NFPA 110 Emergency Power StandardsUpdated for 2026Commercial Grade

Whole House Standby Generator kW Sizing Calculator

Calculate required generator kilowatts (kW), starting surge wattage for HVAC compressors and well pumps, transfer switch amperage, and natural gas supply.

Regional Market Calibration:Adjusts trade labor, concrete mix, and building codes to local city averages.

Popular Dimension Presets:

Raceway & Conductor Cross-Section (NEC Ch. 9)NEC 40% Max Fill Rule Enforced

Visual packing conforms to NEC Chapter 9 Table 1 physical space guidelines.

Project Dimensions & Material Inputs

Central Air Conditioner / Heat Pump

Deep Well Submersible Pump

Water Heater Type

HVAC Soft Starter Installed?

Recommended Generator Capacity

22 kW Standby Generator (Air/Liquid Cooled)

Peak Starting vs Continuous Load

22 kW Peak Surge | 11 kW Running Watts

Contractor Bill of Materials (BOM) Breakdown

Item / Material Spec	Quantity	Unit / Package	Installation Notes
Whole-Home Automatic Standby Generator (22 kW)	1	Generator	Powered by Natural Gas or Liquid Propane
200-Amp Automatic Transfer Switch (ATS)	1	Switch	Whole-house service entrance rated disconnect
Gas Supply High-Capacity Pipe (1-in to 1-1/4-in)	20	Feet	Maintains required BTU fuel flow under full motor load
Pre-Cast Concrete Generator Mounting Pad	1	Pad	Engineered leveling base anchored to subgrade

Estimated Project Cost Range (DIY vs. Turnkey Contractor)

National Average

DIY Raw Materials Only

$5,740 – $8,220

Cost of raw lumber, concrete, shingles, wire, or stone without equipment rentals or labor.

Licensed Contractor Turnkey

$12,760 – $18,360

Full installation: permits, site prep, skilled trade labor, equipment, and structural warranty.

Estimated Sweat Equity

~$8,580

Average trade labor savings if executed as a skilled DIY homeowner project.

Verified Trade Contractor NetworkScope Auto-Synced

Compare Up to 3 Free Quotes from Licensed Local Contractors

Skip the heavy equipment rentals, structural liabilities, and municipal permit delays. Connect directly with pre-screened, licensed, and insured trade specialists in National Average.

100% Free Service Zero Obligation Pre-Calculated Project Specs

⚡ Local pros respond in < 2 hours

Emergency Standby Load & Starting Surge Calculation

Rendering formula...

Load Shedding Math for 4-Ton HVAC + Well Pump

HVAC Starting Inrush Surge = 4 tons × 3,500W (with Soft Starter) = 14,000 Watts.
Base Household Appliances + Lighting = 3,500 Running Watts.
Major Appliances (Gas Water Heater + Well Pump) = 4,000 Watts.
Total Initial Peak Demand = 21,500 Watts (21.5 kW).
Standard Selection: 22 kW standby generator guarantees seamless whole-home transfer.

Engineering Tip: In National Average, adding a micro-air soft starter to your AC compressor drops starting surge by up to 65%, allowing you to buy a smaller generator.

Quick Reference Sizing & Coverage Table

Standard commercial specifications and pre-calculated project benchmarks.

Pre-Calculated

Home Size & AC Load	Running Watts	Peak Surge Watts	Recommended Generator kW	Turnkey Installed Price (Unit + ATS)
1,500 sq ft (No Central AC)	4,500 W	7,000 W	10 kW – 14 kW	$5,500 – $8,200
2,200 sq ft (3-Ton AC + Gas)	7,500 W	14,000 W	18 kW Standby	$7,800 – $11,500
3,000 sq ft (4-Ton AC + Well)	10,500 W	20,000 W	22 kW – 24 kW	$9,500 – $14,000
4,500 sq ft (Dual AC + Electric)	16,000 W	32,000 W	26 kW or Liquid-Cooled	$13,500 – $21,000

NEC Article 702 / NFPA 54 Fuel Gas Code

NEC 702 Optional Standby Systems & Gas Flow

Generators must be equipped with an Automatic Transfer Switch (ATS) having mechanical interlocks to prevent backfeeding into the utility grid. Siting must maintain a minimum 5-foot clearance from operable windows, doors, and vinyl siding per NFPA guidelines.

Frequently Asked Questions

What size generator do I need to power a whole house with central air?

For most homes between 2,000 and 3,000 square feet with a 3 to 4-ton central air conditioner, an 18 kW to 24 kW standby generator is required to handle AC compressor start-up surge.

What is an HVAC soft starter and why is it recommended?

An HVAC soft starter (like Micro-Air EasyStart) ramps up compressor voltage gradually, reducing inrush starting surge amps by up to 70%. This allows you to run your central AC on a much smaller, cheaper generator.

Does a 22 kW generator produce full power on natural gas?

No. Generators are rated on liquid propane (LP). On natural gas, energy density is lower, derating a 22 kW generator to approximately 19.5 kW.

How much gas does a whole-house generator burn during an outage?

A typical 22 kW standby generator burns approximately 2.5 to 3.5 gallons of propane per hour, or 180 to 250 cubic feet of natural gas per hour at 50% load.

Next Step In Your Project