Resistance of Ducts

Resistance of Ducts (Allowance for surface conditions)

**Resistance of Ducts (Allowance for surface conditions)**
Surface	Chart reading to be multiplied by
Asbestos cement	0.8
Asphalt cast iron	6.0
Aluminium	0.8
Brickwork	4
Concrete	2
Fibreglass	0.8
PVC	0.8
Sheet iron	1.5
Sheet steel	1.0