If you are embarking on a major house renovation with at least partial opening of walls and floors then it may be worth your while to take a hard look at the entire hot water delivery system and plumbing layout in your brownstone to determine if you can introduce a new high efficiency approach. 

The LEED® for Homes Guidelines include LEED® credits for instituting various kinds of water saving and energy saving measures, including such things as high efficiency hot water heaters, hot water pipe insulation, hot water recovery systems and efficient distribution systems that meets certain prescribed standards. The points vary depending on the kind of plumbing system installed (conventional, central manifold or hot water recirculation systems, see below). Separate LEED® credits can be earned for installing solar hot water heating systems.

The following options are currently available on the market:

Drain-Water Heat Recovery
Hot Water Recirculation System
Central Manifold Distribution System
Integrated Water Heating and Home Heating