Double & Triple Wall Insulated Class "A" Chimneys
Quick Summary of this Document
(for those who want the basics in a flash)
Legal Disclaimer - This document is not designed to replace your owners
manual. It is written to provide an overview of safe installation practice.
Consult your hearth professional, building officials and owners manual for
the specific installation needs of your appliance. You can find a list of
installers certified by HEARTH,
an education foundation.
OK, we're going to talk a little about how to properly install a woodstove.
The first thing we have to do is to forget about the woodstove and concentrate
on the most important part of an installation - the chimney.
RULE #1 - Every Woodstove Must Have a Chimney
This means that either a sound masonry chimney (more on these later) or
a UL approved Stainless Steel Class "A" Insulated Chimney. No,
you cannot use stovepipe through the window or roof !
Now that we have that out of the way, let's look at the most popular
option, the Class "A" Insulated Chimney. The diagram above shows
the three most common installation types. Type #1 would be common
in any single story construction. Regular black stovepipe is run upwards
from the stove and connects with the Insulated Chimney at a special support
box located immediately below the ceiling level. Insulated chimney then
is stacked up until the required height is obtained. All chimneys must extend
a minimum of 3 feet above the roof surface and 2 feet higher than any part
of the building within 10 feet. Type #2 shows an "out and up"
chimney, which exits thru a wall and continues up along the side of the
home. If desired, this chimney could be boxed in with wood framing and stuccoed
or sided to match the home. Type #3 is similar to type #1 in that
it is a single story installation, but different componets are needed due
to the slanted ceiling. In this case, the pipe is supported by a bracket
at the roof level, and Insulated Chimney Pipe hangs down partially into
the room to connect to the stovepipe.
Things to remember
The details as to the building of masonry chimneys are beyond the scope
of this document, however there are a few safety and performance issue to
keep in mind. It is commonly known in the Hearth Industry that 80-90% (or
more !) of the masonry chimneys in the US are constructed improperly. The
sad truth is that some masons spent so many years building low-temperature
chimneys for oil burners, gas burners and fireplaces that the art of proper
chimney construction has become almost lost.
What's wrong with most masonry chimneys ?
These deficiencies can be easily addressed by a competent mason, and
a properly designed and built masonry chimney is a work of art that can
last for generations. For the proper information on building masonry fireplaces
and chimneys go to Jim Buckley's Fireplace
pages.
Things to Remember
What'd you say, Bunky ? You've got an fireplace or chimney which has sat unused and is just waiting for a stovepipe to be shoved into it ! Not so fast - some thought processes are required here. Lets start with the fireplace.
In the "olden days" (yes, I was there), folks just shoved the
stove in front of the fireplace, and stuck a piece of stovepipe up toward
the damper area. If they were real smart, they fit some old fiberglass insulation
around it so as to stop too much room air from excaping up the chimney (made
the stove draft stronger too).
Chimney professionals soon saw that there were a lot of problems with this
setup. The stoves drafted poorly, created lots of creosote and the more-than-occasional
chimney fires ! As a result of these problems, the Hearth Industy and the
National Fire Protection Association put together a set of more modern guidelines.
First, determine if you have a masonry fireplace and chimney. If you have
a metal (zero clearance) fireplace and metal chimney, your options are very
limited. Only a few inserts are tested for use in these "pre-fab"
fireplaces. Check with your local Hearth Retailer --and confirm in the installation
manual or manufacturers literature.
Assuming you have a "real" brick fireplace.......
Here are the basics
Using another exisiting chimney
Houses with unused chimneys tend to be older homes, as these structures
were often built with multiple chimneys for heating, cooking, etc. Often,
these older chimneys are not safe to use without some upgrading. They can
be lined with approved stainless steel pipe or restored with special masonry
processes (ask your chimney sweep). Pay special attention to the wall pass-through,
which is the area where your stove pipe will connect to your chimney. Any
wood or combusitble material in this are must be cut back to comply with
building codes. Special insulated sleeves are available to accomplish this
transition.
Stovepipe is used to make a connection from a free standing stove to
it's metal or masonry chimney. As previously mentioned, it is not to be
used for passing through Walls, Floors or Ceilings. There are two kinds
of Stovepipe, Single Wall (one layer) and Close Clearance (two walls). Here's
the lowdown on Stovepipe:
Single Wall Stovepipe
Single wall stovepipe is designed to connect a woodstove to a nearby chimney.
It is available in different thicknesses (24 ga. or 22 ga.) and is usually
painted with a high temperature black paint. Some manufacturers produce
stovepipe in porcelain enamel colors to match their stoves.
As a general rule (check your label and instructions), stovepipe must be
kept at least 18" from any combustible wall , ceiling or furniture.
This distance can be reduced in two different ways:
Stovepipe can usually be trimed to size with a tin shears or a hacksaw.
Heavier gauge pipe can be more difficult to cut, so these pipes use adjustable
slip joints, which eliminate the need for trimming. When assembling your
stovepipe, use black furnace cement to seal between each piece. In addition,
use three sheet metal screws at each joint in the pipe.
Attach the pipe securely to the stove and chimney, assuring that it is rigid
and tight.
Close - Clearance Stovepipe
This is a double wall stovepipe with a stainless steel inner wall and a
black painted outer wall. An air space in between the stovepipe walls serves
as an insulating layer, allowing this special pipe to be as close as 6"
to combustibles. Do not confuse this double-wall interior piping with the
Class A Chimney described in the beginning of this document-- this stuff
is for interior use only ! Ask your Hearth Dealer for more information
about this type of Stovepipe.
Underneath your Stove
My first experience with lack of proper floor protection came when I was
homesteading in West Virgina. Our house had no central heating, but there
was a fireplace ready to serve our heating needs. Even back then (1970)
I knew that Fireplaces don't usually heat well, so I went to the hardware
store and bought a $20. sheet metal woodstove. It didn't fit into the fireplace,
so I took the legs off and sat it directly on the hearth of the fireplace.
That night, we lit a roaring fire and settled in for a peaceful winter eve.
Suddenly, we smelled something burning !...smelled like wood. After a frantic
search we discovered that the floor underneath the fireplace hearth was
smoldering.
There are a number of approved materials for underneath a woodstove. Some
of them are:
Different stoves have different requirements, but all woodstoves need to have a non-combustble base underneath. This base should extend a minimum of 8 inches around all sides of the stove and 16 inches in front of any loading doors. In addition, the stoveboard should extend underneath and horizontal run of the stovepipe connection to the chimney.
On the Walls
All stoves must be installed a safe distance from combustible walls. This
distance varies depending on the stove model, from as little as 10"
to as much as 36" or more. This distance can be reduced by one or both
of the following methods:
Quick 1-2-3 Summary of this Document
The Stovepipe
The Floors and Walls