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January 13, 2009
Steam Pressure & Leaks
Our ancient boiler finally bit the dust, so we hired Keyspan / National Grid to replace it with a Burnham IN6 gas-fired steam boiler, for our one-pipe steam heating system. We have a four-story townhouse.
The original system & the radiators seemed to work fine without any troubles until now. For reference we used Size No 4's air valves on the 1st floor, increasing to Size D on the top floor.
Three of our radiators have sprung leaks since the new boiler has been installed. They hiss & whistle and water burbles from the air valves, and now water is also leaking from the pipe-to-radiator connection as well.
So the installer reduced the pressure from 5 psi to 3 psi, but this hasn't stopped the hissing and leaks. They said the radiators were not in their scope of work, and suggested that I should hire another plumber to correct the problem.
The manufacturer literature for Burnham cites numbers like 0.5 psi to 2 psi, so the 3 psi to 5 psi range that Keyspan used seems high. Could this be forcing steam out of the radiator pipes in unexpected ways? Am I even comparing correct numbers?
I am going to try replacing the air valves with new ones, but I need to know why the radiators might be leaking. Before I call in another plumber, any suggestions what may be going on?
Comments
Wait for Master Plvmber, and I'm no expert, but your instinct sounds right. We're set below 2 and don't have your problem. I can't imagine it's the valves.
Posted by: slopefarm at January 12, 2009 3:14 PM
The fact that I keep losing jobs to people like this makes me crazy. Did you pay them? Why are they not taking responsibility for this?
One pipe steam heat can and should operate under 1.5 psi on the high end. More than that is a noisy and senseless waste of fuel.
Most can operate between 0.25 and 1.0 pounds per square inch (psi) or 4-16 *ounces* per square inch. The device that regulates the pressure in the system is called a pressuretrol. It can be adjusted to work between 0.5 and 1.5 easily. If you want less pressure, you can have something installed called a vaporstat which replaces the pressuretol and allows the boiler and system to operate in ounces of pressure rather than pounds. Though not cheap, it's a great investment and a real quiet-downer for a residential steam system.
The fact that these problems surfaced after the new boiler was installed leads me to believe that the boiler is oversized and/or the boiler piping is just plain wrong.
Another thing that goes wrong with steam boiler installations is that the returns clog up and prevent the condensate (water that used to be steam) from making its way back to the boiler quickly enough.
Standard operating procedure here is to install a flush port, a large open-ended valve, to the return piping to allow for the periodic flushing of sediment accumulated in the return pipes.
All steam boilers have a threaded outlet near the top to allow for the installation of a skim valve. New boilers need to have the oils used in manufacturing and installation "skimmed" off the top of the water by way of this valve. Draining and flushing the boiler doesn't have the same affect as the oils stick to the sides as the boiler drains out. Look in the Burnham Independence manual for the tapping labeled "surface blow off".
Every boiler replacement price we provide includes a return trip after two weeks of run time to skim, service and inspect the entire system. If your installer didn't do that, you'll need to get him or another qualified steam-heat contractor to do a service call.
Hope my vent/answer helps.
Master Plvmber
http://www.GatewayPlumbing.com
Posted by: Master Plvmber at January 12, 2009 5:26 PM
as usual, master plumber is bang on...lol... another thing that these kinds of installers tend to do is basically sawzall out the boiler to steam system connection, slide the new boiler in place where the old one was and reconnect the new boiler to the older than god configuration. if the old steam header was not properly sized, or is not high enough over the water line to allow for dry steam on the makeup, you are doomed to have knocking and condensate problems...good luck
Posted by: eman1234 at January 12, 2009 5:54 PM
eman1234, you're right. Reusing the old header usually makes for more work and a less-good installation.
Piping configurations are not interchangeable from boiler to boiler.
The things people try to get away with......
Posted by: Master Plvmber at January 12, 2009 6:03 PM
There's Keyspan for you! I chose them to replace my boiler because they had faithfully maintained the previous system successfully for years.
