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Gold Mine

Looking for official documentation stating that certain classes of German boilers are limited to 75°F (167°F) supply temperature under "normal (e.g. most efficient)" operating mode.

My own system is so simple that you don't need a drawing. 1" supply and return lines from the Vitodens connect to gravity mains (3") via 1¼" transition. Differential pressure bypass valve (1¼") between supply/return near boiler piping. Air purge in the supply line; wye strainer in the return. Isolation valves for service. Original plain expansion tank with Air-Trol fitting. TRVs on all the rads. Nothing else save the "super-simple" radiant loops (baths) that currently just tap into the mains at any convenient location.

Old boiler (W/M CGM) and circulator (B&G 100) are still installed, but are completely isolated when the Vitodens is operation. Can completely isolate the Vitodens and operate the old. Had planned on some head-to-head economy tests this season but with natural gas so high right now, I'm too cheap.


  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Found this article while searching for "proof" of 187°F German government imposed supply temp limitations for certain types of boilers.

    Don't be put off by the title or the manufacturer name. EXCEPTIONAL info regarding condensing, modulating, maintaining low operating temperatures, physical laws governing ANY boiler, payback calculation, etc., etc., etc.

    Medium and Large Boilers
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    More GREAT Info

    This is the "real stuff"!!!!! TRVs are assumed of course...

    Condensing Technology PDF

    Condensing Technology HTML
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Still can't find the answer to my original quest, but 75°C (167°F) supply with 60°C (140°F) is VERY frequently mentioned as "worst case" for condensing boilers throughout the European Union.
  • jp_2
    jp_2 Member Posts: 1,935

    what is your orginal quest? i understand you have no prim/sec piping in your set up? got a drawing of your piping?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Here's the System Diagram

    "Direct connected, single circuit"

    This from the 6-24 model with built-in DHW production. Ignore the DHW portion.
  • Aidan (UK)
    Aidan (UK) Member Posts: 290
    75°C (167°F) supply

    I'm not sure about the boilers, but the standard method for rating the heat output of radiators (EN 442, part 2) requires an inlet temperature of 75°C (167°F), a return temperature of 65°C (149°F) and an air temperature of 20°C. This is an EEC standard. The numbers seem similar to the ones you have.

    The manufacturers usually quote the heat output under these standard conditions and provide correction factors for different water or air temperatures.
This discussion has been closed.