I've created an Accidental Trombone from my water heater vent piping

artnking

DIY guy here who just installed a new Westinghouse 50-gallon water heater, model WGR050NG076. This is the same as the HTP PH76-50. I used 2" PVC piping for air intake and vent from my basement, and sideways through the concrete wall and venting on an outside wall. I inadvertently created a trombone. The water heater fan is on a resonant frequency that causes a low frequency rumble that can be heard throughout the house, and outside in the yard.
Here is a link to a 1-second video of the outside vent. You can hear the noise in the video.
https://goo.gl/photos/Ma5VWEWywwKHwiks7

Here's a link to two photos, showing the PVC piping inside and outside the house.
https://goo.gl/photos/14TLmnnnY9gWqi9e8

I'm looking for advice on how to get rid of my accidental trombone. Thank you!

Jamie Hall

The only way to get rid of a resonance is to change either the driver -- which is the fan, which you can't do -- or the length of the pipe. Which you can do. That may or may not work...

hot_rod

You might be able to dial away the sound, not unlike the foghorn post below. Did you check the burner operation with a combustion analyzer?

Abracadabra

Isn't the exhaust too close to the window?

j a_2

Abracadabra said:

Isn't the exhaust too close to the window?

Not if it's a direct vent, and it appears to be....but worth checking the book....you definitly don't want the intake air sucking in the exhaust...HO sit back and read the manual, come back with any clarifications you may need help with...Beg borrow or steal a combustion analyzer, but do get one and post your readings...can't help much with out those readings

Gordy

artnking

Jamie Hall said:

The only way to get rid of a resonance is to change either the driver -- which is the fan, which you can't do -- or the length of the pipe. Which you can do. That may or may not work...

I've got the space to change the pipe length and layout. My total pipe length is well below the maximums called out in the manual. If I re-routed the pipe and made it a foot longer, or broke up the longest run, would that likely help?

artnking

j a said:

Abracadabra said:

Isn't the exhaust too close to the window?

Not if it's a direct vent, and it appears to be....but worth checking the book....you definitly don't want the intake air sucking in the exhaust...HO sit back and read the manual, come back with any clarifications you may need help with...Beg borrow or steal a combustion analyzer, but do get one and post your readings...can't help much with out those readings

The distance from the vent and the intake and the window are well in excess of the minimums called out in the manual. I'm a newbie, so this may be a dumb question, but please explain how readings from a combustion analyzer would help me with my resonant noise problem.

Bob Bona_4

Excess air can cause light off harmonics. Would be good to get a baseline on your combustion settings.

Ironman

It's not the piping - if it's the correct size.

The harmonics is in the combustion which is why a combustion analysis is MANDATORY.

As Bob mentioned, probably too lean a fuel/ air mixture.

The CSST connector that you used in the gas line can also be a factor. Either get rid of it or go at least one diameter larger.

Your problem is a common occurrence with negative pressure gas trains and we deal with it often. Get the combustion mixture to the rich end of the manufacturer's specs and get rid of the connector. One or both should silence your trombone.

artnking

Ironman said:

It's not the piping - if it's the correct size.

The harmonics is in the combustion which is why a combustion analysis is MANDATORY.

As Bob mentioned, probably too lean a fuel/ air mixture.

The CSST connector that you used in the gas line can also be a factor. Either get rid of it or go at least one diameter larger.

Your problem is a common occurrence with negative pressure gas trains and we deal with it often. Get the combustion mixture to the rich end of the manufacturer's specs and get rid of the connector. One or both should silence your trombone.

Ironman, you were exactly on target with your advice. I finally got on the schedule with a local heating contractor who came out with his combustion analyzer and gas manometer. With a little help from the Westinghouse tech support people, he was able to adjust the mixture and eliminate the harmonic noise. As a bonus, his combustion analyzer showed that his changes had also increased the efficiency from 87% to 95%.

Thank you Ironman!

Ironman

Glad that fixed it.