Generac Guardian Series 5875 – 20,000W Standby Generator Review

Generac Guardian Series 5875 - 20kW

Generac Guardian Series 5875 – 20kW

Generac Guardian Series 5875 is an automatic standby generator than can provide up to 20,000W, This unit is CARB complaint.

Standby generators are an ideal source of backup power for your home. They power up automatically within seconds when you have a power outage without having to manually start them up. This means that your home will never be without power whether you are at home or away.

Generac is one of the leading manufacturers of generators. The company was formed in 1959 and was the first to introduce affordable home standby generators. The engines of these generators are designed specifically for generators and the rigors they have to go through. Generac today is the leading manufacturer of home standby generators. The Generac Guardian Series range from 8kW to 60kW, see the current similar units below.

Power Output and Generation

The Generac Guardian Series 5875 generator has a power output of 20,000 watts when running on liquid propane and an output of 18,000 watts when running on natural gas.

It uses a V-twin 999cc Generac OHVI® Engine that is air cooled and meets the CARB requirements of California.

The engine is protected by a number of alarms. These are low oil pressure which will shutdown the unit if less than 5 PSI, high engine temperature shutdown, over crank shutdown (doesn’t start within certain crank cycle), over speed shutdown, RPM Sense Loss shutdown, under-frequency shutdown (less than 50 hz), internal fault, under-voltage (less than 60% of normal), over-voltage (greater than 110% of rating for 3 seconds and 130% of rating greater than 0.2 seconds.

Electrical output.

It is rated to provide 240 volts AC current and has a 90 amp circuit breaker. maximum continuous load current is 83.3 amps for LP and 75 amps for NG.

It comes 200 amp smart switch. See more on transfer switch below. The 14kW and 17kW have options for a 100 amp pre-wired switch with upto16 breaker positions.

Generac uses the trademarked True Power Electrical technology which produces a sine-wave and harmonic distortion of less than 5%. This makes it good for sensitive electronic equipment like computers and audio/visual media components.

Generac uses electronic torque-matching of surge load to the engine to optimize fast response to changing loads.

Note that the battery does not come with this system it must be purchased separately.

Fuel Type and Noise Levels:

As a standby design The Generac Guardian Series 5875 generator is designed to be directly connected to either liquid propane or natural gas.

When running on liquid propane, this generator has a fuel consumption of 2.08 gal/hr running at 50% capacity and when running on natural gas it consumes 205 ft3/hr at 50% capacity.

Noise:For generator of its size it is very well enclosed with an Aluminum sound attenuated (insulated) enclosure. It’s very quiet; producing only a 66 db sound level at a distance of 23ft. Which is in the range of the ultra quiet portable generators.

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Dimensions and Weight

Generac 5875 Small Foot Print

Generac 5875 Small Foot Print

The Generac Guardian Series 5875 generator has dimensions in inches of 48 x 25 x 29 ( L x W x H ) and it weighs in at 451 lbs.

For a standby generator, this generator is quite compact. In size it’s width and height are similar to most portable generators, however, in length it’s just over 1 1/2 feet longer.

This Model comes with an Sound attenuated Aluminum enclosure painted in Gray.

This foot print is relatively small and should be easy to fit in most locations that you would like to set about your home or office.

Typical Uses and Needs

The Generac Guardian Series 5875 generator is designed to be directly hooked up to either your 300 gallon propane tank or to your natural gas source.

It is an automatic generator which means that it senses the power coming into your home from the power grid. When you have a power outage, this generator automatically switches the power source from the power grid and turns itself On to power your home. When the power grid comes back on line, the generator automatically switches your home to the power grid and turns itself to standby mode. With this generator you do not have to worry about ever losing power to run your home.

With 20,000 watts of output it can run everything in your home just like you normally do.

Display & Control Panel, Start-up


Since this unit is specifically set up for use to directly connect to your house utility panel via a transfer switch there is however, one convenience outlet at 120V and 15 amps in a compartment on the right side of the generator.  This compartment has the main circuit breaker and LED indicator lights to provide

The control panel is located under the lid of the enclosure. It is intended to be operated by qualified service personnel. The interface is a Human Machine Interface (HMI) touch panel to get access to the various functions of the unit. Generac Brands this as Evolution Controls.

