Reheat Coil Calculator - HVAC Calculator Toolbox

About this calculator Calculates leaving air conditions (dry bulb, wet bulb, relative humidity, and temperature rise) downstream of a reheat coil, given entering conditions and coil capacity.

Use when You need to determine the leaving air conditions downstream of a reheat coil given entering conditions and coil capacity.

Formula Leaving DB = Entering DB + (Capacity × 1000) ÷ (CFM × 1.08)

Variables

Reheat Capacity Reheat capacity in MBHCFM Airflow in cubic feet per minuteEntering DB Entering dry bulb temperature °FEntering RH Entering relative humidity as a percentageAltitude Elevation above sea level in feet

Reheat Capacity (MBH)

Coil capacity in thousands of BTU/hr

CFM

Supply airflow through the coil

Entering DB (°F)

Air temperature entering the reheat coil

Entering RH (%)

Relative humidity of entering air

Altitude (ft)

Elevation above sea level in feet

Leaving DB (°F) —

Leaving WB (°F) —

Leaving RH (%) —

Temp Rise (°F) —

What is a reheat coil?

A reheat coil is a heating element installed in the supply duct downstream of a cooling coil, used to raise the temperature of cold supply air before it enters the conditioned space. Reheat is commonly used in variable air volume (VAV) systems where the central air handler cools air to a low temperature for dehumidification, and individual zone reheat coils warm it back up to meet each zone's temperature setpoint. Because the coil heats the air, the leaving dry bulb temperature always rises above the entering temperature. Humidity ratio remains constant through sensible heating, so relative humidity and wet bulb temperature both decrease as the air temperature rises. This calculator determines the leaving dry bulb, wet bulb, relative humidity, and temperature rise for a given coil capacity, airflow, entering conditions, and altitude.

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