# Flue cap



## GettingBy (Aug 19, 2010)

A guy working off the back of a truck said I had no flue cap and so he wanted to sell me a new one for my NG furnace, and a chimney cap. 

$100.

When the snow melted I climbed on the roof and found he was telling the truth; no cap, possibly for years. It wasn't on the roof so maybe it was never installed.

A flue cap is on order, for about $40. The pipe is 7.5" dia.

Meanwhile, should I be making a hole in the wall to check that the bottom of the flue pipe is not rusted out? We have CO detectors but they have never alarmed.

I don't have or want a chimney cap.


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## flashheatingand (May 3, 2008)

I am under the impression that there is a metal exhaust vent running through the chimney that is uncapped? If so, One should flash over the top of the chimney with a piece of sheet metal. Then put the cap and coller on the vent pipe.


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## flashheatingand (May 3, 2008)

Anybody hear of decorating the vent and cap to look like a snowman or something?


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## GettingBy (Aug 19, 2010)

Thanks.
Did it.
It turns out the OD of the fitting was an interference fit with the ID of the flue pipe. No tools or fasteners req'd.
So, do I need to inspect the bottom of the heavy metal flue pipe for rusting out?


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## unicursalhex (Jan 17, 2011)

That entire vent run most likely needs to be replaced depending on how long it was without a cap. At the very least you should inspect it by shining a flashlight down from the roof. If there are signs of rust (which i'm sure there is) it would be foolish not to replace the piping, all it takes is a nice hole to develop over time and best case you get nasty headaches, worst case you never wake up


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## GettingBy (Aug 19, 2010)

unicursalhex said:


> That entire vent run most likely needs to be replaced depending on how long it was without a cap. At the very least you should inspect it by shining a flashlight down from the roof. If there are signs of rust (which i'm sure there is) it would be foolish not to replace the piping, all it takes is a nice hole to develop over time and best case you get nasty headaches, worst case you never wake up


I'll start at the bottom since water would accumulate there. If that's not rusted out I should probably be OK. The pipe wall is almost 3/16" thk.

I had a Mustang with an exhaust system leak and that taught me the symptoms of CO poisoning pretty well.

Thanks for your input.


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## GettingBy (Aug 19, 2010)

Turns out the bottom of the flue pipe is visible and more or less accessible, and the joint between the heavy bottom cap and the round sheet metal duct looks rusted open for 1/3 of its circumference. 
To check for a hole, I'll put a candle flame and run the furnace, looking for a disturbed flame.

If there is a though hole I'll have to remove some of the rectangular duct that this pipe rests on and put on a new bottom cap. This pipe bottom was visible all along if I only took the trouble to look.
Apparently only the roof pipe has thick walls, the inwall stuff is just sheet metal.

So, thanks to all those who replied to this thread and thanks to the guy cruising the neighborhood who tried to sell me a new cap for motivating me into checking this out.

I guess the CO detectors never went off because the warm exhaust carried the CO up with it.

The houses in this neighborhood are all similar so I'll warn the neighbors.


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## beenthere (Mar 5, 2009)

A CO detector in the basement should be mounted at the top of the basement stairs. This is where the CO will rise to.


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## mrjoebiz (Jan 27, 2011)

*Do you need a chimney cap? Take a look!*

:thumbup:
There are many different reasons given by chimney sweeps, masons, HVAC pro's, and fireplace retailers, as to why you need a chimney cap, and this can often confuse the issue. Today we'll take an in-depth look at the different types of chimney caps and answer this question once and for all.
Your chimney will be either a brick or masonry chimney, with (round, square, or rectangular) or without (square or rectangular) a clay/terra cotta flue.
OR
A metal chimney, having a round top.
Metal chimneys are sometimes used for woodstove venting, pre-fab fireplace venting, and sometimes gas venting. All metal chimneys need to have a cap, and here are a few reasons why:

