How Many Amps Does a 1500W Space Heater Draw?
Quick Answer
- At 120V: 1500 ÷ 120 = 12.5 A
- At 240V: 1500 ÷ 240 = 6.25 A
- Formula: I = P / V (amps = watts ÷ volts)
- Circuit note: 12.5 A leaves very little headroom on a standard 15 A circuit, avoid stacking other loads on the same circuit when the heater runs.
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Space heaters are one of the most circuit-critical household appliances. At 1500 W, a typical plug-in space heater running on a standard North American 120 V outlet draws 12.5 A, nearly the full practical capacity of a 15 A branch circuit by itself. Understanding that number helps you plan which other devices can safely share the circuit and when it makes more sense to use a different outlet on a separate circuit.
The formula
I = P / V
Where I is current in amps, P is power in watts, and V is voltage in volts. Divide watts by volts to get amps. This is the same power relationship used in the Watts to Amps Calculator.
Worked examples
Example 1, Standard North American outlet (120 V):
I = 1500 / 120 = 12.5 A
A 15 A circuit at 120 V has 1800 W of theoretical capacity. A 1500 W heater uses 83% of that capacity on its own. Add a phone charger, a lamp, or a laptop and you are approaching or crossing the practical planning limit.
Example 2, 240 V circuit (some baseboard heaters and some regions):
I = 1500 / 240 = 6.25 A
The same heater at 240 V draws only half the current. This is why many permanently-installed baseboard heaters use 240 V, more efficient use of conductor capacity.
Example 3, Heater on lower power setting (750 W at 120 V):
I = 750 / 120 = 6.25 A
Many portable heaters have a low setting at half wattage. The current drops proportionally, giving the circuit more headroom for other loads.
Voltage and wattage comparison table
| Heater wattage | Voltage | Current draw | Circuit headroom on a 15 A breaker |
|---|---|---|---|
| 750 W (low setting) | 120 V | 6.25 A | ~8.75 A remaining |
| 1000 W | 120 V | 8.33 A | ~6.67 A remaining |
| 1500 W (full power) | 120 V | 12.5 A | ~2.5 A remaining |
| 1500 W | 240 V | 6.25 A | N/A (20 A circuit typical) |
| 2000 W | 240 V | 8.33 A | N/A (20 A circuit typical) |
Headroom figures above are simplified estimates. Real usable capacity also depends on other loads already on the circuit and continuous load planning guidelines.
Circuit planning: what 12.5 A really means
A standard 15 A residential branch circuit in North America is rated for a maximum of 15 A, but for loads that run continuously, generally defined as three or more hours, many electrical planning approaches recommend limiting load to 80% of the breaker rating, which is 12 A on a 15 A circuit. A 1500 W heater at 12.5 A already slightly exceeds this planning guideline on a 15 A circuit.
In practice this means: run the heater on its own dedicated circuit when possible, use the low setting if you also need to run other devices from the same outlet group, and avoid using long or lightweight extension cords, which add resistance and create a voltage drop and heat risk at high current. If you are weighing a temporary cord anyway, read Can You Run a Space Heater on an Extension Cord? before trying it.
Always check the actual nameplate on your heater, some models list their input current directly. The nameplate value is more accurate than a wattage-based estimate for planning purposes.
FAQ
Will a 1500W space heater trip a 15A breaker?
Not on its own under normal conditions, but it leaves very little margin. If other devices are already on the same branch circuit, or if the heater draws slightly above its nameplate rating due to voltage variations, the combined current can exceed 15 A and cause the breaker to trip. The most common scenario is running a heater and a hair dryer or microwave on the same circuit simultaneously.
Can I use an extension cord with a space heater?
Space heater manufacturers and fire safety organizations generally advise plugging heaters directly into a wall outlet rather than using an extension cord. At 12.5 A, a lightweight or long extension cord can overheat because its conductors are not rated for sustained high current. If an extension cord is unavoidable, use a short, heavy-gauge cord rated for at least 15 A.
Does the heater's thermostat affect current draw?
Yes. When the thermostat cycles the heater off, current drops to near zero. When it cycles back on, it returns to full draw (12.5 A at 120 V full power). The average current over a heating cycle is lower than the peak draw, but breaker sizing is based on peak current, not average current, so the 12.5 A figure is still the relevant number for circuit planning.
Is a 1500W heater the same current load as a 1500W hair dryer?
For planning purposes, yes, both are approximately 12.5 A at 120 V. However, heaters are typically run for extended periods, while hair dryers are used briefly. The sustained nature of heater use is why continuous load planning guidance is particularly relevant for heaters.
What size circuit is best for a dedicated space heater?
A dedicated 15 A or 20 A circuit gives a 1500 W portable heater enough room to operate without competing with other loads. A 20 A circuit provides more comfortable margin for full-power sustained use. For permanently wired baseboard heaters, sizing follows specific code rules, consult a licensed electrician and your local electrical code.
Related tools and guides
Disclaimer: Results are informational estimates for learning and planning only. Always follow the applicable electrical code and consult a qualified licensed electrician for safety-critical work.