Manual D Friction Rate (Available Static Pressure)
The static pressure left over for the duct after the equipment takes its share, and the friction rate that sizes it.
Example
You enter
- Blower rated ESP at design CFM (in wg) 0.6
- Total component drops (in wg) 0.42
- Total effective length (ft) 180
You get
- Available static pressure 0.18 in wg
- Design friction rate 0.100 in wg/100 ft
Checked against published worked examples from: ACCA / Energy Efficiency Partnership; Shums Coda Associates.
Details, formula, and sources
ScopeASP = blower ESP - component drops, friction rate FR = ASP x 100 / total effective length (in wg/100 ft). 0.60 ESP, 0.42 drops, 180 ft TEL -> 0.18 ASP, 0.10 FR (a healthy target); a 300 ft run softens it to 0.06, needing larger ducts. Drops above the blower static flag an unworkable system. The full Manual D layout governs.
Formula or tableASP = blower_ESP - component_drops; FR = ASP x 100 / TEL (in wg per 100 ft).
Source and editionThe ACCA Manual D friction rate (available static pressure over total effective length), by name.
Free accessThe available-static-pressure and friction-rate relations are the published ACCA Manual D residential duct-design method.
What governsEstimate. AHJ and licensed professional govern.
API field namesblower_esp_inwg, component_drop_inwg, tel_ft, asp_inwg, fr_inwg_100ft
- Available static ASP = blower ESP - total component dropsACCA Manual D
- Friction rate FR = ASP x 100 / total effective lengthACCA Manual D
- TEL longest supply+return path incl. fitting equivalent lengthsscope of this tile