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This post is about what size generator to run furnace in 2023.

Understanding what size generator you need to run your furnace is essential for keeping your home warm and cozy during power outages. A properly sized generator ensures your furnace operates efficiently and provides the necessary heat during those cold winter months. In this comprehensive guide, we will dive into the importance of a generator during power outages, its role in running a furnace, and help you determine the ideal generator size for your specific needs.

We found that WEN 56380i Super Quiet 3800-Watt generator is the best to run the furnace in 2023.

The purpose of this guide is to help you determine the right size generator for your furnace. We will explain the different types of generators and their features, provide information on calculating your furnace's wattage requirements, and discuss fuel efficiency and run time considerations. Additionally, we will offer tips for generator safety and maintenance to ensure that your generator remains in optimal condition.

Let's get started.

Importance of a generator during power outages

Having a generator during power outages is crucial for maintaining comfort and warmth in your home. It helps prevent frozen pipes and potential water damage while ensuring the safety and well-being of your family. Generators also provide power for essential appliances and devices, minimizing disruptions to your daily routine.

A generator plays a vital role in running a furnace by supplying the necessary wattage for its operation. It supports the furnace's blower fan and motor, powers other heating appliances such as space heaters, and provides clean, stable power for sensitive electronics. A generator also allows for continuous heating during extended power outages, ensuring that your home remains comfortable.

What Size Generator to Run Furnace? Expert Tips for Warmth and Comfort Guaranteed

Understanding Furnace Power Requirements

Before selecting a generator to run your furnace, it's essential to understand your furnace's power requirements. This section will discuss the different types of furnaces and their wattage requirements, as well as the importance of considering additional appliances and loads when sizing your generator.

Types of furnaces

There are three primary types of furnaces: gas, electric, and oil. Each type has its own power requirements, which can impact the size of the generator you need.

Gas furnaces typically use a lower wattage than electric or oil furnaces because they rely on natural gas or propane as their primary fuel source. 

Electric furnaces, on the other hand, use electricity to produce heat, which can result in higher wattage demands. Similarly, oil furnaces use oil as fuel and typically have higher power requirements compared to gas furnaces.

Determining wattage requirements

To determine the wattage requirements of your furnace, you'll need to consider both its starting and running wattage. The starting wattage is the initial burst of power needed to start the motor, while the running wattage is the ongoing power required to operate the furnace. You can find these values in your furnace's owner's manual or on its label.

Alternatively, you can consult a professional HVAC technician for assistance in determining your furnace's power requirements.

Considering additional appliances and loads

When sizing your generator, it's crucial to account for other appliances and loads in your home that you may need to power during an outage. These can include essential items such as refrigerators, freezers, lighting, and sump pumps. Make a list of all the appliances you want to power and calculate their combined wattage requirements.

Adding this total to your furnace's wattage will give you a better idea of the overall power needs for your home, helping you choose the right size generator.

Generator Sizing Basics

Selecting the right size generator for your furnace is crucial to ensure your home stays warm and comfortable during power outages. This section will discuss the differences between running watts and starting watts, the advantages of inverter generators compared to conventional generators, and the benefits of dual fuel technology.

  • Running watts vs. starting watts
    When sizing a generator, it's important to understand the difference between running watts and starting watts. Running watts refer to the continuous power required by your furnace and other appliances, while starting watts are the initial surge of power needed to start the motors. Generators are rated by their maximum output, so you'll need a generator that can provide both the starting and running watts for your furnace and any additional appliances you plan to use. To determine the appropriate generator size, add your furnace's starting watts to the running watts of all other appliances you want to power.

  • Inverter generators vs. conventional generators
    Inverter generators offer several advantages over conventional generators, particularly for running sensitive electronics and appliances like furnaces. Inverter generators produce clean, stable power with less voltage fluctuation, making them suitable for powering sensitive electronics. They are also typically quieter and more fuel-efficient than conventional generators. However, inverter generators can be more expensive and may have lower maximum output. Depending on your needs, an inverter generator may be the best choice for running your furnace and other appliances during a power outage.

