Two Boilers, best piping method?

GW

hello,

are there some pros and cons to connecting two boilers together before the primary versus piping them into the primary independently? Most drawing show the 1st method (connected before they reach the primary).

I have a job where the original guy must have had a rough night, stumbled in the next morning and piped the primary boiler pump backwards. This is a large home, two boilers, a huge wall of activity (13 zones) on the other side of the boiler room. I'm gonna re-pipe some things and smarten up some of the radiant zones (currently fixed mix with on/off controls). Currently the two boilers are separately connecting to the primary loop.

I feel that if I tie the two boilers together I may get some flow through the second boiler when only the primary boiler is on. The expansion tank is up on the primary loop, so checks are not really an option, or as I type this, perhaps the pressure would simply push through the checks.

The close space tee method for both boilers (the way it is now) into the primary above may be better. This job has two G234 Buderus units, and the primary has the 2107 with the 242 card for two boilers. Is there a way to just get ONE boiler to come on for a DHW call? There are only two people in this house and the HO doesn't want both boilers coming on (makes good sense to me too).

Thanks for any comments,


gary

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