When it comes to electric heating, one of the first questions homeowners ask is, “What breaker size for electric furnace do I need?” Or, “What circuit breaker size for electric furnace is appropriate for safe operation?” These questions are critical because an undersized breaker can trip repeatedly, while an oversized breaker can create a safety hazard.
The Goodman MBVK electric furnace is a popular choice for all-electric homes, manufactured housing, and heat pump backup applications. Understanding how to select the proper breaker size ensures your furnace operates efficiently, safely, and reliably. In this article, I’ll cover key concepts, calculations, installation considerations, and safety practices that every homeowner or HVAC technician should know.
Why Breaker Size Matters for Electric Furnaces
The circuit breaker is the first line of defense between your furnace and your home’s electrical system. It protects both the furnace and the home from overheating and electrical fires by shutting off power if the current exceeds safe limits.
Choosing the correct breaker size for electric furnace ensures:
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The furnace receives enough power to operate all heating elements
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Circuit overloads are prevented
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Breaker trips are minimized
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Electrical code compliance is maintained
A properly sized breaker is not just about avoiding nuisance trips—it’s about safety and long-term system reliability.
How Electric Furnaces Draw Power
Electric furnaces like the MBVK rely on resistive heating elements to generate heat. These elements draw significant current, depending on the furnace’s capacity (typically measured in kilowatts).
For example:
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A 10 kW electric furnace on a 240V circuit draws approximately 41.7 amps (10,000 W ÷ 240 V = 41.7 A)
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A 12 kW unit would draw 50 A at 240 V
Because electrical circuits should not be loaded to 100% continuously, the National Electrical Code (NEC) recommends a 125% safety margin when sizing breakers for continuous loads like furnaces.
So, using the 10 kW example:
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41.7 A × 1.25 = 52.1 A
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The next standard breaker size is 60 A
This calculation ensures the furnace can run safely without nuisance trips while remaining compliant with electrical codes.
For general electrical safety and load calculation guidelines, Electrical Safety Foundation International offers detailed resources for homeowners and technicians.
Calculating Circuit Breaker Size for the Goodman MBVK
The Goodman MBVK comes in multiple models with varying heating capacities. When sizing a breaker:
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Determine the furnace’s rated current draw (from the specification sheet)
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Apply the 125% factor for continuous loads
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Select the nearest standard breaker size
Example Calculation
Suppose your MBVK model draws 35 amps continuously at 240 volts:
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Multiply by 1.25: 35 × 1.25 = 43.75 A
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Choose the next standard breaker size: 50 A
This ensures adequate current supply while providing built-in safety.
Keep in mind that electrical panels in mobile homes and older homes may limit breaker size. Always verify panel capacity before installation.
Wiring Considerations
Breaker size is only one piece of the puzzle. Proper wiring is equally important. NEC guidelines recommend:
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Copper conductors sized for the furnace load
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Wire insulation rated for continuous loads
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Proper termination in the breaker panel
For example, a 50 A breaker typically pairs with 6 AWG copper wire. Using a smaller gauge wire increases the risk of overheating and fire, while unnecessarily large wire is cost-inefficient.
Manufacturer guidelines, including the Goodman MBVK installation manual, provide exact wiring requirements based on model and load. For wiring charts and installation instructions, the Goodman MBVK Manual is a useful reference for homeowners and contractors.
Continuous Load Considerations
Electric furnaces operate as continuous loads, meaning they can run for several hours at a time. Continuous loads require special consideration because running the furnace at full rated current continuously will heat the wires, potentially causing failure if the breaker and conductor are undersized.
NEC Article 210.19(A)(1) specifies that conductors must handle 125% of the continuous load. The MBVK installation manual explicitly recommends following this guideline to prevent nuisance trips and ensure safe operation.
Common Mistakes When Sizing Breakers
Even experienced homeowners and some contractors make mistakes when sizing breakers for electric furnaces. Common errors include:
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Using the furnace’s nominal amp draw instead of the continuous load factor – Leads to breaker trips
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Selecting a smaller breaker to “save money” – Increases risk of overheating and nuisance trips
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Ignoring wire gauge requirements – Creates a safety hazard
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Assuming older homes’ panels can handle modern loads – May require panel upgrades
For troubleshooting and safety tips on electric furnaces, HVAC.com provides practical guidance for homeowners dealing with breaker trips or insufficient heating.
Upgrading Electrical Panels for High-Capacity Electric Furnaces
Some homes, especially older mobile homes or site-built houses, may need a panel upgrade to support modern electric furnaces like the Goodman MBVK. Signs that an upgrade is needed include:
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Breaker trips immediately when the furnace starts
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Multiple devices on the same circuit overload frequently
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Panel cannot accommodate larger breaker sizes
A licensed electrician can evaluate your panel, calculate load requirements, and upgrade wiring and breakers to safely support a new electric furnace. For guidance on electrical panel upgrades and safety tips, the Electrical Safety Foundation International provides detailed recommendations.
Safety Considerations
Breaker size, wiring, and installation practices all play a role in safe operation. Key safety takeaways:
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Never bypass the breaker or install an oversized breaker to prevent trips
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Ensure all wiring meets NEC standards
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Confirm that the disconnect is accessible near the furnace
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Inspect the system annually for wear, corrosion, or loose connections
The MBVK incorporates multiple internal safety devices, including limit switches and sequencers, to further protect your home from electrical hazards.
Summary: Selecting the Right Breaker for the Goodman MBVK
Selecting the proper breaker size for electric furnace operation is essential for efficiency, safety, and longevity. Here’s a quick checklist:
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Determine the MBVK model’s rated amp draw
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Multiply by 1.25 for continuous load
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Select the next standard breaker size
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Match conductor wire gauge to breaker rating
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Ensure panel can handle the additional load
Following these steps will prevent nuisance trips, protect your home’s wiring, and ensure the MBVK delivers reliable, safe heating throughout the winter.
Final Thoughts from Jake Lawson
Electric furnaces like the Goodman MBVK offer dependable, low-maintenance heating—but only when the electrical system is correctly configured. Proper breaker sizing is the foundation of safe, effective operation. By understanding how to calculate load, choose the right breaker, and verify wiring, homeowners can maximize comfort while protecting their home and family.
With the right breaker, proper wiring, and adherence to NEC standards, your MBVK furnace will provide quiet, efficient, and reliable heat for years to come.
