Search for Outdoor Design Temperature

Temperatures here are 99% Heating Desing Temperatures
from the US. Dept. of Energy EPW database.

Country Code
Temperature (°F)

This tool displays the impact of glazing geometry and U-value on occupant thermal comfort during winter months in the absence of perimeter heat.

= Draft Discomfort                  = Passing
= Radiant Discomfort = Failing

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3 ft

Graph Type



Outdoor Design Condition

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Façade Geometry


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Warning! Thermal comfort cannot be achieved given the current glazing geometry and space/occupancy conditions, regardless of glazing performance. This is commonly due to low indoor air temperatures or low clothing values.

Indoor Conditions


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  1. Measure of the window’s thermal performance. If the window panes are large (small impact of the frame) use the center of glass U-value. With assemblies where frame elements are prominent, it is recommended to use the assembly U-value. If using a room-side low-e coating, it can be selected under advanced options.

  2. U-value required to meet the PPD threshold at the specified occupant distance from façade.

  3. If there is a risk of condensation, the interior window surface temperature is within 5°F of the space’s dew point temperature. This happens when the indoor relative humidity is high and the outdoor temperature is low.

  4. A value represenintg one of the coldest expected outdoor temperatures during the annual occupancy period. ASHRAE recommends using a temperature at 1 percentile of the year (where only 1% of hours are colder than this temperature). This value varies with the climate of the project and you can search for your climate's temperature to the right.

  5. Temperature of the indoor air (or the indoor thermostat set point). For radiant discomfort calculations it is assumed that this also represents the temperature of the indoor surfaces. Low indoor air temperatures can cause occupant discomfort regardless of the glazing configuration.

  6. Relative humidity indoors. This factors into to the thermal comfort calculations as well as the potential for condensation. During winter, this is usually around 20% unless the space is humidified.

  7. Select if the window includes a low-E coating on the interior side of the inner most pane of glass (aka. a room-side low-e coating). Room-side low-e coatings can decrease the U-value of a window, improving the thermal performance and reducing the potential for radiant discomfort. However, they also increase the potential for downdraft discomfort and condensation risk.

  8. Emissivity of the low-e coating located on the room-side surface of the inner-most pane of glass. This is obtained from the manufacturer. If unknown assume 0.2.

  9. R-Value of the wall assembly, including thermal bridges.

  10. Average indoor air speed induced by the mechanical system. Typically ranges from 10-30 fpm.

  11. Insulating value of clothing.
    0.6 clo = trousers/knee-length skirt + long sleeved shirt
    0.8 clo = trousers/knee-length skirt + undershirt + long sleeved shirt
    1 clo = trousers/knee-length skirt + undershirt + long sleeved shirt + long sleeve sweater

  12. Metabolic rate of the occupants. 1 met = seated resting. 1.2 met = typing or standing.