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Which Buderus to choose - G115WS/5 or G215WS/3

Hey_Obie Member Posts: 66
I am trying to figure out which of these oil fired boilers I should choose. Both of the boilers have similar features. I wanted to go with the G115WS/5, but I am concerned about the size of the Return piping being only 1". That seems too small to me. My current piping is 1 1/4" and I just added DHW on a 3,000 square foot old farm house. One inch justs scares me.

Here is the comparison of the two models. Any thoughts areciated

G115WS/5 vs G215WS/3

BTU/Hr 136,000/134,000

GPH 1.0/1.1

Vent Size 5/6"

Supply Pipe Size 1 1/4" / 1 1/2"

Return Pie Size 1" / 1 1/2"

Weight 476/400

Sections 5/3


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,385

    the heat loss? Unlike most things in life,bigger is not better in this case!
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  • Hey_Obie
    Hey_Obie Member Posts: 66
    I wish I could calculate heat loss easily

    To calculate the heat loss in my house, it would require a very experienced person. It is not simple at all and I would not trust my calculation. The house was built around 1890 and an addition has been added in 1985. Some of the house is insulated and some is not. It has a partial cellar and 2 crawl spaces. Most of the windows have been replaced but some have not. There are some air leaks in some of the old attic windows and the front door is original and has single pain glass on the side panels. So on and on it goes.

    But I guess I should give it a try. Is there a website or document that will guide me through the heat loss process?

    FYI - The units I am looking at are smaller than what I currently have. I have an old HB Smith that has a low and high rating of 140,000 to 160,000 and currently has a 1.35 gph nozzle.

    So I am comfortable dropping to a 1.0 GPH nozzle with a Net BTU/HR of 119,000. Smaller than that, am I am afraid of being too small on the coldest months of the year. But that is why you do the heat loss calc.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    blow it

    back up to 1 1/4 at the return if you need more than 80K to heat the home. Water will just see the 1" port as a bump in the road.

    Have to do that heat loss. I would try to use the G115 if possible, the 215's are beasts, burners are bigger and noisier. Try to get that loss to under 40 BTU per square foot by insulating/tightening up the envelope/at least anticipating future envelope improvements when doing the heat loss.

    I remember your posts about zone valves for your proposed indirect water heater, and my two cents is that I would use a dedicated pump for the indirect. Always. 

  • Hey_Obie
    Hey_Obie Member Posts: 66
    BTU Rule of Thumb


    Since you mnetion BTU/sq ft, I remembered that I found this BTU Rule of Thumb on the Weil McClain site a couple of months ago. This doesn't take into account R value of insulation and lots of other things. I guess that is why it is a rule of thumb. It is a basic table of Climate vs BTU usage per square foot.

    Climate BTU/sq ft

    Hot 20

    Moderate 35

    Cold 50

    I live in Northern MD, which I would call a moderate climate. If I take into account that parts of my house are not insulated to today's standard, that would bump me up to maybe the 40 BTU/sq ft that you mentioned. At 2800 sq foot house, that would put me at 112,000 btu.

    The G115WS/4 is real close to being undersized depending on whether you are supposed to compare Gross Output (109000) or Net IBR (95,000). If you compare to Gross Output, then I am right there. If you compare to net output, then the G115WS/5 (gross 136,000, Net 119,000) is the right one using this rough rule of thumb.

    But I will stay away from the 215. Noise is currently an issue with my current system. So a quiet burner is better.

    Life is full of choices

  • Robert O'Brien
    Robert O'Brien Member Posts: 3,385

    NX is the quietest in a G115
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