Proper Duplex Plumbing
If everything works now, you can leave it the way it is.
If you can plumb a single house, it should be a no-brainer to do separate plumbing for each unit in a new duplex or apartment building.
Select locations for separate water meters for each unit. The building feed should first branch and go to these meter locations (individual meters not mandatory while tenants do not pay their own cold water). From the respective meter locations branch off to the respective water heaters and also build on the separate cold water systems.
Water heaters nowadays should each have expansion tank mounted in the cold water feed above. If not and some hot water flows back into the cold line, the amount is too small to make a difference if you did not have separate cold water systems for the apartment house.
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.
Last edited by AllanJ; 01-26-2011 at 09:52 AM.