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  1. #1
    Join Date
    Jun 2012
    Posts
    12

    High pitched whine from furnace

    Hello everyone,

    We just recently had a Lennox XC14 installed in our newly built home. The system works very well but after the installers left, I noticed a high pitched noise (like a hair dryer in the background) in the kitchen and living room. The furnace is directly below and in the middle of these two rooms.

    This has been going on for about 3 weeks now, here are some extra details.

    1) Had the installer back. We noticed that one of the cold air returns in the living room wasn't working at all. It is not connected to the system at all. So of course that becomes his escape: the noise is because of the lack of air return, have your builder hook it up.

    2) Had the builder's HVAC guys in to see what they had to say. The design of the house calls for 2 air returns in that area, not 3. The non functional one was a mistake. They couldn't hook it up there due to a joist being in the way, so they did it in another location. Whoever was in charge of cutting the holes still cut that one out.

    3) Told the installer about it, demanded that he come back to inspect everything. He is still using the "you need more air flow excuse". We will see how that works out.

    4) I was using one of those fancy 3M Filtrete filters. I noticed that when I took it out, that the sound would go away. Not sure what the MERV rating is on it but I bet it is very high.

    I have a feeling this could be an air flow issue of some kind. Not sure why the introduction of an AC coil would cause this noise. No one is able to answer this question.

    In any case, to test the air flow theory, I purchased a cheap MERV 2 filter. The noise is still there but it is much better. I am not sure if this filter is best to protect the internals of the furnace though. From my research, many people suggest cheap filters and to replace them monthly. I wonder if this is just a little too cheap? I tested out MERV 7 filter for fun but that ups the volume on the noise.

    5) Also from my research, I tested out the 2 air return grills for harmonic noise. There was indeed some, so I replaced them with plastic grills and that helped a bit. There is still some noise though, more of course when bumped up to MERV 7.

    6) The furnace was quite leaky, so I have been going at everything I can find with foil tape. Can't say that it has helped yet with the noise but the basement doesn't feel like a meat locker anymore.

    There were some leaks in and around where the filter goes in and also on the plenum (body of the furnace I believe). All sealed up now.

    I read that the blocker door seal could cause this kind of noise, will test that out soon. Not holding my breath though.

    7) This noise happens when heating, cooling or just using the fan. The tech also adjusted the speeds down 1 notch as a test (ie AC medium, heat low). The noise didn't go away. Everything is back to their original settings.

    It is very hard to pin point the noise when near the furnace. It seems like it could be coming from around where the filter is or from where the AC coil is. Upstairs it is most notable near the returns. If there was a problem in and around the filter, you would think that the noise would have been there before the AC install?!

    When the tech comes this week, I am going to stuff the 3M filter back in there so that he really hears the noise!

    In the meantime, I was hoping that some could answer the following question: why would the introduction of the AC coils bring up this noise?

    Thanks for any help,
    Phil

  2. #2
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,504
    The ONLY pleated filter suitable to use in a residential system is a 5" thick "air bear" type merv 8 to 11 filter. Using the 1" thick pleated filters adds a lot of restriction to your HVAC system air flow. If you're using 1" filters, just go with a quality 1" fiberglass filter, unless you are using the 5" thick pleated units. I'm sure you'll find the "whistle" is around the doors of the blower/furnace unit and due to the excessive air flow restriction from the 1" pleated filter.

    The VERY WORST filter is the 1" pleated that uses filter paper similiar to your coffee maker!! Horrible air flow problems!!!

  3. #3
    Join Date
    Mar 2010
    Location
    North Ridgeville, Ohio
    Posts
    161
    I do agree with wahoo that high efficiency filtration is what should be used instead of 1 inch pleated.

    To answer your question the new coil probably has a higher pressure drop thus creating even more of a restriction. Static pressures tests should be performed to solve your problem. Although it sounds like you need to find another contractor as this test should have been performed from the get go.

