B vent

Electbc

I have an old Utica Gas Boiler which will need replacing sometime this decade. I added a second story,
demolished the chimney and vented the boiler and water heater with B vent. This has been working fine for 20 years.
My problem is a low clearance in the basement where they are located. I can just get the fittings from single to double wall to fit. My" T" is facing up/down and tap is sideways to vent the W/H with the boiler coming up from underneath.
Can I reposition the "T" so that the tap it going up to the double wall and the two appliances opposing each other on the "T"? This would give me the clearance needed to replace the boiler with a larger one. Or would a "y" be required?
Also the B vent is 6" the existing boiler is 5", the old W/H was 3" but the new one should be 4", I replaced the W/H with one of the same size but kept the 3 " vent.
I can get a deal on a 4 year old Boiler, bigger than I need, but at $500 a Weil McClain it would be hard to pass up. This unit is a 6" vent. Will my 6" B vent be too small for a 3" or the 4" and a 6?
(Assuming the T opposing appliances are OK of course.)
If I cannot do either one I would settle for a smaller boiler and a 5" vent.

unclejohn

There are code books for that and they change almost weekly it seems.

pecmsg

Electbc said:

I can get a deal on a 4 year old Boiler, bigger than I need, but at $500 a Weil McClain it would be hard to pass up.

What kind a deal is it if it wastes fuel, short cycles, will require more maintenance?

"If it seems too good to be true it probably is"

motoguy128

I installed a salvaged boiler. It’s so much work to relocate it and get the piping to match up, especially if it’s steam, that I’m not sure it was worth it.

Not nearly as bad if it’s hot water.

I agree. Being oversized won’t do you any favors. Odds are the one you have now is lonely already oversized to the heat loss oif not the load already.

Although, High mass radiant with cast iron radiators , if that’s what you have, is pretty forgiving since most were gravity systems and have 100 gallons of water or more in them.

If you have hot water. Maybe consider a wall mount high efficiency combi boiler instead and replace both and abandon the chimney and say 10% or more on fuel.

Electbc

It is Hot water, the system used to be Upright convectors which were recessed into the outside wall with no insulation behind to the outside. The house was built in 1959 and the state of the art insulation at the time was that paper stuff which was stapled at the top and pulled down as an accordion, I forget the name of it. I had a contractor blow cellulose insulation shortly after we bought the house.
As we went along I replaced the convectors with baseboard. The system had 3/8 copper tubing loops to each convector from a manifold. I kept the 3/8 to feed the baseboard. The boiler is 100K in 80K out and 69,600 Net I.B.R.
We put on a second floor and kept the same boiler, it works fine and is adequate most of the time. We have 5 zones so we aren't heating the whole house at the same time. On the coldest days in Northern NJ, the unit runs for long stretches. The second floor is one baseboard loop with 3/4 copper. When I replace it I will go up to about 140k,. I agree that the Weil McClain deal was too big for my home, it was a thought. Thank you for input and preventing me from buying it, now it will cost me another 2K, LOL.
I do have flexibility in location but the B vent connection is the tightest. The smaller unit would give more flexibility due to the shorter height but even the 140 has a 6" vent.