Electrical & HVAC Calculators
Use these tools for early planning only. Final electrical and HVAC work must be designed and verified for the actual installation.
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Electrical & HVAC Calculators
- Mini Split Sizing CalculatorEstimate mini-split capacity from conditioned area, an editable BTU-per-square-foot factor and building adjustment.
- Generator Sizing CalculatorEstimate generator running and starting capacity from total running watts, the largest additional surge load and an editable reserve margin.
- Breaker Size CalculatorEstimate minimum circuit ampacity and breaker requirement from continuous and noncontinuous load currents using editable multipliers.
- Wire Size CalculatorEstimate the minimum conductor circular-mil area from current, distance, allowable voltage drop and conductor resistivity.
- Voltage Drop CalculatorEstimate conductor voltage drop and percentage voltage drop from current, one-way length, conductor resistance and circuit voltage.
- Air Changes per Hour CalculatorCalculate air changes per hour from room volume and supplied or exhausted airflow.
- Duct CFM CalculatorEstimate airflow through a rectangular duct from duct dimensions and average air velocity.
- BTU CalculatorEstimate heating or cooling capacity from conditioned floor area and an editable BTU-per-square-foot design factor.
- Electrical Load CalculatorEstimate total electrical demand, apparent power and current from connected load, demand factor, voltage, phase factor and power factor.
- Heat Pump Sizing CalculatorEstimate preliminary heat-pump capacity from floor area, design-load intensity and an editable sizing adjustment.
Related Guides
- Air Changes Per Hour: What ACH Means and How to Calculate It
Understand air changes per hour (ACH): what it measures, ASHRAE targets for different room types, how to calculate the airflow needed, and why it matters for indoor air quality.
- Breaker Size Guide: How to Size Circuit Breakers for Any Load
Learn how to size circuit breakers correctly using NEC rules. Covers the 80% continuous load rule, motor circuit sizing at 250%, AFCI/GFCI requirements, and common household circuits.
- BTU Calculator: How to Size an Air Conditioner or Heater for Any Room
Calculate the BTU capacity you need to cool or heat any room. Covers the 20 BTU per sq ft baseline, adjustment factors for climate and insulation, and common sizing mistakes.
- Duct CFM Calculator: How to Size HVAC Ductwork for Proper Airflow
Understand how to calculate CFM requirements for HVAC ductwork using room size, air changes per hour, and the Manual D friction rate method.
- Electrical Load Calculator: How to Estimate Home Panel and Circuit Loads
Learn to calculate your home's electrical load for panel sizing, service entry, and circuit planning. Covers NEC Standard Method, demand factors, and what drives panel capacity.
- Generator Sizing Guide: How Many Watts Do You Actually Need?
Calculate generator wattage for home backup or job site use. Covers running vs. starting watts, essential circuit loads, and the difference between portable and whole-home standby generators.
- Heat Pump Sizing Guide: How to Choose the Right Tonnage
Size a heat pump correctly for heating and cooling by climate zone. Covers the Manual J approach, heating vs. cooling dominant sizing, and cold-climate heat pump performance.
- Mini Split Sizing Guide: BTU, SEER, and the Right Size for Your Space
Size a mini split for any room with the BTU-per-sq-ft method. Covers available mini split sizes, SEER ratings, single-zone vs. multi-zone systems, and installation requirements.