Boiler roaring with tuba-like harmonic note

[Sandy Pittendrigh]

I have a relatively new Energy Star Triangle Tube furnace--efficient enough the exhaust pipe is a 6" inch PVC pipe. Or is it 4" inches? Hot water radiator system.

I had a spurting overflow valve problem a few months ago--that this forum helped me to diagnose and correct. Now I want to fix another problem. One that's been there from the getgo.

Everything now works well except one remaining problem. This furnace makes a trombone like roaring note when it starts up, that the neighbors are complaining about. Sounds a bit like a harmonic note from a guitar, crossed with a tuba.

Is this because of some odd frequency to an internal fan? Or what? Can it be fixed? My plumber has gone out of business and disappeared.

 

[Dana]

The air intake vent pipe and the exhaust vent pipes are both acoustic resonators with a natural resonant frequency. Adding or subtracting some length to either may affect how easily the the resonance gets started.

 

[Sponsor]

 

[Reach4]

I am wondering what happens to the sound if you grasp the pipes at various points. If the sound goes away as a result, there may be a treatment that does not involve adjusting the pipe length. On the other hand, it probably will not help. It seems easy enough to try, even thought it may be wasted effort.

 

[Dana]

It's a bit hard to test the changes if it's only making the noise during an ignition cycle, unless those ignition cycles are frequent.

The more right-sized the boiler is for the heat load and the better dialed in the outdoor reset curve, the fewer ignition cycles there will be. If it's only happening 1-2x per day while the neighbors are home it's a very different level of nuisance than if it's going of 6-10x per hour all night long.

 

[BadgerBoilerMN]

A condensing boiler can make noise, inside or out, if it not properly commissioned.

Review the boiler startup sheet left to you by your factory-trained installer--the guy you gave the money to.

The Triangle Tube Solo startup sheet can be found in the installation manual.

Note in particular pages 56 and 57, the latter of which asks for combustion information only available by means of an electronic flue gas combustion analyser. Proper setup can cure delayed ignition, nuisance lockouts, raw fuel discharge to daylight, fouling of combustion chamber, ignitor, flame sensor, vent pipe, and condensate trap and drain line. And yes, even stop harmonic resonance, or in this case more accurately called "combustion-driven oscillations".

This covers the subject pretty well I think...just kidding. I going to bite this apple later.

In short, it is a gas/air issue and is more frequent in some ModCons and specific models thereof and often manifested or exacerbated by poor installation and/or commissioning. Though manipulating the "natural resonators" may help adjusting the gas/air mix, with the right tools and factory support or training is the only sure way to eliminate or mitigate noise while keeping your equipment within factory specs. i.e. safe, efficient and reliable.

Every ModCon should be set up with such a device operated by a trained technician. Without this information no one can help. And no, Dana can't do it in his head .

 

[Sandy Pittendrigh]

Thank you all for the replies. I did add length to the vents and it didn't help. I'll look at the "commissioning" information. I do have all that stuff. I would say this happens 3-4 times a day. Usually at night. We have a well insulated house with South facing windows. So we warm up well during the daytime. Unless there's a cold front inversion. This is Montana.

 

[Dana]

Almost all boilers (and certainly the Triangle Tube boilers) have to be re-tuned to compensate for elevation in most MT locations, ergo the need for a trained tech with the proper tools & experience to check up on it every year or three. (Even if it's not playing Sousa marches when firing up. ) You may have to contact Triangle Tube to find somebody local who has that experience. There may be as many or more amateur plumber installed mod-cons in some places as there are certified tech installed units.

The definition of "local" can be pretty loose in MT though, where there are often miles & miles of miles & miles between the big dots on the map.

 

[Sandy Pittendrigh]

Had a plumber visit--who used and expensive fuel something-or-other meter to tune the system. Roaring is now gone.
All is fine now.