Dave Dewitt, aka The Pope of Peppers, wrote an extensive wonderful article on everyone’s favorite pepper, the Habanero. Here’s just an exerpt of Dave’s article:

Although the species is renowned for the high heat level of its pods, we should remember that all heat levels are found in the chinense, from zero to the hottest ever measured. The typical commercial habanero averages between 80,000 and 150,000 Scoville Units but has great variability depending upon climate and stress. In a series of experiments at New Mexico State University, Paul Bosland and Peggy Collins tested the same variety of chinense, an orange habanero from Yucatán, grown under different conditions. In 1992, grown outside in a field, the pods measured 357,992 Scoville Units. The same variety, grown in the greenhouse, measured 260,825 Scoville Units. The variability of pungency approached thirty percent, which illustrates the role played by the environment in the heat levels of chile peppers. However, when cooks use habaneros and their relatives, they can assume that the recipes are hot, although it is wise to taste-test the habaneros first by placing a tiny sliver on the tongue and then chewing it up. Of course, the heat level can be adjusted by varying the number habaneros used, by increasing the amounts of the other ingredients in the recipes, or by removing the seeds and placental tissue to decrease the heat of the habaneros.

Read more about the habanero pepper here.