Briggs & Stratton Fortress 35kW Liquid Cooled Standby Generator Single PhaseBriggs and Stratton 35 kW Fortress Standby Generator Liquid cooled, emergency grade backup power that starts automatically in seconds (Automatic Transfer Switch required) The Briggs and Stratton 35 kW Fortress is the sweet spot standby generator for larger homes and light commercial sites that need real coverage, but do not want to jump all the way to the biggest units in the lineup. It delivers 35,000 watts of liquid cooled, 1800 RPM performance with

Briggs and Stratton 35 kW Fortress Standby Generator

Liquid-cooled, emergency-grade backup power that starts automatically in seconds (Automatic Transfer Switch required)

The Briggs and Stratton 35 kW Fortress is the “sweet spot” standby generator for larger homes and light commercial sites that need real coverage, but do not want to jump all the way to the biggest units in the lineup. It delivers 35,000 watts of liquid-cooled, 1800 RPM performance with clean, regulated power for modern electronics and a warranty package that is hard to beat.

With the required automatic transfer switch (ATS) installed, the Fortress system senses an outage, starts automatically, and restores power within seconds. When utility power returns, it switches back automatically.

Why the Fortress 35 kW is a smart fit

Full 35 kW on natural gas or propane

Unlike some higher output standby models that produce less on natural gas, this unit is rated at:

• 35,000W on Natural Gas
• 35,000W on Propane (LP)

That makes planning easier when you want strong output without guessing what you will lose when running on NG.

Big power without oversized footprint

The 35 kW Fortress uses the same commercial-style standby format, but in a package that stays manageable for residential installs:

• 91 in L x 39.4 in W x 41 in H
• 1540 lbs

It is substantial equipment, but still sized for typical standby pads and placement constraints on larger homes.

4.3L liquid-cooled 6-cylinder at 1800 RPM

This Fortress model uses a 4.3L industrial 6-cylinder liquid-cooled engine designed for long-run reliability and steady performance.

Benefits of 1800 RPM liquid-cooled design:

• Lower mechanical stress than high-RPM air-cooled units
• Smoother, quieter operation for its class
• Better temperature control during extended outages

Automatic backup that works like it should

With an ATS installed, the system:

• Detects utility power loss
• Starts automatically within seconds
• Transfers the home or building to generator power
• Monitors utility restoration
• Transfers back to utility once stable

Important: Automatic transfer switch required and not included.

Clean, stable power for sensitive electronics

The Fortress 35 kW is built to play nicely with today’s electronics-heavy homes and offices.

• Brushless alternator
• Automatic Voltage Regulation
• Designed for stable output that supports computers, networking gear, security systems, and modern HVAC controls

This is the kind of power quality that keeps a backup system from creating new problems during an outage.

AMF controller that keeps you informed

The Briggs and Stratton AMF Controller (UL Recognized) is designed to make ownership straightforward:

• Alpha-numeric scrolling display
• Diagnostic monitoring and fault codes
• Simple weekly exercise scheduling

Weekly exercise is a big deal. It keeps the system ready and helps catch issues before a real outage forces the test.

Cold weather ready and service friendly

Pre-installed block heater

Supports easier starting and more consistent performance in cold weather.

Weather-ready enclosure and service access

The Fortress enclosure is built for outdoor standby duty with convenient service access points that reduce disassembly during routine maintenance.

Turnkey extras included

• Automatic battery charger
• Hour meter

Performance specs that matter

Electrical output

• Rated watts: 35,000W
• Voltage: 120/240V single-phase
• Frequency: 60 Hz
• Rated amps: 146A
• Circuit breaker size: 175A
• UL listed: Yes

Fuel consumption

Natural Gas

• 50% load: 258 ft³/hr
• 100% load: 405 ft³/hr

Propane (LP)

• 50% load: 2.86 gal/hr
• 100% load: 4.46 gal/hr

Engine

• Engine: Briggs and Stratton
• Displacement: 4300 cc
• RPM: 1800
• Starting: 12V auto start
• Low oil shutdown: Yes

Requirements and install notes

• Automatic transfer switch required (not included)
• Starting battery required (not included)
  Listing references 775 CCA. Always confirm exact battery spec in the installation manual for the selected configuration.
• Concrete mounting pad required (not included)

This is an emergency-grade standby unit and should be installed to code by qualified professionals, especially for fuel supply sizing and transfer switch integration.

Warranty coverage

• Consumer warranty: 6 years
• Commercial warranty: 2 years

The consumer warranty includes parts, labor, and travel, which is a major value in this class.

Bottom line

The Briggs and Stratton 35 kW Fortress is a high-capacity, liquid-cooled standby generator for homeowners and light commercial sites that want strong whole-building backup, clean power for electronics, and consistent output on either natural gas or propane. Add the required transfer switch and proper fuel supply, and it becomes a fast-starting, reliable power plan that is ready for long outages.

Resource

Manuals:

Generator Sizing Chart

Spec Sheet

Product Manual

Controller Manual

Warranty 

Energy Systems Central is an authorized dealer of BAS Energy Systems.

Warranty Document