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Thread: Bosch Greenstar 151 Combi

  1. #1

    Default Bosch Greenstar 151 Combi

    Any thoughts on these?

    I haven't used one to date. Am considering using one for a system consisting of two zone infloor heat (concrete basement slab and garage slab) and DHW requirements, and possibly hydronic air handler in future if second story requires supplemental heat...

    thanks

  2. #2
    In the trades Dana's Avatar
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    Default

    What is your design condition heat load? What's the BTU/hr out of the proposed air handler?

    The minimum nominal output of the would be about my peak design heat load, in a climate similar to most southern Ontario locations, and I'd almost never get the benefits of modulation out of a beast that size. It's almost certainly oversized for any one of your zones, but the thermal mass of the slabs may protect it from short-cycling it to death on zone calls. At max output it's more than 4x oversized for my 99% design condition whole house heat load, and enough heat to run 3 low-flow showers continuously forever.

    All good heating designs start with a room-by-room/zone-by-zone heat loss calculation at the outside design temperature for your location. Sizing the boiler appropriately for both the peak & average loads as well as the output of the heat-emitters can make a huge difference in comfort & efficiency, and oversizing the boiler is the enemy of both.

    New construction, or retrofit?

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