  • Dual fuel technology
    Dual fuel technology allows a generator to run on either gasoline or propane, offering more flexibility in fuel choice and increased runtime. This can be particularly beneficial during extended power outages when gasoline supplies may be limited. By having the option to switch between fuels, you can ensure that your generator continues to power your furnace and other appliances, keeping your home comfortable and safe. Additionally, propane has a longer shelf life than gasoline and produces fewer emissions, making it a more environmentally friendly option.

What Size Generator to Run Furnace : Best Generator To Run Furnace

Here is the detailed summary of top picked best generator to run furnace.

The WEN 3800 Watt Inverter can power even the most delicate devices with a total harmonic distortion of less than 1.2 percent when compared to a pure sine wave.

With its digital screen, you can quickly access any data you might require. Keep an eye on things like power output, fuel level, and how long the engine can operate.

The spark arrestor in our TT-30R outlet makes it legal to use in all national parks and forests while still providing up to 28 amps of quiet electricity.

The WEN 3800 Watt Inverter Generator's compact size, built-in wheels, and folding handle make it easy to move and store.

Even with the heat blowing, the capacity never surpassed the 20% level, and that was with me hooking up my refrigerator, gas furnace and blower, a couple of televisions, internet, lights, etc. 

Sufficient energy for all of your requirements during the cold season. 

This is our best pick generator to run furnace.

Specification for WEN 3800 Watt Inverter Generator

  • Running Wattage: 3400W
  • Starting Wattage: 3800W
  • Run Time:  8.5 Hours (on 50% load)
  • Fuel Tank Size: 2.2 Gallons
  • Noise Level: 51 dBA (from 22 feet)

Your purchase of Champion Power Equipment 200988 4500-Watt will be backed by Champion Support's three-year limited warranty and our support center network's 24/7/365 availability for FREE.

You can link up to two inverters together to boost output using the Parallel Kit (sold separately) and the included standard 50-amp RV outlet. Easy to carry thanks to the foldable design and indestructible tires.

With 4500 beginning watts, 3500 running watts, up to 14 hours run time, and 3150 running watts, up to 21 hours on propane, the Extended Run Time 61 dBA is perfect for recreational vehicles, tailgating, and camping.

Real-time monitoring of voltage, frequency, and working hours are provided by Economy Mode, and the EZ Start Dial makes starting the machine a breeze.

Since its running output (what it can consistently handle) is only 3150 watts or 26 amps, this can power your refrigerator, furnace fan, some lights, a TV, or a small window AC without the rest of the house's electrical appliances.

It is incredibly economical to operate because of its compact dimension.

Specification for Champion Power Equipment 200988 4500-Watt Generator

  • Running Wattage: 4500W
  • Starting Wattage: 3150W
  • Run Time: 14 hours on gas and 22 hours on propane (25% load)
  • Fuel Tank Size: 2.3 Gallon (Gasoline)
  • Noise Level: 61 dBA (from 22 feet)

If you need a backup power source for your residence, look no further than the Westinghouse WGen9500 Portable Generator, which has 12 500 peak watts and 9 500 running watts. 

Its heavy-duty 457cc 4-Stroke OHV Westinghouse Engine can operate for up to 12 hours on a single tank of gas. This generator's remote start key fob and push-button electric start make remote lighting a breeze. 

The User-friendly control panel highlights the unit's Transfer Switch Ready L14-30R and larger 14-50R outlets, which can power multiple large items at once with a single cable hookup, including an air conditioner, refrigerator, sump pump, lights, and an entertainment center. 

In order to keep you up-to-date with real-time data and routine upkeep, the VFT Data Center shows you data on volt output, frequency, and lifetime hours. The sturdy, never-flat wheels, foam grip handle, and lift bracket make it easy to move from place to place, allowing you to power your home, travel trailer, or work location quickly and easily. 

The generator can be easily started and stopped with the press of a button, thanks to the inclusion of an electronic start system. 

The air-cooled overhead valve construction of the 457cc Westinghouse engine allows for cooler, more fuel-efficient operation, while the cast iron cylinder sleeve ensures years of dependable use. 