:sad:--Rain! Without a cap, the rain will run into your stove, fireplace or heater and will have nothing but a negative impact on both the chimney itself and your heating unit. 
--Good rain caps, with screen guards, will keep birds and other animals from enjoying the warmth of your chimney and possibly clogging it with nests. 
:wallbash:--Metal chimneys are usually made of two or three layers of metal walls, with air or insulation between them. Without a cap, water and moisture can get into these layers and cause deterioration of both the insulation and chimney itself.
There are quite a few reasons to have your masonry chimney properly fitted with a cap, whether there is a clay flue inside of it or not.
--Rain and/or Moisture! This combined with the heat, will deteriorate both the clay flue and the brick/mortar of the chimney. These defects can lead to a chimney fire or carbon monoxide poisoning, depending on your heating unit.
--A properly mounted chimney cap will steer ice and rain away from the chimney crown, which is the cement on top of the chimney structure. This will help the life of the crown and eliminate possible cracking of flue tile.
:clap:--Once again, like a metal chimney, aood rain cap, with a screen guard, will keep birds and other animals from enjoying the warmth of your chimney and possibly clogging it with nests. 
Now that you know you need a chimney cap, lets go over the different kinds that are available.
We suggest a high grade of stainless steel cap:tank:, whcih will last the longest.(rust and corrosion)
Most models feature side screening which keeps most birds and small animals out of the chimney and also keeps larger sparks from existing the chimney, hence the term spark arrestor.
These caps are mounted onto the chimney in various ways, the most popular being screws which are spaced around the base angle of the cap and tightened against the flue tile. If the chimney is unlined or the flue does not protrude far enough out the top, inside mounting models can be used. If neither of these methods work, manufacturers also provide mounting angles or other fasteners which can be lag bolted or cemented down to the top of the chimney.
Here are our recomendations 
Single Flue-
Multi Flue-Engineering sets this cap head and shoulders above the rest, and makes it the most popular cap in the industry. SwingTab reversible mounting strips allow you to swing the mounting strips in or out as needed for the best fit. Crowns that used to be too narrow, no longer are with SwingTabs. They may even eliminate the need for a custom-made cap. The Chimney Protector is the best knock-down design on the market. It comes partially assembled. You finish the cage construction by inserting two hinge pins. You have two options for attaching the lid-wing nuts or cap crews. Nuts, screws, masonry anchors and mountung adhesive are included. 
wind resistant-
These caps are great if you are experiencing downdrafts and back-puffing.
Metal Chimney caps (Class A)
This cap attaches to the Class-A chimney system by sliding inside with a tight friction fit. The Guardian Caps main use is for top termination of a factory built chimney relining job. 
Single Flue/Terra Cotta mounted-
Single flue chimney caps mount directly to clay flue tiles. You can use this type of chimney cap on a chimney that is relined with a metal flexible chimney liner or a chimney with only a clay flue liner.
Custom chase covers with or without spark arrestor-
A chase cover is designed to cover a chase on the top of a chimney. It protects the chase from water and environmental damage. In most cases they are built out of stainless steel. Also, these chase covers are installed on factory built chimneys.
Custom and Custom Copper Caps-
You just might need a a cap that fits your other needs that are not mentioned above. Sizes, hights, looks and copper are all possibilites. Remember, the more you go "outside the box" with your caps, the more you will spend!
If you are a contractor and would like more info, let me know!
CHIMNEY CAPS !!hone:


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## MAULEMALL (May 16, 2010)

I believe you have forgotten pour in place cast liners...


Probably the only way I would go if I had a chimney that needed repair.


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## GettingBy (Aug 19, 2010)

Wow. . ."ask and ye' shall receive".

I inquired about a bottom cap that is a press fit. He told me that I might have a pipe within a pipe.

To get access I need to cut a hole in a closet wall unless I want to tear out quite a bit of duct work. 
Rather than fix the closet wall drywall I'll make an access plate out of Masonite that I can fasten and remove with screws into the nearby studs.

Chiseling off the existing rusting cap will be the worst part of this adventure but I have abrasive disks that to into my drill chuck.
There is a heavy metal sleeve that is around the bottom edge of the sheet metal round duct and I'm not sure what holds it. 
Maybe I'll make a custom cap - I doubt this pipe gets very hot at this bottom stub.

Right now this cap is resting on an existing rect. duct. I hope it is held up in other places.

You guys are good :thumbsup: 

And nobody hassles me on this forum. I had to threaten legal action with one poster on another forum. The guy just wouldn't quit.


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## GettingBy (Aug 19, 2010)

1/4 th of the cap circumference is oozing rust but it doesn't seem to leak air.
Grainger sells a duct sealant.
The pipe rests on one rect. duct and butts up against another.
My cap consists of a plate and a band.
I will push some rustoleam in the gap, coat both cap parts with sealant and assemble in place, and get one more CO detector.

Anyone objecting to this shotgun marriage of cap and pipe, speak now, or . . .


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