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Generators

The Ultimate Diesel Generator Buying Guide + 4 Generators Review

Diesel generators keep things running in the absence of grid power, whether it’s your household appliances, industrial machines, critical medical equipment, or power tools. Where there is no access to grid power, diesel generators rank high among your most accessible prime power options.

We have all had that one or two weeks to forget after a hurricane or violent winter storm left us without power. After the harrowing experience, most of us vow never to go through that again. That we will be prepared with a diesel standby generator fully set up by the next hurricane season. 

Whether it lasts a short time or drags on for days, a power outage is a major inconvenience. Without a way to power your appliances, your food will spoil because of a lack of refrigerated storage. 

Without a backup power supply, you will struggle to keep warm, while at the workshop work will grind to a halt. A diesel standby generator will ensure the disruption of a blackout is only momentary. In the medical field, it will literally save lives.

This guide will cover everything you need to know about diesel generators. We will go through the different types available, discuss how they work, and give you tips on what you need to look for when shopping for one. The buying guide will go one better and review five of your best diesel power generator options.

Let’s get started!

Types of Diesel Generators

Mobile diesel generator for emergency electric power

Diesel generators burn and convert the chemical energy contained in diesel fuel to mechanical energy that it then uses to generate electricity. In short, they use an internal combustion engine to produce electricity. Self-contained on the generator will be a fuel tank, a radiator, and a control panel.

The electrical energy diesel generators produce can run electrical equipment varying from small household appliances to large industrial machines. Because of their versatility and relative fuel economy when compared to alternative power sources, they can be deployed to various applications as either standby or prime power sources.

It’s important to base your choice of diesel generator on your power needs. Below we discuss the types you will be choosing from.

Portable generators

Portable generators are designed to be easy to move and transport. Because of their small size, these generators have limited capacity and are only suitable for temporary power needs. 

Because of their portability, these generators are perfect for use in remote areas. There are also models available that can meet the immediate power needs of a mid-sized home. The smallest portable generators work best for tailgating and camping, and other applications where you are powering small appliances and devices.

Inverter diesel generators

Inverter generators are a type of portable generator with an electronic upgrade that automatically adjusts engine speed to meet the power needs of the connected load. They also convert DC to AC power at a much higher frequency, a quality that allows them to prevent power fluctuations, which is a common weakness of traditional diesel generators.

In terms of fuel consumption, inverter generators are far more efficient. Their ability to regulate engine speed based on load saves fuel. Because they don’t use as much fuel, their fuel tanks are usually smaller than other generators of similar capacity. 

Inverter generators also run more quietly than standard diesel generators, the larger ones of which can make quite a racket. For this reason, inverter generators are perfect for camping and for people who live in areas where there are strict rules on noise pollution.

Standby generators

Standby generators are typically larger and heavier than the other types of generators we have discussed. Once installed, they will remain stationary unless they really need to be moved. 

Suitable for facilities with considerable power needs, diesel standby generators are designed to automatically kick in once grid power is lost. For the purposes of this buying guide, we will mostly refer to diesel standby generators for the home.

Where there is a planned or unexpected outage, standby generators are an excellent backup that will save you from having to shut your business down. At home, these generators will have the capacity to meet all your power needs. It will prevent food spoilage and keep your home heated in winter and well cooled in summer.

Are Diesel Generators Better Than Gas?

Diesel generator for emergency power supply

You may be familiar with gasoline generators and have one in your garage right now. So why are we recommending diesel generators specifically? Gas generators have their place and will be cheaper, but diesel generators have numerous benefits over their gasoline cousins.

More fuel-efficient

Diesel generators are far more fuel-efficient, generating more power for the same amount of fuel than gasoline generators. This makes them a good choice for large facilities and applications where they are the main source of electricity. 

Diesel has more energy density and is, therefore, more cost-efficient than gasoline. It also stores better and is less flammable, which makes it a safer option for home and commercial environments. 

Stronger build quality

Another advantage of choosing diesel generators is their sturdy build quality. Because they have to withstand tough use conditions and handle prolonged use, their manufacturers take extra care to ensure they are durable. 

