Fans.
All rehearsal rooms should have at least 2 fans.
And not the adoring groupie kind.
One for the drummer, and one for the rest of the band.
Just as good in the winter as in the summer.
Better parking, storage, access and security will encourage bands to bring their own gear, so you may not need to invest so heavily in amps for the rooms.
Naturally, you'll still need a drum kit and PA for each, though..