What Size Generator to Run a Furnace? (Electric And Gas Furnace)

To run a furnace during a power outage, you’ll need a generator that matches your furnace’s power needs. For a gas furnace, a 2000 to 3000-watt (2 to 3 kW) generator is usually enough. But for an electric furnace, which draws more power, you might need a generator as large as 10,000 to 12,000 watts (10 to 12 kW). Choosing the right size generator depends on your furnace type and its wattage requirements. In this guide on what size generator to run a furnace (electric and gas furnace), we’ll break down everything you need to know—from calculating wattage to understanding the best generator options. Keep reading to make sure you’re ready for any power outage!

Understanding the Power Needs of Furnaces

Choosing the right generator for your furnace isn’t just about buying any generator; it’s about matching your furnace’s specific power needs. Understanding these needs ensures your furnace runs smoothly without overloading the generator or causing damage. Whether you have a gas or electric furnace, knowing the starting and running watt requirements is key. Let’s explore why knowing these requirements is so crucial and how you can determine them accurately.

Why Knowing Furnace Power Requirements is Crucial

When it comes to running a furnace with a generator, understanding power requirements is non-negotiable. It helps you avoid common pitfalls like overloading the generator or underpowering the furnace. Not knowing this information could lead to more frequent shutdowns or even potential damage to your equipment.

• Starting Watts vs. Running Watts: All appliances, including furnaces, need an initial surge of power to start up. This is called “starting watts.” Once everything is running smoothly, the power needed drops to “running watts.” The difference between these two can be substantial. For instance, a furnace might need 1,200 watts (1.2 kW) to start but only 600 watts (0.6 kW) to keep running. If your generator can’t handle the starting watts, it may shut down or cause a power failure.
• Why Both Are Important: It’s crucial to account for both starting and running watts when selecting a generator. Running watts tell you what the generator can handle during continuous operation, while starting watts indicate its capacity to power up the furnace without tripping or shutting down. For a gas furnace, for example, a generator must cover both the blower fan’s starting watts and the running watts to maintain consistent operation without any interruptions.

In essence, understanding these two wattage requirements ensures you have the right generator that keeps your furnace running without a hitch, especially during power outages.

How to Determine Your Furnace’s Wattage Requirements

Before you purchase a generator, you need to determine exactly how much power your furnace requires. This step is crucial because it helps in calculating the appropriate generator size that can manage both starting and running wattages without failing.

• Where to Find Wattage Information: To find the wattage requirements for your furnace, start by checking the owner’s manual or looking for a label on the furnace itself. These labels often provide key details like voltage (V), amperage (A), and sometimes even wattage (W). If this information isn’t available on the unit, you can visit the manufacturer’s website or contact their customer service for the specific power requirements.
• Calculating Wattage Requirements Using Voltage and Amps: Understanding the calculation is straightforward. If you know the voltage and amps, you can easily find the wattage by using this simple formula:
  Watts = Volts x Amps
  Let’s break this down with an example:
  If a furnace operates at 240 volts (V) and draws 20 amps (A), the calculation for running wattage would be:
  Watts = 240 volts x 20 amps = 4800 watts (4.8 kW)
  This tells you the running watts needed. For the starting watts, which could be 1.5 times more, you might calculate:
  Starting Watts = 1.5 x Running Watts = 1.5 x 4800 watts = 7200 watts (7.2 kW)
  This means you’d need a generator capable of handling 7,200 watts (7.2 kW) to start the furnace and 4,800 watts (4.8 kW) to keep it running.
• Differences in Power Needs Between Gas and Electric Furnaces:
  • Gas Furnaces: Typically, gas furnaces use less power because they only need electricity for smaller components like the inducer motor, draft blower fan, and control board. For instance, a gas furnace with a 1/3 HP blower fan may need around 1,800 watts (1.8 kW) to start and 600 watts (0.6 kW) to keep running.
  • Electric Furnaces: In contrast, electric furnaces need more power overall since they rely entirely on electricity to generate heat. An electric furnace may need up to 10,000 watts (10 kW) or more, considering both the heating elements and the blower fan.

Detailed Table for Reference: Understanding Generator Size for Different Furnace Components

To help you determine the appropriate generator size for your furnace, the table below provides detailed information about the starting and running watts needed for various components. This information is particularly helpful when deciding on a generator for either a gas or electric furnace, as it gives you an idea of the power requirements for each type of furnace setup.