As an owner of the unit you will need to only understand the auto, manual and Off buttons. The Auto button activates the automatic function of the unit and it also allows the system to start and exercise the engine every seven days. In this function the system will automatically switch the power from the grid to the generator when it senses a drop in power from the utility grid.

The Off button shuts down the unit and prevents the automatic start of the unit.
The Manual button will start the engine but it will not transfer the home to the generator power unless the utility grid has a failure.

The menu system navigation is meant for a qualified service technician who will use this feature to diagnose the unit and check its operations.


The generator is normally setup for automatic transfer of power from the utility grid to the generator in case of power failure.

Automatic transfer operation

To select the automatic operation of the unit

  1. Make sure that the transfer main switch contacts are set to the Utility position.
  2. Be sure that the utility power is available to the terminals of the transfer switch.
  3. Press the Auto button on the control panel.
  4. Set the main circuit breaker to the On position.

In this option the generator will automatically start up if the power is lost from the utility grid within 10 seconds. The engine will run for 5 seconds to warm up and will then automatically transfer the power from the grid to the generator. When the power returns to the utility grid the generator will automatically transfer the load on to the utility grid and initiate a shut down of the generator.

Manual mode

  1. The generator will transfer the load from the utility to the generator if the utility power fails.
  2. It will transfer the load back to the utility when the power returns.
  3. The engine will continue to run unless it is removed from the manual mode.

Exercise Mode

  1. The generator is equipped with an exercise timer. Once the timer is set the generator will start and exercise itself every seven days on the day and time specified.
  2. The generator will not exercise if it is already running in the Auto or Manual mode.
  3. If the generator is exercising, it will only transfer the power from the utility to the generator if the utility power fails.
  4. The exercise settings can be changed any time via the Edit menu.

Shut down

To turn the generator Off when in Auto mode and when it is running follow the following steps.

  1. Turn Off the main utility disconnect.
  2. Turn Off the main line circuit breaker on the generator.
  3. Turn the generator Off.

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Transfer Switch

Generac Smart Switch and PMM

The transfer switch provided for the 20kW is the 200 amp rated Smart Switch. Note that the 100 amp pre-wired is available only with the 14kW and 17kW models.

This is wired generator to external connection box to transfer switch connected to main panel. The smart switch is billed with the management to be able to wire your full main panel and can manage power needs up to the generator rated output..

The Smart Switch has a Digital Power Management (DPM) technology and can manage to air conditioner loads without additional hardware. There is also the capability to manage 4 large loads with Generac 6186 50-Amp Digital Load Management Module, PMM also known as Power Management Modules (PMM), which are sold as a separate kit.

The Smart Switch is a 2 pole ( 2 x 120V) configuration used in single phase. It has a NEMA outdoor rating of 3R.

Care, Maintenance and Use

The Generac Owners manual is extensive and covers many of the care and use procedures as well as in depth information of various parts of the generator.

Proper maintenance is important to keep the generator operating at its peak and to extend its useful life. The controller of the generator will give prompts for the schedule A or schedule B maintenance to be performed on the generator.

The Schedule A maintenance consists of maintaining the oil, the oil filter and the tune up while the schedule B maintenance consists of maintaining the oil, the oil filter, tune up, air cleaner, spark plugs and valve clearance. Though the controller will tell you the type of maintenance that is needed you must also do a periodic check up and maintain the generator. These are the suggested guidelines.


  1. Inspect and clean the cooling louvers.


  1. Inspect and check the fuel lines.
  2. Check the general condition of the generator for vibrations, noise and any leakage.
  3. Check the engine oil.

Every 6 months

  1. Check the electrolyte of the battery.

Every 2 years or 200 hours

  1. Change the oil.
  2. Change the oil filter.
  3. Do a complete tune up ( to be done by an authorized service personnel ).

Every 400 hours of use

  1. Inspect and change the air cleaner.
  2. Inspect and change the spark plugs.
  3. Inspect the valve clearance.

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Warranty and Repairs

The Generac Guardian Series 5875 generator is covered by a 5 year limited warranty with varying amounts of service and coverage. The unit should be registered and there should be a proof of purchase and records of maintenance.

The warranty only applies to wired and permanently mounted units. The warranty is transferable between ownership of the original installation site.