In the event that low oil is discovered, the engine will shut down automatically to prevent damage. All required pollution levels are achieved, as set by the EPA and CARB. Also coverage for Labor and Components for Three Years and a Widespread System of Support

Specification for Westinghouse 12500 Watt Portable generator

  • Running Wattage: 9500W
  • Starting Wattage: 12500W
  • Run Time: 12 hours
  • Fuel Tank Size: 6.6 Gallon (Gasoline)

In the Eco-Mode, WEN 56225i generator's motor will automatically change its fuel consumption to maximize fuel economy, thereby extending the generator's run time and engine life.

Silent operation (only 53 decibels) means it won't disrupt your space where power is required the least.

Connect two inverter generators together via the WEN 56421 Parallel Connection Kit for a combined output of more than 2250 volts.

The WEN 2250W Inverter Generator has a gasoline shutoff feature as well. This function cuts gasoline to the generator, causing it to run until all of the gas in the carburetor has been used up before powering down. This prevents the buildup and obstructions produced by stale fuel inside the carburetor, requiring less servicing and extending the life of the device.

The WEN 2250 Watt Inverter is extremely portable thanks to its lightweight construction (it only weighs 48.5 pounds) and integrated carrying handle.

Using the WEN 56421 Parallel Connection Kit, you can easily connect two WEN inverter generators together to share power. Built-in overload protection and indicator lights join low-oil and low-fuel automatic shutdown to keep your generator and your devices secure from harm.

This would be perfect for running your furnace and some accompanying LED lights.

Specification for WEN 56225i Generator

  • Running Wattage: 1800W
  • Starting Wattage: 2250W
  • Run Time: 6 hours (on 50% load)
  • Fuel Tank Size: 1 Gallon (Gasoline)
  • Noise Level: 53 dBA

With its ability to run on both gasoline and liquid propane, the Champion Power Equipment 201052 3800-Watt Dual Fuel Portable Generator is a good choice for those in need of a portable power source. 

The electronic start is battery-operated and features Cold Start Technology for easy ignition even when temperatures are low. Start using your Dual-Fuel generator immediately with either gasoline or propane, thanks to our unique fuel selector switch. 

The 224cc Champion engine runs on gasoline, producing 4750 starting watts and 3800 running watts; at 50% load, it can operate for 14 hours on a full barrel of fuel. 

With a 20-pound propane tank, it can operate for 10.5 hours at 50% load, producing 4275 starting watts and 3420 running watts. This unit has a Volt Guard built-in surge protector that prevents overloads and keeps your equipment secure, and it only makes as much noise as a vacuum from 23 feet away (68 dBA).

There are multiple power receptacles, including a 120V 30A RV (TT-30R), a 120V 30A locking outlet (L5-30R), and two 120V 20A household outlets (5-20R). 

It is also  EPA  and CARB-compliant generator, as it is backed by a 3-year limited warranty and FREE lifetime technical assistance provided by Champion Support and our nationwide network of service centers.

Specification for Champion Power Equipment 201052 Generator

  • Running Wattage: 3,800W
  • Starting Wattage: 4750W
  • Run Time: 14 hours on Gas, 10.5 hours on propane
  • Fuel Tank Size: 4.7 Gallon
  • Noise Level: 68 dBA

Factors to Consider When Choosing Generator for Furnace 

When determining what size generator to run your furnace, there are several factors to consider beyond just the power output. It's important to think about fuel efficiency, run time, clean power for sensitive electronics, noise level, and portability to ensure you select the best generator for your needs.

  1. 1
    Fuel efficiency
    A generator's fuel efficiency is an important factor to consider, as it can impact operating costs and the amount of fuel you need to store. Look for generators with features such as eco-mode or variable engine speed, which can help conserve fuel and increase run time. Inverter generators are generally more fuel-efficient than conventional generators.

  2. 2
    Run time
    Generator run time is crucial during extended power outages. Ensure that the generator you choose can provide enough power to run your furnace and other essential appliances for an adequate amount of time. Check the manufacturer's specifications for run time at various load levels to determine if the generator will meet your needs.

