We'd like to upgrade to an indirect water heater, after our standalone gas water heater died. We have a boiler in our radiant heating floor system that we can use. Usually only 2 people take a shower / bath at once, but the washer and dishwasher may be running.
Here's what our radiant system looks like now.
(Edited with zman's suggestions below)
My first thought was to minimize changes with this design. Configuring the boiler to domestic hot water priority ensures that either the radiant circulator or the DHW circulator runs, but not both at once.
Most designs I've seen use primary secondary piping though, which requires another pump. If only one pump runs at a time, what's the benefit of this over the previous design?
1. I calculated 20 feet head for the indirect DHW circulator based on the numbers below. That seems high. Did I make a mistake?
Indirect water heaters @ 10 gpm:
Lochinvar SIT050 => 3 ft head
HTP Superstor Ultra SSU-45n @ 10 gpm => 7.9 feet head
KBN-150 @ 10 gpm flow (with "typical" piping) => 12 feet head
Total 19.9 feet head @ 10 GPM
2. If the primary-secondary design is the way to go, how do I size the boiler pump?
3. What can I do to improve this? Reliability and longevity are more important to me than initial system cost.
I haven't found many plumbers with experience in boilers and indirect water heaters in N. California, so I'd like to make sure I understand everything before asking a local plumber to work on it.