Makeup water, boiler or system loop

Robert_H

I’m in Installing a Vitodens B2HA-19 with the Viessmann Low Loss Header, no DHW. The installation manual shows the expansion tank and makeup water in the boiler loop, between the LLH return and the input of the circulator which is pumping into the boiler.  This makes sense; protects the boiler and “pumps away” etc.  However, I have seen installation diagrams and pictures showing the Expansion tank and make up on the system side of the LLH as well.

When would you put the makeup on the system side vs. the boiler side?

Thanks

Robert

Steamfitter66

i don't use Viessmann

Just not in my supply chain with parts availability etc. I would install the M/U and exp tank on the air eliminator on the primary loop. No shock worries there. Works best as a system approach.

Robert_H

Steamfitter,

Just to clarify,  by "primary loop" do you mean the boiler loop?

Thanks

Robert

Steamfitter66

Boiler is secondary

So it would be in the house piping.

Jean-David Beyer

by "primary loop" do you mean the boiler loop?

That is why I try to remember to call the one with the boiler in it the BOILER LOOP and the one with the loads in it the SYSTEM LOOP.  Some people call the one with the boiler in it the primary loop, and the one with the loads in it the secondary loop. And some do it the other way around.



I do not know what they do if you have a big loop with a circulator and no loads in it.; just Closely Spaced Ts (CST). Off one CST is a loop with a boiler and a circulator in it. And there are several other loops off that one with a circulator in each with the loads on it. Is the one with no loads and lots of CSTs the primary loop, the boiler a secondary loop, and the other loads secondary loops? I have seen systems like that (in books) with tertiary loops off the secondary ones. In such a case it is probably best to draw the whole thing out and label them Loop 1, loop 2, etc., to avoid confusion.



I am glad I am a homeowner with only a Boiler loop and a System loop,

but with the indirect water heater across the Boiler loop.

Steamfitter66

Boiler is secondary

as is anything else that comes off the primary on closely spaced Ts But its also boiler piping or distribution piping as well. Most of us install a modified primary secondary piping in respect to the boiler tie in to the house distribution piping.

I prefer Fire tube boilers and direct piping if possible but it has to be designed carefully.

Robert_H

What i've read

about Closely spaced Ts says the primary loop is the that flows strait through the Ts the secondary is off the bulls. I've seen examples of CSTs with the boiler on the primary and with the boiler on the secondary. There must be reasons for doing it either way.