The warranty allows in the first two years a limited comprehensive coverage on mileage, labor and parts. The mileage is limited to 100 miles round trip to and from an authorized Generac service dealer.

Year three there is a limited comprehensive coverage on parts and year four and five cover limited comprehensive coverage on the engine and alternator.

Consumer Comments

The Generac Guardian Series 5875 generator gets 4.1 out of 5 stars on Amazon. Most of the customers who bought this unit were very satisfied with it. They liked the peace of mind, knowing that the generator would turn On automatically if they had a power outage.

They also like the fact that if there was a power failure they would not have to do anything and this generator would restore the power to their home. They also liked the fact that this generator could supply enough power to run the whole house.

They commented on how this unit was probably the best investment added to their home. Also on the peace of mind and great feeling to know when the power goes out this generator automatically runs the whole house! It’s worth every dollar spent. They highly recommend it to anyone requiring backup power for the whole house.”

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Pros & Cons


  1. Fully automatic, comes on when there is a loss in power from the utility and shuts off when the power is restored.
  2. It can run the whole house.
  3. Is directly connected to the main Propane or natural gas supply, so there is no question of running out of fuel.
  4. Is very quiet.
  5. Does not require as much maintenance as other generators.
  6. Is quite compact for its performance.
  7. It does not require you to be at home to start the generator in times of power outages.


  1. It is more expensive than other portable generators.
  2. It is relatively expensive to install.


The Generac Guardian Series 5875 generator is available at many outlets. It is available at Amazon for around $5000.00. Check the latest pricing here:

Generac Guardian Series 5875 20kW Standby Generator With Transfer Switch (CARB Compliant)

Installation costs will vary depending on how much you do yourself or if you have it professionally installed. Do realize that at 450 lbs that it’s going to take some help to get it installed. Also if you are hooking to natural gas and are uncomfortable with installing this on your own, you’ll need to get a plumbers help. Although you can install the electrical side yourself you may consider also hiring an electrician to do final hookups for inspection.


Accessories available for this generator include a maintenance kit.
Generac 5665 Maintenance Kit for 20kW, 999cc Engine

You can also get a mobile link for wireless monitoring of the generator.
Generac 6463 Mobile Link for Wireless Remote Monitoring for (USA only)

You can also get a wireless remote in home monitor.
Generac 5928 Wireless Remote in Home Monitor – Basic (Nexus)

For those living in cold climates, there is a cold weather kit available for the engine which helps to keep the engine at a temperature where it can start at any time. Generac Cold Weather Kit – Fits 760, 992 and 999CC Engines, Model# 5947

Battery Requirements

One item that is required is the purchase of the startup battery. Group 26R, 12 Volts and 525 CCA Minimum
Wet Cell Battery, Use With Generac Standby Generators

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When considering a generator as a back up power source for your home, the Generac Guardian Series 5875 – 20kW fulfills all your requirements. It is fully automatic and comes On when you have a power failure and shuts Off automatically when the power is restored.

It can supply up to 18kW to 20kW of continuous power, which means that it can run your whole house. It is directly connected to the Propane source or natural gas source which means that you do not have to worry about the fuel or running out of fuel as you would with a gasoline powered generator.

Though it is expensive as a unit along with the installation as compared to portable generators, it gives you peace of mind to know that you will always have power in your home whether you are at home or not.

Similar Generation Units:

Other Guardian Series Similar to the 5875 at other wattage levels. Click links to see latest pricing on Amazon.

Generac Guardian Series 5882 8,000 Watt Air-Cooled Liquid Propane/Natural Gas Powered Standby Generator Without Transfer Switch (CARB Compliant)

Generac Guardian Series 5871 10,000 Watt Air-Cooled Liquid Propane/Natural Gas Powered Standby Generator With Transfer Switch (CARB Compliant)

Generac Guardian Series 5872 14,000 Watt Air-Cooled Liquid Propane/Natural Gas Powered Standby Generator With Transfer Switch (CARB Compliant)

Generac Guardian Series 5873 17,000 Watt Air-Cooled Liquid Propane/Natural Gas Powered Standby Generator With Transfer Switch (CARB Compliant)

CorePower Series

Generac 5837 CorePower Series 7,000 Watt Air-Cooled Natural Gas/Liquid Propane Powered Standby Generator with Transfer Switch

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