Vehicle Heating Dynamics

The atmosphere and the windows of a car are relatively “transparent” to the sun’s shortwave radiation (yellow in figure below) and are warmed little. However this shortwave energy does heat objects that it strikes. For example, a dark dashboard, steering wheel or seat temperatures often are in the range of 180 to over 200 degrees F.

These objects (e.g., dashboard, steering wheel, childseat) heat the adjacent air by conduction and convection and also give off longwave radiation (red) which is very efficient at warming the air trapped inside a vehicle.

Objects Heated by the Sun Warm Vehicle's Air

Hot Car in 60 Minutes

Vehicle Heating Study

Studied temperature rise in enclosed cars on 16 dates between May 16 and Aug. 8, 2002. (see graph of 16 case days)
Ambient temperature were between 72 and 96 degrees F
Dark Blue mid-size sedan with medium grey interior
Also tested with windows “cracked”
Published in Pediatrics 2005 (Click here to download)

Average Temperature Rise

Heating Study Summary

Average elapsed time and temperature rise
10 minutes ~ 19 deg F
20 minutes ~ 29 deg F
30 minutes ~ 34 deg F
60 minutes ~ 43 deg F
1 to 2 hours ~ 45-50 deg F
2 to 4 hours ~ 50-55 deg F

Summary Table of Temperature vs. Elapsed Time

Two-thirds of the heating in the first 20 minutes
“Cracking” the windows had little (i.e., < 3 deg.) effect
Vehicle interior color probably biggest factor