How do I calculate the humidification capacity needed for my facility?
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- Issue Time
- Sep 14,2026
Work in mass, not floor area. Base load in kg/h is volume (m³) × air changes per hour × the absolute humidity gap Δg (g/m³) ÷ 1,000. Then add infiltration — 15% for tight construction, 25% average, 40% for high traffic — allow for hygroscopic material absorbing 10–30% of what you supply, and apply a 1.2–1.3 safety factor. Sizing on area alone is the most common and most expensive error.
The calculation in four steps
Volume
Length × width × height to the ceiling, not to the roof steel. A 1,200 m² hall with a 5 m ceiling is 6,000 m³. Internal plant and racking reduce it slightly; ignore that for now, it sits inside the safety factor.
Air changes
Take it from the HVAC specification or measure it. Guessing here is the biggest single source of error: a large warehouse at 8 ACH needs three to four times the capacity of the same building at 2 ACH.
Δg from a chart
Read absolute humidity at the outdoor design condition and at the target indoor condition. At 20 °C, moving from 30% to 50% RH is about 5.2 to 8.7 g/m³, so Δg ≈ 3.5 g/m³.
Allowances
Add infiltration, add the absorption of dry stock and packaging, subtract genuine credits such as people and wet processes, then multiply by 1.2–1.3 for equipment ageing and future changes.
Two worked examples
Printing hall. 400 m² at 4 m ceiling gives 1,600 m³. Three air changes per hour, 22 °C, lifting 40% to 55% RH — Δg ≈ 2.9 g/m³. Base load is 1,600 × 3 × 2.9 ÷ 1,000 = 13.9 kg/h. With 25% infiltration that is 17.4 kg/h, and with a 1.2 safety factor the design capacity is about 21 kg/h — two 12 kg/h units, or one 24 kg/h unit with headroom.
Electronics hall. 1,200 m² at 5 m gives 6,000 m³. One and a half air changes, 20 °C, lifting 30% to 50% RH — Δg ≈ 3.5 g/m³. Base load is 6,000 × 1.5 × 3.5 ÷ 1,000 = 31.5 kg/h. With 25% infiltration and a 1.2 safety factor the design capacity is about 47 kg/h — two 24 kg/h units.
The limits worth knowing
Every number above depends on the air change rate, which is the quantity people are most confident about and most often wrong. Tracer-gas testing is cheap next to the cost of a system that runs at 100% duty forever and still never reaches setpoint. Be careful with credits too: people are usually quoted at 70–180 g/h each, but that figure comes from dehumidification load work and assumes a working population that is actually present.
Representative project configuration
A contractor had sized a hall from floor area alone and proposed four 6 kg/h units. Tracer-gas testing put the real air change rate at 2.6 ACH, not the 1.0 assumed.
The area-based figure would have run flat out continuously and never held 45% RH. East Dehumidifier asks for measured air change rates before quoting on retrofit jobs for exactly this reason; on new builds the figure comes from the HVAC design and is checked at commissioning.
Inputs, ranges and what they do to the answer
| Input | Typical range | Effect on capacity | How to get it |
|---|---|---|---|
| Space volume | Site specific | Linear | Drawings, measured to ceiling |
| Air changes per hour | 0.5–8 | Linear, largest single lever | HVAC spec or tracer gas test |
| Δg, absolute humidity gap | 1–8 g/m³ | Linear | Psychrometric chart |
| Infiltration | 15% / 25% / 40% | Additive | Envelope quality, door duty |
| Hygroscopic absorption | 10–30% | Additive, decays over time | Stock type and turnover |
| People and wet processes | 70–180 g/h per person | Credit, subtract | Occupancy schedule |
| Safety factor | 1.2–1.3 | Multiplier | Standard practice |
Design note: if your calculation says the unit will run at 100% duty all winter, the calculation is wrong or the machine is undersized. A correctly sized system cycles, and cycling is what keeps transducers and nozzles alive.
Related questions
Want the load calculated?
Send volume, measured air change rate, current and target RH and design outdoor condition. East Dehumidifier will return the full calculation, not a rule of thumb.