Fireplaces - The
Magic and the Mystery
Fireplaces are no longer used as the
primary source for heating homes, but the magic of a fire stills makes
a fireplace a valued part of any home. There are few things nicer than
a cheery fire, especially on a cold winter night. By the same token,
there are few things more distressing than a fireplace which doesn't
draw - belching smoke into the home, chasing people out, setting off
smoke detectors, and dirtying everything in sight. Why do some draw
perfectly, and others so poorly?
are many factors which affect fireplace performance. Some of the more
important are listed here:
- Ratio of Fireplace Opening
to Chimney Flue Size: The area of the
flue should be roughly (1/12) one twelfth the size of the opening
Height: The taller the better, but at
least 3 feet above the roof and 2 feet higher than anything within
10 feet of it.
and Location: Full
width of firebox and at least 6 inches above the top of the opening.
The damper is usually closer to the front of the fireplace than
Slope and Smoothness: The chamber above
the damper should be as smooth as possible, and should slope no
more than 45o as it funnels the smoke from the damper
opening into the chimney.
fireplaces break at least some of the rules of good design and yet
many work well despite this. Fireplace
design is more of an art than a science. Because there are so many
factors which affect the draw, it is impossible to know how "perfect" the
unit has to be to work. What about solving the problem of a fireplace
doesn't draw well?
Improving the Draw
- Reduce the Opening Size:
This can be achieved by laying an additional
row of firebrick on the floor of the firebox. Even before this is
done, the solution can be simulated by holding a piece of metal
over part of the opening and watching to see if the draft improves.
Move the Fire
Back: Often the
fire is simply too close to the front of the firebox.
Add Air: A
fireplace which is starved for air won't work properly. Sometimes
opening a window in the room with the fireplace
will supply enough air. Fireplace draw is more difficult to achieve
if the house is under negative pressure. Don't have exhaust fans
on while trying to start a fire. Most furnaces also work like
fans. It is easier to start a fire when the furnace is in an off
cycle. Glass doors help to protect the fireplace from negative
effects in the house, especially if combustion air can be brought
in from outside.
Flue: This is a trick most people know
about. Pushing a burning piece of rolled-up newspaper up past the
damper will help overcome the column of cold air in the chimney
and allow a good draft to be established quickly.
We didn't suggest damper
or smoke chamber modifications because they are expensive and should
be considered last resorts.
of this site Copyright 2015/2016 Carson,
Dunlop & Associates Ltd. All rights reserved.
No text or graphical
material may be copied from this site without the express written permission
Carson, Dunlop & Associates Ltd. Line drawings are from the Carson
Inspection Training Program
Inspection Software Tool - Horizon