Duct Static Regain Calculator
Static pressure regain at a duct expansion.
Enter your values
ⓘ Live results
Results
- Upstream velocity pressure
- 0.0898 in wc
- Downstream velocity pressure
- 0.0399 in wc
- Static pressure regained
- 0.0374 in wc
Quick answer
Static regain occurs when duct velocity decreases at an expansion, converting some velocity pressure back into static pressure.
Regain = 0.75 x (VP1 - VP2), where VP = (FPM/4005)^2
How to use the Duct Static Regain Calculator
- 1Enter the duct velocity just before an expansion or branch takeoff.
- 2Enter the lower velocity just after the expansion.
- 3The 0.75 regain factor converts most of the recovered velocity pressure back into usable static pressure for downstream duct.
Worked example
Using the values the calculator loads with:
Inputs
- Upstream velocity1200 FPM
- Downstream velocity800 FPM
Results
- Upstream velocity pressure0.0898 in wc
- Downstream velocity pressure0.0399 in wc
- Static pressure regained0.0374 in wc
Frequently asked questions
What is static regain design used for?
Large commercial systems use it to size each trunk segment so the recovered pressure offsets friction loss in the next segment, keeping static pressure nearly constant at every outlet.
Is this relevant to small residential ducts?
It's mostly a commercial design method; residential systems typically use the simpler equal-friction method instead.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
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Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.