HVAC & Electrical Engineering Guides
109 free, in-depth engineering guides covering HVAC system design and electrical calculations — ASHRAE, GB 50736, SHASE, NEC, IEC standards.
HVAC Design Guides
AC Size Calculator Guide: How to Choose the Right AC Unit
Complete AC size calculator guide with BTU charts by room size, climate zone, and ...
AC Size for Room: Ton by Square Footage Table
AC size for room by square footage. Quick-reference table from 100 to 3,000 sq ft ...
AC Tonnage Chart: What Size AC for Your Home?
AC tonnage chart by house size. Find the right AC tonnage (1-5 ton) for your home....
What Ton AC for 1,000 Sq Ft? Sizing Calculator
What ton AC for 1,000 sq ft? 1.5–2 tons in moderate climate, 2.5 tons in hot clima...
What Ton AC for 1,500 Sq Ft? Exact Sizing
What ton AC for 1,500 sq ft? 2.5–3 tons in moderate climate, 3.5–4 tons in hot cli...
What Ton AC for 2,000 Sq Ft? Complete Guide
What ton AC for 2,000 sq ft? 3–3.5 tons in moderate climate, 4–4.5 tons in hot cli...
Bathroom Exhaust Fan CFM Guide
Complete bathroom exhaust fan CFM guide. Learn the 1 CFM per sq ft rule, bathroom ...
Boiler Sizing Guide: How to Size a Boiler
Boiler sizing guide with BTU charts by home size and climate zone. Steam vs hot wa...
What Size Breaker for Water Heater?
Find the right breaker size for your electric water heater by wattage. NEC 422 com...
BTU Calculator Guide: How Many BTU Do You Need
Complete BTU calculator guide with formulas, charts by room size and climate zone,...
BTU Chart: Heating & Cooling by Room Size
BTU chart by room size for heating and cooling. Quick-reference table from 100 to ...
BTU Per Square Foot: Complete Sizing Chart & Formula
How many BTU per square foot do you need? Complete chart by room type and climate ...
How Many BTU Do I Need? Room-by-Room Sizing Guide
Find out exactly how many BTU you need for any room. Room-by-room BTU sizing chart...
BTU to Ton Conversion: HVAC Sizing Made Simple
Convert BTU to tons and kW instantly. Includes conversion table, formula, and expl...
Central AC Sizing: Tonnage, SEER & Cost Guide
Central AC sizing guide. How to choose the right tonnage, SEER rating, and underst...
CFM Calculator Guide: Airflow Requirements for Every Room
CFM calculator guide with charts for every room type. Learn how to calculate CFM f...
CFM Chart: Airflow by Room Size
Quick-reference CFM chart by room size and type. Find the required airflow for bed...
CFM Per Square Foot: HVAC Airflow Guide
Complete guide to CFM per square foot for HVAC sizing. Learn the standard 1 CFM/sq...
Cooling Capacity Calculation: kW, Ton & BTU/h
Cooling capacity calculation in kW, tons, and BTU/h. Conversion formulas, efficien...
Cooling Load Calculation: ASHRAE Heat Balance and RTS
Current ASHRAE method selection, hourly commercial workflow, formulas, and a worked internal-load subtotal.
Duct Size Chart: CFM to Duct Diameter | HVAC Calculator
Complete duct size chart: CFM to round duct diameter from 4-inch to 20-inch. Inclu...
What Duct Size for 3 Ton AC? Complete Sizing Guide | HVAC Calculator
Find the right duct size for a 3 ton AC unit. Main trunk: 16-inch round or 10×12 r...
HVAC Duct Sizing Guide: Manual D Method
Complete HVAC duct sizing guide using ACCA Manual D. Duct size charts, friction ra...
Expansion Tank Sizing Guide: Complete Calculator
Expansion tank sizing guide with formulas, charts, and step-by-step examples. Cove...
How Many BTU Furnace Do I Need? Sizing Guide
How many BTU furnace do you need? Sizing guide by house size, climate zone, and AF...
