Residue on oil fired furnace venting

Does anybody know what the white/pinkish powdery residue on the venting pipe for an oil fired furnace is/caused by. Is it a bad thing? Also, rusty residue on inside of furnace/AC cabinet and staining on floor. Common occurance with AC units?





The white powder is likely due to water entry from chimney and galvanized metal corrosion from carbonic acid, created when exhaust from oil furnace and water mix.

As to rust it could be a bad condensate pump on bottom left of furnace spilling water during A/C season use.

= combustion byproducts.

Staining is a condensate leak from the a/c coil above the furnace. There are numerous causes for these leaks (posted in other threads). You can’t evaluate the condensate issue in the winter as you will not produce the condensate needed to create the problem. The unit can be opened and evaluated by the HVAC guy.

= combustion byproducts.

I hope that vent is sealed at that penetration point into the chimney. I see a big gap around the vent area.

I can also see that the seams (on the vent connector) are not sealed properly. If you look real close, you’ll notice that the white stuff (in question) is coming from the seam area (while venting). I don’t see sheet metal screws at this seam.

If the seams are leaking that bad, then you have improper venting. Something is preventing the exhausts from escaping through the chimney.

I second what Raymond posted. It looks as if you have a moisture issue here. Galvanized metal oxidizes over time with moisture “assist”. Another thing no one has point out yet is the rust stain on the floor sure looks to me like the condensate pump or something else is not moving water away too well.

What about the distance to combustion materials guys ?? What do you see in the breach point at the Flue/ smoke pipe going into the chimney? PVC piping in close proximity to the flue… 6 " clearance for a singled wall flue to combustionable material… :wink: If this were products of combustion (which is also white-ish curly flakes ) then you should be reading a lot of CO at operation of furnace… and smell aldehyde’s (rotten socks )… Bad !! and that would be seen near the draft hood (generally speaking and not up the flue pipe like in your picture).:shock:

Anyway it needs a proper eval by a HVAC tech for several issues… Rusty …no good so there could be some “future” appliance life span “short’in” issues…:smiley:

I knew this was the right place to ask, thanks for the answers.


Did it look like this? This furnace vented into a clay lined chimney. The blower compartment floor was rusted, rust stains at chimney clean out as well. Damaged masonry chimney cap which was allowing water into the flue.