One Problem Radiator

denick

I replaced my boiler. Vented the mains but have one problem radiator. It is the last radiator on an almost 75' 2" main. I added 2 Big Mouth vents. Steam gets to the vents in less than 6 minutes on a start up that isn't completely cold. The radiator is the last one on that main. The takeoff for this radiator is 8" before the main vent 3/4" riser. The radiator is a 1900 ish 2 column that in "balancing Steam Systems" says it has .025 cf of air per sf of EDR. It's 38" tall and that's 4 sf a section, it's 12 sections. Using the math method that's 1.26 cf min. If I use 4 minutes as the time for the radiator to heat across that would be .315 cf min. From that a Gorton D would be perfect. Well it's not. I've tried C's and 6's not much difference. It gets about 5 sections hot and a few more warm. So I reviewed the venting pages of "Lost Art" and the pages about John Schultz's venting big radiators. I tried something out of curiosity because it will be a while before I can drill and tap for a second vent. I put 2 vents in the same vent hole. Picture attached. It made it about 60% better using 2 #6. I then tried C's and then D's they cut back on the improvement some. I then tried 2 #5 and they are the same as the 6's. I wonder why it works because my radiators don't fill across the top and then down the way it is reasoned this works for big radiators in the book? I'd appreciate your thoughts.

JUGHNE

What size and how long is the runout to this rad?
And the slope need to be more drastic for counterflow.

denick

The runout is 5'. The pitch is 1/2 a bubble on an 18" level.

delcrossv

75' of 2" main. Is the main insulated?
How many other rads are on the line, and how are they vented?

denick

The main is insulated. There are 7 other radiators on that main. The three upstairs are Gorton #4. The downstairs are Gorton #5 and #6

delcrossv

As an experiment, you may try swapping the 6 for a 5 and the 5 for a 4 just to see if you get more steam to the end.

ethicalpaul

I don't understand what issue you're trying to solve, the description was confusing to me, but you seem to be trying to vent this radiator really fast. I think that is a mistake regardless of what issue you're trying to fix.

dabrakeman

I would try to further slow down the other radiators on that main. Also, does steam reach the ends of all of your mains at about the same time?

You have true steam radiators which are joined only at the bottom rather than top and bottom as in the water/steam compatible radiators which join at top and bottom. I have the same. I actually believe there is some advantage to these radiators in that they always heat up evenly section by section even on the fastest venting radiators. Makes task of balancing a little easier.

KC_Jones

ethicalpaul said:

I don't understand what issue you're trying to solve, the description was confusing to me, but you seem to be trying to vent this radiator really fast. I think that is a mistake regardless of what issue you're trying to fix.

I agree with this I am a bit confused.

Is the room getting to temperature? I ask this because we have people come on here often thinking that the radiator not heating all the way means there is a problem. Most of the time they probably won't heat all the way across, the criteria should be if the room is maintaining temperature.

cross_skier

I have similar size mains and had inconsistent heat on some  large radiators.  Sometimes too hot, often too slow to start heating.  Not sure if this is your problem but what worked for me was to vent the heck out of the mains and to switch to multiple medium size radiators.  I have 6 Gorton 1's and an Hoffman 75 on an antler.  I also added a Gorton D on a 1/4" long nipple tapped into the middle of the main.  I replaced a large 70 sq ft radiator with two 30 sq ft radiators.  I used a 4 wheel pipe cutter and a coupling to add the second feed on a different wall of the same room.  This was a lot of work but fixed the problem

SteamingatMohawk

@denick you said, The main is insulated. There are 7 other radiators on that main. The three upstairs are Gorton #4. The downstairs are Gorton #5 and #6

Depending on their distance from the boiler, typically the downstairs vents are smaller than the upstairs.

A quick sketch would help, including the vent size.

denick

The problem I didn't clearly explain is, the radiator on the end of the long main doesn't heat enough to heat the room it is in. Which with the large doorway into the next room draws heat out of that room. Which has the thermostat in it. I made this drawing to explain the layout.

KC_Jones

You need to slow down the other radiators.

I'd say drop all the other first floor radiator vents at least one size each, then put a 6 on the problem radiator. After that if that room overheats you could start upsizing the others, one at a time, until things balance out.

Most of the time slowing down radiators is more effective for balance than speeding up.

SteamingatMohawk

You didn't post the size of the vent on #8. Are the Big Mouths on the radiator itself or at the end of the supply portion of the piping (assuming single pipe steam)?