  3. 3
    Clean power for sensitive electronics
    Your furnace may have sensitive electronics that require clean, stable power. Inverter generators produce a cleaner power output with fewer voltage fluctuations, making them an ideal choice for powering sensitive electronics. Make sure the generator you choose provides clean power to prevent damage to your furnace and other appliances.

  4. 4
    Noise level 
    Noise level is an important consideration, especially if you live in a residential area with noise restrictions or have neighbors close by. Inverter generators typically operate more quietly than conventional generators. Look for generators with features like noise-reducing enclosures or mufflers to minimize disruptions during use.

  5. 5
    Portability and storage
    The size and weight of the generator can impact its portability and storage requirements. Portable generators are designed for easy transport and storage, making them a popular choice for homeowners. If you plan to move your generator frequently or have limited storage space, consider a generator with wheels or a compact design to make transportation and storage more manageable.

Generator Size Recommendations to Run a Furnace - User Guide

Selecting the right size generator to run your furnace is crucial for efficient and reliable operation. Here are some recommendations based on the type of furnace you have, along with considerations for additional appliances and sensitive electronics.

Generator to Run Furnace - User Guide

Portable generator for small-to-medium-sized furnaces

For small-to-medium-sized furnaces, a portable generator can provide the necessary power to keep your home warm during a power outage. Look for a generator with enough wattage to accommodate your furnace's requirements and consider additional appliances you may want to power simultaneously.

A portable generator with a wattage range of 2,000 to 4,500 watts should be sufficient for most small-to-medium-sized furnaces.

Standby generator for larger furnaces and additional appliances

For larger furnaces or homes with multiple heating systems, a standby generator may be more appropriate. Standby generators are permanently installed and can provide power to your entire home, including your furnace and other essential appliances, during a power outage.

They typically have higher wattage capacities and can be powered by natural gas or propane, making them a convenient and reliable option for larger homes.

Inverter generator for energy-efficient furnaces and sensitive electronics

If your furnace is energy-efficient or has sensitive electronics, an inverter generator may be the best choice. Inverter generators produce cleaner power with fewer voltage fluctuations, making them ideal for powering sensitive electronics.

They are also more fuel-efficient and quieter than conventional generators. Look for an inverter generator with the appropriate wattage capacity to meet your furnace's power requirements and ensure a stable power supply for your heating system.

How Big Generator do you need to Power a Furnace?

Choosing a furnace generator requires careful consideration of several variables. It's important to consider the furnace's starting and running watts, as well as the power needs of any other machines that may be on at the same time.

A gas furnace can be powered by a generator producing only 2,000 watts. Electrical and gas heating systems have distinct power draws in actual use.

In contrast to an electric furnace, gas heaters have a low power consumption. Only the blower engine, draught inducer motor, and control board require electricity. However, electric furnaces can't function without a constant supply of energy.  

How to Figure Out How Much Electricity a Furnace Needs?

First, you'll need to know how many volts, amps, watts, or horsepower your furnace's parts use. Check the owner's manual, the stickers on your furnace, or the labels on the electrical parts. Then you can use this watt-volt-amp calculator to figure out how much power it needs.

The most important part of a gas furnace is the motor for the blower fan. To get the wattage, multiply the voltage by the amperage. The rated or running watts is the value you'll get.

The starting watts will be between two and three times this number. In the same way, if you know both the voltage and the wattage, you can divide the watts by the volts to find the amperage.

How to Pick a Generator to Power Your Furnace?

Here are a few things to consider when choosing a generator to power a furnace. Essential things to think about are:

  • The size of the furnace.
  • The type of fuel it uses.
  • The weather where the furnace will be used.

Size of the Furnace

When choosing a generator, the most important thing to consider is the furnace's size. About 50,000 BTUs is the average for a home furnace. But furnaces can be anywhere from 25,000 BTUs to more than 100,000 BTUs. Also important is the type of fuel that the furnace uses. Most homes have natural gas furnaces. But Oil and propane furnaces are also used.


It is another important thing to think about. It is important to consider the climate where the furnace will be used. Furnaces are made to work within a certain temperature range. A high-capacity generator may be required if the furnace is used in a very cold winter.

