Wiring a Garage That Actually Stays Warm
Garage Heater Installations in Missoula for detached garages and workshops running on undersized electrical service
Edison Electric handles garage heater installations in Missoula for homeowners whose garages were never wired to support a dedicated heating circuit. Most detached garages built through the 1980s and 1990s in this area were roughed in with a single 20-amp circuit—enough for a shop light and a power tool, not enough for an electric unit heater drawing 30 to 60 amps. Edison Electric evaluates the existing panel capacity, determines whether a subpanel is needed in the garage structure, and sizes the circuit correctly before any heater goes in.
The installation process starts with a load calculation on the garage's existing electrical service, or an assessment of what needs to be run from the home's main panel. Conduit routing, wire gauge, breaker sizing, and heater placement are all decided before rough-in begins—because a heater mounted in the wrong location, or fed through undersized wire, creates a tripping circuit or a fire hazard. For attached garages, the work typically involves running a new dedicated circuit from the main panel; for detached structures, a separate feeder or subpanel is often the cleaner and code-compliant path.
Schedule an on-site evaluation to review your garage's current electrical capacity and confirm what the installation will require.
How Electrical Capacity Shapes Every Heater Install
Garage heater installations are not a plug-and-mount job. The heater type—forced air, infrared, unit heater—determines the amperage draw, which determines the wire gauge and breaker size, which determines whether the existing panel can absorb the new load. A 240-volt forced air heater rated at 5,000 watts draws roughly 21 amps continuously, meaning the circuit needs to be sized for at least 30 amps under code. Infrared heaters produce radiant heat that warms objects and surfaces rather than cycling air, making them a practical choice for open-bay garages where ceiling height pushes warm air away from the work area.
Once the circuit is in and the heater is mounted, the difference in the space is immediate and measurable: the garage holds a stable temperature rather than responding only to a portable unit that takes an hour to move the ambient temp by a few degrees. Outlets and lighting circuits in the garage continue to function normally because the heater is on its own dedicated breaker—not competing with anything else already running in the space.
Missoula's older neighborhoods like the Rattlesnake district have a significant share of detached garages that were originally built as carriage houses or storage structures, with electrical added later as an afterthought. Those buildings frequently have aluminum wiring on older branch circuits or panels without room for additional breakers, both of which affect how the heater circuit is approached and whether a subpanel is the right answer before the heater goes in.
Common Questions About Garage Heater Installations
Garage heater installations raise specific questions about wiring, circuit sizing, and what the work actually involves. The answers below address the electrical side of the installation—the part that determines whether the heater performs safely and reliably over time.
What size circuit does a garage heater typically require?
Most 240-volt garage heaters require a dedicated 30- to 60-amp circuit depending on the unit's wattage rating—a 7,500-watt heater draws about 31 amps continuously, which means a 40-amp circuit is the minimum code-compliant installation for that unit.
How is the heater location determined during installation?
Placement is based on ceiling height, garage dimensions, and the location of the electrical feed point, with clearance requirements from combustibles factored in for any unit producing convective heat.
Why does a detached garage often need a subpanel rather than a single circuit run?
A long feeder run from the main panel loses voltage over distance, and if the garage will ever support additional circuits—lighting, outlets, a compressor—a subpanel sized appropriately from the start is a more practical and code-sound solution than running multiple individual feeders.
What does a permit cover in a garage heater installation in Missoula?
Missoula County electrical permits cover the new circuit, the breaker, and the connection to the heater itself; the permit process includes a rough-in inspection before walls are closed and a final inspection once the heater is energized.
How do you know the existing panel can handle a new heater circuit?
A load calculation compares the panel's total capacity in amps against the sum of all existing and proposed loads—if the available headroom is insufficient, upgrading the main breaker or adding a subpanel is the path forward before any heater circuit is added.
Edison Electric completes garage heater installations in Missoula with permits pulled and inspections scheduled as part of the standard process—the work is finished when it passes inspection, not just when the heater turns on. Contact Edison Electric to arrange a site visit and confirm which installation approach fits your garage's current electrical setup.
