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Old 10-15-2009, 06:35 AM   #1
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Loud, low toned hum from high efficiency furnace.


I just purchased my first home and there is a "Lennox Pulse 21" high efficiency furnace downstairs. I just turned the heat on recently and each time before the blower kicks on through the house there is a loud very low toned hum coming from the furnace that almost seems to vibrate and be heard through the whole house (ranch). It lasts for about 30 seconds before the air starts blowing and the first 30 seconds when it starts blowing and then stops.

Im not sure if this is normal for these or not, Ive never heard this before in anyone else's home. Everything seems to be working fine with it, just the noise causes me a little concern.

I took the panel off and Identified the noise coming from a small round metal muffler looking part that had fiberglass panels around it to soften the noise to begin with.

Also cannot find a manual anywhere in the house or online for this.

Any help would be great. Thank you!!

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Old 10-15-2009, 11:36 AM   #2
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Loud, low toned hum from high efficiency furnace.


That noise is normal with the pulse furnace. it is a good furnace but loud. Also heat exchanger issues are common with this furnace. May want to have it inspected.

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Old 10-15-2009, 02:26 PM   #3
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Loud, low toned hum from high efficiency furnace.


Quote:
Originally Posted by SKIP4661 View Post
That noise is normal with the pulse furnace. it is a good furnace but loud. Also heat exchanger issues are common with this furnace. May want to have it inspected.
What is the
"small round metal muffler looking part" and
how is it making that noise?

http://www.inspect-ny.com/heat/lennox1.htm

Last edited by Yoyizit; 10-15-2009 at 02:28 PM.
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Old 10-15-2009, 05:51 PM   #4
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Loud, low toned hum from high efficiency furnace.


The droning noise is basically a single cylinder internal combustion engine in the Pulse furnace! The muffler damps the noise down somewhat. These were the "buzz bombs" of the mid 80s and famous (infamous?) for this noise. Isolate the furnace from the house so that vibration isn't transferred directly (compliant stand, flexible plenum coupling, etc) and that's about all you can do.

If you have an additional noise that goes away a minute after the furnace starts up and doesn't continue while the furnace is heating, it could be the induced vent motor about to give up the ghost.

Last edited by sktn77a; 10-15-2009 at 06:01 PM.
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Old 10-15-2009, 07:08 PM   #5
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Loud, low toned hum from high efficiency furnace.


Get a Lennox tech to thoroughly check that furnace. The air flapper membrane in that "object" of yours may need replacing. The gas pressure should be checked and Lennox recommends the heat exchanger be pressure tested every 4 yrs. That furnace is like a Porsche and very few people know how to fix it properly. I know them well, started installing them in 1980.
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Old 10-16-2009, 05:38 AM   #6
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Loud, low toned hum from high efficiency furnace.


Thanks everyone for the help. I am going to get someone to come inspect it very soon.

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