Chimney Sizing
Calculating chimney draft and chimney area
Sponsored Links
The capacity of a chimney depends on the potential chimney draft - the pressure difference created by the inside and outside air temperature difference and chimney height - and the chimney area.
The pressure difference in the chimney pulls air and fuel gas from the boiler or fireplace through the chimney and out of the building.
Chimney Draft
The pressure difference or chimney draft can be expressed as:
dpch = h (ρo - ρi) g (1)
where
dpch = pressure draft in the chimney (Pa)
h = height of chimney (m)
ρo = density of outside air (kg/m3)
ρi = density of inside air (kg/m3)
g = 9.81 - acceleration of gravity (m/s2)
(1) can alternatively be expressed as:
dpch = 0.0465 dt h (2)
where
dt = temperature difference between inside and outside air (K, oC)
Chimney Draft Chart
Chimney Area
The velocity of air and flue gas in a smaller furnace should not exceed 2 m/s. Design velocities of larger furnaces should not exceed 10 m/s.
Required chimney area can be calculated as
A = Q / v (3)
where
A = cross-sectional area of chimney (m2)
Q = volume of flue gases at chimney temperature (m3/s)
v = velocity (m/s)
In general 1 kW boiler heat requires 1100 mm2 of chimney area.
Chimney Vent Capacity Chart - Btu/h and kW
Sponsored Links
Related Topics
- Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency
Sponsored Links
Related Documents
- Air Flow and Velocities due to Natural Draft - Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference
- Chimney Area and Boiler Heat Load - Boiler capacity and required chimney area
- Chimneys and Fireplace Sizing - Chimneys and fireplace sizing for fireplaces and stoves burning wood or coal as fuel
- Explosion Doors in Chimneys - Recommended sizes of explosion doors or draught stabilizers for oil firing installations
