White Crusty Mineral Like Stuff in My Oil Burner Flue

I got a question about the white crusty "mineral-like" stuff in my oil burner flue.

Our oil burner, air handler, A/C compressor & A-frame was completely replaced the winter of '05-'06.
All units are Carrier.
The oil burner is a RIELLO 40 F5 with electronic air shutter, mounted in a Carrier 58VMR Multipoise Oil Furnace 154K btu
There is less than 100 gals of oil burned, since installed.
The flue coming out of burner is 6", with new 6" baro before going into chimney
The baro does not have a wieght on the flapper. I don't know what the draft is.
The chimney is a SS double wall, 8" dia.

After 1 month from installation, I have noticed a white crusty mineral-like stuff dripping from each connection in the flue, and dropping onto the floor. I guess it starts as liquid, then drys to this crusty-powdery like consistency.
The Carrier repair man says "it is occuring because the oil burner is too efficient. He can "De-tune" the burner, and that would stop the burner from creating the crusty mineral deposits". I guess that means more of the heat produced would go up the chimney, or I would get less BTUs per gal.

Has anyone heard of this before? Any tips?
Thanks.

I have experienced the same thing with an oil fired hot air furnace I have in a utitlity building that I maintain at 55-60 degrees. I think the diagnosis is correct--the chimney isn't sufficiently warm and condensation is forming in the chimney.

My install has been in for ten years and I haven't had any problems attribuitable to the condensation. Presumably it increased the rate of deterioriation of the smoke pipe and the chimney (I also have a SS insulated chimney but 6") but as I noted it has been going on for 10 years and I haven't had to replace anything yet.

I can echo Bob's comments regarding my oil furnace too. The furnace, not a high efficency unit, is in the unheated basement and mainly assists the coal stove to heat the house. Its been in "use" for ten seasons and I too see the white mineral deposit forming along the joints of the horizontal single wall pipe run to a power vent. I don't tear it down yearly because I typically use <100 gallons per year since installing the Vigilant. The oil furnace was cleaned this fall , first time in 5 years, and all piping is still sound. The white crusty material is ash from the minerals in the oil. I see the same ash in the pipe when it's torn down for cleaning.

"The white crusty material is ash from the minerals in the oil. I see the same ash in the pipe when it's torn down for cleaning"

yup. nothing to be concerned about; diesel (no. 2 distilate oil) is not "ash free". it forms when a little ash combined with acidic moisture that condenses on the flue during burner startup seeps out of joints; it doesn't necessarily mean that you have condensation issues because the liquid that has condensed on the cold flue soon evaporates as the unit heats up during it's cycle. not uncommon at all.

Thanks for the feadback, guys. You put my mind at ease. I guess nothing is required to 'remedy' this.
NOW, if I could only get it to stop dripping on my floor and inside the new furnace. This summer, maybe I'll try to use some refractory cement to better seal the 6" dia flue sections where its leaking from.

Edit: on second thought, I have hi-temp RTV (Silicon) I can use.

DVC500_at_last wrote: Edit: on second thought, I have hi-temp RTV (Silicon) I can use.

I've seen silicone material used on ventilation pipes in the labs I've worked in but it doesn'e seem as thick a the RTV I've used. Is this the same silicone material that is used to seal pipe joints on a DV system? I'm sure RTV will work but the other material seems to have a lower viscosity and looks like it flows into the seam of the joint by itself. RTV I've use is thicker and I'd guess it would need to bee tooled to make a good seal. I've used RTV to seal off small leaks in an oil furnace heat exchanger tube. It will hold up. Just wondering ...

VigIIPeaBurner wrote: I've seen silicone material used on ventilation pipes in the labs I've worked in but it doesn'e seem as thick a the RTV I've used. Is this the same silicone material that is used to seal pipe joints on a DV system? I'm sure RTV will work but the other material seems to have a lower viscosity and looks like it flows into the seam of the joint by itself. RTV I've use is thicker and I'd guess it would need to bee tooled to make a good seal. I've used RTV to seal off small leaks in an oil furnace heat exchanger tube. It will hold up. Just wondering ...

Dave, what I have on hand, is the red, High-Temp RTV. It has the consistency of toothpaste. I mainly use it as a head-gasket sealant on the Stihl chainsaws I rebuid. It looks like the exact same stuff they used on my DVC-500.
I'll pull the pipe sections apart, clean them up, then fill the crimped end of each piece with the RTV. That should be enough to keep the minerals from running out of the cracks.

RTV silicone is available in different viscosities, but not in the consumer market. When I was still working we used an almost watery like RTV as a potting compound. It was used to make molds for items made using the lost wax casting method. We also used in to mold in place the wires of electrical connector contacts. That prevents failures when the connectors are subject to high vibration, like the rocket launching of a spacecraft. High temperature RTV Silicone is amazing stuff. We also used it to protect the rocket launch pad. Hundreds of 5 gal. buckets of the stuff was just poured on the launch pad metal structure and left to cure. Upon rocket launch, some of it ablated away, but it still protected the underlying metal and concrete. Truly a great product.

Available to the general public, the best by far today is made by permatex and it is called "The Right Stuff" comes in cheeze wizz type can as well as tube and caulking gun type.

it is the compound GM uses for all the gaskets in a modern engine less the head gasket.

definitly worth all the money imo

Yanche wrote:RTV silicone is available in different viscosities, but not in the consumer market.
Truly a great product.

Yep, I used it all the time on sealing pressure panels on the C-5A. The grey stuff. I'll never forget that smell. I found it in the form of DIRKO (HT for High Temp) which is from Germany. Used it for many, many years. Same smell
Just recently I found Permatex put out their own version of High Temp RTV. Not sure if its the same stuff, its probably watered down. I'll find out as soon as I open it and get a good wiff.

Regarding the white crust coming out between the flue pipe sections.
I analyzed the crust and found sulfur, zinc, iron, and oxygen.
The largest combustion product form burning oil is actually water. The water combines with the sulfur in the oil and you have sulfuric acid.
The acid dissolved the galvanized coating in the flue pipe and you get zinc or zinc oxide. Below the zinc the acid then dissolves the iron in the duct.
I would imagine the higher the flue gas temperature the less condensation. My system is set up as to cold start so the flue temperature can go down to room temperature if it is warm outside.
Flue pipe is cheap.

-Joe

good information. after having seen this countless times, I had guessed that it was acidic moisture condensing around joints at startup causing minerals (fuel oil ash) dissolved in the in water droplets mixed with flue gasses to precipitate out and form a deposit; it makes sense that it's primarily zinc and iron, the zinc dissolving in the acidic water and then drying later in the firing cycle and creating zinc deposits around the joint.

I have a quick question if someone could answer if a forced air oil furnance is advertised as 83% efficent and the burner is in proper tune what would the expected flue gas temp be? And what kind of temp do think you would see with a magnetic therm. 1 ft up the flue from the furnance?

Thanks

Mine out in the barn usually runs about 200°- 250°F ... the boiler in the house is about the same ... usually a bit hotter at 275°-300°.