As we have said, diesel generators cost more to buy than gas generators. In fact, by as much as three times. But over time, they are less expensive to run, and, with good maintenance, they will outlast gas generators by some margin. 

From an environmental perspective, diesel generators aren’t the most sustainable, but they are better than gas generators. Diesel engines emit less carbon monoxide than gas. However, they produce more carbon soot and would therefore need to be operated in well-ventilated spaces.

Now that we have a clearer understanding of diesel generators, let’s discuss some shopping tips.

Diesel Generator Buying Guide

If you are buying a diesel standby generator after a storm has hit and you are already without power, all the local generator merchants will likely be dealing with a rush of customers. They may not have the time to fill your knowledge gaps on what diesel generator is best for your needs. 

Good thing you are reading this first. Below we will answer a few questions you have to answer to decide what type and size of diesel generator you need to buy.

What are your power needs?

In other words, what is the combined wattage of all the appliances and electronic devices you need to run during a power outage? 

Your first task is to get a pen and paper and make a list of everything you need to power during a blackout. Beside each item, write down the number of watts it consumes. All home appliances will have a nameplate with the rated watts and other specifications. If you can’t find them for some appliances, call up the manufacturer or the retailer you bought them from.

Tally the watt values to get the total wattage for your standby power needs. If you will run all your appliances at the same time, you must add their starting watts to that total as well. The safer approach, however, is to simply start your appliances in order, with the most power-hungry connected first.

What’s the difference between startup and running watts?

Manufacturers want to sell more units and often advertise a generator’s peak or surge watts as its capacity. You must know that this is only the highest wattage a generator can supply, which it can only sustain for a short period of time. After it, the generator must revert to its ‘running watts’. 

Running watts represent the maximum power the generator can supply continuously. This is the most important number for anyone shopping for a diesel generator. 

Not to say you should ignore the peak watts spec as it allows the generator to briefly exceed its running capacity when you first connect an appliance that requires more power to start. 

Remember, appliances require more power to start than they need to run. So a generator’s surge watts compensate for the excess power electric motors need to start up. Without the extra watts, a generator would overload and may burn its motor or catch fire, or the inbuilt circuit breaker would simply engage and shut it down.

In essence, a generator may have the capacity to run an appliance but lack enough generating power to start it. So, it is critical to have a clear idea of your total standby power requirements when sizing your diesel generator. The Generac company provides a handy standby generator sizing calculator here.

Choose a generator that can start as well as run whatever you intend to power. To be safe, your total standby power requirements should not exceed 75 percent of the running watts rating for the generator you are considering. An underpowered generator will not do an efficient job and will have a short lifespan.

Watts and volts… how do they affect generator choice?

To understand the relationship between watts and volts, we first need to talk about amps (or amperes, in full.) Amps measure the volume of electrons in an electrical circuit. It’s like the volume of water passing through a certain point in a continuous pipe. 

The flow of electrons through an electrical conductor is what we know as electric current. Because of something called resistance, electrical cables are rated for amps, which is the maximum volume of electrons they can carry. A thin wire will have greater resistance to electrical flow than a thick one.

Volts, on the other hand, are a measure of the speed of electric current as it passes through a certain point. Using our water example, volts would equate to the pressure of water as it passes a certain point in a pipe. This brings us to watts:

Watts are the product of volts and watts, meaning you get them by multiplying volts by amps. They measure the rate of power flow through a circuit. So, in effect, watts and volts cannot exist without the other. 

Why is it important to know both a generator’s ratings for watts and volts?

While watts specify the total power an appliance needs to run, voltage specifies how fast that power needs to be supplied. Some appliances need their power supplied at a specific speed, which may be a faster rate than a generator is capable of. 

An example is well pumps. Some are rated at 120V and others at 240V, even though they will both require the same amperage to run. In this case, it is essential to know both the voltage and wattage requirements for the appliances and tools you intend to power in order to correctly size your standby generator.

Large diesel standby generators will be rated in kilowatts (kW). A kilowatt is simply any given wattage value divided by 1,000. So 2,000 watts becomes 2 kW.

What Should I Look For When Buying a Diesel Generator?

