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Buyers Guide & Information

Best Diesel Generators Reviewed

Whether you want a portable option or not, stay fuel-efficient and have longer run times with these top-rated brands.

by JohnL

Buyers Guide & Information

Best Diesel Generators Reviewed

Whether you want a portable option or not, stay fuel-efficient and have longer run times with these top-rated brands.

by JohnL

by JohnL

Diesel powered generators can help homeowners power their homes and businesses run complex machinery on-site. If a storm creates a power outage in your neighborhood, what will you do when you can no longer turn on the lights, heat or cool your home, run your electronic devices, or run home appliances such as refrigerators?

When power outages persist, a generator can give you access to electricity. A high-quality diesel powered generator is an excellent tool for keeping your home running during power outages and your business running when a portable fuel source is needed.

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Product

Starting & Running Watts

Runtime

Check Price

Generac 6864, 5000 Running Watts/5500 Starting...

Generac 6864

5,500 Starting / 5,000 Continuous

32.4 hours runtime at 50% load

Generac RD03022ADAE Protector Series 30 kW Single...

Generac RD03022ADAE

30,000 Starting / 25,000 Continuous

90+ hours runtime at 50% load

12KW Cummins Onan QD 12000 Single Phase Diesel...

Cummins Onan QD 12000

12,000 Starting

12+ hours

Generac RD020ADAE Protector Series, 20kW Liquid...

Generac RD020ADAE

20,000 Starting / 15,000 Running

30+ hrs standard, 90+ hrs integrated runtime

20 kW Portable Generator - DeepSea Controller -...

Larson Electronics

20,000 Starting / 15,000 Running

19+ hours

Why Choose Diesel Fuel?

Diesel generators use less fuel compared to other generators such as gasoline powered generators. This makes diesel generators more fuel-efficient and more cost-effective for many people, particularly when compared to gasoline powered generators. Diesel generators are also longer lasting because they do not require carburetors or spark plugs. These generators also do not require as much maintenance, and diesel fuel is less likely to ignite compared to gasoline.

Diesel generators, however, do tend to be both louder and heavier compared to gasoline generators. The heavier components also tend to mean more high-quality parts, and those can also be more expensive. We recommend diesel fuel generators for homeowners interested in a whole house generator or for businesses who need portable generators to travel via truck (such as traveling on a truck to a construction site).


Buying a High-Quality Diesel Generator

Generator Size vs. Power Needs

Consider the size of the generator that you will need based on your power needs. Think about the appliances, devices, and heating/cooling units you will want to operate while you are without power. Do you want to power your entire home? What about a few rooms or essential appliances and devices? Use this power needs calculator to determine the amount of power you need and then choose a diesel generator with the wattage required for your home.

Fuel Storage Size

The fuel storage size needed for your generator depends on how often you plan to use your generator and for how long. Diesel generators range from 12 gallons to 50+ gallons or more. Fuel storage size also affects portability. Portable diesel generators use smaller fuel tanks.

Fuel Efficiency/Runtime

Most diesel generators have runtimes that vary from 20 to 50+ hours depending on the size. Extended tank sizes can sometimes reach 90-120+ hours.

Power Output

The more power a diesel generator sends out, the more devices, appliances, and units that can be powered in your home or at your business site. We recommend using a power needs calculator to determine what power output you need in your diesel generator.

Noise Level

If your generator will be outdoors and you will be indoors, the noise level might not matter to you. However, anything above 70 dB is considered loud. If you plan to work in the same space as your generator frequently, you might want to purchase a muffler for your generator or look for a generator in the 50-69 dB range.

Portability

Will you need to move your generator around your home or yard with ease? Do you own a company that will be using the generator, and you will need to move it from truck to truck? Most generators under 300lbs. are considered portable and are ready to be connected to a wheel set. However, the more portable generators tend to have smaller engines and smaller fuel tanks, so weigh portability against size and strength.

Safety Features

Safety features include circuit breakers, transfer switches, and auto-shutoff features when the generator overheats or is low on fuel. Review all of the safety features available for the generator you are interested in and make sure the generator will be safe to use.

