Single Pipe Steam boiler and operating pressure.

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Old 12-04-08, 07:43 AM
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Single Pipe Steam boiler and operating pressure.

Hi everyone!
I am a new homeowner that is trying to master steamheating. From what I read on forums and recommendations, steam heat operates best at low pressure. I had a guy come skim out the boiler and he raised the numbers on my pressturetrol, Main 3 and Differential at 2. So my system will crank on and shut down at 5psi.
My question is, how come my boiler is producing so much steam? Is it because of bad radiator vents that is not allowing the steam to fill my rads quick?

I can simply lower the limit on the pressuretrol, but this will cause my unit to short cycle a ridiculous amount of times when the t-stat is calling for heat. For example, 2 degrees, the unit will cycle off(due to pressure) a good 10-12x before it reaching the t-stat temp.

How do I go about diagnosing this issue?

Thanks.
 
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Old 12-04-08, 11:59 AM
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Adequate venting is key to making low pressure steam work properly.

Are your radiators getting hot quickly, or does it take a long time for steam to get to them. If it takes a long time, then your problem may be undersized (or missing) main vents and/or insufficient radiator venting. The mains are the pipes that make the loop around the basement, and should have vents near the end of the horizontal run, before they turn down toward the floor.

If the venting of mains is inadequate, then the steam can't push the air out of the way and can't get far enough down the pipe to reach the branches that go to the radiators. If the radiator venting is inadequate, then the steam can't push the air out to heat the radiator. Either way, if the steam isn't reaching and condensing at the radiators at the rate it's designed to, then the pressure builds up quickly. The lower the pressuretrol setting, the more frequent the short cycling. Cranking the pressuretrol up temporarily delays the cycling, but is a bad solution to the problem. You'll spend a lot more fuel pressurizing the steam way beyond where it needs to be.

Now, if your boiler is grossly over-sized, it will also short cycle and you can't do much about this other than underfiring the boiler at a lower rate or replacing it with a properly sized unit.

My own boiler is oversized by 50%, but I'm underfiring it by 30% and it working reasonably well.
 
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Old 12-04-08, 12:49 PM
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Thanks.
How can i underfire my boiler? do i need to modify it myself?
 
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Old 12-04-08, 09:33 PM
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Depends on the burner. Either by reducing the manifold pressure or installing a smaller orifice. You'll need a professional to do it. Without a combustion gas analyzer to check out the combustion by-products you could end up with a hazardous situation in your home, not to mention inefficient combustion.
 
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Old 12-05-08, 06:23 AM
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Just remember code states you cannot reduce more than 20% providing the manufacturer allows it. I know some units may not be reduced. You must look at the rated input and not what it is fired at now. In gas a lot of the units do not come out at 100% of rate. As far as changing gas pressure you are limited to about 0.2 tenths of an inch w.c. The rest has to be an orifice change. DO NOT let anyone pull and plug ant orifices.
 
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