Chimney Plume Watcher?

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Old 02-11-14, 04:49 PM
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Chimney Plume Watcher?

With subzero temps, while driving around town, I've been doing a little study of the appearance of plumes coming out of roof-top chimneys (all gas-fired around here, non-condensing boilers or furnaces are the rule).

Theoretically, if the plume is clear for a few inches above the chimney, before it mixes with colder ambient air and becomes visible, there is no condensation in the chimney (good). In this weather, I have seen no such plumes.

The worst cases I've seen are ice forming around the chimney exit, along with a visible plume. Not good. The plume must be quite cool as well as saturated.

Most typical is a visible plume immediately from the chimney exhaust, but no ice. For this case, there may or may not be condensation in the chimney, I think.

Some houses have rows of long, some 3 ft, icicles hanging all along the eves. I assume that is caused by poor attic insulation, resulting in thawing of snow on the roof that refreezes as it drips from the eves. My house's attic is well insulated, and there are no icicles on the eves.
 
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Old 02-11-14, 06:15 PM
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Funny you should be noticing the same thing that I've been noticing! Great minds!

The advent of higher and higher efficiency appliances is slowly creating a big business opportunity for masons and chimney liner companies!

The plume from my oil burner starts pretty much as soon as it exits the rain cap... no icicles though.

I am still getting some condensation with the 4" liner, but nowhere near what I was getting with the 6".

Before I chainsawed the second floor off and rebuilt it (long story), I had ice damming so bad that the water was running down inside the walls. I had icicles forming at the top of the foundation 2 stories down! It's all good now though. The snow on my roof is the last in the neighborhood to melt!
 
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Old 02-11-14, 06:42 PM
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Hmmmm I was watching the plumes myself when it was single digits...

I noticed the houses with the long stacks had white wispery plumes... Looked like a wood burning stove. All gas here. These are flues that follow the 10/2 rule for roofs...Some are 4ft plus on these old capes...

I figure its because the exhaust has cooled so much as it reached the top. Most were right at or near the cap...

The reason I was looking and anylysing is because mine dont do that.

My boiler is in a shed and comes out a flat rubber roof. I been meaning to extend it since I bought the house 12 years ago... My stack is less then 10 ft from the boiler to the roof...I have maybe only 18" above roof line..


Just my 2 cents....
 
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Old 02-11-14, 09:18 PM
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As you guys know, all chimneys are not created equal. So for those of use who observe smoke plumes during the winter (yes, I also do it) it is important we keep that in mind. How tall, how old, what kind of flue (if any), is it exterior or interior, etc.

In my area oil heat is still quite common (I'd guess it's still 50/50 gas vs. oil) which also makes for a more complicated analysis.
 
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Old 02-12-14, 04:47 AM
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Great thread! When it's in the single digits I can see the shadow of the smoke in the silhouette of my house on the ground in the morning. It's turning to white smoke just above the chimney cap and floats up, up and away. Looks like a post card at times from the street with all the snow.
 
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Old 02-12-14, 06:32 AM
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If you wrap the brick with insulation that is in the unheated attic it will help keep condensation from forming .
 
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Old 02-12-14, 09:04 AM
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If you wrap the brick with insulation that is in the unheated attic it will help keep condensation from forming .
It wouldn't hurt. I've never felt my brick chimney shell to see how warm it is. But, the heat would need to escape the chimney liner and then through the shell.
 
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Old 02-12-14, 09:20 AM
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My feeling on masonry chimneys is that they are dinosaurs, relics of the past, should ALL have INSULATED liners installed and just be used as a 'chase' for getting the liner through the roof.

Todays appliances don't move enough quantity of hot enough flue gas to combat the condensation issue.
 
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Old 02-12-14, 03:36 PM
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My neighbor had a modcon installed before he moved in.

During these -0 temps, his thru wall vent create icicles to form on the soffits and a coating of ice on the brick.

When I mentioned this to him he looked at me like I had two heads.
 
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Old 02-12-14, 04:19 PM
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This winter I've seen a few thru-wall vents with heavy ice accumulation around them. What's to keep the Pex vent pipe itself from icing up internally, just like other plumbing does? Makes me wonder how suitable condensing boilers/furnaces really are for colder climes? The manufacturers specify the venting arrangement, that it has to be above the snow line, etc. (but this year, I've seen drifts up to 8 ft high).
 
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Old 02-12-14, 04:36 PM
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It seems to be a problem only when there is flue gas recirculation.

I have not found any mod cons shut down yet due to the extreme cold.

I have had one boiler lose capacity due to ice buildup in the intake piping.
The exhaust was continually blowing into the intake.
 
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Old 02-20-14, 08:56 AM
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At the risk of a slight thread hijack, what do I need to do in order to use a two-story masonry chimney with a mod-con, rather than venting through the side wall? We are sometimes away for a month or so during the winter, and I don't want to have to worry about snow blocking an intake or exhaust pipe, the boiler shutting down, and the pipes freezing.

There are two flues in the chimney, one for a rarely used fireplace, and another for the old oil burner I need to replace. It seems to me it ought to be possible to run a couple of stainless steel pipes through one flue for intake and exhaust air.

But maybe I am missing something, because everyone I know with a mod con has it vented through a side wall, and then begs their neighbors to make sure the vents are clear when they are out of town during a snow storm; my neighbors might not be that nice.

Is cost the issue with venting a mod con up a lined chimney flue, or something else?
 
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Old 02-20-14, 04:22 PM
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lots of boiler are now certified to use flexible polypropylene venting such as centrotherm.

Check the IOM of the boiler you want to use.

Generally the intake air is still brought in from the outside sidewall.
Some boiler can use inside air for combustion also
 
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