Find the dew point: the temperature where the air’s moisture starts condensing. Add a surface temperature to see whether walls, windows or ducts will sweat.
What dew point tells you
Dew point is the temperature at which the air’s water vapor starts turning to liquid. Any surface colder than the dew point collects condensation, which is how cold walls, windows, ducts and slabs get wet even with no leak.
Worked example
Air at 76°F and 60% RH has a dew point of about 61°F. A 64°F exterior wall is only 3°F above it, close enough to sweat as the night cools. Bring the room down to 45% RH and the dew point drops to about 53°F, leaving an 11°F margin.
Frequently asked
How do you calculate dew point?
From the vapor pressure: find the saturation vapor pressure at the air temperature, multiply by RH, then solve the Magnus equation for the temperature at which that vapor pressure would be saturated. This calculator does it for you in °F.
Why does dew point matter on a water loss?
If the room’s dew point is above the temperature of the coldest surface, moisture keeps condensing there and re-wets materials. A drying goal keeps the dew point a few degrees below that surface.
What is a comfortable dew point?
Indoors, a dew point in the 40s to mid-50s °F usually feels comfortable. Above about 60°F feels muggy and raises the risk of condensation and mold on cool surfaces.
More free tools
This knowledge, built into the software
RestoredOS runs the whole job on the same field knowledge behind these tools — drying logs, moisture mapping, scope, and billing.