# Question regarding thumping noise in ducts



## rtztgue (Jul 9, 2010)

Okay, as you can see I am a low volt electrician so I need to defer to the HVAC guys for this question. I currently live in a house that from time to time has a thumping noise coming from the walls. My thought is that it is something to do with the venitalation and heating, But i just cannnot figure out what it is. So here are some basics.

1. NO A/C in house
2. Gas forced air
3. In the area of the thumping is a gas fireplace. (rarely ever running)
4. There is also a vent about 36 inches by 12 inches in a nearby wall. I was told it it for ventilation.

The thump sounds like a vent in the wall opening and closing. it is random. But when it comes on it will cycle a few time. Thump.. wait. thump-thump, wait... thump. for about 30 seconds. The heater is not going at the time. it is random throughout the day.

I thought it might be a damper connected to my main furnace but I disconnected power and the noise is still there. The damper says "Durozone, multiline" connected to ductwork above my furnace... but as I said power is currently disconnected to it.

I also found a timer in my garage, that took some time to track down, but it just turns on a bathroom fan upstairs. 

And the main reason I am looking for this silly thing is that is sounds like it needs attention. It has gotten louder over the last year and the random on, then off again, sounds problematic.


----------



## flashheatingand (May 3, 2008)

thump, thump, thump....thump thump, thump? Even with the leads disconnected, hmph, is this on an outside wall?


----------



## rselectric1 (Sep 20, 2009)

I'll point you in another direction to check out too.

One "mystery sound" that I have encountered many times is thermal expansion of PVC drain pipes. Does the noise correspond with hot water being run in the house at all?


----------



## overanalyze (Dec 28, 2010)

rselectric1 said:


> I'll point you in another direction to check out too.
> 
> One "mystery sound" that I have encountered many times is thermal expansion of PVC drain pipes. Does the noise correspond with hot water being run in the house at all?


I will second that..or sometimes pvc expansion on furnace exhaust will thump or POP when j hooks are used...


----------



## rtztgue (Jul 9, 2010)

Nothing to do with the water that I can imagine. . I have heard this several times when I am in the area (always the same area of the house) when I am alone and just working on the computer. This AM I heard it about 7 and we were all in bed. Also, there seems to be a bit of a hum when it triggers (sorry, just remembered). So it's. ,thump-hmmmmmm- thump.


----------



## overanalyze (Dec 28, 2010)

Is your water heater a power vent?


----------



## DuMass (Feb 6, 2008)

rtztgue said:


> There is also a vent about 36 inches by 12 inches in a nearby wall. I was told it it for ventilation.


Not sure what the "vent" you mention is about but, can you pull this vent apart to see if there is an actuator motor or blower/fan of some sort in there. 
Is the gas fireplace a vented type? Maybe there is a damper in the vent hood that is flapping open and closed in the wind.


----------



## flashheatingand (May 3, 2008)

Gotta agree with Dumass. The fact that you say the vent is 36x12, makes me wonder if it's a special fireplace. We don't see to many return runs with the dimensions you are mentioning (in private homes).

Is there something in which the heat from the fireplace gets extracted into the ducting or something to that degree? Originally, I was thinking maybe you had a birds nest or something, but don't know of too many birds that humm. 

Eureka!! You must have a humming birds nest in there.


----------



## rtztgue (Jul 9, 2010)

*pix*

Here are some pix. ON the top left of the furnace you may see the damper vent I was telling you about, but it is currently disconnected. Then the fireplace and on the wall to the left of the fireplace, at ground level is the vent I was mentioning. I know sound travels and could make things appear weird, but this thump noise actually sounds like it is in the ceiling just above the one room between that floor vent and the furnace. So, garage with furnace, bedroom, then the living room. Thumb is loudest in the ceiling above the bedroom.


----------



## flashheatingand (May 3, 2008)

Is that a humidifier? on the side. Also, is that an electronic air cleaner? Or is that simply a media filter? If that is an electronic air filter, turn it off for kicks. That might be the culprit


----------



## rtztgue (Jul 9, 2010)

it is an electric air filter. I turned it off and will see what happens. I tried recording the sound yesterday, but the hum is so low that it did not come through and the thump could be heard on the recording but not well. I really listened and it seems like it is in the general area of the furnace ducts, but I sure as heck cannot hear the furnace or hot water tank making any noise when this happens. I hear the noise in the room behind the furnace and water heater. When I hear it start I run into the garage to determine if there is something in there working, but I cannot hear a sound coming from the furnace. I run back into the room just behind that wall you see in the pic and I can hear the thumping and the hum


----------



## flashheatingand (May 3, 2008)

Out of curiosity, is the room behind the furnace a laundry room? If so, many of those homes have an exhaust fan (just throwing darts). Otherwise, you may need to get up in the attic and check out around there.

Feel free to throw out clues. Someone here will likely be able to help out.


----------



## rtztgue (Jul 9, 2010)

*Found It!!!!*

okay so after shutting down the damper, the electronic filter and still hearing the thump I really listened in at the walls. Luckily it did it when I was nearby. Several times I heared it and before I realized what was happening the noise was over....

anyway, I narrowed it down and really looked around... Just outside this room on the outside wall are solenoids for turning on my septic pump. They reverberted on the wall sounding like a damper. It was right between an outside vent, the fireplace flue and whatever the heck that other vent is on the inside of my house near the floor.

Well, now I know what it is. not sure why it will turn on for a few seconds, then off, then on etc. but that is what it is. I was able to verify by opening the control box up and manually turning it on and off.


thanks for the help


----------



## flashheatingand (May 3, 2008)

Don't know about helping, but it'sthe thought that counts... It's good to know the result, as it's something to put in the mental notebook.


----------



## overanalyze (Dec 28, 2010)

Cool..glad you found it! The other vent by the floor looks like a cold air return...at least in the picture.


----------

