Correct Venting for faster Radiator heat up??

As long as everything is sloped to drain…

You may not want to use a C on the attic radiator. The radiator takeoff and riser, at 3/4", are below the 1" minimum size for one pipe steam. If you vent that quickly, the steam and condensate may interfere with each other, causing gurgling and spitting from the air vent. Slower venting may be needed to prevent this.

I believe the attic radiator is not heating because of water trapped in the sagging pipe, not because of a venting issue.

Do not worry so much about the length of time to fill all the radiators with steam. Most of the time a partial fill will satisfy the thermostat and avoid overheating the house. The important thing is that the system heat evenly most of the time, though this may vary in unusual weather conditions.

Regarding the Gorton #2 main vent, you have 90 feet of 2 inch main, right? @steamhead says that's what you need, and you will not find better advice on steam heat.

The #2 vents about four times as fast as the #75. It's a no-brainer.

Try radiator 5 with the orifice plate removed from the vent, see if the steam gets to the radiator faster. If those holes are not lined up correctly with the port underneath or have debris in them it may not vent correctly.

ideally, the order of the radiators on the main should not matter. This is because there should be enough main venting that the whole main fills up with steam before very much steam starts heading to any radiator

Yes, balance/timing problems are almost always due to the venting. That vent in the picture is certainly old.

There can be cases where bad pitch of pipes causes a water trap to form that partially or totally kills steam to the affected downstream radiators.

Think of it this way. Steam takes the path of least resistance. The resistance is the air already in the pipes that needs to be pushed out through vents. Theoretically a well operating system should have adequate main venting such that when steam starts being produced in the boiler the air gets pushed out of the main first because the main venting at its end is vastly greater than the venting at any single radiator. So, steam will travel through the main pushing the air out ahead of it through the main vents. When steam reaches the main vents it/they close so now the path the steam can start pushing air out of the takeoffs and risers going to the radiators. How much goes to any particular radiator vs the others depends upon their relative venting amount. Time to fill any particular radiator depends upon the volume of air in the takeoff leading to it, the volume or air in the radiator and the venting rate of that radiator vs the others. Your control over this whole process for getting steam to radiators evenly includes starting with enough venting on the main to get it to completely vent and fill with steam within about a minute of when steam first reaches the header. It takes longer with a cold system than with pipes because the cold condenses the steam quickly. Next access how long each radiator takeoff to the main is and how big the radiator is to decide relatively how fast of a radiator vent is needed on each radiator.

Did you replace the main vent?

Do that first and then see if you need to slow down or speed up individual rads.

No one can look at your drawing and tell you which rooms are going to be too cold.

I honestly would just forget about worrying about anything until you can get your new main vent.

@dabrakeman excellent idea!

You need more venting.

• Run your system until the main fills with steam
• Let the system rest for 15 minutes
• Run it again until the steam again gets to the 75 (verify the 75 is operating). Time how long this takes.
• Let the system rest for 15 minutes
• Remove the 75
• Run it again until the steam gets to the open pipe. Time how long that takes.
• Install the #2 within 15 minutes, allow 15 minutes to elapse
• Run it again until the steam gets to the #2. Time how long that takes.

Now you will have a series of times that your system took to fill with a variety of vents and even an open pipe. If the #2 took very much longer than the open pipe, then you can consider to add the 75 to it.

Hopefully the 3" to 2" transition was done correctly and the 3" does not have a bunch of water trapped in it.

It has been suggested that larger mains need more venting, which is undoubtedly the case when everything is sized proportionally.

But I believe this is only true if your boiler can supply steam fast enough to overwhelm the venting capacity.

Any boiler will produce enough "gas" to fill any main in a minute or less. But since the steam collapses as it heats the main, "heat" moves along much more slowly. This is also dependent on insulation, and time between calls for heat, and of course on the size of the boiler.

My system has 80 feet of main in a loop, most of it 2.5 inches. When cold, it takes about ten minutes from the time the boiler supplies steam to the time the end of the main gets hot, and that did not change measurably when I used the one inch tap as a "vent." This is with a properly sized boiler for our 320 square feet of radiation, but the house was designed for an EDR of 475 originally. So the main is rather large.

My radiators are vented tightly (MoM #4). I'll be doing some tests over the next week — starting by plugging all radiator vents — to see how venting affects the heating up of the main. The results will be posted on my DIY Installation thread.

cheers -m