One of the most critical aspects of installing or maintaining an electric furnace is ensuring the breaker size for electric furnace is correct. Too small a breaker can lead to nuisance trips and interrupted heat, while too large a breaker can bypass vital safety protections, risking fire hazards. For homeowners and HVAC technicians, understanding how to determine the circuit breaker size for electric furnace is essential, especially for high-capacity systems like the Goodman MBVK electric furnace.
In this guide, I’ll cover everything from calculating electrical load, selecting the proper breaker, understanding furnace wiring requirements, and ensuring safe, efficient operation. We’ll also discuss best practices for troubleshooting breaker issues and how the MBVK is designed to make safe installation straightforward.
Why Breaker Size Matters for Electric Furnaces
Electric furnaces, unlike gas systems, rely entirely on electricity to produce heat. The Goodman MBVK, for example, uses staged electric heat strips and a variable-speed blower to deliver consistent warmth. Each stage of the heat strip draws a significant amount of current, and the breaker size must accommodate this load safely.
Using the wrong breaker can lead to:
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Frequent tripping if the breaker is too small
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Overheating and safety risks if the breaker is too large
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Premature wear on furnace components, including heat strips and blower motors
By consulting the MBVK wiring diagram and manufacturer specifications, you can select a breaker that protects the system while ensuring reliable heat delivery.
Calculating the Correct Breaker Size
Determining the circuit breaker size for an electric furnace involves these steps:
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Identify the total wattage of the furnace
The MBVK furnace comes in various models, typically ranging from 10 kW to 30 kW. The total wattage includes all heat strips and the blower motor. -
Convert watts to amperage
Using the formula:For example, a 15 kW furnace operating on a 240-volt circuit:
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Apply the NEC 125% rule for continuous loads
Electric furnaces are considered continuous loads, meaning you should size the breaker at 125% of the full-load current:Rounded to the next standard breaker size, a 80A double-pole breaker would be appropriate.
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Check manufacturer recommendations
Goodman provides specific breaker sizes for each MBVK model in the installation manual. Always follow these recommendations to ensure safety and maintain warranty coverage.
Ideal HVAC Services provides a detailed guide on calculating furnace amperage and selecting the correct breaker size for various electric furnaces.
Typical Breaker Sizes for Goodman MBVK Furnaces
While each installation may vary, common breaker sizes for MBVK electric furnaces are:
| Furnace Size | Voltage | Recommended Breaker |
|---|---|---|
| 10 kW | 240V | 50A |
| 15 kW | 240V | 80A |
| 20 kW | 240V | 100A |
| 25 kW | 240V | 125A |
| 30 kW | 240V | 150A |
These recommendations assume proper wire sizing, correct staging, and standard operating conditions. Always confirm breaker sizing against the MBVK installation manual and local electrical codes.
The Furnace Outlet offers practical guidance on breaker sizing and wire gauge selection for mobile home and residential electric furnaces.
Understanding Wire Size in Relation to Breaker Size
Breaker sizing cannot be considered in isolation. The wire gauge must match the breaker to ensure safe operation:
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50A breaker → typically 6 AWG copper wire
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80A breaker → 4 AWG copper wire
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100A breaker → 3 AWG copper wire
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125A breaker → 2 AWG copper wire
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150A breaker → 1 AWG copper wire
Undersized wiring can overheat, causing insulation damage or fire. Oversized wiring is safe but can be unnecessarily expensive. Always follow both the breaker specifications and the NEC (National Electrical Code) guidelines for wire sizing.
Goodman Manufacturing provides wiring charts and schematics in the MBVK installation manual to help determine proper wire size for each breaker.
Staged Heating and Breaker Considerations
One of the advantages of the Goodman MBVK electric furnace is staged heating:
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Stage 1: Uses fewer heat strips to meet mild heating demand
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Stage 2: Activates additional strips as needed
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Stage 3: Full heat capacity engaged during extreme cold
Staged heating reduces the load on the circuit at any given time, which allows for more precise breaker sizing and less frequent tripping. When planning a new installation, consider how many stages the furnace has and whether all stages will operate simultaneously. This is crucial for calculating the continuous load and sizing the breaker appropriately.
Common Breaker-Related Issues in Electric Furnaces
Even with the correct breaker size, some issues can occur:
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Breaker keeps tripping
Causes may include clogged filters restricting airflow, failed heat strips, or a malfunctioning sequencer. Checking the MBVK wiring diagram helps isolate the problem safely. -
Breaker doesn’t trip but furnace components overheat
If the breaker is oversized or incorrectly wired, safety devices in the furnace must function to prevent damage. The MBVK’s high-limit switches provide secondary protection, but correct breaker sizing is still essential. -
Intermittent heat
This often occurs if there are loose electrical connections at the breaker, terminal block, or sequencer. A wiring diagram simplifies troubleshooting and ensures all connections are secure.
HVAC training resources emphasize that proper breaker selection and periodic inspection of electrical connections prevent most furnace electrical issues.
Installation Best Practices
When installing a Goodman MBVK electric furnace, keep these breaker-related best practices in mind:
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Always use a double-pole breaker for 240V systems.
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Verify the breaker amperage matches the manufacturer’s specification.
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Ensure the wire gauge meets NEC requirements.
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Install a dedicated circuit to prevent overload from other devices.
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Double-check wiring against the MBVK electric furnace diagram for safety and efficiency.
Following these steps reduces the likelihood of trips, overheating, and other operational issues.
Maintaining Your Breaker and Furnace Connection
Maintenance can prevent breaker-related problems:
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Inspect the breaker for signs of wear, corrosion, or arcing.
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Ensure terminal screws are tight and wires are properly seated.
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Periodically check the furnace wiring connections, especially at the sequencer and control board.
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Replace breakers that show signs of degradation, even if they haven’t tripped frequently.
Routine maintenance keeps both your furnace and breaker system operating safely and efficiently.
Why the MBVK Electric Furnace Simplifies Electrical Planning
Goodman designed the MBVK with electric installations in mind:
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Clear wiring diagrams simplify breaker sizing and wire selection.
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Modular design allows easy access to heat strips and blower connections.
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Staged heating reduces maximum amperage draw at any given time.
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Integrated safety features provide secondary protection in case of electrical anomalies.
Homeowners and HVAC technicians alike benefit from this thoughtful design, making electrical planning less intimidating while maintaining safety.
Final Thoughts from Tony Marino
Selecting the proper breaker size for electric furnace is not optional—it’s essential for safe, reliable heating. The Goodman MBVK electric furnace makes this process straightforward through:
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Detailed wiring diagrams and manuals
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Staged heat strips to optimize load
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High-limit switches and thermal cutoffs for safety
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Clear manufacturer specifications for breaker and wire sizing
Understanding your furnace’s electrical requirements, consulting the MBVK wiring diagram, and adhering to NEC guidelines ensures long-lasting, worry-free operation. For both new installations and replacements, proper breaker sizing guarantees that your furnace delivers consistent, efficient heat while protecting your home and family.