Furnace Wattage

A 3500-watt generator can power a furnace, but this is not recommended. The furnace will put a lot of stress on the generator, which wasn't made to handle that load.

A 4000-watt generator can run a furnace. But the time the generator can run will depend on the size and type of furnace. If the furnace is electric, the generator will need to be able to give it enough power to keep running.

FAQs About Right Size Generator To Run Furnace

Selecting the right size generator to run your furnace can be a daunting task, but with a little knowledge, you can make an informed decision. In this FAQ section, we address some common questions and concerns about generator sizing, types, and features to help you choose the best generator for your furnace.

Generator to Run Furnace - FAQ
  1. 1
    How do I calculate the wattage required to run my furnace and other essential appliances?
    To calculate the wattage required, first, check the power specifications of your furnace and appliances. Add the running watts of all devices you want to power simultaneously. For devices with starting watts, add the highest starting wattage to the total running watts.

  2. 2
    What is the difference between inverter generators and conventional generators when powering a furnace?
    Inverter generators produce cleaner, more stable power, making them ideal for sensitive electronics. Conventional generators may have larger fuel tanks and higher power output, but their power quality may not be suitable for some sensitive devices.

  3. 3
    Can a portable generator safely run a gas furnace during a power outage?
    Yes, a portable generator can safely run a gas furnace during a power outage if it's properly sized and installed with a transfer switch. Ensure the generator is placed outdoors and far from any vents or windows to avoid carbon monoxide poisoning.

  4. 4
    How does dual fuel technology benefit furnace operation during power outages?
    Dual fuel technology allows a generator to run on both gasoline and propane, providing flexibility in fuel choice, longer run times, and potentially lower operating costs.

  5. 5
    What size generator should I choose for an electric furnace?
    To determine the right size generator for an electric furnace, calculate the total wattage needed by adding the furnace's wattage and any additional appliances. Choose a generator with a power output that meets or exceeds this wattage requirement.

  6. 6
    How do I determine the running and starting watts for my furnace?
    Check the furnace's owner's manual or nameplate for wattage information. If only the amperage is listed, multiply it by the voltage (typically 120V or 240V) to determine the wattage. Consider both running watts and any additional starting watts.

  7. 7
    What are the safety precautions to consider when using a generator to power my furnace?
    Ensure proper ventilation for the generator, use a transfer switch, and store fuel safely. Also, regularly inspect and maintain the generator to ensure safe and reliable operation.

  8. 8
    How can I ensure clean power for my furnace and sensitive electronics during a power outage?
    Choose an inverter generator or a generator with built-in voltage regulation to provide clean, stable power for your furnace and sensitive electronics.

  9. 9
    Are there energy-efficient generator options for running a furnace?
    Inverter generators are generally more energy-efficient than conventional generators. Additionally, some generators feature eco-mode or variable engine speed, which can improve fuel efficiency.

  10. 10
    How do I properly install and maintain a generator for use with my furnace?
    Install the generator using a transfer switch, follow the manufacturer's guidelines for maintenance, and conduct regular inspections to ensure optimal performance.

  11. 11
    Can a solar generator provide enough power to run my furnace during a power outage?
    Solar generators can power smaller, energy-efficient furnaces in some cases, but they may not provide enough power for larger furnaces. Always check the generator's power output and compare it to your furnace's power requirements.

  12. 12
    What are the standout features to look for in a generator when selecting one to power my furnace?
    Look for features like clean power output, fuel efficiency, dual fuel technology, quiet operation, portability, and easy maintenance. These features will help ensure a reliable and efficient generator for your furnace needs.

Could a generator power your furnace?

There are two types of generators that can power a gas furnace: portable 

and permanent. Even though permanent generator installations are preferable for heating a house, portable generators are a viable alternative. 

If you need to run your furnace, it's important to get a generator with enough wattage. These are your most cost-effective choices in the event of a power outage, but they also tend to be the most elaborate. Here are some suggestions for using portable engines with heating systems.

A portable generator can be connected to a standard electrical socket by using a special adapter. Make sure the plug is connected to the generator and not the gas heater, though, if you plan on using both appliances at the same time. 

