Dew Point Calculator Coil Check
Dew point at a glance from a dry-bulb and one humidity reading — RH off the space sensor or wet-bulb off a sling psychrometer — with wet-bulb, grains, and enthalpy alongside. The Coil Check field turns that dew point into the answer you actually want on an over-humidity call: drop in the supply / leaving dry-bulb and it says whether the coil is pulling the air below saturation (dehumidifying) or just cooling it sensibly while the space rides up.
Input
Coil check — optional
Your supply / leaving-air dry-bulb (or any cold surface temperature), checked against the dew point. Leave it blank for a plain dew-point read.
Output
Field notes — the over-humidity call
Read the return-air dry-bulb and RH off the space sensor (75 °F / 55 %, say) and the tool gives the return dew point (about 57.8 °F). Now compare your supply / leaving dry-bulb to it. Leaving below that dew point (55 °F) means the coil is wringing out moisture; leaving above it means you're cooling sensibly only and space humidity climbs — the failure mode behind most over-humidity complaints.
Why leaving-air dry-bulb is a fair yardstick: the coil's fin surface is colder than the air leaving it, so if the leaving air is already below the entering dew point, the surface is well below it and condensation is certain. Above the dew point it's a strong sign of little latent removal — a coil whose surface just dips under the dew point can still shed a trace. Active-dehumidification sequences hold the supply several degrees below the space dew point on purpose. For the full AHU process train and altitude-adjusted coil capacities, step up to the psychrometric chart.