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Hydronic Air/Dirt Separator Sizing Calculator

Calculate the minimum connection size for a hydronic air/dirt separator at the system's design flow rate.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Minimum connection diameter

5.74 in

Check your inputs

Effective air/dirt separation requires low velocity at the separator itself — confirm the manufacturer's rated maximum velocity and connection size for your specific separator model rather than assuming a generic value.

Running these inputs gives 146 mm as the minimum connection diameter. Expect some drift against the real job; the calculation is solid but conditions on site are not. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Add the equipment this sizes

This result is a specification — 5.735 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Minimum connection diameter = √(4×system flow rate ÷ (π×maximum velocity)), sizing the separator's pipe connection to keep flow velocity low enough (commonly under ~0.3-0.6 m/s) for effective air and particulate separation

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Frequently asked questions

Why does an air/dirt separator need such a low design velocity compared to regular pipe?
Air and dirt separators work by giving entrained air bubbles time to rise and particulates time to settle out of the flow stream — that only happens effectively at low velocity, commonly around 0.3 m/s, far below the velocities typically allowed in ordinary hydronic piping.
Is the connection size the same as the rest of the system's pipe size?
Not necessarily — because the separator needs a much lower velocity than the main piping, its connection is often sized larger than the adjoining pipe to slow the flow down as it passes through the unit.
Should I use the manufacturer's rated size instead of this calculation?
Yes — this is a general velocity-based estimate. Confirm the actual rated maximum velocity and connection size for your specific separator model against the manufacturer's data before final selection.