    Sent from my Desire HD using Tapatalk 2
    Do, or do not. There is no try.

  4. #4
    Join Date
    Jul 2009
    Location
    Ontario, Canada
    Posts
    913


    Could be that the blower door panel is slightly loose causing it to whistle. Simple test is run the fan and press your hand against the door to see if it goes away. If yes, remove door and bend the metal down for a tighter fit. Seen this a lot with lennox furnace doors, not sure if you have a lennox furnace though.

    If your 1" filter rack has a cover, it may not be sitting well or snug.

    Bypass humidifier, sometimes when the damper is closed, air the escapes through can cause a whistle--just adjust the damper to see.

    These are just some examples......

  5. #5
    Join Date
    Jun 2012
    Posts
    12
    @wahoo: indeed, I have come to see that the pleated 1" filters do restrict the air flow quite a bit. Once this noise is resolved, I will look for something better than the MERV 2 one that I am using. Not even sure what it is made of but it doesn't look like it would stop much.

    @sideburns05: what exactly is a static pressure test? I spent some time going over the furnace last night and it really does sound like it's coming from where the coils are. I can hear it on two of the sides.

    @johnt2_2002: I tested out the blower door, no luck. If it matters, the furnace is an Amana. As for the filter cover, the noise is there with or without it. Also tried adjusting the damper in the humidifier without any success.

    The technician is coming over tomorrow morning. What kind of questions should I be asking him? I really need to be all over him or I know he will try and take the easy way out by saying everything is fine.

    Thanks for the help guys!
    Phil

  6. #6
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,739
    In the meantime, I was hoping that some could answer the following question: why would the introduction of the AC coils bring up this noise?

    blower will be running on a higher speed for a/c than it did for heat, if you are short on return air this is when it will show up.

  7. #7
    Join Date
    Jun 2012
    Posts
    12
    Quote Originally Posted by t527ed View Post
    In the meantime, I was hoping that some could answer the following question: why would the introduction of the AC coils bring up this noise?

    blower will be running on a higher speed for a/c than it did for heat, if you are short on return air this is when it will show up.
    Hi t527ed,

    This was one of the first things that was tested when I brought it up with them. The sound happens when heating, cooling and just using the fan. The tech also tested out reduced speeds for both heating and cooling which did not change anything.

    As a test, he created a small air return on the body of the air return duct just to see if it would help at all. It did not, so that was sealed back up.

    Due to that, I am very skeptical that adding another air return on the main floor would actually do anything. What are your thoughts on that?

    The builder says there are only supposed to be 2, not 3. I don't want to have to spend anything on something that "might" work.

    Phil

  8. #8
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,739
    without seeing and hearing it everything is just a guess, maybe air passing around a poorly installed evap coil or something inside the plenum vibrating??????????

    try posting some pics....... we like pics.

  9. #9
    Join Date
    Jun 2012
    Posts
    12
    Quote Originally Posted by t527ed View Post
    without seeing and hearing it everything is just a guess, maybe air passing around a poorly installed evap coil or something inside the plenum vibrating??????????

    try posting some pics....... we like pics.
    Indeed, it's all a guess. For me, it's a mystery. I will try to get some pictures of the install tonight.

    I know nothing about AC coils, so excuse me if this is a silly question: I am assuming that air is supposed to pass through it and not around it, correct?

    Phil

  10. #10
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,739
    correct

  11. #11
    Join Date
    Jun 2012
    Posts
    12
    Here are some pictures.

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    Phil

  12. #12
    Join Date
    Jun 2012
    Posts
    12
    Let me know if you guys can see all of the pictures. For some reason the site will only let me see the first one. Strangely enough, I do not have permission to look at the other four.

    Phil

  13. #13
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,739
    i can see 5 pictures, nothing really jumps out as a problem.
    does not look like a Lennox coil, any make and model #s for indoor coil installed?

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