search  current discussion  categories  kilns & firing - misc 

back pressure/fireplaces/wood stoves

updated fri 29 mar 02


vince pitelka on thu 28 mar 02

> If I understand correctly, back pressure is the reason you can sit next
> to a fireplace and be cold, as all the cool air in the house is being
> sucked past you and up the chimney along with the heat from the fire;
> but an Oregon woodstove like ours, with a reverse-draft lever and a
> cooktop, will generate enough heat to drive us out of the room...

Kelly -
On older stoves there is an outlet damper which creates backpressure, but
most newer wood stoves instead have a controllable inlet flue (often
thermostatically controlled) which regulates incoming air to control
combustion. So in those stoves there usually isn't any back pressure. And
you might be surprised to know that the best fireplaces (the ones designed
by Count Rumford and used in so many American colonial houses and in so many
newer houses today) are quite efficient. The flue and chimney draw only
enough to exhaust the smoke, but the fireplace design is wide and shallow,
so as to radiate a very wide angle of infrared. The only thing a fireplace
is good for is infrared radiation, which hits surfaces in the room and turns
to heat. Most of the fireplaces built during the 20th century are quite
deep, and there is far too much draw in the chimney. The angle of infrared
radiation is very narrow, rendering them extremely inefficient.

A good wood stove heats by both convection and infrared radiation, and it
efficiently heats the surrounding air while only drawing minimal air from
the room. A wood stove is ALWAYS more efficient, but a well-made Rumford
fireplace is amazingly efficient. Reproductions of Count Rumford's pamphlet
on fireplaces are available somewhere. I have one somewhere, packed away in
some box. Perhaps someday I will come across it again. I have a lot of
stuff packed away in boxes.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home -
Work -
615/597-6801 ext. 111, fax 615/597-6803