Burned flex duct lining

[lil' randy]

We recently had service call where one 6" flex closest to the air handler on top of the metal supply plenum appears to have caught fire ( soot on ceiling around vent) and completely burned no signs of it the vinyl lining, discolored the insulation and melted the Mylar coating. Equipment is an American Standard air handler with electric heat 8.0 kw on a four ton, (second floor in Houston) doesn't need much heat. Variable speed blower comes on consistently and temp rise not excessive' plenum temps in the 90s. Duct goes to a bathroom. Checked for wiring touching, in almost twenty yrs in the Hvac world never seen a duct burn.

[genduct]

I wonder if it could have "seen" the radiant energy from the hot heat exchanger and cooked?

[littlebigdad]

With global warming and you being in Texas I guess it could happen

[catmanacman]

change the filter more often

[corny]

Just wondering.... but did this home at one time have ceiling heat..... Ive never seen a fire started by ductwork coming into contact with old ceiling heat wires....but Ive seen ductwork electrically energized by ceiling boots getting up against ceiling heat wires that had not been disconnected.

[captube]

Maybe the element shot a piece of hot metal. They don't last long after that so you would of probably noticed.

[lil' randy]

Changed the heat kit because my technician saw some discoloration on the heat strip, but I an still not convinced even if the strip touched ground this could happen

[hearthman]

If it truly was from combustion then it was an "unfriendly fire" and therefore a covered peril by all insurance. Since you said there was "soot" on the ceiling, that means the repair will be much more than just replacing a duct or repairing the appliance. You now have particulate damage and probably all over the place but don't realize it. These cases can easily get into tens of thousands of dollars for clean up, paint, replacement, laundry, etc. If this is your first trip ever to this house, you might consider referring them to a public adjuster, who will do all they can to run the cost up for every little thing including paying you to repair the duct and unit or replace it.

If you have serviced this unit previously, then you have to be concerned about subrogation. This is where the insurance company pays to clean up the mess then sues you for recouping their losses.

[thermojohn]

You sure it may not have been caused by a lit torch flame? That flex 'foil' just melts to nothing with just an accidental swipe with a flame feather. Look and see if it may have been close to where an evaporator coil or copper line may have been soldered recently.

Y'know no one would want to admit it, so look at it really good.

[MicahWes]

Probably just had a blower fail sometime and the strips got it mighty hot? The limits on some of those heat kits are pretty high, and if heat from the strips was allowed to rise up from the heaters into the plenum during a blower failure, the temp up there could climb much higher than the actual vicinity of the heaters...Maybe.