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Trap Primer Flow Rate Calculator

Calculate the total water flow needed for a trap primer system serving multiple floor drain traps.

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

Total trap primer flow needed

0.24 L/s

High confidence

With the figures above, the total trap primer flow needed comes to 0.24 L/s. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 0.24 L/s — 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

  • Total trap primer flow = number of fixtures served × flow rate per fixture, the standard method for sizing a trap primer distribution system's total demand

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Frequently asked questions

Why does total trap primer flow matter?
The distribution line and its water supply connection must be sized to deliver the combined flow rate of every floor drain trap it serves at once, not just a single fixture's flow rate.
Where do I get the flow rate per fixture?
Use the trap primer manufacturer's rated flow rate per outlet or fixture — this varies by trap primer valve model and design.
Does this account for pressure loss in the distribution piping?
No — this only totals the demand flow rate across all fixtures served. Sizing the actual distribution pipe and checking pressure loss along the run is a separate calculation.