Product Manual

Black Stag Installation and Operation Manual

Good System Design

Inside chimneys are preferred because even

when no fire is burning, there is normally

upward flow in the system.

Inferior System Design

Outside chimneys are a problem

because when no fire burns they will go

into cold backdraft if the stove is

installed low in the house.

8.4.2 Why the chimney should penetrate the highest heated space

When it is cold outside, the warm air in the house is buoyant so it tends to rise. This

tendency of warm air to rise creates a slight pressure difference in the house. Called ‘stack

effect’, it produces a slightly negative pressure low in the house (relative to outside) and a

slightly positive pressure zone high in the house. If there is no fire burning in a heater

connected to a chimney that is shorter than the warm space inside the house, the slight

negative pressure low in the house will compete against the desired upward flow in the

chimney.

There are two reasons why the

chimney in the house at right will cold

backdraft when it is cold outside and

there is no fire burning in the stove.

First, the chimney runs up the outside

of the house, so the air in it is colder

and denser than the warm air in the

house. And second, the chimney is

shorter than the heated space of the

house, meaning the negative

pressure low in the house will pull

outside air down the chimney, through

the stove and into the room. Even the

finest stove will not work well when

connected to this chimney.