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

HTM

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

The water volume is not germane to boiler sizing.

Jamie Hall

Nor is the size of the piping fittings, at least within reason. Not to worry.

HTM

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
appreciated.

Fred

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

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

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

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

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

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

You can't size it properly without the heatloss. If your friend isn't doing them that would be a red flag for me.

newagedawn

btuh/10000= gpm, thats what you need to size supply and return

newagedawn

peerless and buderus are excellent boilers

HTM

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

Newagedawn - could you please elaborate on your return and
supply sizing comment? Thanks.

HVACNUT

@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

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

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

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.