Optimizing my indirect-fired domestic hot water storage tank

skiereric · November 2022

I have a primary secondary setup where DHW has priority. I have spent a lot of time researching, but have come up empty on what is an optimized setting for DHW.

I feel the boiler is responding to a call quite often for DHW, which interrupts the heating call.

Here are the facts.

4000 square foot home, broken into two apartments, with a total of six people.

The boiler is a Weil Mclain 97+ 155.
The capacity of the indirect-fired domestic hot water storage tank is 51.3 US Gallons

The variables I can adjust are
-Boiler Supply Temp - Currently set to 185F
-Circulator Speed (UPS 26-99 FC)- Currently set to High
-Mixing Valve - (Adjusted to provide 115F water)
-Emerson Type 11B76 - 4 Aquastat with a fixed 4F differential with a dial with a setting between cold, norm,hot - I am at "norm"

Any thoughts on adjustments that could be made to reduce the number of calls for DHW? or any other steps I can take to gather more data?

hot_rod · November 2022

A pic of the piping would help. Many installers prefer to take the indirect off the boiler as a parallel loop, instead of off the primary loop.

Then you get direct flow from boiler to tank for fastest recovery.

If the indirect is taking a long time to recover, the coil could be limed over reducing the heat transfer.

if that is a 155,000 boiler, it could
recover a 50 gallon tank in 10- 15 minuted depending on loads and tank temperature

kcopp · November 2022

If you are getting a lot of calls for hot water that implies that you are using a fair amt of hot water.... any way to reduce the output? Lower flow shower heads? Dripping faucets?

SuperTech · November 2022

A thermostatic mixing valve is a good upgrade for any water heater.

Optimizing my indirect-fired domestic hot water storage tank

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