Calculate a normalized dew-point margin or solve for surface, dew-point, or indoor temperature. This custom index is not a standard condensation-resistance product rating.

Custom dew-point margin, not a tested AAMA or NFRC product rating.

Related Calculators

Normalized Dew-Point Margin Formula

The following custom index compares a surface temperature with dew point and indoor temperature. It is not the AAMA condensation resistance factor (CRF).

M = (Tโ‚› - Td) / (Tแตข - Td)

Variables:

  • M is the normalized dew-point margin (dimensionless)
  • T_s is the surface temperature
  • T_d is the dew point temperature
  • T_i is the indoor air temperature

To calculate the normalized dew-point margin, subtract the dew point temperature from the surface temperature. Then, divide the result by the difference between the indoor air temperature and the dew point temperature.

What is Condensation Resistance Factor?

Standard AAMA CRF is a comparative product rating obtained under prescribed test conditions, using cold-side air temperature and weighted surface measurements. This page instead calculates a custom dew-point margin: M = 0 means the surface is at dew point; M = 1 means it is at indoor air temperature. Negative M indicates a surface below dew point. Indoor air must be above its dew point. This comparison does not certify a product or guarantee condensation-free performance.

How to Calculate the Normalized Dew-Point Margin?

The following steps outline the custom dew-point calculation. Select another solve mode when a temperature is unknown.

  1. First, determine the surface temperature (T_s).
  2. Next, determine the dew point temperature (T_d).
  3. Next, determine the indoor air temperature (T_i).
  4. Finally, calculate the normalized dew-point margin using the formula M = (T_s – T_d) / (T_i – T_d).
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Surface Temperature (T_s) = 20ยฐC

Dew Point Temperature (T_d) = 10ยฐC

Indoor Air Temperature (T_i) = 25ยฐC

M = (20 – 10) / (25 – 10) = 2/3, approximately 0.666667. The surface is 10ยฐC above dew point.