Questions about breaker size for an electric furnace come up more often than almost any other electrical topic in home heating. Homeowners notice a tripped breaker, a newly installed furnace with multiple disconnects, or a panel that looks far more crowded than expected—and suddenly they’re wondering whether their system is wired correctly or safely.
Electric furnaces are powerful appliances, and the Goodman MBVK electric furnace is no exception. While it is known for reliability and straightforward design, it depends entirely on proper electrical sizing to operate safely and efficiently. When breaker sizing is misunderstood or misapplied, homeowners may experience nuisance trips, limited heat output, or premature component wear.
In this article, I’ll explain how circuit breaker sizing works for electric furnaces, why the MBVK uses multiple breakers in many configurations, and how to understand what your system actually requires—without turning your electrical panel into a guessing game.
Why Breaker Size Matters More for Electric Furnaces Than Gas Systems
Electric furnaces convert electrical energy directly into heat through resistance elements. Unlike gas furnaces, which rely on fuel combustion and use electricity mainly for controls and blowers, electric furnaces draw significant amperage when heating.
That makes breaker sizing critical for three reasons:
-
Safety – Preventing overheated wiring and fire risk
-
Performance – Ensuring all heating elements can operate
-
Longevity – Reducing stress on components and connections
The breaker size is not simply a protective device; it is a foundational part of how the furnace is designed to function.
Understanding Circuit Breaker Size for Electric Furnace Applications
When discussing circuit breaker size for electric furnace installations, it’s important to understand that there is rarely a single universal breaker size. Electric furnaces are modular by design.
The Goodman MBVK can be equipped with different heat strip kits, each with its own electrical demand. As heat capacity increases, so does the required amperage.
Breaker sizing depends on:
-
Total kilowatt (kW) rating of the heat strips
-
Voltage (typically 240V)
-
Number of heating stages
-
National and local electrical codes
-
Manufacturer specifications
This is why two homes with the same furnace model may have very different breaker configurations.
The Goodman MBVK and Modular Heat Strip Design
The MBVK electric furnace is designed to accept a range of electric heat kits, allowing installers to match heating capacity to the home’s needs. Each heat strip kit has a specific amperage draw and corresponding breaker requirement.
For example:
-
Smaller heat kits may require one 40–60 amp breaker
-
Larger configurations may require two or more 60-amp breakers
-
High-capacity setups may split loads across multiple circuits
This modular approach improves efficiency and flexibility but also means breaker sizing must be calculated precisely—not guessed.
How Electric Furnace Breaker Sizing Is Calculated
Breaker sizing follows a basic electrical formula:
Amps = Watts ÷ Volts
Since electric furnaces are continuous-load appliances, most electrical codes require circuits to be sized at 125% of the calculated load.
For example:
-
A 10 kW heat strip at 240V draws approximately 41.7 amps
-
Applying the 125% rule brings the required circuit capacity to about 52 amps
-
This would typically be protected by a 60-amp breaker
This calculation framework aligns with guidance published by the National Electrical Code, which defines continuous load requirements for electric heating equipment.
For homeowners wanting deeper insight into how electrical loads are classified, the National Fire Protection Association provides detailed explanations through its electrical safety standards documentation, which supports these sizing principles.
Why Electric Furnaces Often Use Multiple Breakers
One of the most confusing aspects of electric furnace installations is seeing two, three, or even four breakers labeled for a single heating system.
This is not a mistake.
The Goodman MBVK uses multiple breakers because:
-
Heat strips are staged in separate circuits
-
Electrical loads are distributed to reduce stress
-
Service panels have amperage limits
-
Redundancy improves reliability
Each breaker protects a specific portion of the heating system. If one circuit trips, others may still operate, allowing partial heat rather than a total shutdown.
Common Breaker Sizes Used With the Goodman MBVK
While exact breaker sizing must always follow the manufacturer’s data plate and installation manual, typical breaker sizes for electric furnaces include:
-
30 amps (small auxiliary heat kits)
-
40 amps
-
50 amps
-
60 amps
It is not unusual for a Goodman MBVK system to use two 60-amp breakers in higher-capacity installations. This does not mean the furnace is inefficient—it means it is delivering the necessary heat safely.
What Happens When Breaker Size Is Too Small
Undersized breakers are one of the most common causes of electric furnace complaints.
When the breaker size is too small, homeowners may experience:
-
Frequent breaker trips
-
Furnace not heating enough
-
Only partial heat operation
-
Heat shutting off during cold weather
-
Blower running with no heat
In these cases, the furnace is often protecting itself. Heating elements draw exactly the amperage they are designed for, and an undersized breaker cannot support that load.
Risks of Oversized Breakers
Just as dangerous as undersizing is oversizing a breaker.
