Replies

1. 
   Scott | Jun 10, 2011 09:57pm | #1

   >>>Any suggestions on how to

   >>>Any suggestions on how to balance and control the outlet temp?

   The only strategy I've ever heard of is to make the outlet piping the same length on the way to the manifold.

   Otherwise, consider running them in series.

2. 
   rich1 | Jun 11, 2011 01:13am | #2

   Put a tempering or mixing valve on the common outlet and set it at 120.  Set the the w/h's to 140. 

1. 
   DanH | Jun 18, 2011 10:00am | #5

   Put a tempering or mixing valve on the common outlet and set it at 120.  Set the the w/h's to 140.

   That won't do anything to balance the two units.

   But one could, in theory, use TWO tempering valves, feeding heater A to the cold side of valve 1 and the hot side of valve 2, and vice-versa for heater B, with the valve outputs teed together.  Then if the temp in one of the heaters dropped below the setpoint for the valves the flow would all go through the other heater.

   Downside is the expense and the fact that the (likely uneven) flow restriction of the valves would probably upset any "natural" balance between the units.

3. 
   oops | Jun 11, 2011 12:48pm | #3

   parallel water heaters

   I don't know the answer, but just curious. Have never seen them in parallel.

   Why in parallel and not in series. What is the advantage?

1. 
   DanH | Jun 18, 2011 09:54am | #4

   One advantage is that bypass is much simpler.  Another is that the "wear" on the units is about even, vs putting 90% of the load on the "cold" heater in the series case.  And you can get a hair more total flow.

   But the balance issue is always a concern.