Price & Warranty

Typically, generators come with a warranty between one to five years. Consider the length of the warranty when purchasing. A more expensive generator will typically come with a more substantial warranty. More expensive generators also come with higher quality build parts and more power (watts).


5 Best Diesel Generators Reviewed

1. Generac 6864

best portable diesel generator

Noise Level

Not specified, but loud.

Fuel Tank Capacity

12-gallon fuel tank

Starting & Running Watts

5500 Starting / 5000 Continuous

Runtime

32.4 hours runtime at 50% load

Warranty

Yes, two-year limited warranty

The best portable diesel generator on our list is the Generac 6864. This diesel generator comes with a powerful engine running at 5500 starting watts and 5000 running watts. It weighs 273 lbs. and is the most portable option on our list without sacrificing power. If you want a generator that you can move around the backyard, ranch, or construction site, then this is a great option. A wheel kit can be purchased and added to the unit. This generator is also made with superior build materials, including a durable steel frame. The large fuel tank can hold 12 gallons and offers more than 30 hours of runtime at 50% load. The control panel is simple to use and provides an hourly meter to track maintenance as well as a single touch electric start. 

Black Tail Mountain Ranch wrote on Lowe’s, “Just finished a 10-state tour delivering HighMont beef to the western states and the Generac XD-5000 ran perfectly. We had it in a ventilated stock trailer and fuel consumption was minimal and performance was excellent. It ran four large freezers without fail.”

Some users have reported that this diesel generator is loud and may require a muffler. If you plan to work or live in the same space as the generator, then we recommend purchasing a muffler. However, if this generator is going to power your home and will be outdoors while you are indoors, you may not need a muffler or mind the excess noise.

This diesel generator doesn't have enough power to run a whole home, but can efficiently run several rooms and high-powered appliances and devices. You will need to purchase a battery for this diesel generator as it does not come with its own. This generator is easy-to-use, powerful, portable, and durable.

Pros

  • Powerful 5500 Starting/5000 Continuous Watt Engine
  • Portable at 273 lbs.
  • Durable Steel Frame

Cons

  • Not enough power to run whole house
  • Does not come with battery
  • Loud and may require muffler

2. Generac RD03022ADAE

best 30kw diesel generator

Noise Level

70dB

Fuel Tank Capacity

61 gallons

Starting & Running Watts

30,000 Starting kW / 25,000 Continuous kW

Runtime

90+ hours runtime at 50% load

Warranty

Yes, five-year limited warranty

The best 30kw diesel generator on our list is the Generac RD03022ADAE model. This diesel generator delivers extreme power at 30,000 kW (far above the standard wattage on most generators, a single kW is equal to 1,000 watts of power). This diesel generator can easily power your entire home or a massive building for business owners.

The model is quiet at 70dB and can hold 61 gallons of fuel for a 90+ hour runtime at 50% load. This model has a double-wall base fuel tank that is durable and practical for diesel fuel storage. An LCD display is color-coded and includes backlit buttons for easy use. An external viewing window allows users to check on the internal components and determine if maintenance is needed. This model also has a quiet-test mode, which tests the generator’s effectiveness weekly and allows the generator to run at a lower RPM saving fuel.

This generator is massive at 1,957 pounds and one of the most expensive generators on our list. Most homeowners won't need this kind of power, but homeowners with farms or multiple properties will appreciate this power. We recommend having this unit installed professionally and purchasing this unit only if you need the additional power. If you want the most powerful diesel generator that is both fuel-efficient and durable, then this model is perfect for you. This model also comes with an impressive five-year warranty.

Pros

  • Strong, powerful 30,000 Starting kW
  • Double-walled base tank
  • External viewing window for inspections

Cons

  • Heavy item
  • Expensive

3. Cummins Onan QD

best RV diesel generator

Noise Level

66 dB

Fuel Tank Capacity

NA

Starting & Running Watts

12000 kW Starting

Runtime

12+ hours

Warranty

Yes, two-year warranty

The Cummins Onan QD 12000 single phase diesel generator is the best RV diesel generator on our list. It is completely enclosed and computer-controlled so that you receive constant steady energy. It is quiet at 66 dB and won't upset RV neighbors while camping and traveling. An electric fuel pump is easy to use with automatic glow plugs. The internal system is mounted to limit vibration, which is why these are the quietest generators on our list. Although this model is heavy, once installed, these units can be ported in and out of the RV on wheels with ease.

