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Rheem 90 plus Gas Furnace very Loud. Noise Mitigation suggestions please

linger12 Member Posts: 2
I live in portland Oregon and have a small 1800 sq ft home built in 1914 with no insulation. Home came with a circa 2003 Rheem Classic 90 plus that vents out the side of the house 15 feet from the neighbors house and 20 feet from my bedroom window.

It is incredibly loud to say the least..

Exhaust Noise A) Sounds like a Jet engine. Crazy loud. I can hear it from two houses away. I think the exhaust pipe is too small and too many 90 degree bends? the pipe seems to be about 2 3/4 inches? Would folks use a larger pipe with fewer bends? would that matter? how about the Outside?

Airflow Noise B) Airflow noise coming out the furnace/vents. When the furnace is on I think the air is pushing so hard out of the furnace and into such a small cavity of ductwork it is very loud. When it turns off there is an audible relief. I was recently in a house with forced air and could feel the hot air but could barely hear a blower. Seems to me the air cavity is too small for the blower speed.. too much air equals lots of sound? That and a like of ability to vary the blower speed?

Thanks in advance.. I posted pictures of exhaust pipe..


    HVACNUT Member Posts: 5,452
    Its probably the induced draft motor. Bad windings? Pretty easy to replace if your handy.
    If it hasn't been serviced lately, have a pro check the whole system and do a combustion test. 
  • mattmia2
    mattmia2 Member Posts: 8,825
    Both blowers could be dirty, that can increase noise by a lot. the inducer fan is probably in to correctly sized piping. the duct work for the furnace may be too small or have vents closed ot balancing dampers closed off too much. higher velocity equals more noise(although if it is connected to the original gravity duct work, that is usually fairly large)
  • HomerJSmith
    HomerJSmith Member Posts: 2,307
    edited February 2021
    How long is the intake and the exhaust vent (Length)? You are only allowed a combined length of so many feet for 3" PVC pipe. That includes the 90 deg fittings too which must be taken into account. Yours are sharp 90 deg and are certified for pressure. But, many installer use a DWV PVC 90 deg fitting. I was told by the manufacture that the DWV fittings are not certified for pressure. But, DWV fittings have less pressure drop tho and are preferred by many installers .

    Vent runs that are above the Rheems specs must have the pipe size increased to 4".

    I don't know what size the vents are but 3" is required, that is an overall width of 3-1/2", that's the pipe.

    The take off of the vents from the furnace is a 2" take off and as I remember, not more than a foot before increasing to 3" pipe. It appears that your vent size is a 2" pipe which would be 2-1/2" outside dia. I always went to a 3" pipe as close to the furnace take off as I could. What does the markings on the pipe say the pipe size is. If it is 2", you are looking at your problem. Under sizing a vent is hard on the heat exchanger, too.

    That looks like 6" shiplap siding and I would say your vents look too, too small.

    I might add that the last 2' feet out of the wall is 2" pipe with a wind deflector in the exhaust vent.
  • HomerJSmith
    HomerJSmith Member Posts: 2,307
    edited February 2021
    I've installed allot of these Rheem and Ruud furnaces and the requirements are in the instruction manual.
  • linger12
    linger12 Member Posts: 2
    Thank you everyone…

    i will clean my furnace

    I do see that my exhaust pipe is 2.5 inches around so per HOmerjsnith I am likely looking at my problem.   At two inches it’s two small.  I will come up with a plan to go a 3 inch exhaust (2.5 internal) while trying to reduce 90 degree bends. 

    I will also check out the dmv pvc 90 pipes. 

    also per h0merj my exhaust pipe is 3 inch and it should be 3.5.  

    All around my exhaust piping seems to small.  (It’s about 20 feet from my furnace to the outside) 

    Lastly I will read the manual. 

    Thx again everyone.
    EBEBRATT-Ed Member Posts: 14,472

    Your furnace is likely too big for the house. That won't cause the exhaust noise issue but could contribute to your duct issues.

    What I would do:

    Down load the manual and read it especially the exhaust and air intake requirements.

    Keep in mind that in some locations PVC is no longer allowed for the flue exhaust. You may have to use a product like Centrotherm

    Download the Slant Fin app and do a heat loss on your house.

    Since you furnace is approaching 20 years old if you find it way oversized (which it likely is) you can start putting money aside if your staying in the house to get a new furnace in a couple of years