Erica Wisner wrote:
The proportion of flow in the two sizes (120 mm vs 150 mm) will be:
r = radius of 120 mm diameter pipe = 60 mm
R = Radius of 150 mm diameter pipe = 75 mm
Ratio of cross-sectional area for flow to go through = pi*r*r / pi*R*R
= (60*60/75*75) (the pi's cancel out)
= 3600 / 5625
= 0.64
Conclusion: even though 30 mm sounds small, you will lose more than one third of the flow area.
-Erica
Erica,
Is the volume of air flow dependant on the smallest cross-sectional area of the gas path, or does the expanding flue gases heated by combustion draw incoming air through the smallest cross-sectional area at higher velocities dependant on chimney length?
Curbie
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