Furnace Size Calculator Guide: How Many BTU Furnace Do You Need
Furnace sizing guide with BTU charts by home size and climate zone. AFUE efficienc...
Heat Pump Sizing Guide: Choose the Right Size
Heat pump sizing guide with BTU charts, COP ratings, and climate zone recommendati...
Heating Load Calculation: ASHRAE vs GB Method
Heating load calculation comparing ASHRAE (US) and GB 50736 (China) methods. Step-...
Heating Load Calculation Guide: ASHRAE Method
Complete heating load calculation guide. ASHRAE degree-day method, Manual J proced...
How to Calculate CFM for a Room
Learn how to calculate CFM (Cubic Feet per Minute) for any room. Step-by-step form...
HVAC Unit Converter Guide
Comprehensive guide to HVAC unit conversion covering power, air flow, pressure, te...
Mini Split Sizing Guide: BTU by Room Size
Mini split sizing guide with BTU chart by room size. How to choose the right mini ...
Pipe Flow Calculator Guide: Velocity, Flow Rate & Pressure Drop
Pipe flow calculator guide with velocity charts, friction loss tables, and the Haz...
Pipe Insulation Guide: Thickness, Material & Energy Savings
Pipe insulation guide with R-value charts, thickness tables, and energy savings ca...
Pump Head Calculation Guide: Complete Formula
Pump head calculation guide with friction loss tables, pipe sizing, and circulator...
Radiator Sizing Guide: How to Size a Radiator
Radiator sizing guide with BTU output charts by radiator type and size. Cast iron,...
Rectangular to Round Duct Conversion: Formula & Chart | HVAC Calculator
Convert rectangular duct to round duct with the formula D = 1.3 × (A×B)^0.625 / (A...
SEER Rating Guide: What It Means & Why It Matters
SEER rating explained. What is a good SEER rating, SEER vs SEER2, cost comparison,...
Underfloor Heating Calculation: Flow Temp & Spacing
Underfloor heating calculation guide. How to calculate flow temperature, pipe spac...
Water Heater Expansion Tank Sizing Guide
Water heater expansion tank sizing guide with charts by tank size and temperature....
What Size AC Do I Need? Calculator + Guide
What size AC do you need? Use our calculator and sizing guide to find the right AC...
Window AC BTU Guide: Size Your Unit Correctly
Window AC BTU sizing guide by room size. Find the right window AC BTU rating for y...
Electrical Design Guides
Allowable Voltage Drop: NEC 210.19 Requirements
NEC allowable voltage drop explained. NEC 210.19, 215.2, and 310.15 requirements. ...
Wire Ampacity Guide: NEC 310.16 Tables
Complete wire ampacity guide with NEC Table 310.16, derating factors for temperatu...
Ampacity of Copper Wire by Gauge
Detailed ampacity table for copper wire by gauge and insulation type. Covers THHN,...
Amps to Watts Guide: Conversion Formula & Calculator
Complete amps to watts conversion guide with formulas for DC, single-phase AC, and...
Appliance Energy Cost Calculator Guide: Annual kWh by Appliance | HVAC Calculator
How much does it cost to run home appliances? Complete guide with annual kWh and c...
AWG to mm² Guide: Wire Gauge Conversion Chart
Complete AWG to mm² conversion chart with metric equivalents, wire resistance, amp...
Box Fill Guide: NEC 314.16 Electrical Box Sizing
Complete NEC 314.16 box fill guide with conductor volume tables, box sizing charts...
What Size Breaker for AC Unit?
Find the right breaker size for your AC unit by tonnage. NEC 440 compliant sizing ...
What Size Breaker for Dryer?
The standard electric dryer breaker is 30A. Learn about NEC 220.54, wire requireme...
Breaker Sizing Guide: NEC Circuit Breaker Selection
Complete breaker sizing guide with NEC rules, 80% continuous load rule, breaker tr...
