Field tools · Calculator
External Static Pressure (ESP)
Drop your supply-side and return-side manometer readings, pick the installed coil / filter / heater section, and ChillFlow resolves the system ESP against the ACCA residential target of ≤ 0.50 inH₂O.
step ±0.05
step ±0.05
After commissioning / annual tune-up.
Standard efficiency — replace annually.
Heat-pump in cooling mode (no strip / gas).
ACCA / SMACNA residential — single-stage blower.
ESP high — outside residential band. Inspect coil / filter / duct for severe restriction.
- Supply: 0.30 + Return: 0.30
- Coil: 0.20 · Filter: 0.10 · Heat: 0.00
- Total: 0.90 inH₂O
- Residential target: ≤ 0.50 inH₂O ok · 0.50–0.80 high · ≥ 0.80 err · ≥ 1.00 critical
step ±0.5
Enter system tonnage to surface the Rule-of-400 expected airflow and a matching friction-rate row from the reference table below.
Reference
Friction-loss reference
Typical hairpin friction rates — ACCA Manual D / SMACNA ballparks, not a substitute for system design.
| Size | CFM (low–high) | Friction (inH₂O/100 ft) | Velocity (FPM) | Notes |
|---|---|---|---|---|
| 6" | 60–120 | 0.12 | 600 | Branch run-out, low CFM. |
| 6" | 121–200 | 0.20 | 900 | Branch run-out, design upper end. |
| 8" | 90–180 | 0.06 | 500 | Branch run-out, typical. |
| 8" | 181–280 | 0.10 | 700 | Branch run-out, design mid. |
| 8" | 281–400 | 0.18 | 900 | Typical trunk transition. |
| 10" | 180–320 | 0.06 | 500 | Small trunk / branch. |
| 10" | 321–500 | 0.09 | 700 | Trunk mid. |
| 12" | 300–500 | 0.04 | 450 | Residential trunk, low end. |
| 12" | 501–800 | 0.07 | 650 | Residential trunk, typical. |
| 12" | 801–1100 | 0.10 | 800 | Residential trunk, upper end. |
| 14" | 500–800 | 0.04 | 500 | Large trunk / lead duct. |
| 14" | 801–1200 | 0.06 | 700 | Large trunk, design mid. |
| 16" | 800–1200 | 0.03 | 500 | Lead / trunk, low end. |
| 16" | 1201–1600 | 0.05 | 700 | Lead / trunk, design mid. |
Round and rectangular rows are for straight galvanized steel run-out / trunk. Flex duct runs fully extended (≥ 4 ft) — kinked or coiled flex roughly doubles the friction rate.
ESP bands follow ACCA Manual D / SMACNA residential targets. High-velocity systems use a tighter ≤ 0.20 inH₂O band. Verify against the OEM air-handler spec sheet before adjusting blower speed.