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The Generac Guardian™ 20kw aluminum home standby generator has been discontinued and is not available for purchase at this time.


Generac Guardian™ 20kW Aluminum Home Standby Generator

Generac Guardian Power Equipment and Accessories
Model: 6250
(Based on expert analysis, manufacturer ratings and customer reviews)
4.5 out of 54.5 out of 54.5 out of 54.5 out of 54.5 out of 5
6 Reviews
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  • Features
  • Specs
  • 17
  • 6
  • Articles
  • Accessories
Run Watts
Rated Watts
120/240 Single-Phase

Product Video Disclaimer: "PED is not responsible for any variances from the product in this video and the item you purchase. Please review all product specs prior to purchase."

Fully Automatic Operation When Paired With Generac Smart Switch™

Generac OHVI Air-Cooled Engine
Features plateau honed cylinder walls and plasma moly rings
Full pressure lubrication system w/ 2 year oil change interval
Aids in cooling the engine for longer life

Operates On Clean Burning, Efficient Natural Gas or LP (Vapor)

Skewed Rotor Design For Smooth Output Waveform "Clean Power"
Automatic voltage regulator equipped for +/- 1% regulation

Evolution™ Digital Controller Monitors & Controls All Functions
Provides system status for wireless monitors & Mobile Link™

Sound Attenuated Weather Proof Enclosure
Attractive styling with lockable acess doors
Incorporates electrostatically applied epoxy paint technology
Sound dampening enclosure limits sound pressure to a low 66dB(A)
Matching fascia kit and 12" flexible fuel line included

Built-in Battery Charger (Battery Sold Separately)

Automatic Transfer Switch - ATS (Sold Separately)
Select the ideal ATS & PPM modules for load shed capabilities

Automatic Operation Only & Listed to UL2200 Standards For Safety

5-Year Limited Warranty & 24/7/365 Customer Care
Engine Brand
Generac OHVI
999 CC
Consumer Engine Warranty
5 Years
Commercial Engine Warranty
5 Years
Engine RPM
3600 RPM
Low Oil Alert/Shutdown
Product Specs
120/240 Single-Phase
60 Hertz
Surge Watts
20000 Watts
Rated Watts
20000 Watts
Fuel Type
LP/Natural Gas
NG Power Capacity
18000 Watts
LP Power Capacity
20000 Watts
NG Fuel Consumption @ 50% Load
205 (BTU: 205,000 BTU/HR) ft³/hr
NG Fuel Consumption @ 100% Load
308 (BTU: 308,000 BTU/HR) ft³/hr
LP Fuel Consumption @ 50% Load
2.08 (BTU: 188,760 BTU/HR) gallons/hr
LP Fuel Consumption @ 100% Load
3.85 (BTU: 349,388 BTU/HR) gallons/hr
Rated Amps
83 @ 240 Volts (Single Phase) Amps
Decibel Rating @ 7m
66 dbA
Transfer Switch
Automatic (Not Included)
Not Included (525 CCA)
A/C Ton Rating
Mounting Pad
Composite (Included)
Cooling System
Air Cooled
UL Listed
Grade Type
Made in USA
541 Pounds
Product Style
Standby Generator
Product Length
48 Inches
Product Width
25 Inches
Product Height
29 Inches
Consumer Warranty
5 Years
Commercial Warranty
5 Years
Need Help? Ask Our Experts.
  17 Questions
Q: Are there recommended installation distances from other items? I have an AC unit near where I would like to place the generator. Also, would it be okay to be under a porch? There is about 5' from the ground to the bottom of the porch.
by Matt from Pennsylvania on June 18, 2014

A: The minimum distances can be found in the installation guide we have available on the site on the product page under the specs tab in the download document section.....

Installation Guide

The unit needs at least 3 feet clearance on the sides of the unit for proper air flow and 3 feet from the front for proper maintenance. Also, the unit requires a minimum of 5 feet clearance from the top of the unit. These units cannot be installed under a porch. These units also require a minimum of 5 feet from any window, door or ventilation opening.