Thank you Master Plumber for your troubleshooting ideas.
Posted by: vicki_vale at January 12, 2009 6:28 PM
i hope that they at least used a float type low water cutoff instead of a probe type low water cutoff
Posted by: eman1234 at January 12, 2009 6:47 PM
Does the <1.5psi guideline for boiler pressure apply to larger boilers as well (eg, for a 25 unit apartment building)?
Also, how does the pressuretrol work in conjuntion with a Heat Timer? If the pressuretrol is working properly, will the boiler be cycling on/off during the heating phase of the heat timer cycle?
Last, where would a flush port generally be found? In the return piping near the boiler? Or some location above the boiler water line?
Thanks as always for info.
Posted by: arches at January 12, 2009 7:10 PM
That pressure rule applies for big boilers, too.
The Empire State Building runs on 3psi. Any plumber worth his salt knows that by now.
Pressuretrols have two different functions when working with Heat Timers. One is they signal to the control that the system is full of steam and cycle timing begins.
The other is they temporarily cut off power to the burner circuit in the presence of rising pressure in a redundant high-limit configuration.
Either function is kind of sucky. There are better ways to signal a Heat Timer.
A flush port is at the lowest part of the return line generally at the nearest or farthest points from the boiler. A flush port above the water line would be no help.
Posted by: Master Plvmber at January 12, 2009 7:44 PM
if you signal the heat timer for the "heat met" with a sensor at the furthest point from the boiler in the heating system you would have a lot better control than a simple "pressure met" as a signal...the latter gives you no idea what is going on outside the boiler room...admittedly the "pressure met" is really cheap to set up,but it makes no sense in the actual heating of a building
Posted by: eman1234 at January 12, 2009 8:03 PM
eman1234
re:
"if the old steam header ...is not high enough over the water line to allow for dry steam on the makeup, you are doomed to have knocking and condensate problems"
Is the 'header' the outgoing hot steam pipe that runs horizontally away from the boiler, and the 'water line' the return condensate?
Could you please explain in more detail what this means, and why the same configuration of pipes would now collect condensate, when previously with the old boiler it would drain correctly?
Since the new boiler install, i do notice there is definitely a sloshing sound in pipes now, and I saw that the leaky condensate from one of the failed radiators had rust and black specks in it too. I thought for sure that Santa was going to leave coal in my stocking, but it seems to have come out of the radiator water instead. : (
Posted by: vicki_vale at January 12, 2009 8:55 PM
WoW! This sure is a technical thread! Thanks!
Posted by: Rick at January 12, 2009 9:32 PM
the steam header is an oversized pipe that the boiler feeds into...in an ancient installation boilers fed into maybe a 2 inch line...later plumbers understood that feeding steam into a big 4 inch pipe allowed you to get rid of most of the water that is generated during the process of turning steam into water.. if the distance between the line on the sight glass where the water is supposed to be in the boiler when it is making steam is not 22 inches below the header, water will be forced up ahead of the steam , and you will will hear a sloshing sound , accompanied by leaking steam vents...etc...these are concerns that should be addressed by a heating professional, not a homeowner
Posted by: eman1234 at January 12, 2009 9:38 PM
good info eman, thanks. just wanted to add: emphasis on "should"...and if the homeowner doesn't know anything, there's no way to know the "professional" is not really professional.
This is why it's good that you post the detailed info....
The "boiler guys" left my pressure at the highest setting and I still have no oil filter...things I 'shouldn't' have to worry about, but here I am. I'm sure there are tons more mistakes on my setup if I only knew...
Posted by: townhouser at January 12, 2009 10:50 PM
"Pressuretrols have two different functions when working with Heat Timers. One is they signal to the control that the system is full of steam and cycle timing begins.
The other is they temporarily cut off power to the burner circuit in the presence of rising pressure in a redundant high-limit configuration.
Either function is kind of sucky. There are better ways to signal a Heat Timer."
