What Size Generator To Run Furnace

If you’ve ever experienced a power outage during the cold winter months, you know how crucial it is to have a generator to keep your furnace running. However, determining the right generator size can be a confusing task. It’s important to select a generator that has enough power to not only keep your furnace operational but also handle any additional electrical loads in your home. In this article, we’ll guide you through the factors to consider and provide you with valuable insights on finding the right size generator to run your furnace, ensuring your comfort and safety during power outages.

How Does a Generator Power a Furnace?

Understanding the Basics

When it comes to powering a furnace, a generator plays a crucial role. A generator works by converting mechanical energy into electrical energy, which is then used to power various appliances in your home, including the furnace. It essentially acts as an alternative source of power during times of electrical outages or when the main power supply is not available.

Types of Furnaces

Before delving into the specifics of generator sizing, it is important to understand the different types of furnaces available. The three main types include natural gas or propane furnaces, oil furnaces, and electric furnaces. Each type has its unique power requirements, which should be taken into consideration when selecting a generator.

Power Requirements for Furnaces

Furnaces, regardless of their type, have different power requirements. It is crucial to know the power consumption of your furnace to ensure that the generator you choose can handle the load. The power consumption typically varies based on factors such as the furnace size, heating capacity, and overall efficiency. Having this information is essential for accurately sizing the generator for your specific furnace.

Factors to Consider When Choosing a Generator

Furnace Power Consumption

The first step in determining the appropriate generator size for your furnace is to know its power consumption. This information is usually specified by the manufacturer and can be found in the furnace’s manual or product specifications. The power consumption is typically measured in watts and represents the amount of energy required to operate the furnace.

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Starting vs. Running Watts

Another important factor to consider when selecting a generator is the difference between starting watts and running watts. Starting watts refer to the initial surge of power required by the furnace to start up, while running watts indicate the continuous power needed to keep the furnace running smoothly. It is crucial to choose a generator that can handle both the starting and running wattage of your furnace to avoid any power issues.

Efficiency Ratings

Efficiency ratings play a significant role in determining the power requirements of a furnace. Furnaces with high-efficiency ratings require less electrical power to generate the same amount of heat compared to less efficient models. Therefore, it is important to consider the efficiency rating of your furnace when calculating the generator size.

Multi-Appliance Considerations

While the focus is on powering the furnace, it is essential to consider other appliances that may run simultaneously during a power outage. Depending on individual needs, appliances such as refrigerators, lights, or even medical equipment may also need to be powered by the generator. Taking these additional appliances into account is crucial when determining the appropriate generator size.

Voltage Requirements

Different furnaces may have varying voltage requirements. It is important to ensure that the generator you choose matches the voltage needs of your furnace. Typically, most furnaces in residential settings operate on 120 volts or 240 volts. Choosing a generator with the correct voltage compatibility ensures that your furnace operates safely and efficiently.

Calculating the Generator Size for Your Furnace

Step 1: Determining Furnace Power Consumption

Begin by consulting the furnace’s manual or product specifications to determine the power consumption in watts. This information will be crucial for accurate sizing of the generator.

Step 2: Factoring in Starting Watts

To account for the initial surge of power required to start the furnace, consider the starting watts specified by the manufacturer. This will help you determine the generator size needed to handle the initial power demand.

Step 3: Considering Efficiency Ratings

Take into account the efficiency rating of your furnace. If your furnace has a high efficiency rating, it will consume less power to generate heat. This may allow for a smaller generator size, providing potential cost savings in the long run.

Step 4: Accounting for Other Appliances

Consider any additional appliances or equipment that may need to be powered simultaneously during a power outage. This could include lights, refrigerators, or medical devices. Take their power consumption into consideration when sizing the generator.

Step 5: Sizing Based on Voltage Requirements

Ensure that the generator you choose matches the voltage requirements of your furnace. Select a generator that can supply the correct voltage, typically either 120 volts or 240 volts, to ensure safe and efficient operation.

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Common Generator Sizes for Furnaces

Small Portable Generators

Small portable generators typically range in size from 1,000 watts to 3,000 watts. These generators are suitable for powering smaller furnaces with lower power consumption requirements. They are compact, lightweight, and easy to move around, making them a convenient option for emergency power needs.

Mid-Range Portable Generators

Mid-range portable generators range from 3,000 watts to 7,000 watts. These generators are more powerful and can handle larger furnaces with higher power consumption. They are still portable and offer a good balance between power output and convenience.

Large Portable Generators

Large portable generators have power outputs ranging from 7,000 watts to 10,000 watts. These generators are capable of handling larger furnaces or multiple appliances simultaneously. While they are heavier and less portable than smaller options, they provide more power for extended power outages or higher energy demands.

Standby or Whole House Generators

For those seeking a more permanent solution, standby or whole house generators are the ideal choice. These generators are designed to power the entire house, including the furnace, during a power outage. They are typically connected directly to the home’s electrical system and can provide a seamless transition between the main power supply and generator power.

