The new set (and new house) starting with season three was necessitated by the show moving to another network. This was the last episode broadcast by CBS. Starting with the next season, the show was broadcast by ABC.
It was actually a change in production companies that facilitated the move to the new house. The networks had nothing to do with it since LITB was already being broadcast on ABC starting with season 2 til the end of the series. CBS declined to renew LITB after season 1.
June mentions to the boys that their new house will be on Lakewood Avenue. The house they are in now is 485 Mapleton Drive.
Last episode on the original set.
Not only was this the last show filmed on that set, but the writers saw fit to write in at the end how the Cleavers were going to be moving to a new house, thereby making the transition easy.