The Aprilaire 5000 electronic air cleaner was redesigned in May of 2005. The new Model 5000 now has a wider frame, the ealier 5000 was 11-3/8" wide and the new 5000 has a 12" wide frame. The access door / power pack was also made wider as well as equiped with a new latch design. The new 5000 also has longer ionizing wires, 25" where as the earler model had wires 24-15/16" in length. The stainless mounting bracket for the ionizing wires was also changed.
The new Model 5000 has identical performance to the earlier. The new 5000 uses the same internal power supply, same ionizer frame, same filter housing and same 501 filter.
The photo below shows the new and old model 5000. Most notably the door is different.