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Bosch greenstar 151 single zone

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morgo
morgo Member Posts: 8
in Gas Heating
As I start my install of my wall hung bosch greenstar 151p ZWB42_3 I just want to verify this simple layout will work for my 1200sq.ft. single zone home. All the baseboard is on the first floor and so is the boiler.  My main concern is the boiler pump being sufficient. Thanks in advance for any info.

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  • morgo
    morgo Member Posts: 8
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    I'm guessing by the lack of comments my question isn't clear  Or maybe to vauge.
    I have read hear and other forums that the internal pump in the greenstar is only for circulation in the boiler. When I found this layout in the bosch application manual I though it looked like a  very simple and inexpensive option. But I want to do this right. My plumber who is my neighbor says he'd probably still do a primary/secondary with a manifold and another pump. What say you?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,870
    edited October 2023
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    How much baseboard and what’s the head loss of that baseboard? You can certainly pipe it this way if you keep the head loss within the constraints. 

    Also, be prepared for short cycling! (Unrelated to how it’s pumped) 
  • hot_rod
    hot_rod Member Posts: 22,201
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    Right above the drawing shows a note indicating what the requirement is for direct piping
    a circuit not to exceed 4 gpm snd 12’ of head

    So you need to calculate the loop you intend to connect to. I doubt you need more than 4 gpm? 40,000 btu/hr?

    next is to calculate the pressure drop if your circuit. How many feet if tube, how many elks, valves, other fittings

     That boiler may have setting to avoid short cycles
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • morgo
    morgo Member Posts: 8
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    Thanks for the input, I'm hoping the plumber will calculate that.(over my head) but he is allowing me to give him a hand laying out, making connections ect. to save a few bucks on labor and I just want to have everything lined up for him  the best I can.
     As far as the short cycling is concerned I had 3 different people quote me with this boiler so i assume its sized correctly? does anyone know if adding the fw200 controller with the outdoor reset would help with that issue?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,870
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    As far as the short cycling is concerned I had 3 different people quote me with this boiler so i assume its sized correctly? does anyone know if adding the fw200 controller with the outdoor reset would help with that issue?
    No, it’s oversized. It’s minimum fire is 36kbtu, which could very well be smaller than your maximum heat loss. But that’s the world of combis, to get the DHW capacity, you usually short cycle on heat. The Bosch is worse than most because it’s minimum fire is much higher than other options. 

    ODR is a great idea and will save money but won’t help with short cycling.
    Teemok
  • morgo
    morgo Member Posts: 8
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    Hot water fan, 🤦‍♂️ that doesn't give me a warm fuzzy feeling. To top it of my plumber just had a heart attack and not able to help much for a while so I'm going for it. I just had propane hooked up today and I plan on trying to calculate my pressure drop tomorrow like hot rod said. Is there any advantage as far as short cycling is concerned to either the direct piping  or P/S loop?
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,870
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    No, it will short cycle either way. Direct pumping saves you a circulator and the associated energy costs. 

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