Diesel standby generators are a long-term investment for your home. If you make a poor choice, you are going to be living with it for a long time. To make sure you don’t look back at your generator purchase with regret, here are features you must keep in mind when you make your selection:

Starting mechanism

There are different generator starting mechanisms, which come with varying levels of convenience. Your options range between electric key, push start button, remote start, and automatic start. 

While a remote start will allow you to start the generator from inside the house, which is convenient if a power cut happens at night or in bad weather, an auto-start works better. 

With an auto transfer switch, the generator starts automatically as soon as grid power is lost. This is especially convenient when power goes out in your absence.

Automatic shutoff

Important for safety than convenience is an automatic shutoff feature. Essentially, this switch turns off the generator if it is overheating, the oil level is low, or too much carbon monoxide has accumulated around the generator. This prevents generator damage and protects you from injuries caused by the generator catching fire due to an overload short circuit.

Fuel capacity

You don’t want to have to wake up in the middle of the night to top up fuel. So it’s important that you choose a generator with a good tank capacity. It helps that the larger diesel standby generators have their tank capacity expressed in liters used per hour. A fuel gauge will help you monitor the fuel level to avoid any surprises.

Automatic voltage regulator

Do you intend to run sensitive medical equipment on your diesel generator? If you will, you will need it to have an automatic voltage regulator. This feature ensures a stable power output by compensating for any voltage load variations.

Warranty, delivery, and installation

Though technically not features, you will need to buy from a manufacturer or vendor that offers a reasonably long warranty. Large standby generators can have warranties as long as 5 years.

As standby diesel generators are heavy and unwieldy, they need specialized equipment to transport and install them. Make sure the supplier offers delivery and installation. If the delivery is not free, make sure to include the cost in your final price.

How to Use a Diesel Standby Generator Safely

Standby diesel generators are typically stationary machines that are permanently installed on the property. Choose a spot that is close to your home or facility’s electric panel or breaker box. 

You will need to cast a concrete slab at least 20 feet from the house. Make sure the surface is level and that the generator’s exhaust directs fumes and soot away from windows and doors to protect your indoor air quality. 

If you are hooking up the diesel power generator to your home’s electric service, you will need a transfer switch. For that work, you must hire a certified electrician to make sure the installation is safe and compliant with local codes. 

For your safety, avoid starting fires anywhere near the generator and keep any sparky tools well away from it. If not using an auto-start, always turn the generator on before plugging your appliances in.

Diesel generators are known for their noise. So while newer models run much quieter than old ones, you may need some soundproofing to dampen the noise. There are several ways you reduce the noise your generator makes, including:

  • Noise deflectors or soundproofing enclosures,
  • Adding rubber feet and other anti-vibration mounts
  • Upgrading the exhaust muffler with a larger one

Diesel generators require very little maintenance besides regular oil changes, fuel and air filter replacements, and periodic inspections by a qualified person. Wifi-ready wireless digital monitors are some of the modern enhancements that can help you monitor your standby generator and tell you what it is and is not doing.

Do not attempt to repair the generator yourself, neither should you ever tamper with the outer casing. Should you encounter any problems with the generator or feel that something is amiss, call a qualified technician or the one recommended by the manufacturer.

Ready to shop for a diesel generator? Below we review our top picks for the best diesel generators for home use.

Review of 4 the Top-Rated Diesel Generators

Generac 6864 Diesel Powered Portable Generator

Sometimes a proper whole house standby generator is in the plans but a power emergency hits before the budget has come together. Faced with a harsh winter or a scorching summer, you may be forced into buying a smaller diesel generator that can run just your essential appliances.

The Generac 6864 is possibly the most powerful diesel generator you can find in the ‘portable’ class. We highlight ‘portable’ simply because you can move this generator around, not that you can lift it and easily lug it around. It is heavy, which is why it is designed with an integrated lifting eye.

Powered by a tier 4 EPA and CARB compliant Yanmar L100W engine, this 5KW generator has enough power for home use during a power emergency. With a running watts rating of 5,000 watts, you can run your most critical appliances and lights for over 24 hours on the same tank of diesel. In fact, the generator can run for 32.4 hours on 50 percent load.

