HVAC
13 calculators
Load, tonnage, airflow, ductwork, hydronic flow, and efficiency checks.
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Free HVAC, Plumbing & Electrical Calculators
Use practical calculators, workflow guides, and clear methodology notes to make faster planning decisions without hiding the assumptions behind the numbers.
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Plumbing
13 calculators
Pipe sizing, fixture flow, drainage, water heating, pressure, and volume checks.
Open Plumbing hubElectrical
8 calculators
Power/current conversion, breaker sizing, wire sizing, voltage drop, and conduit checks.
Open Electrical hubFeatured calculators
Common starting points across the three main trades.
hvac
BTU Load Calculator
Estimate room heating and cooling BTU load from area, ceiling height, insulation, and sun exposure for faster HVAC...
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AC Tonnage Calculator
Convert conditioned area and insulation assumptions into estimated BTU demand and AC tonnage to shortlist practical...
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CFM Airflow Calculator
Calculate required airflow CFM from room dimensions and target ACH so HVAC teams can estimate ventilation and comfo...
Open calculatorplumbing
Water Heater Size Calculator
Estimate recommended storage water heater gallons from occupants, bathrooms, and simultaneous hot-water demand for...
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Pipe Size Calculator
Estimate nominal supply pipe size from fixture count, run length, and material assumptions to support quick plannin...
Open calculatorplumbing
Drain Slope Calculator
Calculate total vertical drop for drain runs from slope per foot so plumbing crews can set elevations quickly and a...
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Watts Amps Volts Calculator
Calculate watts, amps, or volts by entering any two known electrical values for fast field checks and planning esti...
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Voltage Drop Calculator
Estimate voltage drop across conductor runs for early branch and feeder planning.
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Breaker Size Calculator
Estimate breaker sizing from connected load assumptions and basic continuous-load planning factors.
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Sizing HVAC equipment
Planning plumbing runs
Checking electrical loads
Why BuildCalcTools
Fast
Calculators are built for quick field checks on mobile or desktop.
Practical
Inputs and outputs match common HVAC, plumbing, and electrical planning questions.
Transparent
Calculator pages explain formulas, assumptions, limitations, and common mistakes.
Free
No account is required to run calculations, share results, or read guides.
Guides for better calculator use
Short explainers that connect calculator results to real planning decisions.
Planning guide
How to Use Trade Calculators for Better Field Decisions
This guide shows a repeatable process for turning fast calculator outputs into better field decisions. It is designed for technicians, estim...
HVAC guide
How HVAC Load and Equipment Sizing Work
HVAC planning works best when capacity, airflow, and duct assumptions are checked together instead of treated as separate guesses.
HVAC guide
Understanding CFM and Duct Airflow
Airflow calculations connect equipment sizing to comfort. This guide explains how CFM targets and duct velocity checks fit together.
Latest articles
Practical notes that explain the numbers behind your calculator results.
Electrical · Apr 4, 2026
Understanding Voltage Drop in Simple Terms
Understand voltage drop with practical field examples and simple ways to reduce risk on long runs.
Read articlePlumbing · Apr 3, 2026
Common Pipe Sizing Mistakes
The most common planning errors in pipe sizing and how to catch them before install.
Read articlePlumbing · Apr 2, 2026
How to Choose the Right Water Heater Size
Learn how to estimate tank size from real usage patterns and avoid undersized or oversized water heater selections.
Read articleHow the calculators are built
BuildCalcTools separates mathematical conversions, rules of thumb, estimates, and code-sensitive decisions. Results are planning aids, not replacements for local code, manufacturer documentation, or licensed review.