Starting immediately, the WV variable speed water-to-water units with Serial Number M19090400 and thereafter, will include the upgraded UPM-XL (UPMXL 25-124) variable speed load and source pumps. Any WV unit prior to this serial number will consist of Magna GEO (MAGNA 32-140) for both pumps. The WV was originally designed with a single Magna GEO pump internal to the unit as the load pump for the hydronic system and a choice of a single Magna GEO or a two-pump flow center (one variable speed, one constant speed) for the source piping (ground loop). The new UPM-XL pump upgrade provides similar performance as the Magna GEO but is more efficient (max. energy use for the Magna GEO is 230 Watts; max. energy use for the new UPM-XL is 180 Watts). This technical bulletin will provide some guidelines on pump sizing, since there is a slight difference in performance.