Zero Clearance Fireplace Questions:


1.  Have you ever had an incident involving a Zero Clearance Fireplace?

2.  Is it safe to burn wood in these types of fireplaces provided you do annual cleaning?


Zero Clearance Fireplace Information:


Zero clearance fireplaces are factory built units made from sheet metal or cast iron. They are also known as pre-fabricated fireplaces because they come ready to install. Zero clearance fireplaces are so named because they are sufficiently insulated to be installed within close range of combustible materials, such as walls or wood framework, without requiring a masonry foundation. Many apartment and condominium complexes come with a one. Some come with glass doors, and some only have spark arrestor screens.

The flue is the passageway in your fireplace that allows the smoke to rise up and out of it. The dimensions of your flue, as well as every component of your fireplace are based on measurements that are dictated by Uniform Building and Fire Codes.


As the smoke rises up your flue, it clings to the walls of the flue, thereby closing off the flue. Since the flue of a Zero Clearance Fireplace is usually an 8" round pipe (as you can see in the picture below) that runs up the interior the wooden/brick enclosures, they will get filled up and closed down quicker than a masonry fireplace during use.

Solids burn up as carbon, which is called soot, which builds upon itself to close down the interior dimension of your flue, causing it to become ineffective. But more importantly, Creosote is an inevitable by-product of burning wood, and is formed when wood smoke condenses on the inside of a cool chimney.


To Prevent This... Zero Clearance fireplaces must be cleaned yearly if used!

If creosote is left unchecked and allowed to build up over a period of time, it can superheat, and turn into 3rd degree creosote. This is the cause of chimney fires.

So the cleaning of your chimney not only returns your flues interior dimensions to it's proper working dimensions, but if early, can stop creosote build up before it is un removable with a sweep, and other actions are needed to ensure your chimneys safe use.

The good news about Zero Clearance Fireplace liners is that they are made of metal, and Creosote can not get a permanent foothold on it like they can with masonry fireplaces, which are made of bricks with pours. Cleaning them yearly will handle any creosote
problem your unit may have.

When cleaning a zero clearance fireplace flue, both soot and creosote are removed from the fireplace pipe.

Generally speaking, local professional Chimney Sweeps, often times retired or off duty firefighters will come out to inspect your chimney, but it does not need to be cleaned, there is typically still a service call charge for this.

I look forward to getting additional input from folks out there that are actual Chimney Sweeps. This holiday season many of you will experience an unnecessary structure fire due to problems with the fireplace. This post is written to enable everyone to be just a little bit smarter and have a clue as to how to prevent the fire in the beginning and ensuring that everyone goes home the next morning.

Happy Holidays!

CBz 

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Prefab and zero clearance fireplaces are usually considered the same thing they can be very different. Prefab fireplaces may be made just for gas burning logs. Using just insulation to keep heat away from combustibles. Zero clearance fireplaces are safe to burn wood provided installation was done properly. The fireplace has standouts that keep it far enough away from combustibles. Also this creates an air flow around the fire place. When these are tampered with combustibles get to close to the fireplace and a fire occurs. These fireplaces also use a triple wall flue which creates three chambers. The center chamber is for smoke and heat from the fire place. The next chamber gets heated from the inner chamber and creates an up draft of air. The third chamber is connected to the second chamber at the bottom. The air in second chamber going up pulls air in third chamber down. This down draft from outside air keeps the flue cool. Sometimes the do-it-yourselfer does not lock these flues together properly and causes a gap that may cause a fire.
So... if the zero clearance fireplace was installed by the builder in the home then it's safe to assume that you can burn wood in these fireplaces without having to worry about overheating the adjacent 2x4's that frame the fake chimney? I've been under the impression that over time, pyrolysis occurs in the framework, and in some cases is cause for spontaneous ignition and the resulting chimney fire.

I'm hoping that there are no stories of zero clearance fireplace fires... Both my fireplaces in our home use zero clearance designs... One fireplace has the gas logs and the other... is empty.

Thanks for your input Dave. CBz
Yes they are safe to burn wood if they are made to burn wood. The fire place that has the gas logs may have a flue that is to small to burn wood. The flue could also exit out the wall. Pyrolysis of 2x4s or other wood occurs when they are in direct contact with heat. Zero clearance have a small space. If spontaneous ignition were to get in the framework it is no longer a chimney fire.
We respond to several chimney fires every Winter season, some involving these pre-fab/zero clearance fireplaces. Personally, I find them easier to extinguish, as opposed to hand-built masonry fireplaces, so long as you catch them early enough before they get into the wall framing. Regardless, every type of fireplace and chimney should be cleaned yearly, before using them regularly for the season.

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