WH31 monitor the Temp & Humidity only, and supports 8 channel (You can add WH31 maxum 8 units to work with one gateway/hub/console).
WH32 indoor coded monitor the barometric pressure, Temp & Humidity, and supports one channel only. It's design for upgrade HP2550 and HP3500.
WH32 outdoor coded supports one channel only to connect console, for there are complex algorithm to calculate Feels Like, App Temp and Dew Point. It's design for replace data of WS69 WS80 WS90 or upgrade WS68 WH40.