If you have to intermittently run a few power-hungry electric motors, like a sump pump, the generator can summon a bit more power to start them, thanks to its 5,500 peak wattage.

We love how fabulously fuel-efficient the Generac 6864 is, but we were just as impressed by the output options it offers. These include four 120, 20 amp outlets for standard appliances and two twist locks – a 120V and a 120/240V with a voltage selector switch. All outlets have dedicated circuit breakers in case of short circuits or overloads.

For the price of this generator, we however didn’t like that you have to buy the battery and portability kit (wheels and handles) separately. You can’t run the generator without the battery, while the wheel kit is needed if you are going to be moving it in and out of storage. Add the heavy duty cable that you will also have to buy and the costs really pile up.

SUMMARY

Generac 6864

Pros

  • High power capacity for a portable generator
  • Excellent fuel economy
  • Large fuel tank saves you from constant refilling
  • Sturdy steel roll cage with lifting eye for easier transportation
  • Has an electric start option for those that can’t handle the pull start
  • Fuel tank cap has a fuel gauge fitted to it that makes it easy to check the diesel level

Cons

  • Peak wattage is rather low when you consider the running wattage
  • Expensive, especially when you factor in the battery and portability kits that you have to buy separately
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Cummins Onan Quiet Diesel RV Generator 10HDKCA-11506

It’s likely that you are looking for a diesel generator for home, not for an RV or motorhome. But there are several reasons why this 10kW RV generator from Cummins may still be perfect for you. 

One attraction is that, when used as a standby generator for home, it produces just as sufficient power. Cummins, in fact, boldly claims that this 10kW generator can run three rooftop A/Cs with 4kW to spare. In a home setting, that’s enough power for your major appliances during a blackout.

An important quality of this generator that adapts it well specifically for RV owners is its low noise output. Its noise level apparently is well within the limit permissible in US national parks. We figure that little detail will be of particular interest if you live in a residential estate with strict rules on generator noise.

The whole design of the generator, in fact, seems to focus on curbing its noise output. A unique housing encloses the muffler and cooling system, reducing noise and simplifying installation in the process. A four-point, fully focalized internal mounting system also reduces vibration, which helps to curb noise.

The Cummins Onan Quiet Series, 10kW Diesel RV Generator has other features that simplify maintenance and operation and improve safety. Remote starting capability means you will not have to leave the house to go and switch it on when the power goes out. Computer control also enables constant speed operation.

A few other features that stand out are the USDA-approved spark arresting muffler, hour meter, maintenance-free electronic governor, waterproof connector for safe and convenient remote operation, low oil alert, digital voltage regulator, built-in self-diagnostic capabilities, and instant a one-touch stop.

SUMMARY

Cummins Onan Quiet Diesel RV Generator

Pros

  • Plenty of power for standby home use
  • Excellent noise reduction capability
  • Clean, Pure Sine Wave Power that protects sensitive equipment
  • Electric fuel pump provides reliable fuel delivery
  • Easy -to-reach top-mounted switch and coolant checking and filling
  • An easy-latch side door provides easy access for maintenance and service
  • Self-diagnostic capabilities that simplify troubleshooting

Cons

  • Not built specifically for home use
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20 kW Portable Diesel Generator – DeepSea Controller

20 kW Portable Generator – DeepSea Controller

If you own a large home, you should now pay more attention. The 20kW portable generator with DeepSea controller by Larson Electronics has power to run a few houses. With a powerful 1,800 rpm, four-cylinder diesel engine, the diesel generator supports 120/240V 60 Hz installation at 43.11 amps. 

This generator has a running capacity of 20kW and peaks at 22kW, which is more than enough to meet the standby power needs for a large home. It has five power outputs and an ATS plug, making it a perfect fit for power hungry operations, including construction sites and remote mining camps. 

We also like the diesel standby generator’s robust build quality, with a steel construction and a powder coated finish that protects it from the ravages of the weather. Though the manufacturer classifies it as portable, it hardly is, weighing 1,543 lbs before it is fueled. 

Because of its weight, this 20kW generator is more suitable as a stationary installation. Speaking of fuel, the generator consumes 1.23 gallons of diesel on full load, which isn’t a lot for 20,000 watts of electricity.

