Air Vent Sizing

fxrgrunt

On most of my radiators I have Hoffman 1As. I keep seeing that they are less than Ideal due to the adjustability not actually being accurate. I was thinking of switching to MOM not adjustable but I am not quite sure how to properly determine the size I need for each radiator. I read in the past that the location from the boiler mattered but then I read that of main venting is proper that you should be sizing primarily off the size of the radiator. The pictured radiator has the following specs.

33 1/2" L x 23"H x 8"W

14 sections

5 columns

Foot long 1" riser

Foot or two of 1 1/4" pipe off main line

Thanks in advance.

Jamie Hall

It can get messy. There is, fortunately, a very simple approach, though it doesn't appeal to the number crunchers among us. Does the radiator heat the room as you want it to be heated? Do the rest of the rooms heat the way you want them to go? If so, the vents on the radiators are OK.

Now a slightly more general approach. You want the mains to be vented quickly, so that steam has a chance to get to all the various radiators at more or less the same time. You want each radiator to be vented just fast enough that during a normal heating cycle it will heat the room as needed. If the room is too hot, slow the venting down.

The Hoffman 1A is a perfectly good vent. Granted it's a bit fussy to adjust, but once you get it dialed in it will stay that way for a very long time unless it's abused.

If it's heating the way you like it, leave it alone.

If you do decide to start changing things to MOMs, get a number of varying sizes. You will need to swap them around on various radiators -- probably several times -- before you get the venting balanced properly.

fxrgrunt

Jamie Hall said:

It can get messy. There is, fortunately, a very simple approach, though it doesn't appeal to the number crunchers among us. Does the radiator heat the room as you want it to be heated? Do the rest of the rooms heat the way you want them to go? If so, the vents on the radiators are OK. Now a slightly more general approach. You want the mains to be vented quickly, so that steam has a chance to get to all the various radiators at more or less the same time. You want each radiator to be vented just fast enough that during a normal heating cycle it will heat the room as needed. If the room is too hot, slow the venting down. The Hoffman 1A is a perfectly good vent. Granted it's a bit fussy to adjust, but once you get it dialed in it will stay that way for a very long time unless it's abused. If it's heating the way you like it, leave it alone. If you do decide to start changing things to MOMs, get a number of varying sizes. You will need to swap them around on various radiators -- probably several times -- before you get the venting balanced properly.

Thanks! I think that particular one works well. I just wanted to know if I was supposed to be doing something different or how it's determine what is correct. I will have a better idea if my dining room radiator is working now after insulating the pipe and everything. That was covered in a thread from yesterday though. I appreciate your time.

wlgann

Mr. Hall's answer is correct. But if you want to dig into it, you can do the math by calculating the volume of air in the pipes between the main and the radiator (there's a table for that, but it's not much in this case!) plus the volume of air in the radiator (there's a table for that, it's also not much). This is a case where there's just not a lot of air that needs to be vented and you can probably use a pretty slow vent, if the main is vented properly. The MoM vents I've been buying come with a bunch of different opening sizes that screw into the vent by hand, and that's worth an extra buck or two. In this case I would either leave it be, since the existing vent is doing a good job, or I would start with MoM's #5 (second slowest) and go from there.

fxrgrunt

wlgann said:

Mr. Hall's answer is correct. But if you want to dig into it, you can do the math by calculating the volume of air in the pipes between the main and the radiator (there's a table for that, but it's not much in this case!) plus the volume of air in the radiator (there's a table for that, it's also not much). This is a case where there's just not a lot of air that needs to be vented and you can probably use a pretty slow vent, if the main is vented properly. The MoM vents I've been buying come with a bunch of different opening sizes that screw into the vent by hand, and that's worth an extra buck or two. In this case I would either leave it be, since the existing vent is doing a good job, or I would start with MoM's #5 (second slowest) and go from there.

Where are you picking up the ones that come with the extra opening pieces?

dopey27177

I agree with Jaime Hall

Venting is not an art or technical item. The technical part will get you to a reasonable state of operation.
There are some issues that occur in steam systems:
A riser that is to long, a branch line the is just to far from the riser or an over sized radiator in a room.
Those exceptions require some vent valve swapping only if the room is under heated or over heated.

The radiators do not need to be heated all the way across in mild weather, the boiler runtime determines if the rads are fully heated,

Jake