We recommend you consult with your local inspector or AHJ (Authority Having Jurisdiction) for your local code requirements as they can sometimes supersede the manufacturers recommendations.

by Mike, Product Expert

Q: I'm interested in the Generac 14 kw standby generator and I want to power it with natural gas. All your other Generac standby generators show a wattage loss of about 2kW when powered with natural gas, but this one does not show a loss in the specs I have reviewed. Is this a misprint in the specs or is this a true output? If I power it with natural gas will it deliver 12 kW or 14 kW?
by Albert Leblanc from Michigan on May 06, 2014

A: This is not a misprint in the specification. The unit will produce 14kW when operating on Natural Gas and LP as tested at the factory.

Also noted on the manufacturers specification sheets is the following....

"Maximum wattage and current are subject to and limited by such factors as fuel BTU/megajoule content, ambient temperature, altitude, engine power and condition, etc. Maximum power decreases about 3.5 percent for each 1,000 feet (304.8 meters) above sea level; and also will decrease about 1 percent for each 6° C (10° F) above 16° C (60°F)."

Specification sheets can be found on the individual product pages under the Specs tab and within the download document section.

by Mike, Product Expert

Q: I have a low pressure nat. gas line in my residence, what is the largest generator I will be able to run without doing major updates ?

by Chuck from Ohio on December 10, 2013

A: The Generac line of home standby systems can now operate on low pressure natural gas. Their low fuel pressure requirement is 3.5" to 5" of water column (1" of water column = 0.036 PSI).....0.123 PSI to 0.18 PSI. This would be for all sizes from 8kW up to 20kW.

Proper sizing of the generator is crucial to the success of any generator installation and requires a good working knowledge of electricity and its characteristics, as well as the varying requirements of the electrical equipment comprising the load.

A certified electrician needs to be consulted for proper sizing and installation of any generator.

When analyzing the electrical load, consult the manufacturer’s nameplate on each major appliance or piece of equipment to determine its starting requirements in terms of amps and voltage which can be calculated to watts using Ohms Law (Amps x Volts = Watts).

When choosing the generator output select a rating that is approximately 20 to 25% higher than the peak load (for example, if the load is about 8 kilowatts, select a 10 kW generator).

A higher rated generator will operate comfortably at approximately 80% of its full capacity and will provide a margin of flexibility if the load increases in the future.

Note: Applications such as commercial, all-electric homes, heat pump systems or geothermal systems require special installation procedures and a certified electrician must be contacted to evaluate and install these types of systems.

by Mike, Product Expert

Q: Guys I need a 20 kW natural gas home stand by with a 150A service rated transfer switch. Is this available as a package deal?

by Harry Donovan from Virginia on December 01, 2013

A: At this time Generac does not pre-package their home standby systems with a 150A transfer switch. You would need to purchase each item individually.....

Generac Generator Model 6250

Generac Switch Model RTSY150A3

Another option would be the Briggs & Stratton line of home standby units which do come with a 150A packaged option....The following link shows the available prepacked 150A home standby systems....

150A Prepackaged Home Standby Systems.

by Mike, Product Expert

Q: Can I use the 100 amp 16 circuit transfer switch with a 20 KW Generac?

by George Bristol from Nebraska on November 23, 2013

A: You cannot use the 16 circuit Generac transfer switch with the 20kW Generac home standby unit. The internal wiring is not suitable for the amperage output capacity of the 20kW unit.

The following switches are recommended for use with the 20kW Generac unit allowing specific circuits......

Generac GenReady Indoor Load Center - Model 5449

Generac GenReady Outdoor Load Center - Model 5454

Generac LTS Load Center with Load Shedding (16 Circuit) - Model RTSJ200A3

by Mike, Product Expert

Q: The install guide says The minimum LP tank size is 250 gallons.

My customer was hoping to avoid this type of tank since it is required to be at least 10' from the house and would need trenching where ledge is. Any idea why they specify it like this?

My customer wanted to go with less obtrusive 120 gallon tanks that are allowed next to the house. Is it just based on capacity or is it more to do with pressure or regulators?

by Rob Saccardo from Massachusetts on November 21, 2013

A: The tank size recommendation is based on BTU output, capacity and temperature. However, some propane suppliers will state a 120 gallon tank is sufficient for a 20kW standby generator but a 120 gallon tanks usable fuel amount is less then the tank size which will also vary depending on temperature.

The fuel consumption of a 20kW is 2.08 gallons per hour when operating at 1/2 load capacity and if calculated into a days use you will be using just under 50 gallons of fuel.

