Shared Venting gas boiler and water heater

[ljansson]

i did a house the other day and this came up, i drew a blank for a moment . i call out the obvious defect of back drafting on the hot water heater. now here is my question.

on a same fuel flue vent: for example.
a system with a separate hot water heater and boiler is sharing the same vent system, the hot water heater is the last on the flue then the boiler the chimney connection ... so it goes hot water heater - boiler then the chimney connection. is this aloud ,,, i had always thought that largest btu unit has to be the furthest away on the connection hook up . any thoughts on this....

[James H. Bushart]

The water heater's vent connector enters the chimney above the furnace because the water heater has a smaller input.