Component	Starting Watts	Running Watts	Example Furnace Type
¼ HP (0.25) Blower Fan	1100-1200W	350-400W	Gas Furnace
1/3 HP (0.33) Blower Fan	1700-1800W	550-600W	Gas Furnace
½ HP (0.5) Blower Fan	2300-2400W	750-800W	Gas Furnace
1 HP Blower Fan	4700-4800W	1500-1600W	Large Gas Furnace
Electric Furnace Heating Element	0W (No surge)	5000-10000W	Electric Furnace
Electric Furnace Blower Fan	1200W	400W	Electric Furnace

The table highlights that gas furnaces generally require less power compared to electric ones. It is critical to ensure your generator can cover both the starting and running watts listed here to avoid any operational issues.

Knowing your furnace’s power needs helps you make an informed choice when selecting a generator. Whether it’s a gas furnace needing fewer watts or an electric furnace requiring more power, understanding these requirements ensures your generator runs efficiently without causing disruptions or damage. In the next section, we will explore specific generator sizes needed for gas furnaces and how to calculate them effectively. Stay tuned to make the right decision for your home!. We have covered some of the top generators for home electronic appliances for you to check.

What Size Generator Do You Need for a Gas Furnace?

When it comes to gas furnaces, understanding the power requirements is essential for choosing the right generator size. Unlike electric furnaces, gas furnaces mainly use electricity for smaller components rather than heating the air. Knowing which parts require power and how much they need helps ensure your furnace runs smoothly during a power outage without overwhelming the generator.

Power Requirements of Gas Furnaces

Gas furnaces are efficient because they mainly rely on gas to produce heat, using electricity only to run certain components. Here’s a breakdown of the key parts that need power:

• Inducer Motor: This small motor helps expel harmful gases from the furnace. It doesn’t need a lot of power—typically around 100 to 200 watts to run.
• Draft Blower Fan: This is the component that requires the most power in a gas furnace. It blows the heated air through your home’s ducts. The size of the blower fan significantly affects the power requirement:
  • ¼ HP Blower Fan: Requires around 1,100 to 1,200 watts to start and 350 to 400 watts to run.
  • ½ HP Blower Fan: Needs about 2,300 to 2,400 watts to start and 750 to 800 watts to keep running.
  • 1 HP Blower Fan: Needs up to 4,800 watts to start and 1,500 to 1,600 watts to run.
• Control Board and Other Electronics: These components manage the furnace’s operations and use minimal power—usually under 100 watts.

Given these different requirements, the generator size will vary depending on the size of the blower fan and the total wattage needed for all components.

Calculating Generator Size for Different Gas Furnace Setups

To determine the right generator size for your gas furnace, you need to calculate the combined wattage of all the components. Here’s how to do it step-by-step:

1. Calculate Starting Watts for Each Component: Identify the component with the highest starting watts, usually the blower fan. For example, a ¼ HP blower fan requires around 1,200 watts to start.
2. Add the Running Watts of Other Components: Add the running watts for other components, such as the inducer motor and control board. If the inducer motor needs 150 watts and the control board 50 watts, that adds up to 200 watts.
3. Combine Starting and Running Watts: The total wattage requirement is the sum of the highest starting watts and the running watts of the other components. For a ¼ HP blower fan, this would be:
   • 1,200 watts (starting) + 200 watts (running) = 1,400 watts.
4. Include a Buffer for Safety: To avoid overloading the generator, add a buffer of about 20-25% to the total calculated watts. This ensures the generator isn’t running at maximum capacity all the time.

Table: Common Blower Fan Sizes and Corresponding Generator Size Recommendations

Blower Fan Size	Starting Watts	Running Watts	Recommended Generator Size (Including 25% Buffer)
¼ HP	1,200W	400W	2,000W (2 kW)
1/3 HP	1,800W	600W	2,500-3,000W (2.5-3 kW)
½ HP	2,400W	800W	3,500-4,000W (3.5-4 kW)
1 HP	4,800W	1,600W	6,500-8,000W (6.5-8 kW)

The table above provides a quick reference for choosing a generator size based on the size of your gas furnace’s blower fan. Adding a buffer is important to prevent the generator from overworking and to ensure longevity.

