Main vent questions - newbie

So are those two main vents venting OK with that pipe pitch issue? No water, gurgling, spitting or anything? Can you witness air being expelled once steam has reached the header at the boiler and begins to travel down the main? Then, witness them closing when the steam reaches them? If they vent fine without issue then I guess you don't need to change anything there. (Sorry if you answered this before somewhere… TG morning, no time to go back and read).

To make a long story short. The vents pictured are doing little because of the back-pitched pipe. That pipe, as you know, fills with condensate, rendering the vents useless.

Your earlier-mentioned concerns are well placed as to how to correct this issue. Removing that end run of the tee to improve the vent piping can turn into a nightmare. That ? 2" x 11/4? x 11/4 ? Black cast iron tee can crack and open up a large can of worms.

If it were me, and I had access to a mega press fitting and tool, I would cut the pipe back and repipe with a mega press ell to the left of the beam. This should fix the venting issue. And while you are at it, build a nice new antler vent set. I hope you can find a Mega press. If you can, do that. There's less chance of cracking a fitting or damaging anything else.

Based on what I am seeing they are at the end of one of the mains after the last run out but piped off of the main incorrectly on their own runout after the turn down to the dry return. Per Dan's book they should be on the main after the last runout but before the pipe in the lower left corner of the picture, dry return, which carries condensation away from the main and the vent so it can do it's job and vent the air out of the system.

The current location will fill with condensate and has no way to drain other then building pressure and blowing water out of the vent which defeats the purpose of having vents in that location.

Note in the picture above the vent is inline and not on an off shute so it does not have issues with puddling and drains properly.

This can easily be fixed by plugging the current extension at the main and placing the vents at the end of your dry returns before they turn down to wets were your danger sign is, they will work as designed since they are not blocked by water in the pipe and your system will breath much better and work more efficiently.

29 % duty cycle does not seem too bad.

So the boiler will be less than 283. A system EDR of 302, that may work fine. You would have to see how well it keeps up on the coldest day of the year.

If it were my system, I'd fix the possible present main vent puddled water restriction as previously discussed. I'd also insulate the 18' main and put an appropriately sized vent on the end of the 18' main.

Based on the pic you posted I agree with @109A_5 you need to insulate the main on the right.

The main vents on the far left should be plugged to eliminate the the pooling of water and blocking the vents from venting. You should relocate the main vents to where the "90 degree T" arrow intersects with the return, the pipe below where you indicated "Vents?" and put them on a six inch nipple so they can drain and vent correctly. This will let your system breath correctly and have your vents in a place you can service them easily when needed.

You probably want two Barnes and Jones Big Mouths or two Gorton No 2's for the vents. The more main venting the better.

If you can't access the end of the main another option to consider is putting a main vent before the radiator valve:

An 18' main is not that long so you might be OK just doing the #6 on the radiator but more venting would be better. What pipe size is the 18' main?

I'll bet the mains are connected in the dry return, just to the left of the fat red downward arrow in the picture above. There's be no reason for a Tee at the left of the image otherwise. If that's the case, it's a good location for the main vent, it just needs to be big enough for both mains… and the air needs to be able to get to it.

At 29 % duty cycle at about 40 degrees and 50% duty cycle at 10 degrees I think I would keep that nozzle size.

Unless you need the heat in the basement from the uninsulated main I'd try to insulate it as best as possible. Maybe the next pipe size or two down to cover 75% of the pipe would help.

Filling the main(s) as fast as possible, minimizing reheating them with each new cycle will provide the best fuel economy and system performance and efficiency.

Slow heating on your long main was your initial stated issue so I would say you just focus on the main venting on that and once done then see how it balances out with the short main.