What Size Generator To Run Furnace?

No doubt furnace is one of the most essential items during the harsh cold. During a power outage for natural disasters or other reasons, you need to run your furnace. In this case, a Portable generator could be a lifesaver item indeed.

In this article,m we will help you determine what size generator you need to run your furnace.

Сan a Portable Generator Run a Furnace?

Yes, a portable generator can run a furnace. The crucial factor is to ensure the generator has sufficient capacity to meet the power requirements of the furnace. Portable generators are typically rated in watts, and your furnace’s power needs, measured in watts or BTUs, should be less than or equal to the generator’s output. Always consider the furnace’s starting and running watts to select the appropriate generator.

How To Choose the Correct Generator Size To Run a Furnace?

Choosing the correct generator size to run a furnace involves the following steps:

  1. Determine the Power Requirement of Your Furnace: Look at the furnace’s manual or data plate for its power usage, typically listed in watts or BTUs. If the power usage is in BTUs, convert it to watts (1 BTU = 0.293071 watts).
  2. Account for Starting and Running Watts: Appliances require more power to start (starting watts) than to continue running (running watts). Ensure your generator can accommodate the higher starting watts.
  3. Consider Other Appliances: If you plan to run other appliances during a power outage, their combined power requirement, along with the furnace’s, should be less than the generator’s output.
  4. Include a Buffer: Choosing a generator with a capacity of 20-25% more than your calculated need is advisable to accommodate additional power needs and prevent strain on the generator.
  5. Evaluate Generator Types: Portable generators are suitable for occasional, short-term use, while standby generators are ideal for frequent or prolonged outages.

Remember, a correctly sized generator ensures your furnace operates efficiently and safely during power outages.

Electricity Requirement of an Electric Furnace

The electricity requirement of an electric furnace is determined by its size and efficiency. Typically, electric furnaces are rated by the kilowatts (kW) of electricity they use. A small, energy-efficient furnace for a 1000- to 1500-square-foot area might use around 10kW. More extensive and less efficient models for more significant areas can consume 15 to 25kW or more.

As an example, let’s consider a 15 kW furnace. This equates to 15,000 watts. If the furnace runs for one hour, it will consume 15 kilowatt-hours (kWh) of electricity.

Remember that the actual power usage depends on factors such as the furnace’s efficiency, the size of the space being heated, and how cold it is outside. Therefore, your furnace may only sometimes operate at its maximum power usage level. For more accurate calculations, consult a heating professional or use the specifics in your furnace’s user manual.

Electricity Requirement of a Gas Furnace

While gas furnaces primarily use natural gas or propane as their heat source, they still require electricity for several vital functions. The electricity powers the blower motor (which circulates air throughout your home), igniter or pilot light, and other controls and safety devices.

The electricity usage of a gas furnace is usually measured in watts. Most residential gas furnaces require between 300 and 800 watts of electricity to power these components. However, the initial start-up of the furnace requires more power, often around 800 to 1,200 watts, due to the additional energy needed to ignite the stove and begin the initial air circulation process.

This is significantly less than the power requirements of an electric furnace, which can consume up to 15,000 to 20,000 watts. Nevertheless, it’s crucial to consider these power needs when planning a power backup solution like a generator.

How To Calculate the Electricity Requirement of a Furnace?

Calculating the electricity requirement of a furnace is relatively straightforward once you have the necessary information. Here are the steps:

  1. Identify the Power Rating: The power rating of the furnace, usually measured in kilowatts (kW) for electric furnaces or in watts for gas furnaces, can be found on the furnace’s nameplate or in the user manual.
  • This rating indicates the electricity it consumes for an electric furnace to produce heat.
  • For a gas furnace, this indicates the electricity required to power auxiliary components like the blower motor and ignitor.
  1. Account for Operating Time: Determine how long your furnace runs each day. This might depend on your climate, home insulation, personal comfort level, and the time of year. For estimation purposes, a furnace in a cold environment might run for 6-8 hours a day in winter.
  2. Calculate Daily Energy Consumption: Multiply the power rating by the number of hours the furnace operates daily to get the total daily energy consumption.
  • For electric furnaces, this calculation would be straightforward (Power in kW x Operating Hours = Energy Consumed in kWh).
  • For gas furnaces, remember that the power rating typically only accounts for auxiliary components, not the gas used to generate heat.
  1. Consider the Furnace Efficiency: Furnaces are not 100% efficient, meaning not all the energy consumed is converted into heat. You can use this to adjust your calculation if you have an efficiency rating for your furnace (usually represented as AFUE or Annual Fuel Utilization Efficiency).

