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What is that white powder on heating appliances and vents? Here's the answer...

Mundo Inspector

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Many of us have an idea what causes it, but here's the whole story:

Due to inadequate combustion exhaust venting, combustion gases cool before they reach the exterior. This is usually caused by an excessively long- or too many bends in the- combustion vent. Cooling combustion gases condense on the inside of the galvanized steel vent where the condensation reacts with the galvanized steel, and the result is corrosion. The first, kinda liquidy, gooey product of this corrosion is zinc hydroxide, which slides down the inside of the vent onto the heating appliance (furnace, boiler, or water heater) where the rest of the moisture evaporates, leaving a white, powdery residue that is zinc oxide. Sometimes it doesn’t make it as far as the heating appliance and you can see it leaking from joints in the vent above the heating appliance.

Now, sometimes this condensation takes place where the vent protrudes above the roof. This makes sense because the vent will be colder above the roof, especially in cold climates, and a colder vent will cause more condensation to develop. Because this takes place way up high, the zinc hydroxide that forms up there will have a long way to travel before it falls out the bottom of the vent connector, and before it reaches the bottom, it may become trapped at bends in the vent. At any rate, some of the gooey zinc hydroxide will dry to powdery zinc oxide while it’s still inside the vent, and some of this powder will be caught up in the slipstream of the draft from the heating appliance and will be carried up, discharged out the vent, and deposited on the roof, and this is why you see white residue on the roof below combustion vents.

On older combustion appliances with vents made of steel that is not galvanized, this residue may be brown because the corrosion product of steel is iron oxide, not zinc oxide.

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Thanks for repeating information that's been discussed to death dozens of times here.

It kind of reads like it's been copied and pasted from elsewhere. If so, please provide attribution. 

Are others seeing many of these old 80% furnaces? They're getting rare around here.  

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Not being a home inspector I only see it from its SEO value... because it's copied from another site it would likely considered negative and no benefit to TIJ. To use duplicate content safely you would need a conical meta tag on this page pointing back to original content. Google would then pass link juice etc. back to the original page. This post is negative towards our seo and Google doesn't care if the original writer posted it or not, and has no way of telling if it was him or someone just ripped it off and posted it here.

Not to mention this isn't a great idea for Kenton either as his original doesn't have a conical either. Larger sites can often rank better with the duplicate content than the originals sites. Conical tags on original content help stop scappers from stealing your content and ranking better than you with it.

This was also posted as a topic not a reply to some question... so very lame indeed!

It's just two paragraphs tho... and certainly not the first or last to be copied up here.

There are probably some changes coming to our posting guidelines directed towards guest posts and link droppers, but this case is already covered in our posting guidelines:



Re-posting To-From TIJ: All initial posts and subsequent responses from participants are copyrighted material of the person that posted the content. Content from this web site may not be copied to another site or displayed in a frame unless written permission has been received from the Editor, The Inspector's Journal. Likewise, participants are warned that copyrighted material that is re-posted to TIJ's Forums is considered pirated and is subject to deletion by the Editor. 

The moderators hate censoring anyone and always try and avoid it, however many of us have wasted hundreds of hours deleting spam... it doesn't take much for a spammer or link dropper to get banned here. Simply because they waste our time!

Kenton came up to TIJ riding the line... in this and his other recent posts... my advice would be to become an active participant of the community by posting original content, before dropping links and trying to gain a biz advantage.


Advertising: The purpose of the TIJ Forums is to provide answers, not an advertising venue.

He can also talk to us about advertising costs if he wants to go that way.

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