The Cummins Onan Quiet Diesel RV Generator is a smaller version of this model and whisper-quiet for users who prefer a more quiet engine. This model has half the power of the larger model, but still maintains most of the larger model's features. This model is an excellent choice for RV owners because it meets the National Park Service sound level requirements so you can confidently take it on any camping trip across the United States. If you often travel in your RV and need a reliable generator, these are your two best options. The sheer power on both of these models with quiet engines makes them perfect for traveling.

Pros

  • Completely enclosed system
  • Computer-controlled speed
  • Cummins Onan RV model meets National Park Service sound level requirements

Cons

  • Expensive
  • Heavy at 816 lbs.

4. Generac RD020ADAE

best diesel standby generator for home use

Noise Level

65 dB

Fuel Tank Capacity

33.5-gallon fuel tank capacity

Starting & Running Watts

20,000 kW Starting / 15,000 kW Running

Runtime

30+ hrs standard, 90+ hrs integrated runtime

Warranty

Yes, five-year limited warranty

The Generac RD020ADAE Protector Series is the best diesel standby generator for home use. It is powerful and robust, but not as large as other models. This diesel generator model is fully enclosed in a durable aluminum enclosure. At 65 dB for operation, this diesel generator is quiet and won't bother the neighbors. A smart battery charger ensures that you won't run out of battery when you need it most. This unit is a standby unit, which means that once set-up, your unit is set and can be turned on at any time. A multilingual LCD color-coded display comes with backlit buttons and allows you to monitor your machine at any time.

An integrated base tank gives homeowners the ability to run this generator for 90+ hours without refueling. The standard fuel tank provides 30+ hours of runtime. A UV resistant hose ensures that the sun doesn’t erode your hose. This model has less than 5% total harmonic distortion and is safe for sensitive electronics. An external vent provides a strong exhaust option to cool the generator while it runs.

REM wrote on Generac, "Installed this during a rebuild with doing so kept in mind during planning. No other service disconnect needed in my area and relocated my electrical system around it. Have the same at my mom’s home on a 16kW and most of the time she doesn’t know power has switched over.”

If you want a powerful diesel generator that is a great standby machine, we recommend this model.

Pros

  • Quiet Operation at 65 dB
  • Fully enclosed aluminum enclosure
  • Long runtime, 30+ or 90+ hours

Cons

  • Expensive
  • No voltage line or amps ratings on display

5. Larson Electronics

Best 20kw diesel generator

Noise Level

65 dB

Fuel Tank Capacity

25 gal fuel tank

Starting & Running Watts

20,000 kW Starting 15,000 kW Running

Runtime

19+ hours

Warranty

Yes, three-year warranty

The Larson Electronics 20kW portable generator is the best 20kw diesel generator on our list. At 65 dB, this diesel generator is not only fuel-efficient but also quiet. This generator includes a Deepsea controller panel that allows users to see into the machine. This can help you determine whether or not there are maintenance problems with the generator.

This diesel generator also has an automatic shutdown feature that causes the unit to shut down if the engine oil rises or the coolant is too low. This unit is made out of high-quality build materials, including stainless steel. This model is perfect for outdoor environments and is both rugged and durable.

For businesses, the telescoping tower capabilities on this unit are helpful. This diesel generator can be used to connect to a telescoping tower that offers large lights perfect for businesses that require outdoor lighting for their parking lot or walkways. The 25-gallon tank is not as large as most of the other units on our list, but if you want a smaller sized generator, then this can be helpful. This generator is an excellent purchase for homeowners or businesses who want a strong yet quiet 20,000 kW motor.