The generator needs to be located outside the home, away from any walls, and out of reach of any curious youngsters. Another crucial consideration when using a generator with your furnace is to hook it up using an extension cable of sufficient quality and stipulate that it be used with your specific model of furnace. If you don't, you might start a fire or get shocked by electricity.


Can I Use a Generator Without Worrying About Damaging My Furnace?

Perhaps you're concerned that using a generator will ruin your heating system. A 3500-watt generator will be adequate to power your home's furnace and other minor appliances. The use of a generator with a greater power output could be required for high-efficacy heating systems. In some cases, surge safety is helpful for high-efficiency devices. Unless you want to spend money on two generators, one of which would have to power the furnace.

Keep the generator outside if you need to use it. People in the building, particularly those near windows, are at risk from the generators' toxic exhaust fumes. Use only high-quality, manufacturer-recommended extension cables with your furnace. An electrical fire or shock could result from a power cable being installed improperly. Finally, it's critical to always double-check area regulations for safety measures

Is It Risky to Use a Generator with a Gas Furnace?

As long as you take the standard precautions when operating a generator, using one to power your gas furnace is perfectly secure. A generator should always be operated in a well-ventilated outdoor area.

If your home relies on a generator for heating and cooling, and you also have a lot of other items that need to be connected to it, you might want to invest in two. The first one can power your home's utilities, while the second can power your heating system. Because of this, your house will be safe from damage caused by the generator overworking itself.

Can a 2000-watt generator power a furnace?

A 2000-watt generator can power a furnace that uses oil or natural gas.

The wattage of these furnaces is 1600 watts when they first turn on and 600 watts when they are running.

On the other hand, if you go higher than a 2000-watt generator that can, that will be beneficial.

Generator Safety and Maintenance

Ensuring the safe and efficient operation of your generator is essential for the well-being of your household and the longevity of your equipment. Here are some essential safety and maintenance tips to follow when using a generator to power your furnace.

  • Proper installation (transfer switch)
    A crucial aspect of generator safety is proper installation, which includes using a transfer switch. A transfer switch isolates your home's electrical system from the main power grid, preventing back-feeding and potential hazards. Have a professional electrician install the transfer switch to ensure safe and proper operation.

  • Regular maintenance and inspection
    Like any piece of equipment, your generator requires regular maintenance and inspection. Check the oil level, air filter, and spark plugs routinely, and follow the manufacturer's recommendations for maintenance schedules. Periodically inspect the generator for signs of wear or damage, and address any issues promptly to ensure optimal performance and safety.

  • Safety precautions (ventilation, fuel storage)
    Safety precautions are vital when operating a generator. Always run your generator in a well-ventilated area to avoid carbon monoxide buildup. Never operate a generator inside your home, garage, or other enclosed spaces. Store fuel for your generator in approved containers and in a safe, cool, and dry location away from living areas and ignition sources. Following these precautions will help protect your home and family while using a generator to power your furnace.


In conclusion, understanding what size generator to run your furnace is crucial for maintaining the comfort and security of your home during power outages. By considering factors like your furnace type, wattage requirements, and additional appliance loads, you can make an informed decision about the most suitable generator for your needs.

We found that WEN 56380i Super Quiet 3800-Watt generator is the best to run the furnace in 2023.

Generator to Run Furnace-Summary

Selecting the right size generator to run your furnace is essential for ensuring efficient and reliable operation, preventing potential damage to both the furnace and the generator. It also guarantees that you have sufficient power to keep your home warm and cozy during a power outage.

A properly-sized generator for your furnace not only supplies power to keep it running but also contributes to the comfort and security of your home and family during power outages. With the right size generator to run your furnace, you can maintain a warm and well-lit living space, even when the grid is down.

If you're in need of a generator to power your gas furnace, there are many suitable options available, including portable and affordable models. In case you lose power again during a cold spell or other inclement weather, having the right size generator to run your furnace will be critical to keeping your home warm.

We hope this guide on what size generator to run your furnace will help you in deciding the best generator for your needs.