10 Reasons why steam heated buildings heat unevenly
Volume 5/ Issue 3/ December 2018
1. The system can’t vent fast enough.
If you can’t evacuate air from the system, steam can’t enter. It’s very important to vent the system quickly, to allow the steam travel to all radiators. Main vents are vital to the proper distribution of steam, so make sure to check them.
2. The boiler is piped incorrectly.
Modern steam boilers require the near boiler’s piping to help produce “dry” steam. Today’s boiler steam chambers are much smaller than the old ones, and steam riser connections are smaller than they used be.
3. The boiler is undersized.
A steam boiler’s job is to produce enough steam to fill the entire piping system and all the radiators. The job of the cold pipes and cold radiators is to condense this steam, but if the boiler can’t produce enough steam to overcome this mass of cold iron, the steam will not make it out to the furthest radiators. This is why you must size the boiler to the connected load, and then make sure the burner is fired to that load.
4. The steam traps have failed.
Two-pipe systems have radiator traps, and float and thermostatic traps. Their job is to pass air and condensate into the return piping, while preventing the steam from getting past the radiators and the ends of the mains. When these traps fail in the closed position, the air can’t get out, so the steam can’t get in. But when they fail in the open position, the steam passes into the return lines. Once there, it brings the returns to the same pressure as the supply lines and, with no difference in pressure, the steam stops moving. You have to make sure the steam traps are working properly for the system to operate efficiently.
No. 1A adjustable steam radiator vent and No. 40 steam radiator vent
5. The insulation has been removed from the pipes.
Steam mains are insulated so steam can reach all the radiators. When insulation is removed, the exposed steel piping becomes one very large radiator, and this additional load condenses the steam before it can reach all the radiators. If you see pipes that have their insulation removed, we suggest you either re-insulate them or make sure the new boiler is sized for this additional load.
6. The steam pipes are pitched incorrectly.
When installed correctly, steam mains and horizontal runouts are pitched to allow the condensate and steam to co-exist in the same pipe. Over the years, a building settles and pipe hangers loosen up, changing the pitch of the pipes and allowing condensate to pool along the piping. These puddles will condense the steam as it passes by, creating uneven heat throughout the building. Make sure the steam mains and runouts maintain their proper pitch.
7. The quality of the steam is bad.
If the boiler water is dirty or has a film of oil on its surface, the boiler will make “wet” steam. Because water droplets rob the steam of its latent heat, it condenses in the piping before it reaches all the radiators. Check the quality of the boiler’s water by looking at the gauge glass. When the boiler is making “dry” steam, the top portion of the glass will be dry. While the boiler is operating, raise the water line to within one inch of the top of the gauge glass. If water pours over the top, the boiler water is dirty and needs to be cleaned.
8. The wet return lines are partially plugged.
If the steam system has wet returns and is heating unevenly, make sure the returns aren’t plugged. If they are, the condensate will back up into the return, trying to overcome the additional pressure drop created by the plugged returns. Condensate will also back up into the main vents, closing them off before all the air is removed from the mains. This can create very uneven distribution of steam throughout the system.
9. Someone has set the pressuretrol too high.
Radiator steam vents have a rating that’s known as “drop-away” pressure. This rating has to do with the maximum system pressure at which the vent’s float can drop down to re-open when the steam condenses in the radiator. If someone raises the pressuretrol setting beyond the vent’s “drop-away” rating, it’s possible to close all the radiator vents in the system, and this leads to uneven distribution of heat throughout the building. Always check the pressuretrol setting on the boiler, as well as the “drop-away” rating of the vents in the system.
10. You haven’t contacted your local Bell & Gossett representative about your steam heating questions or problems.
Bell & Gossett’s people are well versed on all steam heating subjects, and they’re willing to share this information with you. All you have to do is give them a call.
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