Without doubt, one of the most notable features of this brushless generator is the DeepSea controller. The controller itself features a wide viewing panel that allows you to monitor every aspect of the generator, including runtime, frequency, and battery voltage. 

Great for your safety and for the health of the generator, the controller has support for programmable notifications for high water temperature, low oil pressure, under/over speed, and under/over voltage. The generator will automatically shut off if it detects low water temperature, low engine oil pressure, low coolant, overspeed, and or an overcrank.

SUMMARY

Portable Diesel Generator – DeepSea

Pros

  • Great fuel efficiency
  • Robust build adapts it to demanding work applications
  • Designed with several safety and protective features
  • Integrated lifting eye for easy transportation
  • Low noise, thanks to overall design and noise-reduction features
  • Auto start option enhances convenience

Cons

  • Though said to be portable, the generator is heavy
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Winco DR175F4 WINPOWER Diesel Generator

If we were to pick one truly powerful diesel standby generator that would power everything in your home, it would be the Winco DR175F4 3-phase diesel generator. A literal diesel power station for your whole street or office block, this generator outputs an incredible 175,000W. Though a considerable investment, it will deliver years worth of peace of mind and is well worth its price if you live in an outage-prone region.

With this monster diesel generator installed, your power needs are covered, whether they are prime or emergency. It is our recommendation if grid power in your neck of the woods is not reliable.  This diesel generator can be set at 120/208 volt 3 phase or 277/480 volt 3 phase and, with a massive 560-gallon fuel tank, will guarantee days of runtime at standard household loads.

You won’t have to worry about frying your sensitive equipment as the generator’s power quality rates at less than 5 percent total harmonic distortion. With an integrated 200-amps smart transfer switch, you also won’t have to stress about the inconvenience of trotting outside in the middle of the night and in bad weather to manually turn the generator on.

The 175kW diesel power generator has digital control capability, thanks to the Deep Sea 7310 MKII Controller. The digital controller is useful for remote starting and automatic safety shutdowns and will also provide immediate performance information. 

The feature-rich DeepSea digital controller supports 7 languages, has 8 configurable inputs, provides both current and historical status information, and can be configured as a remote display module. Power-up can be configured in stop, manual, or auto mode.

SUMMARY

Winco DR175F4 WINPOWER Diesel

Pros

  • Capacity to meet the prime power needs of homes of all sizes
  • Powder-coated, corrosion-resistant aluminum finish provides protection from weather damage
  • Multilingual digital controller avails useful information on the operating condition
  • Industrial build quality ensures durability
  • Incorporates a marine-grade 5-amp battery charger

Cons

  • Expensive
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FAQs

Are diesel generators better than gas?

While noisier and more expensive to buy than gas generators, diesel generators have more fuel economy and produce significantly low levels of carbon monoxide. They also have a stronger build quality and require little maintenance. In terms of safety, diesel fuel is also less flammable than gasoline.

What are the preventive maintenance tasks carried out for diesel generators?

Diesel generators are renowned for their strong, reliable build quality and require minimal maintenance work. Standard maintenance tasks include inspecting for possible damage, topping oil and coolant, and replacing air and fuel filters.

What are the common problems of diesel generators?

Most diesel generator failures are caused by low oil, short circuits, overloads, and overheating caused by low water levels. Low battery voltage is also a common factor in starting problems.

How long can I run my diesel generator?

Diesel standby generator runtime depends on the fuel tank’s capacity. But, whatever the capacity of the fuel tank is, the recommendation is not to run your generator for more than 500 hours at a time. These 500 hours translate to about 3 weeks of continuous operation.

Do they make small portable diesel generators?

There aren’t many small portable diesel generators available, with options starting at 3.5kVA. A possible reason is manufacturers haven’t found a viable way to make truly efficient small diesel generators whose power output compensates for the noise and smoke they would make. Another is that the generator would still be too heavy for the power they produce.

Final Word

You may never know how much of a convenience and lifesaver a diesel standby generator is until a hurricane rolls through town, leaving you without power. If you have yet to invest in a home standby generator, we trust you now have all the information and shopping options you need to make the right choice so you will be prepared for the next outage.