How do you stop cold water pipes from sweating?

Heating & HVACPsychrometric Thermodynamics

Dew Point & Condensation Calculator (Magnus Formula)

Calculate the exact dew point temperature from ambient air temperature and relative humidity to predict when uninsulated cold water pipes will sweat.

Heating & HVAC Field StandardsPsychrometric Thermodynamics

Engineering formulations calibrated to IPC, UPC & NEC specificationsSub-Zero Cold Climate Tolerances

Quick Summary & Key Answer

Dew point is the temperature to which air must be cooled for water vapor to condense into liquid water. At 72°F and 55% relative humidity, the dew point is 54.8°F. Any cold water pipe carrying 45°F groundwater in this room will sweat continuously unless protected by closed-cell foam insulation.

Dew points above 65°F feel uncomfortably humid and muggy.
Insulating cold water pipes with 1/2" foam stops pipe condensation completely.
Condensation dripping off uninsulated pipes is frequently mistaken for plumbing leaks.

Interactive Calculator

Adjust inputs for real-time results

Ambient Air Temperature°F

°F

Relative Humidity (RH)%

Calculated OutputHIGH CONDENSATION RISK (Cold pipes will sweat)

Calculated Dew Point Temperature

54.9°F°F

Dew Point in Celsius: 12.7°C
Incoming Cold Water Pipe Temp: ~45°F - 50°F (Alaska winter)
Vapor Pressure: 14.72 hPa

Note: Whenever pipe surface temperature falls below the dew point, moisture vapor condenses into liquid droplets (pipe sweating).

Why Cold Water Pipes Sweat

Cold groundwater cools copper pipes below the ambient room dew point, causing surrounding moisture vapor to condense on the exterior pipe wall.

Frequently Asked Questions

Common questions regarding this calculation and code compliance

Wrap cold water supply pipes in closed-cell elastomeric foam pipe insulation (like Armaflex) and seal joints with vapor-barrier tape.