Example Calculations for Different Gas Furnace Configurations

To better understand the process, let’s walk through an example of calculating the generator size for a gas furnace with a ¼ HP blower fan:

1. Determine the Starting and Running Watts:
   • Blower Fan (¼ HP): 1,200 watts to start, 400 watts to run.
   • Inducer Motor: 100 watts to run.
   • Control Board: 50 watts to run.
2. Total running watts = 400 (blower fan) + 100 (inducer motor) + 50 (control board) = 550 watts.
3. Calculate Total Starting Watts:
   • The highest starting watt component is the blower fan at 1,200 watts. So, the total starting watts are 1,200 watts.
4. Combine Starting and Running Watts:
   • Starting watts (blower fan) + running watts (other components) = 1,200 + 550 = 1,750 watts.
5. Add a Buffer:
   • To account for a safety margin, add 25% to 1,750 watts:
     • Buffer = 1,750 x 0.25 = 437.5 watts.
     • Total generator size = 1,750 + 437.5 = 2,187.5 watts. Round up to a 2,200-watt (2.2 kW) generator.

If you plan to run additional appliances simultaneously, like lights or small electronics, you should include their wattage in the calculation to ensure the generator can handle the load.

Choosing the right generator size for a gas furnace involves understanding each component’s power needs and accounting for both starting and running watts. Adding a buffer is essential for preventing overload and extending the life of your generator. In the next section, we’ll explore the specific requirements for electric furnaces and how to size generators for those setups.

Why Inverter Generators Are Preferred for Running Furnaces

When it comes to running furnaces, especially during power outages, inverter generators are often the top choice. They provide a reliable source of electricity that’s essential for both gas and electric furnaces. Unlike conventional generators, inverter generators deliver cleaner and more stable power, which is crucial for the sensitive electronics found in modern furnaces. Let’s explore why a clean power supply is important and which inverter generators are ideal for this purpose.

Clean Power Output and Sensitive Electronics

Furnaces, particularly newer models, come equipped with sensitive electronic components, such as control boards, sensors, and blower motors. These components require a stable and clean power supply to function correctly. Here’s where the concept of harmonic distortion comes into play.

What is Harmonic Distortion?

Harmonic distortion refers to the fluctuations and “noise” in electrical power. Conventional generators can have high harmonic distortion, which means the electricity they produce isn’t as smooth or stable. This “dirty” power can cause electronic components to malfunction, wear out faster, or even fail altogether. For furnaces, especially those with advanced electronics, this can lead to costly repairs.

Why Inverter Generators Are Better:

Inverter generators produce what’s known as “clean power,” with less than 3% total harmonic distortion (THD). This low level of distortion ensures a smooth and stable current flow, making it safe for sensitive electronics like those in furnaces. Additionally, inverter generators adjust their engine speed based on the power demand, providing more consistent voltage and frequency. This helps prevent power surges that could damage the furnace’s components.

Choosing an inverter generator for your furnace reduces the risk of damaging its sensitive electronics and extends the life of your equipment, ensuring reliable operation during power outages.

Recommended Inverter Generators for Furnaces

Selecting the right inverter generator for your furnace involves considering several factors, including wattage capacity, runtime, and fuel efficiency. Here are some popular inverter generators that are well-suited for running both gas and electric furnaces:

• Honda EU2200i: Known for its reliability and low noise levels, the Honda EU2200i provides 2,200 starting watts and 1,800 running watts. It has a runtime of up to 8.1 hours on a single tank of gas, making it efficient for prolonged use. It’s an excellent choice for smaller furnaces or gas models with lower power needs.
• Champion 2000W Inverter Generator: This generator offers 2,000 starting watts and 1,700 running watts with a low THD output, ideal for sensitive electronics. It’s compact, lightweight, and provides a decent runtime of up to 11 hours at 25% load. It’s a great budget-friendly option.
• Westinghouse iGen2200: With 2,200 starting watts and 1,800 running watts, this generator features a fuel-efficient engine that can run up to 12 hours on a 1.2-gallon tank. It also offers low harmonic distortion, making it safe for furnaces and other home electronics.