Capacitor Bank Sizing for Power Factor Correction: kVAR Tables & Motor HP Guide | Free Calculator
Capacitor bank sizing guide with kVAR by motor HP tables, individual motor correct...
Capacitor Code Guide: Color Codes, Markings & Values
Complete capacitor code guide with ceramic disc codes, electrolytic markings, EIA ...
Conduit Fill Guide: NEC Chapter 9 Tables
Complete NEC conduit fill guide with tables for EMT, PVC, and rigid conduit. Maxim...
Copper vs Aluminum Wire: Cost, Ampacity & NEC Rules
Copper vs aluminum wire comparison. Cost, ampacity, NEC rules, and when to use eac...
Electrical Load Guide: NEC Article 220 Calculations
Complete electrical load guide with NEC Article 220 demand factors, service entran...
Electrical Quote Guide: How to Estimate Electrical Work
Electrical quoting guide with material cost tables, labor rate estimation, NEC-com...
Electricity Cost Guide: kWh Rates & Bill Calculator
Complete electricity cost guide with average rates by state, kWh calculation, appl...
Electricity Cost per kWh by State & Country (2025) | HVAC Calculator
Average electricity cost per kWh in the US and worldwide. Compare rates by state, ...
Energy Guide: kWh, BTU, Joules & Unit Conversions
Complete energy unit guide with conversions between kWh, BTU, joules, therms, and ...
Heat Loss Calculation for Buildings: Formula & Example
Heat loss calculation formula and example for residential and commercial buildings...
Heat Loss Per Room: Calculation Table & Formula
Heat loss per room calculation with reference table by room type. Formula for wall...
How Many Solar Panels Do I Need? Calculator by Usage | HVAC Calculator
Find out how many solar panels you need based on your monthly electricity usage. C...
How to Calculate Electricity Bill: Formula & Examples | HVAC Calculator
Learn how to calculate your electricity bill with the simple formula: Bill = kWh ×...
How to Calculate Heat Loss: Step-by-Step Guide
How to calculate heat loss for buildings. ASHRAE method with formula, worked examp...
How to Size a Breaker: Step-by-Step Guide
Learn how to size a circuit breaker step by step using NEC 240, the 125% continuou...
HP to kW Guide: Horsepower to Kilowatt Conversion
Complete HP to kW conversion guide with formulas, motor efficiency tables, and NEC...
Insulation Resistance Guide: Megger Testing & IEEE 43
Complete insulation resistance guide with megger testing procedures, IEEE 43 stand...
Lumen Guide: Lighting Design & Foot-Candle Calculator
Complete lumen guide with foot-candle requirements by room type, LED wattage equiv...
Motor Current Guide: FLC Tables & NEC 430
Complete motor current guide with NEC Table 430.248 (single-phase) and 430.250 (th...
Motor FLA Chart: Full Load Amps by HP | Free Calculator
Complete motor FLA chart with full load amps by horsepower for single-phase and th...
Motor Starter Sizing Guide: NEMA Sizes & Overload Protection | Free Calculator
Complete motor starter sizing guide with NEMA starter sizes, overload protection c...
Motor Wire Size Guide: NEC 430 Requirements | Free Calculator
Complete motor wire size guide per NEC 430.22. Wire sizing tables by HP and voltag...
Offset Bend Guide: Conduit Bending Formulas & Charts
Complete offset bend guide with shrink constants, multiplier tables, and NEC condu...
Ohm's Law Calculator: Free Online Tool
Free Ohm's Law calculator: enter any 2 values (voltage, current, resistance, power...
Ohm's Law Examples: 10 Real-World Problems
10 solved Ohm's Law examples from simple to complex: DC circuits, series/parallel ...
Ohm's Law Formula: V=IR Explained with Examples
Master Ohm's Law formula V=IR with clear explanations, the power triangle (P=VI, P...
Ohm's Law Guide: V = IR with Examples & Calculator
Complete Ohm's Law guide with formulas, the triangle mnemonic, worked examples for...