A 120 gallon tank has 72 usable gallons with the BTU output varying depending on temperature. A 120 Gallon tank BTU/HR output capacity based on 40 degrees F is 248,240 BTU/HR and a 20kW, at start-up, requires 349,388 BTU/HR which is more then a 120 gallon tank can supply. To properly size a generator to your fuel source you need to size it to it full load start-up BTU/HR requirements.

A 250 gallon tank has 150 usable gallons with the BTU output also varying depending on temperature. A 250 Gallon tank BTU/HR output capacity based on 40 degrees F is 507,600 BTU/HR and is well within the requirements of the 20kW generator.

With that said, a 120 gallon tank does not offer enough BTU/HR output capacity to supply a 20kW generator. This is why Generac recommends a minimum 250 gallon tank with strong recommendations for a larger tank.
by Mike, Product Expert

Q: What type of oil should I use in my Generac home standby generator?
by Jim from Illinois on November 11, 2013

A: The maintenance section in the Generac's home standby owner's manual lists that the oil type is based on temperature ranges specific in your area.....

SAE-30 above 32º F (0º C)
10W-30 between 40º and -10º F (4º and -23º C)
Synthetic 5W-30 for all temperature ranges

All new models come with SAE-30 oil in them and have been test run at the factory for 25 hours and no break-in is required. The first oil change would be at 2 years or 200 hours, whichever comes first.

by Mike, Product Expert

Q: Jim I have a 100 amp Pre-Nexus service rated transfer switch. Can I use this with a nexus generator? I've heard there is some special wiring for the battery charger to work
by J. Depp from California on November 04, 2013

A: Thank you for your interest in Electric Generators Direct!

There is a special kit that needs to be added to the switch to accept the 120V connection which provides the power to the internal generator controller for the charger. These kits are available from your local Generac dealer - Part Number: 0H92540SRV.

by Mike, Product Expert

Q: I have a new 2013 Generac generator and I'm wondering what oil it came with? I would like to top it off properly after the installation.

by John from New Jersey on October 18, 2013

A: The Generac 2013 automatic standby generators are shipped with a SAE 30 non-synthetic oil. If you are located in an area that receives snow, it is recommended to perform an oil and filter change to switch to a synthetic 5W-30 oil to promote proper generator operation. The cold weather kit is also recommended.

The appropriate intervals for oil changes and other maintenance items will be located in the owner’s manual in the Maintenance Schedule.

Current production models do not require any break in, so if the Maintenance Schedule in the owner's manual indicates that oil changes only need to be done every 2 years or 200 hours, you could drain the existing oil and switch to synthetic 5W-30 right away.

by Mike, Product Expert

Q: Q: I just purchased a 20KW generator and would like to know the max distance that I can run 1/2 inch steel pipe to my generator?

by Johnnymack from Rhode Island on September 28, 2013

A: Per Generac you cannot us 1/2 inch pipe at all on a 20kw or any of their air cooled generators as this does not provide enough volume of fuel to the unit.

Here are the fuel pipe requirements on a 20kw Generac Model 6244 or 6250.....

Natural Gas:

1/2 Inch: Cannot Use
3/4 Inch: Cannot Use
1 Inch: Max Distance 20 Feet
1-1/4 Inch: Max Distance 130 Feet
1-1/2 Inch: Max Distance 305 Feet

Liquid Propane Vapor:

1/2 Inch: Cannot Use
3/4 Inch: Max Distance 15 Feet
1 Inch: Max Distance 115 Feet
1-1/4: Inch: Max Distance 480 Feet

Add 2.5ft per any bend, tee or angle in the pipe to the overall distance.

Gas Pipe sizing is one of the most commonly made mistakes. A properly sized gas pipe is critical to the proper operation of the generator. The generator inlet size has no bearing on the proper gas pipe size.

by Mike, Product Expert

Q: What is the recommended time frame to change the break-in oil on my Generac 20kW generator?

by Karin Green from New Jersey on August 10, 2013

A: All of the new 2013 Generac Home Standby generators have been pre-run at the factory for 25 hours. So, no break-in period is required.

by Mike, Product Expert

Q: I just purchased the Generac Guardian 20kw model 6244 from your site. I am planning to pour the base this weekend for the generator. My question is what size should I make my pad? I would like to set the anchors in the concrete before it dries. What kind of anchors is recommended and what size should they be? What Type of oil is recommended and do I need to purchase an oil filter?
by Mark Muczynski from Michigan on July 30, 2013

A: The installation drawing is available on the site under the specs tab in the download document section. This will provide dimensions of the generator where you will want to make the pad at least 6 inches larger on all sides. You will also find the location of the holes for mounting the unit to the concrete pad. Generac recommends 3/8 inch lag bolts designed for concrete.