Pros

  • Strong 20,000 kW power
  • Quiet operation at 65 dB
  • Includes 25’ Telescoping Tower capabilities

Cons

  • 25 gal tank is lower than other generators on the list
  • Small size

Diesel Fuel Compared

Vs. Gas

Diesel fuel is more cost-effective than gasoline when it comes to running a generator. Diesel can be burned more slowly while providing the same level of energy, so a fuel tank on a diesel generator can provide greater runtime than its gasoline powered counterpart. Diesel fueled generators also tend to require fewer maintenance fixes over time. Diesel generators cost less to run but cost more to purchase upfront. They may be too expensive for homeowners on a budget.

Vs. Propane

Diesel fuel is more fuel-efficient compared to both gasoline and propane; however, propane is more fuel-efficient than gasoline. Propane is also environmentally friendly and a clean gas to burn. Propane generators are often the best choice for homeowners because propane also has a long shelf life. Propane generators often come in more portable sizes, quieter models, and are cheaper to purchase.


Standby vs. Portable Diesel Generators

Portable diesel generators tend to be louder and produce significantly less power compared to standby diesel generator models. Portable diesel generators tend to be cheaper and can easily be wheeled from location to location. However, standby diesel generators offer greater fuel storage options and far greater power. Standby generators are also already in place when storms arise or power goes out so they can immediately be activated. Portable models must be taken out of storage and plugged in. The standby diesel generator model might be more expensive, but it is more convenient, more powerful, and offers higher fuel storage.


Setting Up Diesel Generators

RVs/Camping

To install a diesel generator in your RV or camper, you must first start by finding the inlet receptacle and connecting the transfer switch. Both of these items must be directly connected to your diesel generator. We recommend working with a professional technician to ensure that your diesel generator is hooked up correctly.

Home

Most homeowners will want to hire a professional to set up their diesel generator because homeowner’s insurance only covers damages if the generator was installed by a professional. Each diesel generator has its own installation instructions but involves connecting the inlet receptacle to your home’s transfer switch.

Marine

It is dangerous to place a portable diesel generator on a boat. We recommend speaking with boating professionals to learn more about how to get additional power on your boat.


Frequently Asked Questions (FAQs)

Are diesel generators more efficient than gas?
Yes. Diesel generators are more fuel-efficient than gasoline generators. Diesel provides more energy and can, therefore, be burned more slowly. Diesel generators are also more cost-effective when compared with gasoline generators.
Is it safe to use diesel generators to power sensitive electronic devices?
Yes. Diesel generators can be used to power sensitive electronic devices as long as the total harmonic distortion is below 10%. Most diesel generators fall into this list, and all of the diesel generators on our list are below 10% THD.
How long do diesel generators last?
Diesel generators last approximately 30,000 to 40,000 hours before requiring significant maintenance. This tends to be approximately 15 to 45 years, depending on how often you run your generator.
Can I convert a diesel generator to gas?
Most diesel generators can convert to natural gas. However, this will impact the power of the machine. If you want to convert a diesel generator to gas, you may want to consider looking at our best natural gas generator list. If you still want to convert, speak to a professional diesel and natural gas technician.
Which oil should I use for my diesel generator?
You should use synthetic oil in your diesel generator. Check the instruction manual for specific instructions on the type of oil to use (5W-40 or 15W-40 synthetic oil, for example).
Do I need a professional to install diesel home generators? If so, how much does installation cost?
You can install your diesel home generator by yourself, or you can hire a professional. If you have never installed a home generator, we recommend hiring a professional. You can hire a professional for approximately $400 to $1,500 to perform the install. Diesel generators tend to be heavy and difficult to maneuver, so professional installation is often recommended.

Conclusion

Purchasing a diesel generator prepares you for power outages at home and at your business. If you need extreme power to run a large home or business with high wattage needs, we recommend the strong 30,000 kW Generac RD03022ADAE model.

If you want a more affordable diesel engine for your home and have fewer power needs, we recommend the impressive and portable Generac 6864. For RV enthusiasts, we recommend the Cummins Onan Quiet Diesel RV Generator.

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