Uneven distribution of Heat in Gas/Hydronic System

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Old 12-11-07, 01:45 PM
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Uneven distribution of Heat in Gas/Hydronic System

I'm looking for advise on what the issue could be, I've attached a photo of my boiler setup. Here is the scenario: I have a 4 story townhouse with about 24 cast iron radiators (6 per floor). The system is single zone, water circulating each radiator having their own return. The boiler distributes the heated water through 2 different lines (as seen in the picture). The problem is that the radiators fed from the line on the left "branch" are not getting very hot, some on the upper floors are not getting hot at all. Also, once the boiler is called for heat, the water temp heats up fast and high, high enough that the boiler shuts off. My first thought is that the circulator is the culprit. But please lend you expertise to the resolution of this issue.

 
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Old 12-11-07, 04:09 PM
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Looks like the Kodak gallery doesn't allow linking, so here's the URL for the picture.

This doesn't work either...

Try posting the picture on www.photobucket.com (free) and provide a link here.
 
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Old 12-11-07, 07:51 PM
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Here is the pic

Thanks for the tip...
 
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Old 12-12-07, 02:45 PM
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I a four story building, you will need quite a bit of pressure ... so the first thing is to tell us what the pressure reading on the gauge on the boiler is.

Is this a new development for you ? Or perhaps you've recently moved in ?

If you have 4 stories, and the boiler in the basement, it's possible that you might have almost 50 feet of elevation from the boiler to the highest radiator. If so, you would need about 25 PSI on that gauge when the system is COLD, and when that water heats, the pressure will go up.

With that many radiators in the system you have a large water volume. That small expansion tank may not be big enough for the job. It's possible that if you do find the pressure to be low on the boiler, and you take steps to increase it, you will find your pressure relief valve opening up and spilling water.

So let us know the pressure, and we'll go from there ... (while you are at it, tell us the temperature also, it should be on the same gauge)
 
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Old 12-13-07, 04:30 AM
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This is not a new development (the house is almost 100 years old), I have been living here for the past 5 years and for the most part the heat has been fine with the exception of the occasional need to bleed air from one particular radiator on the top floor.

When cold the pressure is at 15 psi, when called for heat the temp rapidly (within 10-15mins) gets to 240 degrees and a little above 20psi and shuts off. Presumably because the temp is so high.
 
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Old 12-13-07, 02:50 PM
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I'm afraid that the only way to get rid of the occasional air problems you are having would be to bump up the system pressure, and install larger expansion tank (or tanks). This would also more than likely improve the uneven heating situation.

I'm quite sure that if you increased the pressure to where it would need to be, you would have relief valve opening.

240* is quite a high temperature... but your temp gauge on the boiler may not be entirely accurate. If it were my system, I wouldn't really want to see much over 200 or so.

Your pressure increase of 5 PSI from cold to hot is reasonable, but I'm willing to bet that some of your radiators currently have some air in them and are acting as 'extra' expansion tanks, because with that much water in your system (you said 24 standing radiators, yes ?) that little tank that's on the boiler isn't big enough.

So, if you wanted to 'fix' this problem, you would start by increasing the system pressure, bleeding all the air out of all the loops, carefully estimating the volume of water in the system based on the rads and piping, and install properly sized expansion tank(s) as needed. In fact, you would probably need MORE expansion tank than usual because your system at say 25 PSI cold could not tolerate much more than a TWO PSI increase from cold to hot.

I bet this system has been troublesome since the day it was installed...
 
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