What Size Breaker for Space Heater?
A space heater requires a 20A breaker with 12 AWG wire on a 120V shared 20a circuit. This is a continuous load — breaker rated at 125% of actual draw.
🔌 Wire Length & Voltage Drop Check
Space Heater Wiring Guide — NEC Requirements
Most space heaters draw 12.5A at 1500W/120V. This is a continuous load when run for 3+ hours. On a 15A circuit, a 1500W heater leaves almost no headroom — use a 20A circuit.
Pro Tip
💡 Never use an extension cord with a space heater. Plug directly into a wall outlet on a circuit with minimal other loads.
Why a 20A Breaker?
The space heater draws approximately 12.5A at 120V (1500W). As a continuous load (3+ hours), NEC 210.20 requires the breaker at 125%: 12.5A × 1.25 = 15.6A → 20A breaker.
Wire Sizing per NEC 310.16
For a 20A/120V circuit, 12 AWG copper is required per NEC Table 310.16 at 75°C. For runs over 75 feet, upsize to 12 AWG. Use our Wire Size Calculator and Voltage Drop Calculator.
Complete Parts List
To wire a space heater circuit: a 20A single-pole breaker, 12 AWG NM-B cable (Romex) for interior runs or THHN/THWN-2 in conduit for exposed runs, a NEMA 5-15 or 5-20 receptacle, cable clamps, and appropriate junction boxes.
Disclaimer: This guide is for reference only. All electrical work must be performed by or verified by a licensed electrician. Local codes may differ from NEC.