Installation Drawing

You will also find the owner's manual available where it discusses proper maintenance and oil requirements based on temperatures in your area.

Owner's Manual

When changing the oil it is also recommended to change the oil filter. The following link is for the recommended maintenance kits available for the Generac model 6244...

Basic Maintenance Kit

Maintenance Kit with 5W30 Synthetic

Maintenance Kit with 10W30 Synthetic

Maintenance Kit with 10W30 Standard
by Mike, Product Expert

Q: I need a 20kW natural gas generator. But they seem to only come with a 200A panel. I believe I need a 300A panel. Is there a big price difference in purchasing a 300A panel with the generator? I didn't see it on your website. Can you tell me the price?

by Peter Kearns from New Jersey on July 13, 2013

A: If you have a specific application that does not meet the prepackaged units you would purchase the items individually instead. The packaged systems are put together by the appropriate manufacturer and cannot be altered.

Briggs does not offer a 300A switch so you would need to go to the larger 400A switch if you intend on powering the entire home and that system is already prepackaged. (Model 40396).

Generac does offer a 300A switch so you would purchase the generator by itself (Model 6250) and the switch separately (Model RTSY300A3). Just add each item to the cart and enter your state and zip for the total.

We do recommend consulting with a certified electrician for proper generator sizing and installation.

by Mike, Product Expert

Q: Could you please advise regarding the Generac 6244 vs the 6250?
The pros and cons of one vs the other, any preference recommendation?

by John O'hearn from Maryland on June 26, 2013

A: They are exactly the same generator except one comes with a transfer switch and the other one is the generator only.

Model 6244 includes the 200A Automatic Transfer Switch.

Model 6250 is the Generator Only.

by Mike, Product Expert

Q: What size NG line for 18 kw generator?
by Bill from New Jersey on June 13, 2013

A: The pipe size is based on the distance the generator is from the fuel source.

***The 18/20kW requirements are:

Natural Gas (NG)-

3/4" - Cannot Use
1" Pipe - Max 20 Feet
1-1/4" Pipe - Max 130 Feet
1-1/2" Pipe - Max 305 Feet

Liquid Propane Vapor (LP) -

3/4" - Max 15 Feet
1" Pipe - Max 115 Feet
1-1/4" Pipe - Max 480 Feet
Note: LP Pipe sizes are using a second stage regulator.

The pipe sizes are measured by inside diameter (ID) to include any fittings, valves (Must be full flow), elbows, tees or angles. Add 2.5 ft. per any bend, tee or angle in the pipe to the overall distance.


The generator inlet size has no bearing on the proper gas pipe size.

Note: Refer to NFPA 54 for NG or NFPA 58 for LP codes.

Note: Required fuel pressure for natural gas is 3.5 to 7 inches of water column and the required fuel pressure for LP Vapor is 10 to 12 inches of water column.

by Mike, Product Expert

Q: Have a 100 amp service panel and was recommended to buy a 20kw generator and a 100 amp service entrance rated ATS. My question is which generator brand would you recommend for value, dependability, and service? Many local installers recommend Generac but a couple have told me that Kohler makes a much better unit and has a better warranty. Don't know who to believe so I will trust your judgement! Also if you could recommend the necessary ATS that would be great! Thanks!
by Robert Gostl from Louisiana on June 04, 2013

A: The new Generac line of home standby systems have been improved greatly and are the top rated generator in the industry today. They also come with the same 5 year warranty that Kohler offers. I would recommend the Generac model 6250 and the RTSY100A3 transfer switch.

Generac RTSY100A3

by Mike, Product Expert

Q: I am looking to purchase a 20Kw generac standby generator. I have two 150AMP panels at my home and would like to set up one generator with two automatic transfer switches. Is this possible or should i go with one 400 amp transfer switch instead?
by Domenic from New York on May 23, 2013

A: I would recommend going with 1 - 300A transfer switch instead of multiple switches for ease of installation and cost.

You would need to purchase the generator and switch separately as they do not package a model with a 300A switch.

Here are the links to each item....

