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Old 02-19-2012, 07:45 AM   #1
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Question for forum member "how" on banging noise


In a recent thread at banging noise , where the poster is asking about banging noise in their heating system, you stated:

"The most common boiler banging sounds that come from different locations are heating pipes that are binding and releasing as they expand. Where those pipes were formally able to slide back and forth on their hangers during that lateral expansion, they are now sticking and then letting go with a banging sound.. "

That sounds exactly like the problem we've been having. We have a hot water (not steam) heating system. We've had the same boiler since '85, with black pipe running along the basement ceiling going up to radiators on floors above. A single metalic-sounding bang occurs every few minutes, both when the system is heating up (the boiler is on), and when the system is cooling down (boiler off), and it comes from different areas.

Your explanation sounds like it makes sense as to what's causing our noise. But when you say "formerly able to slide back and forth on their hangers," what did you mean would have changed that they used to slide but now don't?

The banging we have has, in fact, increased in the last year. The two things that changed are (1) we had some new A/C ducts installed, but I checked and while some pipes are very near the ducts they are not touching them, and (2) I insulated all the supply black pipe with 1"-thick-wall fiberglass tube insulation. When I did that, I insulated AROUND the hangers (perforated pipe straps), leaving a notch at the top where it exits the insulation tube. Have I caused the problem by restricting the movement of the pipe within the hangers with the insulation?

I can provide pictures if that would help. Thanks.

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Old 02-19-2012, 08:12 AM   #2
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Question for forum member "how" on banging noise


IMO (just trying to help) you may have created the situation as the pipes when uninsulated expanded and contracted at a different rate than they do now. They are running hotter and not losing their heat to the surrounding area which in theory should cause them to expand further. It takes VERY little to have pipes move or alter their expansion/contraction pattern. A change in boiler water temp can also change this. I have worked on high press and temp steam and hot water systems and expanding contraction is a fact of life. You will have to stand down there and try see and hear where the sound is coming from and probably loosen some hangers to allow easier expansion.

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Old 02-19-2012, 08:20 AM   #3
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Question for forum member "how" on banging noise


Thanks for the reply, yuri. In addition to your explanation about increased expansion and contraction due to insulating the pipes, I forgot that in the last year we also increased the boiler temperature high limit from 140 to 150, so of course the pipes are also hotter because of that.

Does this sort of expansion and contraction (and the banging that is causing) cause damage to the pipes?
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Old 02-19-2012, 08:37 AM   #4
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Question for forum member "how" on banging noise


Kinda high for a new boiler ..no?

Usually are set to 135*f for new boilers?
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Old 02-19-2012, 08:54 AM   #5
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Been awhile since I did resi boilers but nowadays we try to heat the house with the lowest water supply temp and run the boiler longer as it is more efficient that way. The hotter the boiler the more heat you radiate from it while running and during the off cycle. Not sure if you need that hot a temp in your area but we have other Pros here which can advise about that. It is not good for the pipes but doubt it will damage them. After a yr they will probably expand into a new "happy" position and the sound may or may not go away but I suspect you are running that boiler too hot.
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Old 02-19-2012, 08:54 AM   #6
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Question for forum member "how" on banging noise


It's not a new boiler -- the boiler was installed in 1985 (Weil-McLain series 8 CGM-5). What was new in the last year were some new A/C ducts (not a part of the heating system at all).
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Old 02-19-2012, 08:55 AM   #7
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check above your post for more info.

Plus, modern units use an outdoor air reset device to control the water temp so it is not too hot on mild days and hot enough for the really cold days. Not sure how to retrofit it to your system but some of our other Pros may be able to advise on that. Google it 4 more info.

http://www.pmengineer.com/Articles/F...00f932a8c0____
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Last edited by yuri; 02-19-2012 at 09:06 AM.
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Old 02-19-2012, 09:09 AM   #8
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Question for forum member "how" on banging noise