Factors Affecting Generator Size Selection

Climate and Heating Needs

The climate and heating needs of your area play a significant role in determining the appropriate generator size. Colder climates often require larger furnaces, which in turn may require a larger generator size to meet the increased power requirements for heating.

Backup Power Duration

Consider the expected duration of backup power when selecting a generator size. If you anticipate extended power outages, a larger generator may be necessary to ensure the consistent operation of your furnace and other essential appliances.

Budget Constraints

Budget is an important factor to consider when choosing a generator size. While larger generators offer more power capabilities, they can also be more expensive. Assess your budgetary constraints to find the right balance between power needs and affordability.

Availability of Fuel

Take into account the availability of fuel for the generator. Some generators run on gasoline, while others may use propane or diesel. Consider the availability and cost of the preferred fuel option in your area to ensure a reliable and cost-effective power solution.

Benefits of Properly Sizing Your Generator

Ensuring Furnace Operation

Properly sizing your generator ensures that your furnace receives sufficient power to operate effectively during a power outage. This allows you to maintain a comfortable and warm indoor environment, even in challenging circumstances.

Reducing Risk of Generator Overloading

Choosing the right generator size minimizes the risk of overloading the generator. Overloading can lead to damage to the generator or appliances connected to it. By accurately sizing the generator, you can avoid potential problems and ensure the longevity of your equipment.

Optimizing Fuel Efficiency

A properly sized generator can operate more efficiently, consuming the appropriate amount of fuel needed to power your furnace. This translates into potential cost savings and a longer runtime for your generator.

Protecting Appliances and Electronics

Choosing the right generator size protects not only your furnace but also other appliances and electronics in your home. Insufficient power supply can lead to damage or malfunction of sensitive electronic devices. Avoiding these issues ensures the longevity of your valuable appliances and electronic equipment.

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Choosing the Right Generator for Your Furnace

Consulting Manufacturer Guidelines

Always consult the manufacturer’s guidelines or recommendations when selecting a generator for your furnace. The manufacturer’s specifications will provide valuable insights into the appropriate generator size for your specific furnace model.

Considering Future Expansion

Consider your future needs when selecting a generator size. If you anticipate expanding your home or adding new appliances, it may be wise to choose a generator that can accommodate potential increases in power requirements.

Assessing Noise Levels

Some generators can be quite noisy when operating. Consider the noise levels of different generator models and choose one that suits your comfort level and the proximity of your furnace to living spaces or bedrooms.

Portability and Storage

If portability is a priority, opt for a smaller, more lightweight generator that can be easily moved when needed. Also, consider the available storage space for your generator when making your selection.

Budgeting for Maintenance and Repairs

Factor in the cost of generator maintenance and potential repairs when setting your budget. Regular maintenance is essential to ensure the longevity and reliable operation of your generator.

Installation and Safety Considerations

Professional Installation

It is recommended to have your generator professionally installed, especially if you are opting for a standby or whole house generator. A professional installation ensures proper wiring, connection to the electrical system, and compliance with safety regulations.

Proper Ventilation

Generators emit carbon monoxide gas during operation. It is crucial to ensure proper ventilation to avoid the buildup of this potentially lethal gas. Install the generator in a well-ventilated area away from windows, doors, or vents that could allow carbon monoxide to enter your home.

Adhering to Safety Codes and Regulations

Adhere to all safety codes and regulations when installing and operating your generator. This includes following local electrical and building codes, using appropriate grounding, and using the correct electrical connections and outlets.

Carbon Monoxide Detection

Install carbon monoxide detectors in your home to provide an additional layer of safety. These detectors will alert you if there is a buildup of carbon monoxide gas, allowing you to take immediate action and prevent any potential harm.

Ensuring Proper Grounding

Proper grounding of your generator is crucial for safe operation. Consult a professional electrician to ensure that your generator is properly grounded and meets all safety requirements.

Additional Considerations for Different Types of Furnaces

Natural Gas or Propane Furnaces

If you have a natural gas or propane furnace, consider the availability of these fuels. Ensure that your generator is compatible with the specific fuel type your furnace uses to guarantee seamless operation during a power outage.

Oil Furnaces

Oil furnaces have different power requirements compared to other types. Ensure that your generator can provide the necessary power output for your oil furnace. It is also important to consider the availability of oil for your furnace during extended power outages.

Electric Furnaces

Electric furnaces typically have higher power consumption. Pay close attention to the wattage requirements of your electric furnace and select a generator that can handle the load. Additionally, be aware of the potential strain on your generator due to the high power demand of electric furnaces.


Choosing the correct generator size for your furnace is crucial to ensure reliable operation and provide peace of mind during power outages. By understanding the basics of generator power, considering the power requirements of your furnace, and evaluating various factors such as efficiency ratings, multi-appliance considerations, and voltage requirements, you can make an informed decision about the right generator for your needs. Prioritizing safety, reliability, and the specific needs of your furnace will lead you to select the optimal generator size for your home.

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Albert Stein

Starting this site about today's portable power options was an easy choice as it's one of my passions. Tech changes constantly so you need to make an informed decision before purchasing the wrong products. -Thank you.-

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