Installing a breaker larger than specified can:
-
Allow wiring to overheat
-
Bypass safety margins
-
Increase fire risk
-
Void manufacturer warranties
-
Violate electrical codes
Breaker size must always match both the furnace requirements and the wire gauge supplying the circuit. Oversizing a breaker does not “improve performance”—it compromises safety.
The Role of Wire Gauge in Electric Furnace Circuits
Breaker size and wire size are inseparable. A 60-amp breaker requires appropriately sized conductors, typically #6 copper or equivalent aluminum, depending on installation specifics.
If wiring is undersized:
-
Breakers may not trip when they should
-
Conductors may overheat
-
Connections may loosen over time
-
Heat output may fluctuate
This relationship between breaker size and conductor size is clearly outlined in electrical reference materials published by the U.S. Department of Energy, which emphasize proper conductor sizing for high-load appliances.
Why Manufacturer Specifications Always Come First
Every Goodman MBVK furnace has a data plate and installation manual that specifies:
-
Minimum circuit ampacity
-
Maximum overcurrent protection
-
Approved breaker types
-
Heat kit compatibility
These specifications are not suggestions. They are engineered requirements tested for safety and performance.
Goodman provides detailed documentation for the MBVK that outlines approved breaker sizes for each heat strip configuration, ensuring compliance with both safety standards and performance expectations.
How Electric Furnace Breaker Size Affects Heating Performance
Breaker sizing does more than protect wiring—it directly impacts comfort.
Proper breaker sizing allows:
-
Full heat strip staging
-
Stable heat output
-
Smooth cycling
-
Consistent indoor temperatures
Improper sizing may limit how many heating elements can engage, resulting in a furnace that runs constantly but never warms the home adequately.
Why Breaker Trips Often Happen During Cold Weather
Cold weather increases heat demand, which means more heat strips engage simultaneously. If breaker sizing is marginal, this is when problems appear.
Common cold-weather symptoms include:
-
Breaker trips only during extreme cold
-
Furnace works fine in mild temperatures
-
Heat shuts off overnight
-
System resets repeatedly
These patterns often point to breaker capacity limits rather than furnace failure.
Electric Code Considerations for Furnace Breakers
Electric furnaces must comply with national and local electrical codes. These codes exist to protect homeowners, not complicate installations.
General code principles include:
-
Dedicated circuits for electric heat
-
Proper labeling of breakers
-
Accessible disconnects
-
Grounding and bonding requirements
Electrical code guidance from organizations such as the National Electrical Contractors Association reinforces these practices as essential for high-load appliances like electric furnaces.
Can Homeowners Change Breaker Size Themselves?
This is a question I hear frequently, and the answer is very clear: breaker sizing should only be changed by a qualified professional.
Changing a breaker without verifying:
-
Wire gauge
-
Load calculations
-
Furnace specifications
-
Panel capacity
creates serious safety risks. Electric furnaces operate at high voltage and high amperage, and mistakes can have lasting consequences.
Breaker Size vs. Heat Strip Size: Clearing Up Confusion
Some homeowners assume upgrading breaker size will increase heating output. It will not.
Heating output is determined by:
-
Heat strip kilowatt rating
-
Furnace airflow
-
Home heat loss
Breakers simply allow the system to operate safely at its designed capacity. Increasing breaker size without increasing heat strip capacity accomplishes nothing—and introduces danger.
Signs Your Electric Furnace Breaker Size Should Be Evaluated
You may want to have your breaker sizing reviewed if you notice:
-
Repeated breaker trips
-
Inconsistent heating
-
Recent furnace upgrades
-
Added heat strips
-
Electrical panel changes
A professional evaluation ensures the system is operating within safe parameters.
Why the Goodman MBVK Is Well-Suited for Electric Heating
The MBVK’s modular electrical design makes it adaptable to a wide range of homes. When paired with correct breaker sizing, it delivers:
-
Reliable, staged electric heat
-
Quiet operation
-
Straightforward serviceability
-
Long component life
Its design assumes proper electrical infrastructure—and when that infrastructure is in place, performance is consistent and predictable.
Final Thoughts: Breaker Size Is Not a Guessing Game
Understanding breaker size for electric furnace systems removes much of the mystery surrounding electric heat. The Goodman MBVK electric furnace is engineered to operate safely and efficiently—but only when its electrical requirements are respected.
Breaker size is not about convenience or trial and error. It is about aligning electrical capacity with engineered demand. When done correctly, the result is a heating system that performs reliably, safely, and comfortably for years to come.
If you’re ever unsure, the safest next step is professional evaluation—not experimentation. Electric furnaces reward precision, and the MBVK is no exception.
