Swamp Cooler CFM Calculator (Hot & Dry Climate CFM Sizing)

Required CFM is Room Volume (Area x Ceiling Height) multiplied by your selected air exchange rate and divided by 60, cross-checked against a second, independently-sourced rule of thumb (Room Volume divided by 1.5-3, depending on climate) — both formulas are mathematically the same relationship. A required minimum, rounded UP, never to nearest, computed from the exact Area/Ceiling Height values rather than a pre-rounded volume so a fractional input can't get silently rounded away. The Suitability Screening is an informational flag, not a hard block — evaporative cooling's effectiveness is gated by ambient relative humidity (cross-checked across multiple industrial and residential evaporative-cooling references): under 30% RH it performs close to its full potential, 30-50% RH delivers noticeably less cooling, and above 50% RH performance typically drops sharply, though this simplified RH-tier screening is not a precise pass/fail — actual performance depends on the coincident dry-bulb and wet-bulb temperature at your location, not RH alone, so verify your design wet-bulb conditions before ruling evaporative cooling out entirely. Cooling Pad Area, Relief/Exhaust Vent Area, and Water Usage are all sized from Required CFM UNLESS you enter an Actual Unit CFM that's larger — manufacturers sell in fixed CFM tiers, so a purchased unit (e.g. a 3,000 CFM model bought for a 2,001 CFM requirement) is often larger than the bare calculated minimum, and Phoenix Manufacturing's own owner's manual bases relief-opening sizing on the unit's actual rated airflow, not the load calculation alone; an entered value smaller than the calculated minimum never shrinks Cooling Pad Area, Relief/Exhaust Vent Area, or Water Usage below what the safer calculated minimum requires — but it IS surfaced as an amber undersized-unit warning above, since an undersized unit is a real problem even though this calculator's own downstream figures stay safe. Cooling Pad Area is that sizing basis divided by the selected pad's face velocity (250 ft/min for 4in rigid/cellulose media, 350 ft/min for 6in), a required minimum rounded UP — an undersized pad (too high a face velocity for the airflow) risks incomplete evaporation and water carry-over through the pad; dry spots or pooling on an installed pad are usually a water-distribution problem, not a sign the pad area itself is wrong. Relief/Exhaust Vent Area is approximately 2 sq ft of unrestricted opening per 1,000 CFM (cross-sourced U.S. evaporative-cooler manufacturer guidance) — a genuinely different formula from this site's Attic Ventilation Calculator, which sizes passive attic vent area from attic square footage, not cooler airflow. Estimated Water Usage is a rough LOW-HIGH RANGE (not a fixed spec), scaled from two independently cross-checked real-world data points — actual usage depends heavily on real-time temperature and humidity and will vary. This calculator does not model elevation/altitude correction (a real effect at higher elevations, but no consistent evaporative-cooler-specific correction factor was found across sources) or aspen/excelsior pad media (a real, common, cheaper alternative, but no consistent face-velocity figure was found for it) — see Limitations below.