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Boiler Makeup Water Calculator

Calculate the makeup water rate needed to replace system losses in a boiler/hydronic heating system.

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

Estimated makeup water needed

10.57 gal

Check your inputs

Loss rate percentage varies widely by system age, condition, and maintenance practice — an unusually high or increasing makeup water demand can indicate a leak that should be investigated rather than simply compensated for.

At the values currently entered, the estimated makeup water needed works out to 40 L. Note that total system water volume (l) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Confidence is moderate: the method is sound, but real materials and site conditions vary. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

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

  • Makeup water rate = system water volume × estimated loss rate percentage, a standard method for estimating the water treatment/makeup demand from typical system losses (minor leaks, air venting, maintenance draindowns)

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Frequently asked questions

What counts as a normal loss rate?
The spec-level guidance here is that loss rate percentage varies widely by system age, condition, and maintenance practice — there is no single universal number. Use your own system's monitored history, or a conservative estimate, rather than assuming a fixed rate applies to every installation.
What does a sudden increase in makeup water demand mean?
An unusually high or increasing makeup water demand can indicate a leak that should be investigated rather than simply compensated for by adding more water. Repeated makeup water also introduces fresh dissolved oxygen and minerals that can accelerate corrosion and scale.
Does this account for water treatment chemical dosing?
No — this only estimates the volume of makeup water needed to replace system losses. Any chemical treatment (inhibitors, pH adjustment) dosed proportionally to makeup water volume must be calculated separately based on the treatment product's dosing instructions.