I should have mentioned that our Heat Timer has a sensor on the return, which triggers the cycle start (at 164 degrees). So I guess in our case, the pressuretrol is just serving as a high-limit? For whatever reason, it is set to 6 psi (with a -2 differential) so I don't imagine its doing a lot of limiting.
Does lowering the pressure limits usually require a round of adjustments to the heat timer? Changes to radiator steam vents?
Posted by: arches at January 12, 2009 10:59 PM
Arches: No. The settings should remain if they work.
Posted by: Master Plvmber at January 12, 2009 11:12 PM
Master Plvmber, what is the right way to replace an old boiler? In a few months, I will need to replace an old boiler in an old system (possibly over 100 years old) that was originally steam and then was converted to hot water. Do you do this kind of work?
Posted by: mopar at January 12, 2009 11:24 PM
Yes, Mopar. My company replaces or installs from scratch around 70 boilers every year. We service or repair hundreds.
The right way to replace a boiler is to ignore what's currently installed and put pen to paper to figure out exactly what's needed in terms of heat output, venting requirements, efficiency and control options for that particular building.
Then the selected heat sources must be installed as directed by the manufacturer. Every boiler sold comes with a piping and wiring diagram that must be followed to ensure the intended efficiency and output values are realized.
Posted by: Master Plvmber at January 13, 2009 7:03 AM
Beating my usual drum, old boilers tend to be oversized (olden days: leaky single pane windows, less worry about energy cost, no insulation etc.)
For steam systems, the boiler size needs to match the 'radiation' or radiator capacity. So after a heat load calculation, which will probably wind up to be less than the old boiler size, a few radiators should be downsized (typically on the upper floors) to match the smaller boiler (that's what I did on top 2 rads, which are half the size of the original and keep the rooms warm just fine.)
Posted by: cmu at January 13, 2009 9:27 AM
Thank you, Master Plvmber. I will give you a ring when we are in contract.
Posted by: mopar at January 13, 2009 11:16 AM
btw... vicki... if you want me to come by and look at your situation for an initial free consultation, this is a service that i offer... you can contact me at errol832000@yahoo.con
Posted by: eman1234 at January 13, 2009 8:15 PM
For update, Keyspan made good.
I called in the maintenance contract for service to check the boiler settings. In turn, they called the installer to come back and skim. No sloshing, clonking, no leaks today. Knock on wood.
Also, the pressure was adjusted from 3 psi to 2 psi, and I will watch out for cycle performance and check the farthest radiators over the next while. I am reading the Honeywell pressuretrol as 3 psi on the "main", minus 1 psi for the cut-off? shown next to it, for the final subtractive differential of 2 psi.
For reference, for boiler sizing, the original proposal was based on a larger IN7 which was sized by the contractor from a rule-of-thumb table for no. of radiator units (e.g. Total 14 - 18 no. of radiators). I downsized the actual installation to the IN6 based on my own calculation after measuring each unit myself and looking up the tables for the radiator height & number of fins, etc for a total 375 SF of radiator for a 3,300 sf house. We have really radiators in our poorly insulated extension on the back of the house, otherwise the next smaller model would have worked. On the other hand, our R40 roof insulation doesn't figure into this method of calculation at all.
If I've read the specs correctly, the Burnham Boiler Model steam ratings are:
Model IN5 358sf (Steam output 86,000 BTU)
Model IN6 450sf (Steam output 108,000 BTU I think)
Model IN7 542sf (Steam output 130,00 BTU)
Experts please feel free to jump in if there is disinformation here. Good luck to everyone on their heating projects, and stay warm!!!
Posted by: vicki_vale at January 14, 2009 11:19 AM
Lower your pressuretrol main setting to 2 and the differential to 1.
That's more pressure than you'll ever need.
Posted by: Master Plvmber at January 14, 2009 4:06 PM
Thanks Master Plumber.
(Correction: I meant to say we have really BIG radiators in the extension, otherwise the next size smaller boiler would have matched.)
Posted by: vicki_vale at January 14, 2009 6:35 PM
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