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# Sanity Check Calculating Convector Cubic Ft/Air per SF EDR for + Valve and Balancing Needs

Member Posts: 41
Hi everyone,

I'm working on balancing my steam heating system, a subject I've started in another thread. (which should be vented ok now, update on that to follow after the weekend) I downloaded and read the "Balancing Steam Systems" pamphlet by Gill & Pajek, which I've found most helpful. I'm trying to calculate what my radiators might need for valves, and I was wondering if someone help with the following few questions:

1: Does anyone know the "Cubic Feet of air per square foot EDR" figure on a convection or fin (not sure which is the right term?) radiator like mine? (pictured) This type isn't in the calculation table the pamphlet above provides, and it seems I need it to calculate the correct valves. An attachment question to this would be if it varies at all by length of the radiator

2: PSI- I'm assuming 3PSI boiler pressure is ok, or best? The pamphlet above covers 1-3oz of pressure. Pros and Cons? I'm running a ~12 year old weil-mclain if that matters

• Member Posts: 4,108
For the sake of discussion about steam, pressure is bad. Less is more in this case. 3 PSI is ludicrous in a house. That being said the pressure is a function of venting and boiler size, so if either one isn't correct you will only do so good. I saw you improved the main venting, but the boiler size (I don't know where you are there) is something you are stuck with.

Those convectors have some sort of pipe running through the fins, I would just measure that and calculate the internal volume. I don't think EDR would be the way to go with them.

There will be more to balancing with venting than just the volume. If you have warmer and cooler rooms that will impact venting as well. It's a bit tedious, but not difficult work.

For me I started with the theoretical vent sizes based on calculations, lived with it for a few months through different outdoor temperatures, then adjusted accordingly. I have 7 rads and I think after the initial I outright changed 2 and moved 2 from one location to another. That was just my experience.
2014 Weil Mclain EG-40
Boiler pictures updated 2/21/15
• Member Posts: 7,824
edited January 12
They will do all the major air removal, at less than 2 ounces of backpressure on your gauge. When you are sure of that figure, then try different settings on your radiator vents, as they have only to allow the escape of the air in the radiator, and the riser it serves, and cannot handle the big job without burning extra fuel to push all the air out of their constipated little openings.
Using the cubic foot calculations could still leave you with more time to get the air out. \$\$\$\$\$\$\$—NBC
• Member Posts: 10,383
And don't over think it. Calculation and spread sheets and all are all very fine, but there's no substitute for actually doing the venting. Main vents first.
Jamie

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 41
Thanks all! Mains are in theory done via a Barnes and Jones big mouth. Vertical runners to the 3rd floor I don't think have vents, but I have no idea are they would be in a wall.

Math sanity check to follow once I calculate the tube capacities.... thanks!
• Member Posts: 41
Hi everyone- a quick question: If I have a vertical main feeding two convection tube radiators on my top (3rd) floor, but the radiators are different sizes (32" and 48"), do I need to adjust valves accordingly? The 32" currently heats MUCH faster and warmer, but they have different valves (32" is a Gorton D, the 48" is some mystery el cheapo without markings I intent on replacing, but no idea with what.) so I thought I"d ask before swapping anything into the 48" incorrectly. I would assume another "D", but thought I'd check
• Member Posts: 7,824
The vents should be the same size for each, but maybe not so fast as a Gorton D. Some people here have experienced problems with a large vent short circuiting the interior steam flow in the radiator, thus only filling the rad halfway.
Try a pair of the vents with changeable orifices (Maid of the Mist??), for ease of adjustment.—NBC
• Member Posts: 41
Thanks! I had a used D on hand, so I slipped that in just as a temporary fix. Will see what happens, or if it balances with the other radiator off the same main

Side note- how can you tell if an old valve is good or not? I have a few that "look" ok, but they are ancient...
• Member Posts: 7,824
Generally, if you can blow through them, and they close 1against low pressure steam, they are functional. Old Hoffman’s were very well made.
The main vents are doing more work, and seem to be less long lived. I suspect the Big Mouth to be longer lived than Gorton because of the internal differences.
All vents can be rendered useless, if the pressure gets too high, so yet another good reason to have a low pressure (0-3 psi) gauge.—NBC
• Member Posts: 41
edited January 19
Thanks Nick! I'll report back soon... Running just under 2psi at cutout now (the prior owner had it way high), so I"m hoping all works out.

It looks like overnight nothing has really changed, although the heat in the apartment seems to be spread evenly. So the next question: do I slow the second floor (thermostat floor), or try and speed up the third floor? If I can just get the third floor up 2-3 degrees this project is done!