Remember, these steps give a rough estimation of a furnace’s electricity requirement. For a more accurate assessment, consider consulting with an HVAC professional.

Will a Generator Damage My Furnace?

A generator will not damage your furnace if used correctly, but improper use can potentially cause harm. Here are some key considerations:

  1. Generator Size: Using an undersized generator can harm your furnace. Generators with insufficient capacity may not provide the steady, consistent power needed, causing the furnace to malfunction or even break down.
  2. Power Fluctuations: Generators sometimes produce fluctuations or ‘dirty power.’ These inconsistent power levels can harm sensitive electronics within your furnace.
  3. Correct Installation: For permanent generators, professional installation is vital. Incorrect installation can lead to backfeeding, a dangerous condition where electricity is sent back into utility lines.
  4. Maintenance: Regular generator maintenance is necessary. A poorly maintained generator may fail to provide the needed power or could break down entirely.
  5. Safe Operation: Overloading or running a generator continuously beyond its capacity can lead to overheating and damage.
  6. Use of a Transfer Switch: A transfer switch safely disconnects your house from the utility grid and connects it to the generator, preventing backfeeding and ensuring your generator can safely power your home.

So, while a generator can potentially harm a furnace if misused, correct generator sizing, proper installation, and regular maintenance can ensure safe, effective operation.

How to Connect the generator to the furnace?

Connecting a generator to a furnace requires careful attention to safety and proper electrical connections. Here’s a general guideline for connecting a generator to a furnace:

  1. Safety First: Before starting any work, ensure that the generator and furnace are turned off and the generator is properly grounded. Follow all safety precautions outlined in the generator and furnace manuals.
  2. Determine Power Source: Identify the power source of your furnace. Most furnaces require 120V power, while larger units may require 240V power. Confirm this information in your furnace’s manual, or consult a professional if you need clarification.
  3. Use a Transfer Switch: Install a transfer switch between the generator and your home’s electrical panel. A transfer switch ensures your generator power is safely isolated from the utility grid, preventing backfeeding and protecting utility workers. Consult a licensed electrician for proper installation.
  4. Identify Furnace Circuit: Locate the circuit breaker or disconnect switch that controls power to the furnace. Turn off the circuit breaker or disconnect the switch to reduce power from the main electrical panel.
  5. Connect Generator to Transfer Switch: Follow the manufacturer’s instructions to connect the generator to the transfer switch using appropriate electrical cables. Make sure to use lines of sufficient gauge to handle the generator’s power output.
  6. Connect Transfer Switch to Furnace: Connect the transfer switch to the furnace circuit. Again, follow the manufacturer’s instructions and ensure the connections are secure and properly tightened.
  7. Check Wiring: Double-check all wiring connections to ensure they are tight and secure. Loose links can lead to power interruptions or electrical hazards.
  8. Test the Setup: Once all connections are made, test the setup by starting the generator and turning on the furnace. Monitor for proper operation and check that the stove receives power from the generator.
  9. Follow Generator Operating Instructions: Always follow the operating instructions and safety guidelines provided by the generator manufacturer.

It’s important to note that connecting a generator to your furnace requires electrical expertise. If you need more confidence in your electrical knowledge and skills, hiring a licensed electrician to install is best to ensure it’s done safely and correctly.

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Rayan is an engineer, lives in a farmhouse. He has a passion for electronics and alternative energy. He loves to share his thoughts with other people. That is why he started the blog.

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