Suggestions on removing a main vent

The only damage I think you risk is to the vent itself. If it tears off you will not be in a great situation.

But if it were me, I'd show it who's boss. I've never met a 3/4" fitting that could resist my 18" wrench, and if it does, put a cheater pipe on it and it will beg for mercy.

Or if you are at all concerned, call a plumber to do it. He will be able to fix any damage he does, we hope.

What is that plank in front of it?

When you go to replace it, run an "antler" of pipe using a street 90, a nipple, and an elbow in the general direction of the camera so you have more room to work and maybe be able to install multiple or larger vents as needed.

Large adjustable wrench.

Get a helper and TWO propane torches and simultaneously heat the iron boss that the vent is threaded into. Heat it for three minutes. Instantly remove the vent. A pipe wrench with an extension should do it. If you have the big socket with a two foot extension, that will be an even better choice.

I would jam a smaller pipe nipple or large bolt into it to keep it from collapsing to the shape of an egg.

Or try an "easy out" that is a tight fit, it may not unscrew it but with it tightly engaged on the vent brass then I would get a good bite with good pipe wrench with 3 point contact on the brass itself.

Socket and long breaker bar would work if a tight fit on the flats.

Also if slipping would probably not collapse the vent.

Personally I'd put a 14" or 18" pipe wrench on it, with a cheater if necessary. I wouldn't put fire there.

Did you apply a wrench to the top part and it broke off?

If it turned some it isn't seized and will come out if you don't crush it. Heat won't do anything you haven't already done, you just need the right too to grip it without squeezing it. A smaller pipe wench and a piece of pipe on the handle might do it too, but if you use a pipe wrench it would be a great idea to put a piece of pipe or rod or even a big socket inside it to keep the crushing force from the pipe wrench from crushing it like @JUGHNE suggested. A six point socket wouldn't need the pipe.

I'd probably use a street 45 to a nipple to a street 45 to 2 street 90's(or one street 90 and one nipple with 90 if the tee doesn't give you enough clearance between vents) or put the tee right on the 45 nipple if there is enough space front to back to put the run of the tee parallel to the main and use the 90's to point the 45 straight up.

You can install the two vents, but why if one does the job? Assuming your steam is dry, the brand/type of vent will do more to drain the water than the piping. Getting the vent away from the main may help protect it from hammering if that is a problem. As readers know, I'm not a fan of Chinese vents, but the Maid-O-Mist and Gorton design usually drains water fairly well.

Like this:

If you can rotate the part in green 90 degrees toward you, you can use a 90 instead of a 45 there depending on what works out better.

I think your plan is fine, but I'd use a longer nipple after the elbow and aim the vents in your direction so that they are easier to reach and deal with.

You will also get the correct pitch from them if they are parallel with your main as they would be if the "antler" was pointing in your direction (from the point of view of the photographer).

I can understand the desire for a union, but the way this looks I would actually not want to mess with a union because they can be a little tricky to get installed/tight with just one hand and it looks like in that joist bay you don't have room to be reaching in there too much.

Yeah, I can't see everything in your photo but I would try to have it coming back toward you, roughly along the same axis as the main.

Hi, All I do is hot water, so large grain of salt… I'd think about using a street 45 up from the main. Then a longish nipple at 90 degrees to the main, heading to the right. Then a 90 pointing back, parallel to the main. Install your vent T but then add another T, not a 90, so you can put a plug in the end of it to clean out the antler if ever needed. This approach gives you clearance and working space around the vents as well as keeping them well above the main.

Yours, Larry

I think you are getting a lot of ideas here because there are a multitude of ways to do it. You want the vents to ideally be as high above the main as possible and on an antler that allows condensate to flow back (not horizontal because sometimes horizontal ends up slightly pitched the wrong way…). I am sure you can figure out a configuration that works for you in your space that holds to these two principles. Remember, with the use of just two 90's with a short nipple in between them you can create a pitch to your antler at any angle and pointed in any orientation you want. Think about this concept in your plan.