Ohm's Law Triangle: Visual Guide to V, I, R
Master the Ohm's Law triangle for quick V, I, R calculations. Visual guide with me...
Power Factor Correction Calculator Guide: Formulas, Methods & Savings | Free Calculator
Complete power factor correction calculator guide with reactive power formulas, kV...
Power Factor Correction Guide: Capacitor Sizing & Savings
Power factor correction guide with capacitor sizing formulas, utility penalty calc...
Power Guide: Watts, VA, Power Factor & Three-Phase
Complete electrical power guide with watts, VA, power factor, three-phase calculat...
RC Time Constant Guide: τ = RC Formula & Calculations
Complete RC time constant guide with the τ = RC formula, charging/discharging curv...
Electrical Resistance Guide: Ohms, Wire Resistance & Tables
Complete resistance guide with wire resistance tables, temperature effects, series...
Solar Panel Guide: Sizing, Cost & Payback Calculator
Complete solar panel guide with system sizing by kWh usage, panel wattage, inverte...
Solar Panel Size Calculator Guide: How to Size Your System | HVAC Calculator
Learn how to calculate the right solar panel system size for your home. Covers the...
Solar Payback Period Calculator Guide | HVAC Calculator
Calculate your solar panel payback period. Learn the formula, federal tax credit (...
Temperature Derating Factors for Wire Ampacity
NEC 310.15(B) temperature correction and bundling derating factors for wire ampaci...
Transformer Guide: Sizing, KVA Ratings & Types
Complete transformer guide with KVA calculations, primary/secondary current, trans...
Transformer kVA Chart by Voltage
Complete transformer kVA to amps conversion chart for single-phase and three-phase...
Transformer Sizing Calculator Guide
Learn how to size a transformer using kVA formulas for single-phase and three-phas...
HVAC Unit Converter Guide: Temperature, Pressure, Flow
Complete HVAC unit conversion guide with temperature (°F/°C), pressure (PSI/Pa), f...
Voltage Divider Guide: Formula, Circuit & Calculator
Complete voltage divider guide with the V_out = V_in × R2/(R1+R2) formula, loaded ...
Voltage Drop Calculation for 3-Phase Systems
Three-phase voltage drop calculation formula and example. Covers balanced and unba...
Voltage Drop Chart by Wire Size & Distance
Voltage drop chart showing drop by wire size and distance for 120V and 240V circui...
Voltage Drop Formula: How to Calculate Step by Step
Voltage drop formula for single-phase and three-phase circuits. Step-by-step calcu...
Voltage Drop Guide: NEC Formula & Calculator
Complete voltage drop guide with NEC limits, formula, wire size charts by distance...
Watts to Amps Guide: Conversion Formula & Calculator
Complete watts to amps conversion guide with formulas for DC and AC circuits, brea...
Wire Ampacity Chart: NEC 310.16 Table
Complete wire ampacity chart for copper and aluminum conductors based on NEC Table...
Wire Size vs Distance Chart: How Far Can You Run?
Wire size vs distance chart for 120V and 240V circuits. Maximum wire run by gauge,...
Wire Gauge Chart: AWG to Amps & mm² Table
Complete wire gauge chart with AWG to amps, mm², and diameter conversions. NEC amp...
What Size Wire for 100 Amps? Breaker & Wire Chart
What size wire for 100 amps? 1/0 AWG copper or 2/0 AWG aluminum. NEC requirements,...
What Size Wire for 200 Amps? Service Entrance Wire
What size wire for 200 amp service? 2/0 AWG copper or 4/0 AWG aluminum. NEC servic...
What Size Wire for 30 Amps? NEC Requirements
What size wire for 30 amps? 10 AWG copper per NEC Table 310.16. Includes NEC rules...
What Size Wire for 50 Amps? Complete Guide
What size wire for 50 amps? 6 AWG copper per NEC. Includes NEC rules, conduit requ...
Wire Size Guide: AWG Chart & NEC Ampacity Tables
Complete wire size guide with AWG ampacity charts, NEC Table 310.16, copper vs alu...