| ACH | Construction Type | Typical Use |
|---|---|---|
| 0.05–0.10 | Very tight — blower door ≤ 1 ACH50 | Passive house, high-perf new construction |
| 0.10–0.25 | Tight — energy code compliant new commercial | Most new commercial buildings post-2010 |
| 0.25–0.50 | Average — some air sealing, older construction | Pre-2000 commercial, mid-range residential |
| 0.50–1.00 | Leaky — minimal sealing | Older warehouse, industrial, poorly sealed |
| 1.0–2.0 | Very leaky — open dock doors, large gaps | Uninsulated storage, loading docks |
This infiltration load calculator estimates the heating and cooling loads from air leaking through a building envelope. Enter the building volume (or floor area and ceiling height), an infiltration rate in air changes per hour, site elevation, and the indoor and outdoor design conditions; the tool returns infiltration airflow, the altitude factor, and sensible, latent, and total loads for both seasons.
Infiltration is the uncontrolled leakage that adds to designed ventilation, and it can be a meaningful share of heating load in leaky buildings. Quantifying it shows the payoff from air sealing and feeds the envelope portion of a full load calculation.
| Quantity | Equation |
|---|---|
| Infiltration CFM | CFM = ACH × Volume (ft³) ÷ 60 |
| Altitude factor | (1 − 6.8754×10⁻⁶ · elev)⁵⋅²⁵⁵⁹ |
| Sensible load | Q‑sens = 1.08 · alt × CFM × ΔT |
| Latent load (cooling) | Q‑lat = 0.68 · alt × CFM × ΔW (gr/lb) |
The air change method converts an assumed leakage rate into airflow, then applies the ASHRAE Fundamentals airside constants: 1.08 for sensible and 0.68 for latent heat (with ΔW in grains per pound), each scaled by the barometric pressure ratio for elevation. Cooling sums sensible and latent; heating uses sensible only, since wintertime moisture addition is generally beneficial rather than a load.