Thread: Tarnished vent at oil furnace

Has anyone ever seen this film on a vent before?

I could not think of what it could be from.

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One thing that may have been a contributing factor is that the humidifier appears to have overflowed at some point which dumped enough water on the heat exchanger to cause staining at the floor in the adjacent room..

Assuming the furnace was running at the time, maybe that caused steam to get exhausted out or something but just didn't know if that would cause the strange tarnishing.

It looks like the barometric damper on the vent was not operating properly and the vent overheated.

Looking at the damper. I can't see a counter balance for damper adjustment.

Also looks like a possibility of extreme heat... like when a home owner hits the reset button on an oil burner too many times until it finally ignites!
I have seen the stack from an oil burner turn cherry red from heat while the boiler is almost dancing around the basement due to so much oil in the chamber (flooded) when it ignited.. All you can do is close the oil line and wait for it to burn out (if the house don't catch fire first)..
At the same time, I would expect to see that discoloration at the base of the stack as well,.. not just in the middle.. (perhaps a different mterial?)

Originally Posted by Jon mackay

Has anyone ever seen this film on a vent before?

I could not think of what it could be from.

x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x

Could be from the humidifier running after the call for heat has been met. Without the hot exhaust gases heating the vent after the heat cycle has ended, and with the humidifier still furnishing moisture, the moisture could have accumulated in the vent system.

I would check to see if the humidifier was still running after the heat cycle ended. It should cut out when the furnace ends its cycle. If it doesn't, I would suspect this to be the cause. It may have a bad relay/sensor that lets it keep running.

Floyd
HVAC, Gas, Electirc, Oil Tech

I'm scratching my head here;
How would moisture from the humidifier get into the vent connector?

Jon,

That 4 inch radon pipe that exits at the side of the chimney may be a problem. Check the pipe discharge outside, it should not be below or within 10 feet of the chimney - potential back draft into the house.

The varnish on the vent looks just like the patina that builds up on a bread pan or other metal or glass cooking pan used to bake food containing grease or oils (butter etc.), so perhaps the vent tarnish started as a film of oil or grease, and not water from humidifiers or wherever. I think it is unlikely the vent had been been red-hot as the colour would have changed to black/gray.

To qualify my comment that a red-hot vent pipe would cool to black/grey, in suggesting this I was thinking of mild steel vents rather than stainless steel. In the latter case the result might be different.

Originally Posted by Frank Norman

The varnish on the vent looks just like the patina that builds up on a bread pan or other metal or glass cooking pan used to bake food containing grease or oils (butter etc.), so perhaps the vent tarnish started as a film of oil or grease, and not water from humidifiers or wherever. I think it is unlikely the vent had been been red-hot as the colour would have changed to black/gray.

I second Franks assesment.

This is a film of oil on the pipe that causes this! Somewhat common.

P.S. I did not splain it well Light film of oil from factory and heat gets to it and causes this! Hope this helps.

How close is that clothes rack/pole to the vent? I'm presuming its presence suggests the "area" is serving double duty as a laundry, and that rack serves as a collection point for the hangers, wire, drycleaner freebies, and all, when collected from closets upstairs, and later clean clothes are first hung and staged there.

WAG: a garmet protection bag, such as those supplied by dry cleaners over hanger-hung work (thin clear poly or similar) hung on that clothes pole and wafted towards the vent and melted upon or possibly caught fire when it made contact with the still quite hot vent, leaving that carmelized color at the hot point just before the offset to the thimble. Secondary WAG, a tall plastic hamper made its way too close to the baro and/or the lower section of the connector and it or its contents (poly fabric?) did the same thing (roasted).

Have seen a similar "carmelization" deep red brown when those thicker "oven roasting bags" set in metal pan are baked at much too high a temperature, leaves same residue color very difficult to remove from unlined/finished metal baking pan.

Point being, might be a perspective/photo affect/effect, but the location and proximity of the clothes rack and storage shelf look questionably close in proximity/safety to the vent and there is no apparent protection from draft/wafting clothing, flamable storage, or anything to fall against or encorach upon the required free-air zone around the pictured vent. Would be concerned about storage in the immediate area as well, temporary as it might be during laundry activities, etc.

I have seen this happen to chromed piping that is sometimes used for exposed flue gas fireplaces. Probably the wrong application for this pipe.

I would want to see combustion analysis numbers, esp. the gross stack temp. I have seen pipe damaged in this way from an appliance overfiring. When you approach 800*F, you run the risk of cooking off the galvanized coating, which can look similar to this. Usuallly the mill oils on the steel cook off with the first firing or two but you can also get unburned fuel oil when a homeowner hits the reset button more than once on a unit not firing and where the pipe is oriented with the male ends pointing upwards which allows flue gas condensates and unburned oil to drip onto the exterior of the pipe. This is why woodstove pipe points downwards, to contain the creosote.

The connector is not supported and there is no cleanout in the chimney within 12" of the breeching. If that is a listed liner then your AHJ may not require a cleanout in it.