Factors to Consider When Choosing an Inverter Generator:

• Wattage Capacity: Ensure the generator meets or exceeds the starting and running watts of your furnace.
• Runtime: Look for a generator that can run long enough to handle extended power outages without frequent refueling.
• Fuel Efficiency: More efficient models will save on fuel costs and provide longer runtimes, especially during prolonged outages.
• Noise Level: Quieter generators are ideal for residential use, especially if you’re running them near your living space.

By considering these factors, you can choose an inverter generator that best meets your furnace’s needs and your home’s requirements.

Avoiding Damage to Your Furnace When Using a Generator

Running a furnace on a generator can be convenient, but it comes with certain risks, especially if the generator doesn’t supply clean and stable power. Power fluctuations and surges can lead to damage, particularly to sensitive components within the furnace. Understanding these risks and how to mitigate them is crucial for protecting your furnace and ensuring it operates efficiently.

Potential Risks of Using Generators with Furnaces

Generators that do not provide clean power can cause significant harm to your furnace’s components. Here are the primary risks:

• Damage to the Blower Motor: The blower motor is one of the most sensitive parts of a furnace. Fluctuations in power can cause the motor to overheat or burn out. Replacing a blower motor can be costly and may require a professional technician.
• Control Board Failure: The control board is like the brain of your furnace, managing its functions and safety features. Dirty power from a generator with high harmonic distortion can fry the control board, leading to malfunction or complete failure.
• Reduced Efficiency and Increased Wear: Even if components don’t fail immediately, constant exposure to unstable power can wear them out faster, reducing the furnace’s overall efficiency and lifespan.

Tips to Prevent Furnace Damage from Power Fluctuations

To minimize the risks associated with running a furnace on a generator, consider the following practical tips:

• Use Surge Protectors: Installing surge protectors between the generator and the furnace can help absorb any sudden spikes in power, preventing them from reaching sensitive components.
• Ensure Proper Grounding: A properly grounded generator reduces the risk of electrical faults and makes the setup safer overall. Always follow the manufacturer’s instructions for grounding your generator.
• Regular Maintenance of the Generator: Keeping your generator well-maintained is key to ensuring a stable power supply. Regularly check for any signs of wear, replace filters, and keep the fuel system clean to avoid power fluctuations.
• Install a Transfer Switch: A transfer switch is a device that helps to safely switch the power source from the grid to the generator and back. It prevents back-feeding, which can be dangerous and potentially damage your home’s electrical system, including the furnace.

By following these tips, you can significantly reduce the risk of damage to your furnace when using a generator. Proper planning and setup ensure that you get the power you need without compromising the safety and functionality of your heating system.

Inverter generators are the preferred choice for running furnaces because of their clean power output and stable performance. However, it’s equally important to take precautions to protect your furnace from power fluctuations and potential damage when using any generator. By choosing the right generator and following safety tips, you can keep your furnace running smoothly during power outages, ensuring your home stays warm and safe.

Final Words!

Accurately calculating the generator size needed for both gas and electric furnaces is crucial to ensure smooth and safe operation during power outages. Knowing the starting and running watt requirements helps you pick the right generator that can handle the load without causing any disruptions or damage.

Inverter generators are highly recommended for furnaces because they provide clean and stable power, which protects sensitive electronics and extends the furnace’s lifespan. Following best practices, like using surge protectors, proper grounding, and transfer switches, can further minimize risks and keep your furnace safe.

For the proper results, it’s always wise to consult professionals for proper generator sizing and installation. This ensures your setup is efficient, safe, and tailored to your home’s specific needs, giving you peace of mind when the lights go out.

Related FAQs

What Type Of Generator Is Best For Running A Furnace?

Inverter generators are best as they provide clean, stable power, ideal for sensitive furnace electronics.

How Much Does It Cost To Run A Furnace On A Generator?

The cost depends on fuel type, generator efficiency, and runtime, but generally ranges from $10 to $30 per day.

Can I Use A Solar Generator To Run A Furnace?

Solar generators can run a furnace but need large battery capacity and solar panels, especially for electric furnaces.

What Is The Lifespan Of A Generator When Used With A Furnace?

With proper maintenance, most generators last 10 to 15 years, even with regular furnace use during outages.

Do I Need A Special Outlet For My Generator To Run A Furnace?

Yes, a transfer switch or dedicated outlet ensures safe and efficient power transfer from the generator to the furnace.

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