Author Topic: Roof Airconditioner Humming drives me nuts  (Read 8542 times)


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Roof Airconditioner Humming drives me nuts
« on: April 04, 2007, 05:54:39 AM »
Hi Folks,


I live in a two story condo in Florida. The downstairs neighbor's air conditioner makes a humming noise when running. It is on the roof overhead separated from my wallboard ceiling by a 5 foot wood  raftered and trussed crawl space

The humming is noticible in my bedroom which is only 5 feet away from the air handler closet.  A short 5 foot piece of round metal ductwork must be in a straight line from the  air handler closet  and connect to my room. The duct is in the crawl space overhead

the ducts also run in straight shot from the air handler  about 8-10 feet into the living room...

 in the living room and you hear the same annoying vibrating hum out of the duct

The walls are steel studs. They are covered with drywall. the building is concrete walled with a wooden mansard flat roof with wooden trusses in the crawl space

The ceiling is drywall covered with popcorn ceiling spray stuff. there is 4 inch fiberglass mat insulation between the ceiling rafters in the four foot crawl space/attic

Both airconditioners are mounted  on a rectangular galvanized metal rack on the roof. The rack is mounted by four galvanized  lag screws or bolts down into the ashpalt covered plywood roof...

I tried using the 7/8" rubber and cork vibration pads this weekend from your company my air conditioner guy put them under each corner of the 2 air conditioners

They did nothing. the hum persists when the downstairs A/C is running

It is even more annoying than before

Between my apartment and the roof is a 4 or 5 foot crawl space with wood trusses...

I don't know where the humming vibration comes from

The hum is coming thru the ceiling and possibly the ductwork which is 4"-6" metal round tubing...

we had 3 hurricanes hit us directly....and my neighbor’s  airconditioner was loose on the roof

We never heard this loud a humming in 16 years prior

I wonder if the harmonic humming could be from air conditioning pipes that are attached to the trusses...and could have loosened?

or from the rack bolted to the roof  and transmitted thru the roof into the crawl space..they call this rack a hurricane rack...well they stink!

perhaps some foam attatched around the copper coolant pipes that run from the roof to our condo and then down to his downstairs  and then reattached to the studs with plastic clips or rubber coated metal bands to the wood studs would work

we both share ductwork thru the same  1 foot hole in the roof I suspect that the copper pipes may be loose and vibrating….I don’t know just speculation

 and the air conditioner air handler is in a utility closet upstairs and downstairs ours must share his ducting somehowhis air conditioner makes a thumping noise when it stops(my AC guy said that could be because he installed a single speed air handler)

I have not been into this 4 or 5 foot crawl space that runs the length of the  10 apartment 5 up 5 down building

I wonder about adding a piece of round duct to the straight away that comes into my bedroom...curving the duct might kill the hum

or cut the duct pipe in half and put a rubber sleeve around it  and reconnect it to stop possible vibrations?

perhaps put some vibration pad where the bolts go into the roof ?

I just don't know ....

It annoys me

the cork/rubber vibration pads made it  worse if anything

Vibration could be the problem something loose like a copper pipe that causes vibration the noise is from above the ceiling

maybee they raised his A/C pipes higher where they enter the metal hood that allows it to enter the roof and the vibration is resonating thru the wood trusses?

I am lost as to what else to do next

I can't fit up there in that crawl space(330 lbs 6" 5'

it drives me buggy to hear that low hum

Some suggestions please



  • Guest
Re: Roof Airconditioner Humming drives me nuts
« Reply #1 on: April 05, 2007, 10:42:30 PM »
I think one of your hunches is probably correct.  Since the A/C unit is now on pads, it's likely a coolant pipe is in rigid contact with a truss/joist/stud.

Hire somebody small to get up there, track it down and isolate the vibration.  The pipes are supposed to be insulated anyway..