What causes this??

[caryseidner]

I saw these ice formations on a chimney cap of a house I inspected today. A natural gas water heater and forced air furnace are routed into the chimney. Outside temperature...DAMN COLD! (10 degrees +/-). The color in the photo is accurate. What the heck causes this?

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The neighboring house chimney had the same thing on it. Except the color was white (newer appliances/flue = less rust?).

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I'm guessing there is no problem with this, but I was wrong once.[]

[Terence McCann]

Condensation is forming on the rain cap and dripping down then freezing. The 4 corners are the low point with the middle of the cap being the highest. Flue gas is moist.

A slightly acidic Popsicle.

[Jim Katen]

Aren't they just ice stalagmites caused by the condensation dripping off of the caps?

- Jim Katen, Oregon

[caryseidner]

Yeah. I guess that's all it is. The parts that through me a bit were:

1) The color difference, but that's gotta be rust.

2) I didn't mention in my original post, but these were the only two chimneys on the block that had the stalagmites.

3) I have never seen this before.

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[Mark P]

How about this.. Snow lands on the rain cap, the warm exhaust melts it and then it refreezes when it runs off the corners.

[Brad Manor]

Stalagmites are the ones that grow upwards. Stalactites are the ones that hang down.

-Brad

..... nevermind, I just took a closer look [:-paperba

[kurt]

There's supposed to be a metal liner inside that clay tile liner.

Yes, I know all the local morons say you don't need a metal liner if there's a clay tile liner, but they're wrong.

That said, I see this all the time in winter. Simple condensation, and stalactite/stalagmite formation.

[energy star]

My understanding is a properly sized, new, or well maintained chimney does not need a metal liner. Many older homes have a very large chimney that will be to large for proper draft or the thing is just falling apart inside, in that case you are correct. Is that what you are referring to Kurt?

[AHI in AR]

Originally posted by caryseidner

Yeah. I guess that's all it is. The parts that through me a bit were:

1) The color difference, but that's gotta be rust.

We don't get cold enough around here to see that sort of thing, but I'd guess that the coloration of the "stalagmites" is due to the inclusion of combustion byproducts from previous use as a woodburning fireplace chimney (resins, etc) in the condensation.

[kurt]

Originally posted by energy star

My understanding is a properly sized, new, or well maintained chimney does not need a metal liner. Many older homes have a very large chimney that will be to large for proper draft or the thing is just falling apart inside, in that case you are correct. Is that what you are referring to Kurt?

Any chimney on an outside wall venting gas combustion appliances has to have a metal liner.

I might be wrong on this one, but it looked like it was on an outside wall.

[Jeremy]

Originally posted by AHI in AR

Originally posted by caryseidner

Yeah. I guess that's all it is. The parts that through me a bit were:

1) The color difference, but that's gotta be rust.

We don't get cold enough around here to see that sort of thing, but I'd guess that the coloration of the "stalagmites" is due to the inclusion of combustion byproducts from previous use as a woodburning fireplace chimney (resins, etc) in the condensation.

My thoughts as well. I have seen it with wood burners...and darker.

[caryseidner]

Originally posted by kurt

Originally posted by energy star

My understanding is a properly sized, new, or well maintained chimney does not need a metal liner. Many older homes have a very large chimney that will be to large for proper draft or the thing is just falling apart inside, in that case you are correct. Is that what you are referring to Kurt?

Any chimney on an outside wall venting gas combustion appliances has to have a metal liner.

I might be wrong on this one, but it looked like it was on an outside wall.

It is on an outside wall and there was not a metal liner in it.

Thanks Kurt.

[Brandon Whitmore]

Kurt,

Do you have a code cite off the top of your head by chance?

I don't remember reading this, but I guess I need to re- read the whole book anyways.

PS: Did a quick Google search to see if I could cheat and not look in the IRC. The first article I read was this:

http://www.oldhouseweb.com/how-to-advic ... nace.shtml

I read the whole thing before realizing it was from Bill.

[energy star]

A new chimney on an outside wall does not require a metal liner. If the flue or chimney is to large or needs repair, a liner will serve you best, as the link above points out.

I gotta go do some duct blasting. later.

[Darren]

Kurt;

This is what I was told at a seminar this year (Presented by Julius Ballanco PE, you may know him, he's from Ill.)

Any fan assisted appliance that's connected to an exterior chimney, that chimney MUST be re-lined with a metal liner.

Any fan assisted appliance that connected to an interior chimney, that chimney PROBABLY should be re-lined, but may not have to be (depending on the size).

Is that what you're referring to?

[energy star]

I think he means if you have a water and a fan assist.

[Darren]

Originally posted by energy star

I think he means if you have a water and a fan assist.

No.

If you replace a draft type furnace with a fan assisted one, AND there is a water heater tied into the chimney, then the connector of the water heater should be increased by at least 1 size; doesn't matter if the chimney is interior or exterior.

[energy star]

I'm sorry but I'm not talking about an exterior or interior chimney. The point he is trying to make (I think) is that a gas hot water heater vented to a chimney will vent naturally. This would be a slow upward draft. Now also vent into that chimney a fan assisted flue. It will force it's flue gases up and out the top faster. Most times when we talk fan assisted flue with a gas furnace it means it's high efficiency type furnace with a lower flue temp. With this lower flue temp the walls of a chimney will not heat up as much, preventing the flue from warming up. Now at the same time our gas water heater comes on, trying to vent in a somewhat cold flue with turbulent air in it. This is when cold capping comes into play. This small water heater may not warm the chimney up sufficiently to create the needed draft. So he wants the flue size from the water heater increased to help heat the flue.

He also says that a flue in the interior of the home may be exempt.

[steve morris]

Here in the DEEP SOUTH (FL) your higher eff. furnaces such as 90% you must use plastic pipe to vent the flue due to the category for the appliance. It's rated as a condensating type. A lined chimney with tile or metal would not meet code, and would not last. Read the flue sizing charts in the fuel gas code, the main thing is btu's(heat) and length of flue. There are four categorys of vented appliances, non positive pressure and positive pressure flues flues. condensating and non-condensating(see the definitions in the F.G.C.).. Even here a clay lined chimney has to be very small for a furnace to be vented into it. It takes so much heat to warm the liner up for the draft to start, most of the time you just puddle condensate at the bottom.

[caryseidner]

Originally posted by Jeremy

Originally posted by AHI in AR

Originally posted by caryseidner

Yeah. I guess that's all it is. The parts that through me a bit were:

1) The color difference, but that's gotta be rust.

We don't get cold enough around here to see that sort of thing, but I'd guess that the coloration of the "stalagmites" is due to the inclusion of combustion byproducts from previous use as a woodburning fireplace chimney (resins, etc) in the condensation.

My thoughts as well. I have seen it with wood burners...and darker.

The house was only 40 years old and I don't believe it's fuel source was ever wood or oil. Just natural gas. My (revised) guess is the color was due to the rust on the rain cap, which you can't really see in the photo.

[Jeremy]

Or really heavy smokers.