The Problem with Wood Stove Inserts
F. Scott Davis Chimney Sweep, Inc.

Raleigh/Durham/Chapel Hill
The Problem with Fireplace Inserts


Do any of these look familiar?

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Do you have something that looks like this in your fireplace?

If you do, the chances of it being installed to the proper standards are slim! Most inserts aresimply pushed into the fireplace opening. The stovethen depends on thefireplace flue to vent the by-products of combustion (smoke) to the outside atmosphere. The only protection you have to keepdeadly gasesfrom entering your home is the stove surround. Needless to say, this is not a safe thing!
In this industry we call them "slammers" and theyare
very hazardous!


The Story:
Back in the late 70's and early 80's, when we were going through yet another "energy crisis", where oil/gas prices were up!
Everyone, including me, thought, "put an insert into the fireplace" andeureka! "C
heap heat!"
It was not until the number of chimney fires that had inserts installed started to rise dramatically that the practice of "slamming" an insert into a fireplace was more closely investigated. It was determinedby such entities as The National Fire Protection Association (NFPA), The Wood Heating Alliance and The National Chimney Sweep Guild that there was a very big problem with having such a setup.

What is the problem?
In a nutshell, the flueof the fireplace was to big to vent a stove properly! What! How can that be, bigger is better, right?
Wrong! When it comes to venting technology, bigger is not better, in fact it can be deadly!
A wood stove insert is designed to ventthrough anexhaust 6'' (typical) which is 28 square inches.
A fireplace is designedwith a flue that, at a minimum, is 13" x 13"OD (outer diameter).
A 13" x 13" OD is actually 11" x 11" id(inside diameter). 11" x 11"= 121 square inches. This is 4 times (appx.)larger than what the stove was designed to vent through.

Thissizing difference leads to severalissues:


1)Temperature differential. The"hot" exhaust gases, normally 600-800 degrees,venting through a "cold" chimney and flue. The chimney is going to be whatever the temperature is outside andit must be cold or you wouldn'tbebuilding a fire!
First, lets talk about creosote. Creosote is a natural by-product of burning wood. It can be defined as a combustible deposit that originates as condensed wood smoke, including tar, vapors and other organic compounds. Tar droplets, called "tar fog", is the major component of smoke. Creosote accumulates on thewalls of the flue as the smoke is making its way to the outside atmosphere.Smoke, as is natures law,travels in a spiral.The flue (normally)is square or rectangular in shape, therefore smokecollides with the walls of the flue on its journey upward. This is called "resistance to flow". Anywhere that the hot smoke touches the coldflue it will condense and stick to the surface. It usually condenses into a gooey, gummy, dripping MESS. This gooey, gummy, dripping mess is the fuel of a chimney fire. Depending on conditions of use, you can get into a hazardous situation in as little as 5 weeks. This is why it is important to not just have the correctly sized vent,
but the vent should be insulated! When aexhaust pipeis insulated, there is little temperature variation from the stove to the outside atmosphere. When there is little temperature variation, the creosote accumulation is greatly reduced.


2) Smoke Residence Time. This ishow long the smoke is in the flue.Ideally, The shortest amount of time the smokespends in the flueis best. This can only be accomplished by using the properly sized and insulated ventpipe thatthe stovewas designed, builtand tested for. When using the correctly sized and insulatedpipe, the residence time is far shorter thanwhen using the original fireplace system.

Are You Covered By Insurance?

A major consideration isyour homeowners insurance coverage. Iam not awareof any insurance company that will cover a fireplace insert that is not installed to NFPA 211 Standards. If you have an insert already installed, I would encourage you to talk to your agent or check your policy! Do not get burned, literally!

For more information go to:

http://www.woodheat.org/technology/inserts.htm

en.allexperts.com/q/Chimney-Fireplaces-3286/Chimney-Liner-Wood-stove.htm

A fireplace insert will have aproperly sized and insulated liner with a "direct connection" from the stove, through the chimney and exhausting to the outside atmosphere.
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