Calculator
HVAC Static Pressure Calculator
Two tools in one: diagnose measured total external static pressure (TESP) against the blower’s rated maximum, or design the duct friction rate from available static pressure and total effective length. Free, no signup.
Free
Total external static pressure
0.460 in.wg
92.0% of the 0.500 in.wg rating
Within the blower rating
TESP
0.460 in.wgSupply magnitude + return magnitude
Over / under rating
-0.040 in.wgvs 0.500 in.wg rated max
NCI budget for a 0.500 in.wg system
- Filter (20%)
- 0.100 in.wg
- Coil (40%)
- 0.200 in.wg
- Supply duct (20%)
- 0.100 in.wg
- Return duct (20%)
- 0.100 in.wg
A component reading above its budget is where the restriction hides.
Industry benchmarks
- Rated max ESP (PSC blower)
- 0.50 in.wg
- TESP target
- ≤ 0.50 in.wg
- Clearly excessive
- ≥ 0.80 in.wg
- Friction-rate wedge
- 0.06–0.18 in.wg/100 ft
- Register / grille / damper
- 0.03 in.wg each (ACCA)
What you'll get
Pick diagnose or design
Diagnose sums measured supply and return static into TESP; Design starts from the blower rating and works out to friction rate.
Enter your readings
For diagnosis, enter supply and return static and the blower’s rated max ESP. For design, enter component drops and supply/return effective lengths.
Read the verdict
See TESP vs. the rating with an NCI component budget, or the friction rate against the ACCA 0.06–0.18 in.wg/100 ft wedge.
How it works
- 1
Pick diagnose or design
Diagnose sums measured supply and return static into TESP; Design starts from the blower rating and works out to friction rate.
- 2
Enter your readings
For diagnosis, enter supply and return static and the blower’s rated max ESP. For design, enter component drops and supply/return effective lengths.
- 3
Read the verdict
See TESP vs. the rating with an NCI component budget, or the friction rate against the ACCA 0.06–0.18 in.wg/100 ft wedge.
Why static pressure is the first HVAC airflow diagnostic
Total external static pressure is the blood pressure of a duct system. A PSC blower is rated for about 0.50 in.wg; when measured TESP exceeds that, airflow drops, coils freeze, heat exchangers overheat, and comfort complaints follow. Measuring supply and return static and summing their magnitudes tells you instantly whether the ductwork — not the equipment — is the problem.
On the design side, ACCA Manual D sizes ducts from a friction rate: available static pressure (blower rating minus coil, filter, register, and damper drops) × 100 ÷ total effective length. A friction rate inside the 0.06–0.18 in.wg per 100 ft “wedge” (target ~0.06–0.10) yields correctly sized ducts; below it oversizes, above it starves airflow. This calculator runs both the field diagnostic and the design calculation.
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View statesStatic Pressure Calculator FAQs
How do you calculate total external static pressure?
Measure static in the supply plenum (after the coil/furnace) and in the return before the blower, then add the magnitudes — the return reads negative, so TESP = |supply| + |return|. Compare the total to the blower’s rated maximum (PSC blowers ≈ 0.50 in.wg).
What is a good static pressure reading?
At or below the blower’s rating — about 0.50 in.wg for most residential PSC systems. Readings above the rating indicate restrictive ductwork; 0.80 in.wg or higher is clearly excessive and will hurt airflow, efficiency, and equipment life.
What is friction rate in duct design?
Friction rate = available static pressure × 100 ÷ total effective length (in.wg per 100 ft). Available static pressure is the blower’s rated ESP minus coil, filter, register, grille, and damper drops. The ACCA Manual D acceptable window is 0.06–0.18, with a common target of 0.06–0.10.
Is this static pressure calculator free?
Yes. Every tool on CloseCrew is free for HVAC contractors — no account required.
