds Standard Sizing (1=Yes) flags it -- the displayed 400 CFM is only the largest table entry for reference, not a safe recommendation, and the project needs multiple units or a custom-sized commercial ERV/HRV designed with a mechanical engineer. This is a preliminary sizing estimate, not a full ASHRAE 62.2 compliance calculation or a substitute for a mechanical engineer's ventilation design.