Knocking sound in heating System

Alan M. Engler

I have a problem with our heating system and I would be grateful for your input.

It is a hot water baseboard system that supplies one room of about 400 square feet. For a number of reasons it is designed as follows: The inflow heating pipe comes up into the bathroom, winds around that wall and two of the bedroom walls on the outside of the wall (i.e., protruding into the room), then dives behind one wall (behind our bed), runs within that wall and emerges on the other side of the wall into the closet where, on the outside of the wall (i.e., within the closet itself), it delivers about 500 BTU then doubles back and retraces its steps (through the wall by the bed and out again) back into the bathroom and out.

Here's the problem: There is a loud, repetitive knocking noise that occurs a few seconds after the heat goes on (we hear the thrermostat click) and that is coming from the corner where the pipe enters the wall and turns; i.e., by the bed. It is so loud that it regularly wakes us at night. It is mostly right at the corner but appears to extend, while diminishing, for about 2-3 feet from the corner.

The Heating Contractor and General Contractor believe that it is caused by the expansion of the heated pipes rubbing against wood, of which there is a lot, particularly in that corner. We plan to try a few things, including installing a pump that will slow the flow of the hot water but, if that doesn't succeed, we are going to open the wall for a few feet and make sure that there is adequate clearance for those pipes. Then we'll leave it as is and try it for a while before we close up the wall.

Here are the questions:
1) Does it sound like the correct analysis of the problem?
2) Do you agree with the plan?
3) Is there anything else you can think of that we should be doing, or checking, before we open the wall?
4) Worst case: We would cap the hot water system within the bedroom, and try to come up with an independent heating system of 500 BTU within the closet. Electric might work but I don't like the potential fire hazard. Any other thoughts?

Thank you,

Steamhead

Sounds like you've got it

and I agree that electric baseboard is not a good heat source in a closet- or anywhere else.

Slowing the flow in that baseboard loop is probably not a good idea. You need a minimum of 1 gallon per minute (GPM) for baseboard to work properly and preferably more.

The expansion sounds like it happens very quickly. Do you have a boiler that maintains temperature (180 degrees or so) all the time? If so, the very quick temperature change in the pipes may be part of the problem. If your boiler has a tankless coil for hot faucet water, consider switching to an indirect or adding a storage tank. This will lower your fuel consumption too.

Let us know how you do!

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Tom Anderson

Try eliminating some of your theories other ways before more disruptive measures.

If you believe piping thermal expansion may be the culprit, why not disable the boiler burner start, allow the system piping and water to cool, then have thrmostator call for heat. That may offer a clue about thermal expansion.

Perhaps hammer effect from pump start? Try starting the pump with a main shutoff valve partially closed.

Hope this helps....

Unknown

Same sounds in my baseboard

When that 180 degree water hits that 70 degree copper pipe near the wood , let the banging commence . Its a wonder what noises you get used to after a while . Sounds like the ticking of a recently shut engine , only louder . A cheap fix is to try to get some oil in where the copper rubs against the wood . If that dont work , there are special copper expansion fittings that can be sweat into the baseboard loop - they look like a copper accordian . But for silent free and a more gradual buildup of baseboard temp , an outdoor reset option is the way to go . I wonder if there is a mixing valve made that will gradually increase the temp by itself for this particular problem , if outdoor reset is not feasible ?

hot_rod

Ron's on to a good fix

A reset or weather responsive control would lessen the temperature swings and on/ off cycling.

Might not make the noise disapper completly, but a pretty easy to retro fit option to try. tekmar.com has some info and a good description of how these control function.

Happy "ghostbusting"

hot rod

[Deleted User]

Answer...

the door, it's the pizza man from Dominos!!

Sorry, I couldn't resist:-)

ME

John Myrtle

If it's thermal expantion,

and it does sound like that may be it, there might be a couple of thing you can do.(1) Boiler/ system by-pass. A loop of piping connecting the boiler supply and return. When there is a call for heat, the system only gets partial flow and will heat up slower.(2) Constant circulation in the system loop, with primary, secondary piping to the boiler. Again the system with come to temp. slower. (3) Outdoor reset control. (4) A combination of these previous.