Loud noise from furnace


Old 01-19-02, 01:10 AM
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Unhappy Loud noise from furnace

I have a 24 year old natural gas, upflow furnace. In the morning when it is the coldest , the burners kick on, and after the heat exchanger reaches it's proper temp, the fan starts up, and the unit runs for about a half hour, quiet as a mouse. But after 15 minutes or so, when the burners start up again (before the fan kicks in) it sounds like a jet liner preparing for take-off, i.e. loud humming and buzzing. Is this just an old heat exchanger expanding and contracting, loose flue baffles or ? Please help because I feel as though I live next to the airport.
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Old 01-19-02, 05:31 AM
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Hello Mighty Q. Welcome to the Heating and Cooling Appliance forum.

There could be a very simple reason for the problem description your furnace is displaying and equally as easy to correct solution. However, the optimum correction only applies if all other operations and functions of the heater are set and operating correctly.

The air shutters may be incorrectly set on one or more burners. If the air shutters are adjusted to provide too lean an air mixture, {Opened too wide} the condition you described can or will occur under some ambient temperature conditions.

The air shutters on the burners are on the ends of the burner tubes. There should only be one shutter per burner. A small screw secures each shutter in a set position.

Without having to remove the burner or screw, simply loosen the screw and slighly close or open the shutter of the effected burner.

To identify the effected burner which may appear to be set too lean {Getting too much air} the burner flames may appear to flutter, be blowing like a blow touch, the flames could be lifting slightly off the burner head, etc.

Look for one or two burner flames which should appear to be visibly different when compared to any others while the condition exists, if possible. If your unable to be present while the problem is occuring, adjust the air shutters to a slightly less opened postion but not closed enough to cause the burners to display any yellow at all.

If all else is correct, this simple air intake adjustment should correct the condition. There could be other conditions that can cause the condition too. Many of which not so easy to describe here in a text only format and may not be so easily correctable.

The condition may only happen do to the different expansion and or contraction rates of the burners, orifices, air density, moisture content of the ambient air, etc.

However, more complex reasons could be do to the natural gas pressure within the entire gas piping system, at the time the condition exists. Other reasons could be gas density and volume, the actual gas appliance regulator, the gas companies equipment and several other possible and potential problems only a well trained professional could test for and determine.

Other professionals replying within this forum, may have alternate solutions, suggestions, opinions and or test and repair methods. Check back several times.

Regards & Good Luck
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Last edited by Sharp Advice; 01-19-02 at 05:46 AM.
Old 04-08-08, 08:01 PM
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Smile Great Advice

I had the same problem. After reading your response, I adjusted one of the shutters on my furnace. It worked perfectly - thanks! To test which of the burners was causing the loud humming noise, I covered each up with my hand. I have a Trane XE65.

Thanks again for saving me a service call and all the hassle!


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