Quote:
Originally Posted by yuri View Post
Been awhile since I did resi boilers but nowadays we try to heat the house with the lowest water supply temp and run the boiler longer as it is more efficient that way. The hotter the boiler the more heat you radiate from it while running and during the off cycle. Not sure if you need that hot a temp in your area but we have other Pros here which can advise about that. It is not good for the pipes but doubt it will damage them. After a yr they will probably expand into a new "happy" position and the sound may or may not go away but I suspect you are running that boiler too hot.
By way of explanation, back in the early 2000's the boiler high limit was 150. Then a few years ago the pressure relief valve started expelling water in short bursts once in a while, and an HVAC guy reduced the limit to 140. That didn't solve the problem, so they decided that valve was bad so they replaced it, and that stopped the problem. But they didn't turn the limit back up. I then noticed that though the circulator would keep running, that the burner would cycle on and off, a lot (reaching the high limit quickly). Since it had originally been at 150, I turned it back up to 150, which reduced the burner cycling to a good extent.

At any rate, we live in a suburb about 2 miles N.W. of Washington, D.C. The boiler is a Weil-McLain series 8 CGM-5, natural gas. The house was built in 1931, recently air-sealed. It's a small 3-story (3 including the basement), 1100 sq. ft., stone exterior. Black pipe to radiators. What high limit do you think we should be set at?
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Old 02-19-2012, 09:18 AM   #9
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Question for forum member "how" on banging noise


I don't know your climate but Beenthere and some other Pros who should be here today can help. Hang in here. I think your terminology is a bit off. There is a cut in and out temp for the circ pump and a high limit for safety so it does not overheat. What are your cut in and cut out temps and high limit setting for them. Do you have more than 1 thermostat in the house/ zones?
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Last edited by yuri; 02-19-2012 at 09:20 AM.
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Old 02-19-2012, 09:33 AM   #10
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Post some pics of the boiler with the front door off and the circ pump and piping all around may help too. Do you have a bladder expansion tank or old torpedo one?
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Old 02-19-2012, 09:35 AM   #11
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Question for forum member "how" on banging noise


Thanks, yuri. I'll await their input. If it helps any, I just did a quick Google search, and according to a U.S. D.O.E. climate region table from August 2010, our county (Montgomery, MD) is in climate region 4, and is classified as "Mixed-Humid." As I understand it, our system only has one zone (there are no zone controls). If it makes any difference to describe the radiator piping, each radiator has a separate pipe coming off one of the branches to supply it, and a separate pipe coming off each radiator to a branch on the return.

I just saw your post re posting pictures -- I'll do that shortly.
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Old 02-19-2012, 10:18 AM   #12
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Question for forum member "how" on banging noise


Quote:
Originally Posted by yuri View Post
Post some pics of the boiler with the front door off and the circ pump and piping all around may help too. Do you have a bladder expansion tank or old torpedo one?
The expansion tank is the old-style type, mounted on the ceiling.

I've attached the first of a few pics here, and will upload the rest shortly.

(If you happen to notice it, ignore that victaulic fitting cover -- there's actually a union under there, and I'll be replacing it with a union cover shortly.)
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Question for forum member "how" on banging noise-cimg2203.jpg  
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Old 02-19-2012, 10:19 AM   #13
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Question for forum member "how" on banging noise


Here are the rest of the pics.
Attached Thumbnails
Question for forum member "how" on banging noise-cimg2204.jpg   Question for forum member "how" on banging noise-cimg2205.jpg   Question for forum member "how" on banging noise-cimg2206.jpg   Question for forum member "how" on banging noise-cimg2207.jpg  
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Old 02-19-2012, 10:37 AM   #14
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Question for forum member "how" on banging noise


Should there be more of a positive pitch up on the vent pipe? Looks like the transition elbow 90* to the 4" pitches down a bit and the horizontal section looks fairly level?
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Old 02-19-2012, 10:47 AM   #15
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Question for forum member "how" on banging noise


Quote:
Originally Posted by bob22 View Post
Should there be more of a positive pitch up on the vent pipe? Looks like the transition elbow 90* to the 4" pitches down a bit and the horizontal section looks fairly level?
Thanks for your reply, Bob. It's easier to see in person, of course, but I've attached two more pics which hopefully show that they are pitched OK. In the first picture, the smaller pipe coming from the left is from the domestic HWH, which then merges with the larger pipe coming from the boiler, and then out through the wall.
Attached Thumbnails
Question for forum member "how" on banging noise-cimg2208.jpg   Question for forum member "how" on banging noise-cimg2209.jpg  

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