Sizing Radiator Air Vents

Unknown

I've read Dan's explanations of radiator air vent sizing and still don't get it. We have a 1922 one pipe steam system with eleven radiators on three floors, and the ones on 3rd floor at the far end of the building don't heat well. There are two mains hugging the basement walls. No vents on the mains.

Please help me understand by answering these questions:

1. Why does Dan say to size vents according to radiator size, not location? Gorton recommends taking location into account, which makes sense to me (size a vent according to the volume of radiator PLUS piping leading to it). Even if you vent the mains, isn't the difference in riser length between 1st floor and 3rd floor significant? Why wouldn't putting huge vents on the most remote radiators be BETTER than venting the mains (OK, so I'm chicken about touching the mains...)?

2. Aside from balancing the system, is there something about the operation of air vents that makes it important to size them to the radiator? I can see why a vent could be too small for a big radiator, but why could a vent be too BIG for a SMALL radiator?

3. If the objective is to get the cool air out of the system quickly and evenly at the lowest steam pressure, why not just put the biggest vent available {like a Gorton D) on every radiator? Wouldn't this present less resistance to the approaching steam and get all those radiators filled lickety-split? So what if the closest ones filled first - the last ones wouldn't be far behind. And the velocity of the air escaping the vents would be lower, reducing clogging. Plus, the steam would spend less time in the piping so more of its heat would be released where you want it: in the radiators.

I suspect I'm all wet - please tell me why.

Steamhead

Not \"all wet\"- just slightly

The fact that there are no main vents explains your problem. Those mains hold a lot of air, and if you try to vent the mains thru the radiators you'll get nothing but aggravation.

Venting a steam system is a 2-step process. First you vent the air from the mains, in about a minute. You don't vent the radiators until the mains are full of steam, at which point steam rises into each radiator at about the same time.

Since "Lost Art" came out, we've found more information on sizing vents. You can get your hands on it by ordering Dan's "Dead Men's Steam School" video and workbook. The charts you need are in the workbook, and you get to watch Dan in action on the video (4 VHS tapes) which is not to be missed!

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tombig

Vent Sizing

Main vents are a must. Get the steam there fast. In a single zone house you can balance the system by sizing the vents. You could probably balance this system with radiator vents only but it sounds like boiler is oversized.