Air vent size suggestions, please.

cooltoff

Hello,
One-pipe system in a 3 story brownstone building.
I need help with vent sizing on a couple of small radiators that are in the bathrooms.
In the first floor bathroom is very small, 10'" section of ? baseboard ? see picture attached.
And this radiator currently has a Gorton "D" vent on it which seems way too fast for such a small section but I don't know how figure for baseboard.

And on the upper floors the bathrooms have small 4 tube, 8 section, 20" high radiators. And these have those inexpensive Matco Norca AVA125 vents on them.

Did I forget to give any info?

KC_Jones

What is the main venting like? The main venting needs to be proper before the rad vents can be properly balanced. Many times people put huge rad vents on (like you have) to compensate for improper main venting. If that is on the first floor and doesn't have much run out from the main...a #4 should be more than adequate. I suspect your main venting isn't right and that's why someone put that on there. A D vent is the size of a #1 main vent....it's huge.

cooltoff

You are very correct in that! Currently the front main line has an unidentifiable vent (top pic) and the rear main line has a Maid-O-Mist #67 on it. (bottom pic)
I am planning on changing them both to Gorton #1's.

KC_Jones

How much main do you have? A single Gorton #1 isn't a whole lot of main venting. Unless your main is only 10-12' long you will need more. The general rule of thumb is a Gorton #2 (or 3 #1) for every 20' of 2" pipe. Measure the length and size of the mains then you can determine how much main venting you may need.

cooltoff

Hmmm. Okay. Back to the drawing board on the mains. 45' to the front and 30' to the back. And where might I find examples of putting together multiple main vents. As you can see from the pic of the front main, I don't have a lot of head room.
Now assuming I get the mains venting properly, would a #4 also be good for those upstairs bathroom radiators?

KC_Jones

I noticed the tight quarters. Search around the wall for vent tree and you should be able to find examples of what others have done. I would also suggest buying the balancing steam eBook from the store (especially if you like learning about this stuff). It should help you a lot with this, it's only 10 bucks and goes to charity. Typically you vent a little faster the higher you go in the house because of the pipe runs. There are other factors at work such as radiator size and sometimes location. Also size of radiator to size of room can influence venting rate. Each situation is a little unique. If you get those mains vented properly what you may see is a lot more imbalance in the system, but balancing the system will become much easier. It's all a process.
http://store.heatinghelp.com/Balancing-Steam-Systems-p/300.htm

cooltoff

Got it.
Thanks for your time KC, you've been a great help.

cooltoff

KC, One more question about the tree. Do I have to stay above the level of the main pipe or can I come down below in order to accommodate the height of the #2's?

KC_Jones

No you must stay above the main so water can drain. If you don't have height you can consider using 3 #1 vents for each #2. The final vent cost would be similar just some extra fittings. I have low height and had to do this on my system. Kind of a pain, but not much you can do to change the house.

Mark N

No, how is the water that collects going to drain.

cooltoff

Roger that.
Thanks guys!

Fred

That actually looks like a false tin ceiling above those vents. probably open joists above that. If that's the case, cutting an opening in that tin should give you more than enough room for Gorton #2'S.

BobC

The first vent you pictured looks like it's going to be tight for space. Try use a street elbow and then a 3/4" union to keep everything tight as possible and after adding T's and nipples for as many vents as you will need be sure there is a little slope so water finds it's way back to that main.

Bob