rain caps for a chimney

I have heard good and bad things about chimney caps.
What opinions are there about them, the general idea being to keep rain and weather out of the chimney.
I have heard that they can alter the draft of the fireplace to make it hard to vent a fire. I've heard they aren't even necessary I've heard they can improve heat loss problems.
Those are just a smattering of takes on the matter. I'd be inclined to believe they aren't even necessary but I don't have sufficient experience to say yes or no.
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The only valid reason I would say for having a cap is to keep rodents and other varmints from building a nest in your chimney or living room for that matter. If that isn't a concern, and the amount of rain or snow that falls in isn't a worry to you then you are probably right - the aren't necessary.
As for changing the draft of the chimney, if they are sized properly that should be a minimum concern. And if by "improve heat loss problem" you mean reduce the heat loss - likewise, there should be minimum effect on the air flow. Use a good damper when not burning to prevent heat loss.

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Mark wrote:

If your talking of a normal fireplace a good option is a top mounted damper it seals the top unless you have actual fire going, chan from roof goes to damper contro at fireplace
obviously this cant be used for gas fiored appliances like a furnace
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As far as keeping rain out, no, not needed. Having had a bird in it the chimney, then a squirrel, we have a cap. Spend the extra to get stainless steel. Painted ones rust and can make a mess.
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Definitely get a good stainless steel one. On our previous house I put a junky galvanize one on from Lowes and a bat still got in. Fortuantely he could not get past the glass fireplace doors and eventually apparently found his way out.

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Art wrote:

rain inside can lead to faster detoriation of mortar joints
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wrote:

For a boiler chimney, it can improve draft a bit, because when the boiler fires up, the flue will warm faster. It also reduces the chance of a wind gust blowing DOWN the chimney.
For a steel flue, a cap to keep out rain is essential.
I was at a large reception once and here was a fireplace at one side of the room. A gust blew down the chimney, and everything in the room was instantly covered with a layer of ash and burning embers, including the tables, food, and guests.
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I have a cover cap but no screen to it and have had no problem with animals at all. My damper is shot so I looked into a lock top chimney cap damper but decided on using a chimney balloon instead. I have heard mixed reviews on lock top dampers. Some say they are not durable and they let in air over time. Also they allow air to convect (heat and cool and sink) in the chimney so you get a draft feel from it in the winter. A good thing is though is it shuts the chimney access when closed. I dont think an ainimal could get past a locktop, I just dont think it would maintain airtight over time.
I guess I agree that a stainless cap with a screen and a strong traditional damper or a chimney balloon would be a good combo to stop air, animals and not change your smoke escape draft.
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On Wed, 7 Jun 2006 17:00:36 -0700, "Eigenvector"

I've worked as a chimney sweep in the past, and the Master Sweeps taught me this:

True. If you have an under sized one installed it can really effect your drafting. Make sure, like anything you get, you get a good quality cap, that meets all the height requirements needed for your size flue. Your sweep should help you with making a cap selection, and if you already have drafting problems, he/she can help with a product like (if I remember the name) posivent caps, or resizing the opening of your fire place.

False, weather(rain, snow, etc) mixing with creosol forms an acid that slowly eats away at the mortor and flue lining. Keep the weather out.

unsealed chimneys are a heatloss. Although I have no clue what you mean by the cap, but a free burning fire willl force the air (the warm house air) out through the chimney causing a negative pressure on the house, and drawing in outside cold air.

This is what I've been taught, to try and provide as much information for the customer to make their own decision. They buy a cap, it's a few bucks profit. If they don't, in several inspections, gaps in flue tile might be noticiable, which means big profits relining the chimney. Offering caps actually reduced the chimney sweeps long term profits. :)
Now I'm not a sweep, just repeating what I was taught. So check with your certified Chimney Sweep.
hth,
tom @ www.NoCostAds.com
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wrote:

Okay, I can buy that. How do you clean a chimney that has a cap? Is something special required - like removing the cap beforehand?
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Good caps are made to be easily removed for cleaning and maintenance purposes.
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A cap is no problem for cleanings or inspections. Most caps (or lids) are easily removed and reinstalled.
I second the suggestion to favor stainless steel over galvanized. You'll likely get a lifetime warranty rather than a few years, and maintenance won't be an issue. A galvanized cap will eventually rust, which can stain the chimney.
Often when I've seen caps cause draft issues, it's been with multi-flue caps that cover the entire chimney. If a multi-flue cap is causing draft issues, baffles between the flues often corrects it.
Depending on the sweep, there can be some pretty significant markup on caps. If you're comfortable with your roof and sizing the cap, you shouldn't have major issues installing a single flue cap on your own. The size of liners (and the caps that fit them) vary, so make sure you know the dimensions before purchasing. Single flue caps usually grip the portion of terra cotta extending above the crown of the chimney, while multi-flue caps are drilled and bolted to the chimney. If you're looking at a multi-flue cap, you'll need a hammer drill for installation.
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On Thu, 8 Jun 2006 16:27:08 -0700, "Eigenvector"

It seemed all wood burning fireplaces we cleaned/brushed was from the top, and all caps we found either had thumb screws or small bolts keeping the cap on to the flue. Which made it easy to remove for cleaning.
later,
tom @ www.FreelancingProjects.com
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On Wed, 7 Jun 2006 17:00:36 -0700, "Eigenvector"

I have one on my fireplace chimney and my oil furnace chimney. I don't have any trouble lighting the fireplace. I roll up some newspaper, light it, and put it high in the fireplace, so it starts the draft. (I also use a rectangular cast-iron pan with a porous rock in it (the two pieces are sold together for this purpose) which I pour some kerosene on, to make sure it lights.
But when the cap blew off the furnace chimney and I didn't replace it right away, white crud started coming out of the curved chimney duct that went from the firebox to the actual chimney. It seems clear the water was getting in and washing some of the soot in the chimney out throught the cracks in the pipe. Turning it white somehow. Since I got a enew cap it doesn't happen anymore.
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