Work out humidifier capacity instantly with clear inputs, formula shown and shareable results.
A humidifier has to replace the moisture that leaks away with infiltrating dry winter air. Converting volume and air change rate to CFM, then multiplying by air density and the grains of moisture that must be added per pound of air, gives the water the unit must evaporate each hour.
Moisture load
lb/h = CFM x 60 x 0.075 x Δgrains / 7000; gal/day = lb/h x 24 / 8.34
Latent load
BTU/h = 0.68 x CFM x Δgrains
lb/h = CFM x 60 x 0.075 x Δgrains / 7000; gal/day = lb/h x 24 / 8.34. A humidifier has to replace the moisture that leaks away with infiltrating dry winter air.
Almost all winter humidity loss is infiltration. Halving the air change rate halves the humidifier duty, which is why air sealing usually beats a bigger humidifier.
This calculator takes 3 inputs: Space volume, Infiltration rate, Moisture to add. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.