# W classes, PUE and WUE

Lesson 3 of [Liquid cooling foundations for buyers](https://liquidcooling.fyi/academy/liquid-cooling-foundations.md), 14 minutes.

Three terms appear in almost every quote and every listing. Learn them first. ASHRAE W classes ASHRAE TC 9.9 names the liquid cooling classes W17, W27, W32, W40, W45 and W+. The number is the highest facility water supply temperature in degrees C. W+ means above 45 degrees C. All classes share a low…

The rest of this lesson is for learners enrolled in the course. [See how Liquid cooling foundations for buyers works](https://liquidcooling.fyi/academy/liquid-cooling-foundations.md).

Also on the [web page](https://liquidcooling.fyi/academy/liquid-cooling-foundations/w-classes-pue-and-wue).