Vent microwave out through roof

[Nels]

Model Number

unknown

Age

More than 10 years

I have a microwave that is vented out a flat roof. The unit was installed years ago. The vent pipe sticks up about 3' above the roof, and there were two 90 degree elbows in an upside down "U" attached that made the exhaust blow strait down towards the roof and presumably prevent rain from getting down the pipe and into the microwave. The microwave started making a banging noise (when the fan was not on!) when a wind blows across the roof. The elbows were old and loose and I assumed that the elbows were making the noise.

Today, I replaced the two 90 degree elbows with a hat shaped rain cap but the blowing wind still makes a banging noise. I guess that the wind has access between the hat and the mounting. Did I make a mistake and is the "U" shaped 90 degree elbows the proper way to terminate this vent? Or is it more likely that there is something going wrong at the microwave that is causing this noise?

Any feedback would be appreciated!

 

[jeff1]

Hi,

Kinda sounds like the damper is banging and making the noise.
Yes this means the units comes down to access. Maybe a little felt cna stop the noise.

jeff sr.

 

[Nels]

Hi Jeff,

The microwave does not make noise when we run the exhaust. It only makes noise when it is windy outside.
Please see my drawing, the previous vent 'cap' was a couple of adjustable 90 degree duct elbows which end up facing straight down toward the roof. They were old and the adjustable seams were slightly loose. so I had assumed the elbows were making the noise. I replaced the elbows with a galvanized rain cap hoping that would solve it. It didn't, in fact it may have become louder?

Which of the 'cap' types in my drawing are the proper cap for this vent pipe?
Is it possible that galvanized rain cap is letting wind down to the damper where the elbows are supposed to prevent wind from getting in?

Your advice is much appreciated!

Nels

 

[jeff1]

The microwave does not make noise when we run the exhaust. It only makes noise when it is windy outside.

Yes, that is why I suggested the flapper/damper as that can/will make noise when it is windy outside.

Which of the 'cap' types in my drawing are the proper cap for this vent pipe?

Both work well. I personally like the second version but the first version is just a cheaper way of ending the vent.
Air can get in backwards accidentally when it get windy outside.

jeff sr.

 

[Nels]

Thank you, I appreciate your help!

 

[jeff1]

Your welcome

jeff sr.