| Model | Index | Risk Rating | Effects on the Metabolism of Horses |
| TSI | 1 | <120/130 | Normal cooling of the horse’s body, through evaporation, respiration and sweating, unless the horse is obese or very hairy |
| 2 | >140 | Responsible for heat loss is sweat, which can be aggravated by obesity or very hairy | |
| 3 | >150 | Evaporative heat loss is compromised, especially if the relative humidity is above 50%, but sweat is still important for heat loss | |
| 4 | >180 | The natural dissipation of heat does not occur, and subsequent increases in body temperature may occur. There is great danger for the occurrence of thermal stress | |
| THI | Light | 72 - 79 | Mild risk of thermal stress and responsible for heat loss is sweat. In horses with a lot of hair or obese, a greater impact may occur |
| Moderate | 80 - 89 | Moderate risk of heat stress | |
| Severe | >90 | Severe risk of heat stress |