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Replacement Oil Fired Hot Water Boiler - Is Size of Supply and Return Part of the Decision Process?

HTM Member Posts: 29
It's time to replace an early 1980's Weil McLain boiler - nameplate rating 167,000 DOE. Chimney vented.
Baseboard throughout first level. Recent slim-line cast iron radiators on second floor. A few old baseboards in the basement. Five zones including separate hot water tank. The zone valves have not worked well of late.
A heat loss analysis will need to be done, but I suspect the current boiler is oversized.
Water to and from the boiler is 2" copper. Same size black iron piping manifold above the boiler and a 2" iron main the full length of the basement plus 1" copper lines. Iron and copper water lines span out to baseboard and radiators.
There seems to be a large volume of water to move. Is it advisable to select a new boiler with substantial water capacity and the same 2" supply and return to match the original piping design? Peerless EC-3 would fit those criteria. Some other models by Peerless and Buderus have 1-1/2" connections and hold less water.
Thanks for your guidance.


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,483
    The water volume is not germane to boiler sizing.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jamie Hall
    Jamie Hall Member Posts: 21,105
    Nor is the size of the piping fittings, at least within reason. Not to worry.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HTM
    HTM Member Posts: 29
    Thank you Robert and Jamie for redirecting my focus. Longevity, operating economy. ease of maintenance and minimal noise are what I am looking for. I would also like to take advantage of the radiators needing less than 180 degF. I won't be the installer but definitely take an interest in understanding equipment features.
    Buderus appears to be a quality product. Piping concerns led me away from their 115 series - the 1" return seems to be on the small side. Next step up 215 series with 1-1/2" supply & return seems a better choice.
    I was drawn to the Peerless EC-03 because of its larger piping connections and the data sheet noting it as an "ideal" choice for large volume hot water applications. About 17 gallons water capacity compared to 12 gallons with Buderus. Peerless highlights the same "ideal" choice claim for their 11,75 gallon water capacity WBV-03. Having read varying comments on low mass boilers, the larger water capacity units would seem to work well in my system. The Buderus and Peerless boilers are each about 86 % AFUE.
    Granted, they are different designs. Any comments/advice
  • Fred
    Fred Member Posts: 8,541
    Have you looked at the Energy Kinetics product offering? They seem to get rave reviews for quality, reliability quiet operation. Not a cast iron boiler but that seems to work to their advantage. I think Dan Holohan, himself had one installed in his home last year.
    HVACNUT Member Posts: 5,025
    Neither the Buderus G115 or G215 are low mass boilers.
    Do your heat loss and go from there.
    I believe the G115/5 is fired at 1.00 GPH, while the G215/3 is fired at 1.10 GPH.
  • Paul48
    Paul48 Member Posts: 4,469
    The size of the boiler tappings will support the btu/h rating of the boiler. Size the boiler to the heat loss of your home, and don't worry about the supply and return at the boiler.
  • HTM
    HTM Member Posts: 29
    Thanks to all who have commented. This site is a rich resource of helpful people.
    HVACNUT/Paul48: I had reviewed the Buderus literature. The G115/5 and G215/3 appear to be fairly close performance-wise
    G115 series offers direct vent option.
    In fact, Buderus was my first choice until I had another look at the piping in the basement and thought about the volume of water to be moved. That's what got me considering the Peerless.
    If the heat loss results bear out the two Buderus models, does anyone have reason(s) to favor one over the other? The difference in supply and return sizing is all that stands out to me:
    G115/5 Supply 1-1/4" Return 1"
    G215/3 Supply 1-1/2" Return 1-1/2"
    Larger is closer to what's there now.
    Moving on to burner options, I've read good reports on Riello. But some have said it can be loud when chimney vented.
    Thank you.

    HVACNUT Member Posts: 5,025
    You'll probably find out you need less BTU's than the G115/5. When in doubt go down in size because you only need max output on a design day.
    Look at the BF Riello with ducted outside combustion air.
    Very quiet.
  • HTM
    HTM Member Posts: 29
    HVACNUT - I have confidence in a plumber/HVAC installer I know except that he had nothing to offer re the heat loss exercise. I've read up on it and will do the calculation this weekend. Will advise findings. Thank you.
  • KC_Jones
    KC_Jones Member Posts: 5,409
    You can't size it properly without the heatloss. If your friend isn't doing them that would be a red flag for me.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • newagedawn
    newagedawn Member Posts: 586
    btuh/10000= gpm, thats what you need to size supply and return
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • newagedawn
    newagedawn Member Posts: 586
    peerless and buderus are excellent boilers
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • HTM
    HTM Member Posts: 29
    Waded through a manual heat loss calculation. It was a long slog
    but believe I got it right, or pretty close. My location PA - Delta T 56 degF. Result Just under 96,000 btuh. Buderus net IBR's: G115/4 @95,000, G115/5 @ 119,000, G215/3 @ 117,000.
    Heat loss will improve when the current single pane windows are replaced.
    HVACNUT - you were on target.
  • HTM
    HTM Member Posts: 29
    Newagedawn - could you please elaborate on your return and
    supply sizing comment? Thanks.
    HVACNUT Member Posts: 5,025
    @HTM, What does Delta T 56 degrees mean?
    Your heat loss should be based on a design day. I'm sure it gets colder the 56 in PA.
    What did you use to calculate? If you haven't already tried, download the Slant Fin heat loss app. It's good and it's free.
  • HTM
    HTM Member Posts: 29
    I hashed together a paper & pencil calculation. Followed a Manual J summary I found online. Delta T 56 degrees derived from the difference between 69 degF indoor design temp and 13 degF outdoor heating season design temp for my area in PA.
    Determined u values as well as areas of exterior walls and areas net of windows/doors. Calculated heat loss using u values and Delta T for net walls, windows/doors, ceiling and basement, plus
    a factor for air infiltration.
    The heat loss result points to a boiler just under 100,000 btu/hr. I am still unclear how to know whether Buderus G115 supply 1-1/4" and return 1" are adequate.
    HVACNUT Member Posts: 5,025
    The G115 is designed with the 1" return to prevent shocking the cast iron. It will not have any effect on performance. As with any system, generously sized manifolds are recommended, so increase it to 1 1/4.
    The G215 has what they call a Thermo Stream design, mixing supply and return water internally to prevent shock.
  • HTM
    HTM Member Posts: 29
    Many thanks to HVACNUT and all who have assisted.
    I appreciate the guidance. I've been reading up on other matters
    related to our boiler replacement. These I'll save for another time.