Answers
Quick, code-aware answers to common trade questions — each backed by a free calculator so you can run the numbers for your own project.
NEC Wire Size & Ampacity Calculator (310.16)
- What wire size do I need for a 50-amp circuit?
- Does NEC require 75°C or 90°C ampacity?
- How do I derate wire for high ambient temperature?
- What size wire do I need for a 50 amp hot tub?
- Is romex inside conduit derated?
- Do I have to upsize wire for a long run?
- Does a VFD or EV charger count as a continuous load?
- How many wires can I put in conduit before I have to derate?
Gas Pipe Sizing Calculator (NFPA 54)
BTU Heating Calculator — Furnace & Boiler Sizing
NEC Voltage Drop Calculator (Free)
Water Pressure Calculator (PSI)
- What is normal residential water pressure?
- Why does my pressure drop when multiple fixtures run?
- How much pressure do I lose per foot of elevation?
- Why is my water pressure 90 PSI and is that bad?
- Do I need an expansion tank with a PRV?
- Is 40 PSI too low for a house?
- Why does my PRV whine or vibrate?
- Can I install a PRV myself or do I need a permit?
HVAC Duct Sizing Calculator — Free Friction Rate Tool
Water Heater Sizing Calculator — Tank & Tankless
Fixture Unit Calculator (DFU / WSFU)
Drain Slope Calculator (1/4 per Foot)
DWV Pipe Sizing Calculator (Drain, Waste, Vent)
AC Cooling Load Calculator (BTU) — Free Manual J Lite
Superheat & Subcooling Calculator — HVAC Charging
Heat Pump Balance Point Calculator
SEER vs HSPF Calculator — Heat Pump Savings
NEC Conduit Fill Calculator (Chapter 9)
NEC Box Fill Calculator (314.16) — Free
Drain Sizing Wizard — Step-by-Step DWV Sizing
Expansion Tank Sizing Calculator
Hydronic Loop Sizing Calculator (Radiant Heat)
Pump Head Calculator (TDH) — Friction + Static
Pump Sizing Calculator — Head, Flow, Curve
Water Flow Rate Calculator (GPM)
Pipe Offset Calculator (45° / 22.5°)
ASHRAE 62.2 Ventilation Calculator (Residential)
Plumbing & HVAC Cost Estimator (Free)
HVAC & Water Heater Energy Efficiency Calculator
NEC Dwelling Service Load Calculator (220.82)
Basic Power Calculator (1Ø / 3Ø, Watts & HP)
- How do I calculate three-phase kW from volts and amps?
- What is the difference between apparent power and true power?
- Can I use this calculator to size motor branch-circuit wire?
- Why does my calculated horsepower not match the motor nameplate?
- Do I enter line-to-line voltage or line-to-neutral voltage?
- Can I estimate generator loading with this?
EGC Sizing Calculator (NEC Table 250.122)
- How do I size an equipment grounding conductor from breaker size?
- Is EGC size based on load amps or breaker amps?
- Do I have to upsize the ground wire when I upsize phase conductors?
- Can I run aluminum EGC in conduit feeders?
- What if multiple circuits share one raceway?
- Does this tool size grounded neutrals too?
NEC Motor Circuit Sizing Calculator (Article 430)
Cable Attenuation Calculator (dB)
PoE Power Budget Calculator (Watts)
Class 2 Voltage Drop Calculator (24V)
Low-Voltage Conduit Fill Calculator (%)
Refrigerant Charge Calculator — Superheat
Refrigerant Line Set Sizing Calculator
Walk-In Cooler & Freezer Load Calculator
Solar PV Sizing Calculator (kW)
Solar String Sizing Calculator (NEC 690.7)
- How many panels can I put on one string for a 1000 V inverter?
- Why does winter temperature reduce max modules per string?
- Why do I also need a minimum module count?
- Can I mix different module models in the same string?
- Should I use design heating temperature or record low for Voc checks?
- Does this replace the inverter manufacturer string tool?
Solar Temperature Derating Calculator
Solar DC:AC Ratio & Clipping Calculator
Solar LCOE Calculator ($/kWh)
Solar Battery Backup Runtime Calculator
- How long will a 13.5 kWh battery run my house?
- What is usable battery capacity versus nameplate capacity?
- Can rooftop solar recharge batteries during an outage?
- Should I size for whole-home backup or critical loads only?
- Why does motor startup still trip backup systems?
- Is daily cycling hard on backup batteries?
Solar Payback & ROI Calculator
Sprinkler Flow Calculator (K-Factor)
Sprinkler Friction Loss Calculator (Hazen-Williams)
Sheet Metal Bend Allowance Calculator
Pipe Weight Calculator (lb/ft)
Welding Heat Input Calculator (kJ/mm)
- Can I use CPVC instead of black steel for a residential sprinkler system?
- When do you have to bevel pipe before welding it for fire protection work?
- What is a pre-fabricated pipe spool and why do fab shops build them off-site?
- Do I need a smoke detector or a heat detector in an unconditioned garage?
- What is a NAC and why does my fire alarm panel need a booster for it?
- When does code require VESDA instead of regular smoke detectors?
- What does a jockey pump actually do in a fire-pump system?
- When is a diesel fire pump required instead of an electric one?
- Why does a building need a fire department connection if it already has a city water supply?
- When do you use intumescent coating instead of spray-applied cementitious fireproofing on structural steel?
- How do I pick between firestop sealant, mortar, and wrap strip for a wall penetration?
- When does code require a fire damper vs. a smoke damper vs. a combination damper in ductwork?
- Should fire-protection brackets and apparatus panels be laser-cut or waterjet-cut?
- What does structural welding mean for fire-protection work and which AWS code applies?
- What gets CNC-machined in a fire-fabrication shop and what stays manual?
- How do I choose between FM-200 and Novec 1230 for a clean-agent suppression system?
- When does NFPA 68 require explosion-vent panels instead of a suppression system?
- What's the difference between HSSD and a regular VESDA aspirating system?