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@ethicalpaul wrote "We agree on much, but I don't think I've seen radiator runouts vented by a #4 get much if any steam before a well-vented main."

Paul and I had been going back and forth about this since he wrote "a #4 is not too fast , ever" at the bottom of page 4 of my DIY-boiler-install thread.

I disagreed with this sentiment because I observed MoM-#4-vented radiators start to get hot before the main was completely filled. I have a single main that is a square loop, 20 ft to a side, with fourteen risers branching off, twelve of them active.
The first riser goes to a large radiator on the south side of the living room — where the thermostat lives — and the last riser goes to the living room's north side, with eighty feet of main between them. The earlier observation was that several sections of the south radiator were hot before the north radiator saw steam. Since that one is vented with a #5, it fills quickly and warms the room, eventually ending the call for heat.

Some months back, I had done a simple experiment by maximizing the venting of my main, removing one of my two vents, leaving behind a 1" hole — and I found that the main filled a little quicker, like in 8 minutes instead of 9. No big deal, right? What I didn't do in that test is go around the house checking radiators.

So last night I repeated the exercise, but more carefully.
Once again I removed the MoM main vent, leaving behind a threaded one-inch opening.
I started the call for heat and set a stop watch when the flame came on.
04:54 Steam develops
05:34 The elbow at the start of the main is hot to the touch.
Now I knew I had a few minutes before the main would fill completely. I put my hand over the one inch hole and felt the air pulsating out. A LOT of air.
I opened the valve to my low-pressure gauge and read a fairly stable 5 inches of water column.
[07:55 Cyclegard does its thing]
[09:05 Cyclegrad is finished, burners resumes]
12:32 Seven minutes after the FIRST elbow of the main is heated, the LAST elbow is hot to the touch. At this point, all risers see steam.
12:55 The main vent antler gets hot. At this point, I shut the boiler off, which I had not done in earlier tests.

I went around the house and checked the radiators.
All of them were cold, and so were their riser pipes coming up out of the floor.

I reinstalled the main vent and resumed the call for heat. The living-room south and north radiators heated pretty much in unison. Was Paul right after all? How awkward…

This morning, I repeated the exercise with the main vents in place.
The observed pressure was unchanged, at 5 inches water column.
Once again, as soon as the antler got hot, I cut the power to the boiler and checked my radiators.
They were all cold.
BUT: the steam risers were hot, and steam was just starting to enter the radiators. As soon as the main vents were closed, there was lots of steam available and radiators started heating quickly. The upstairs radiators, which have 20 to 30-ft risers, were well behind, of course.

What did I learn from this exercise?

(i) My main is vented well. I can speed it up a little by playing tricks, but there's no need to add more vents.
(ii) The #4-vented radiators are so slow that they 'steal' only enough steam to heat the risers. Once the main is hot, the radiators farther downstream do a good job catching up. The system is pretty well balanced.
(iii) Once the main is full, there is a LOT of steam available, and the first-in-line radiators heat up quickly. That is what caused me to believe the #4 vents were still too big.
(iv) The main obstacle to even heating throughout the house are the long 1-1/4 inch risers to the upstairs… which is why our bedroom radiator, which is the second-to-last riser off the main, also has a #5 vent on it. It is fairly small, and quickly heats all the way across.

So that's what I did on my summer vacation, submitted here for your edification and reading pleasure.

cheers -matt

So now I'm not only having trouble procuring a mystery part, I'm also not having any luck finding the three-burner bracket I need to support the burner tubes on the far end of the gas manifold. There are none in stock, even at the factory.

When I gently pointed out that they need to be made for the 63-03L model, I was told that Peerless was moving to the '63x' model — which I think™ is the Burnham clone I've read about on the forum recently.

I just hope I'm right in thinking I've got a lifetime supply of Peerless boiler in my basement right now…

As far as the bracket, I might be able to work something up using vent pipe and tin snips. If that looks iffy, I'll just leave everything as is.