Originally Posted By: dbush This post was automatically imported from our archived forum.
Can anyone tell me what is causing a loud “thud” or bang when an electric heating unit kicks on and off. It is primarily when the unit kicks on and the unit is a horizontal unit in a crawlspace with lots (at least 2’) of open room under the unit.
Originally Posted By: rsummers This post was automatically imported from our archived forum.
Pull the blower door off and jump the controls at the unit so you can observe the motor starting it could have a bad mount or something. If it doesn’t make the sound with the door off your duct or R/A intake could be under sized.
Originally Posted By: rpalac This post was automatically imported from our archived forum.
Here’s another educated guess in line with what was said.
I have notice that my oil fired hot air heater makes a loud sound when it starts. I investigated it to find that it was the feed air duct plenum expanding (flexing) and making a loud, BANG!
I researched it some more to find that when my air filter which is a 90% is dirty it restricts the air flow enough that the unit builds up enough back pressure to cause this flexing across the sheet metal duct.
My thought was to put in a stiffener with some quick zap screws to alleviate the sound. (A new filter also works until it gets a little dirty). A close friend of mine who is a steam fitter told me this is not uncommon as one of his repairs in the field. He also explained when they bend duct work you usually see a diagonal crease in the form of an "X" in the front and back face of the duct work. That crease is for exactly that reason, to stiffen the duct surface from flexing.
I thought it was interesting and maybe was in line with what you are experiencing. If not, oh, well. It's a piece of info for the future.
(right now I left it so I know when to change my filter.....it acts like an alarm.)
Bob p.
Originally Posted By: jpeck This post was automatically imported from our archived forum.
I believe Robert P. and Erol on on the right track. We used to refer to this as “oil canning” because of the way … well, I forget why we called it that … whatever , but I think that is the cause of the loud banging.
Originally Posted By: jmyers This post was automatically imported from our archived forum.
Here is another thought on that loud bang. If you have a belt driven blower the loud bang you are hearing may be from the blower motor starting and stressing the metal on the heater around the blower. It causes a loud bang every time the motor turns on. Nothing to really worry about, it is more annoying that anything.
Originally Posted By: jpeck This post was automatically imported from our archived forum.
jmyers wrote:
Here is another thought on that loud bang. If you have a belt driven blower the loud bang you are hearing may be from the blower motor starting and stressing the metal on the heater around the blower. It causes a loud bang every time the motor turns on. Nothing to really worry about, it is more annoying that anything.
Joe Myers
If that is the cause, then the metal is being fatigued as it is being stressed, which could lead to cracking / splitting of the metal over time (a long time). Then, one day the motor may just rip itself out of the housing.
, but I think that is the cause of the loud banging.