Specifications

CW2500 Insert Installation and Operation Manual

9.6 Minimum Chimney

Height

The top of the chimney should be

tall enough to be above the air

turbulence caused when wind

blows against the house and its

roof. The chimney must extend at

least 1 m (3 ft.) above the highest

point of contact with the roof, and

at least 60 cm (2 ft.) higher than

any roof line or obstacle within a

horizontal distance of 3 m (10 ft.).

9.7 The Relationship Between the Chimney and the House

Because the venting system is the engine that drives the wood heating system, it must

have the right characteristics. The signs of bad system design are cold backdrafting when

there is no fire in the insert, slow kindling of new fires, and smoke roll-out when the door is

opened for loading.

9.7.1 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.