how big of generator to run a furnace

3 min read 16-01-2025

Knowing how big of a generator you need to run your furnace is crucial for ensuring warmth during power outages. This guide will help you determine the right size generator for your heating needs, avoiding costly mistakes and ensuring your comfort. Choosing the wrong size generator can leave you shivering in the cold, or worse, damage your equipment. Let's get started.

Understanding Your Furnace's Power Requirements

The first step in sizing a generator is to determine your furnace's starting and running wattage. This information is vital; a generator needs to provide sufficient power not only to keep the furnace running but also to overcome the initial surge of electricity required to start it.

Finding Your Furnace's Wattage:

Check the Manufacturer's Specs: Look for the nameplate on the furnace itself. This usually indicates the unit's amperage and voltage.
Consult Your Owner's Manual: The manual will specify the electrical requirements of your furnace.
Look at Your Electrical Panel: Find the breaker for your furnace; the amperage rating is often listed.

Calculating Wattage:

Once you know the voltage (usually 120V or 240V) and amperage (Amps), use this formula:

Wattage = Voltage (V) x Amperage (A)

For example, a furnace drawing 20 Amps at 240V has a running wattage of 4800W (240V x 20A = 4800W). Remember, this is the running wattage.

Starting Wattage (Surge Wattage):

Furnaces, like most motors, require significantly more power to start than to run continuously. The starting wattage, often called surge wattage, can be 3 to 5 times higher than the running wattage. Therefore, our 4800W example furnace might require 14,400W to 24,000W (4800W x 3-5 = 14400W-24000W) to initially start.

Generator Sizing: Running vs. Starting Wattage

You need a generator that can handle both the running and starting wattage of your furnace. Choosing a generator based solely on the running wattage is a recipe for failure. The generator may not be able to overcome the initial surge, causing it to overload and shut down.

Adding Safety Margin:

It's best to add a safety margin to your wattage calculations. Consider adding 20-30% extra capacity to the total wattage to account for other appliances you might want to run simultaneously (lights, refrigerator).

Example:

If your furnace has a 4800W running wattage and a 19,200W starting wattage, and you want a 20% safety margin, you should look for a generator with a minimum capacity of approximately 23,040W (19200W + (19200W * 0.20) = 23040W).

Types of Generators

Standby Generators: These permanently installed generators automatically turn on when the power goes out. They're ideal for reliable backup power, but they're expensive.
Portable Generators: These are less expensive and more portable but require manual operation.

The best type for you depends on your budget and power needs.

Choosing the Right Generator: Key Considerations

Wattage: As discussed, this is the most critical factor. Choose a generator with sufficient wattage to handle both starting and running loads, plus a safety margin.
Fuel Type: Gasoline, propane, or natural gas generators are available. Propane and natural gas generators often run cleaner and quieter.
Run Time: How long do you need the generator to run? This influences fuel tank size.
Features: Automatic transfer switches, electric start, and other features can enhance convenience and safety.

Frequently Asked Questions (FAQ)

Q: Can I run my furnace on a smaller generator?

A: While technically possible for a short time with some generators, it's risky and can lead to damage to both the generator and the furnace. A consistently underpowered generator will likely fail to start your furnace or quickly shut down.

Q: What other appliances should I consider when sizing my generator?

A: Consider the wattage needs of other essential appliances like a refrigerator, sump pump, and crucial lighting. Add their wattage requirements to your furnace's wattage needs.

Q: How often should I service my generator?

A: Regular maintenance is crucial for optimal performance and safety. Consult your owner's manual for specific recommendations.

Conclusion

Choosing the right size generator for your furnace is a critical decision. By carefully calculating your furnace's power requirements, considering starting wattage, adding a safety margin, and researching different generator types, you can ensure you stay warm and safe during power outages. Remember to consult with a qualified electrician for professional advice on generator installation and safety. Don't hesitate to get professional assistance if you are unsure about any aspect of this process. The investment in a properly sized generator is a significant one, so getting it right is vital for peace of mind during emergencies.