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Model # 40394
MSRP: $4,639.00
Every Day Price: $4,399.00
Every Day Price: $4,399.00
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20kW Home Generator NG/LP and 100 Amp Service Rated ATS with Symphony II Power Management by Briggs and Stratton | 40394

  • Reliable Engine Power - Commercial Grade Vanguard Engine
  • Symphony II Power Management automatically balances the power needs of your home's electrical loads.
  • Rust-Resistant Galvanneal steel enclosure
  • Automatically powers your home in seconds after sensing a power outage.
  • Front exhaust allows the generator to be placed as close as 18" from the home or other structures for custom placement.
  • Manufactures Warranty: 5 Year Parts, 3 Years Labor


Briggs and Stratton 40394 Details and Specifications

20kW Home Generator NG/LP and 100 Amp Service Rated ATS with Symphony II Power Management by Briggs and Stratton

Stop worrying about losing power in your home with the 20kW standby generator system.  The 20kW seamlessly provides backup power to your home within seconds of a power outage.

Lights, TV's, washer and dryer - even two 5-ton AC units - are easily and automatically powered by a dependable commercial-grade Vanguard engine and new, patented Symphony II Power Management technology, requires the purchase of Symphony II Remote Modules.  Up to 8 modules can be added to ensure the generator won’t overload.  The 20kW system also comes with a 5-year limited warranty for unmatched support.

Adherence to National Fire Protection Association safety rules and National Electrical Codes allow placement as close as 18 inches to a home, offering maximum installation flexibility, especially where lot lines are tight and yards are small. These standby generators carry a five-year, limited parts and labor warranty.


Briggs & Stratton powers the 40394 with its own popular and reliable Vanguard 993 cc V-Twin overhead valve engine. The electronic engine governor incorporated into the generator design keeps the Vanguard operating at a constant 3600 RPM, even under heavy and changing loads, to keep the AC signal constant at 60 hertz. The air cooled engine has a fully pressured lubrication system and oil cooler, with a low oil pressure sensor that allows engine shut down to prevent damage.


The 20kW standby unit is factory configured to run on natural gas, but converts easily to liquid petroleum gas (propane) during installation by simply turning a selector screw with an Allen wrench. Operating on LP gas provides up to 20 kW of power. At half-load, the engine consumes about 2.3 gallons of LP fuel per hour. Natural gas supplies up to 18 kW of power, and consumption runs about 83 cubic feet per hour at half load. Fuel consumption varies along with the electrical load and is affected by altitude and ambient temperature.

Backup Power

Standby generators are permanently installed appliances that operate automatically without intervention. A power outage is sensed immediately and after a short delay to prevent unnecessary starts during momentary outages, the engine is started and brought up to speed. The automatic transfer switch disconnects the home from the utility supply lines and connects it to the generator, effectively isolating the home from the electric utility.

The generator's controller continuously regulates the voltage and frequency to provide power that meets or exceeds electric-utility standards and is suitable for sensitive electronics in addition to lighting and appliance loads, including air conditioners.

Transfer Switch

The included 100-amp automatic transfer switch (model 71071) is a service entrance rated switch that includes the service disconnect. It installs indoors or outdoors and is typically placed between the electric utility meter and the main service panel. In this configuration, the switch controls the source of power to the main circuit breaker panel by selecting between utility power or generator power, which eliminates the need for additional subpanels and allows the generator to supply power throughout the home.

The Symphony II Power Management automatically balances the power needs of your home's electrical loads - including high wattage items like air conditioning units, electric stoves and electric dryers.

Options - Sold Separately

The addition of remote power generator modules adds a managed power option which allows the generator to supply power to all your home's high-voltage, high current appliances including dryers, hot water heaters, and well pumps.  Installed directly to a home's exisitng wiring Symphony II automatically manages the distribution of power to the electrical loads, providing power where it's needed while preventing a generator overload.

Maintenance kits include everything necessary to keep your generator running and supplying power, even through extended outages with oil and air filters, filler funnel, and spark plugs. Cold weather kits add two oil warmers and a battery warmer for easier and more reliable starts in cold weather down to -25 Fahrenheit.

Add a wireless monitor and keep track of your generator from indoors and eliminate trips outside during inclement weather.


The exterior cabinet is made from rustresistant Galvanneal steel and painted in a process similar to that used by the automotive industry for years of corrosion- free use. It rests on a prepared gravel bed or concrete pad, is 47 inches wide and 29 inches deep. At just 69db, the generator produces noise similar to a central air conditioning unit.

*You must verify the actual starting amp requirement for your air conditioner(s).


Warranty Information

Manufactures Warranty: 5 Year Parts, 3 Years Labor

Product Specifications

Model Number 40394
Series Symphony
Manufacturer Briggs and Stratton
Made In USA Yes
Rated Watts 20kW
Rated Amps 83.3 LP/75 NG
Voltage 120/240V Single Phase
A/C Ton Rating 2 - 5 Ton
Enclosure Galvanneal Steel
UL Listed Yes
Decibel Rating 69 dbA
Starting System Automatic Start
Low Oil Alert Yes
Hour Meter Yes
Battery Requirement Group 26, 12V, 540CCA Not Included
Mounting Pad Composite Base Attached
Product Weight 500 lbs
Dimensions (Inches) 48L x 34W x 31H (BASE 50.2 x 32.9)
Engine Brand Vanguard V-Twin
Engine Size 993cc
Engine RPM 3600
Cooling System Air Cooled
Alternator Type Brushless
Frequency 60 Hz
Auto Voltage Regulation Yes
Fuel Type Natural Gas (NG) / Propane (LP)
NG Power Capacity 18kW
LP Power Capacity 20kW
NG Consumption @ Full Load 260 cu.ft/hr
NG Consumption @ 1/2 Load 187 cu.ft/hr
LP Consumption @ Full Load 3.75 gal/hr
LP Consumption @ 1/2 Load 2.31 gal/hr
Transfer Switch
Transfer Switch Model 71071
Transfer Switch Amps 100 Amps - Nema 3R Indoor or Outdoor
Transfer Switch Circuits Whole Service
ATS Poles 2 Pole
Transfer Switch Weight 39 lbs
Warranty Information
Consumer Warranty 5 Year Limited Warranty
Shipping Weight 622 lbs
Shipping Dimensions 39H x 72W x 36D
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Shipping Terms

All generators include 24 hour delivery notification and residential delivery. Liftgate service is available on all air-cooled generators and some liquid cooled units – Please call for verification. Free Shipping is curbside service only. Curbside service means the freight company will deliver to your address and lower your generator to the ground. The freight company will not back down driveways, place a generator in a building or where it is being installed. You are responsible for arranging the movement and setting of the generator.

Some restrictions apply to "Free Shipping" you may either view our
Shipping Information page or contact us for details.