RTSY300A3 Transfer Switch

Generac 6250 - 20kW Generator

by Mike, Product Expert

Generac Guardian 6250 Reviews & Ratings
Overall Rating
4.5 out of 54.5 out of 54.5 out of 54.5 out of 54.5 out of 5
Price (5)
I'd Buy It Again (3)
Features (3)
Easy To Use (2)
Quiet (2)
Bad Instructions (2)
Difficult To Use (1)
Unreliable (1)
83% of respondents would recommend this product to a friend
6 Reviews  Sort by 
Total Helpful Votes
27 Helpful Votes
4 out of 54 out of 54 out of 54 out of 54 out of 5
2013 Model Generac 20kw
Brand new unit was extremely hard to start. All Generac would do is provide phone numbers for me to call for warranty work. Problem turned out to be a kinked rubber fuel line inside the Generac. Also, right side locking mechanism badly misaligned and needed modification to work. Quality control definitely was lacking!!! Plastic trim on bottom of unit is a piece of junk. Generac needs to make some improvements!
Cons: Unreliable
Steve Recommends This Generac Guardian Product
Mike, the Generator Expert
Product Expert
In regards to the fuel line issue you had, the installer should of been able to identify that issue fairly easy during installation.
Was this review helpful?
Mark D.
Hillsdale, NJ
Purchased from Power Equipment Direct
Purchased 9/15/13
Total Helpful Votes
12 Helpful Votes
5 out of 55 out of 55 out of 55 out of 55 out of 5
Factory Problem
At start up wire connected to starter solenoid bent and shorted system, had to diagnose and repair. Computer bad from factory, along with bent wire. Had to get Authorized Repair facility to fix. All was covered under warranty, but still not needed. A little more quality control from the factory is needed.
Pros: Easy To Use, Price, Features, I'd Buy It Again
Mark Recommends This Generac Guardian Product
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Larry L.
Coopersville, MI
Purchased from Power Equipment Direct
Purchased 10/21/13
3 out of 53 out of 53 out of 53 out of 53 out of 5
I purchased this unit, poured a concrete pad, had our electricians and plumbers hook the unit up, but I have not been able to start it. We bled the gas line multiple times but the unit will not start.
Pros: Price, Features
Cons: Difficult To Use, Bad Instructions
Larry Does Not Recommend This Product
Mike, the Generator Expert
Product Expert
We're sorry you're having issues starting your generator. I would suggest contacting Generac directly @ (888) 436-3722 x5381. They will be able to direct you to a local service center in your area.
Was this review helpful?
William W.
Jonesboro, LA
Purchased from Power Equipment Direct
Purchased 9/4/13
5 out of 55 out of 55 out of 55 out of 55 out of 5
Exactly What We Needed
A group of us bought this unit to power our very remote hunting camp and we should have done this years ago. It was easily handled, easy to install and bring on line, quiet, power is clean, and well, like I said.....exactly what we needed. Uses two quarts of oil instead of two gallons like our old diesel. Air and oil filters and oil drain are easily accessible, so there is nothing to not like.

This is my second Generac 20KW Guardian. I bought this same unit with the ABT feature for our lake... more
Pros: Easy To Use, Quiet, Price, I'd Buy It Again
William Recommends This Generac Guardian Product
William Would Recommend Power Equipment Direct To A Friend
Web Site


"You guys make it easy!"
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Bill S.
Manassas, VA
Purchased from Power Equipment Direct
Purchased 1/1/14
5 out of 55 out of 55 out of 55 out of 55 out of 5
Good Quality/price/ontime Damage Free Delivery
I'm electrical engineer - didn't have any trouble but a schematic in the installation manul would be helpful.
Pros: Price, Features, I'd Buy It Again, Quiet
Cons: Bad Instructions
Bill Recommends This Generac Guardian Product
Bill Would Recommend Power Equipment Direct To A Friend
Web Site


"Very good experience."
Was this review helpful?
Patrick H.
Thibodaux, LA
Purchased from Power Equipment Direct
Purchased 6/13/14
5 out of 55 out of 55 out of 55 out of 55 out of 5
Great Customer Service & Product
The whole process, from beginning to end, was as smooth and professionally handled as anyone could want. Marissa went above and beyond in helping me with my order. I HIGHLY recommend this company to anyone needing a home generator.
Pros: Price, Exceeded Expectations
Patrick Recommends This Generac Guardian Product
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