Portable Space Heater Wattage for Generator Sizing
About the Portable Space Heater
A standard 1500-watt portable electric space heater using either ceramic, oil-filled radiator, or fan-forced heating technology. As a resistive load, there is no starting surge. Space heaters are the most common supplemental heating option during winter power outages. At 1500 watts, they are rated for a standard 15-amp household circuit and can heat a medium-sized room. Many heaters have adjustable settings of 750 watts (low) and 1500 watts (high), allowing you to reduce generator load when full heating power is not needed.
Generator Sizing for a Portable Space Heater
Running a portable space heater by itself requires a generator with at least 1,875 W of capacity (2 kW), which includes a 25% safety margin. However, you rarely run a single appliance on a generator. When combined with other appliances, the portable space heater contributes 1,500 W to the continuous running load.
The portable space heater is a resistive load, meaning it uses a heating element or simple electronic circuit rather than a motor. Resistive loads draw the same wattage from the moment they turn on until they turn off, with no starting surge. This makes them the easiest type of appliance to run on a generator. When calculating your total generator load, the portable space heater adds a flat 1,500 W to your running total with no impact on peak surge calculations. Resistive loads also produce a power factor of 1.0, meaning they use electricity very efficiently with no wasted reactive power.
To determine the total generator size you need, use our interactive calculator to combine the portable space heater with your other appliances. The calculator automatically handles the starting surge calculation and applies the 25% safety margin to give you an accurate recommendation. Alternatively, browse the scenarios below to see common generator setups that include the portable space heater.
Scenarios That Include Portable Space Heater
The following pre-calculated generator scenarios include the portable space heater in their appliance list. Each scenario shows the total generator size needed for all appliances in the set, not just the portable space heater alone. Click any scenario to see the full appliance breakdown.
| Scenario | Total Appliances | Running Watts | Recommended Size |
|---|---|---|---|
| RV / Camping Trip | 5 | 3,425 W | 5 kW |
| Winter Storm Preparedness | 7 | 3,595 W | 6 kW |
| Off-Grid Cabin | 7 | 4,575 W | 8 kW |
| Elderly / Retired Couple | 8 | 2,885 W | 5 kW |
Tips for Running a Portable Space Heater on a Generator
Running a portable space heater on a generator is straightforward since it is a purely resistive load. There are no special starting procedures or surge considerations. Simply ensure your generator's continuous (rated) wattage exceeds 1,500 W plus the wattage of all other appliances running simultaneously.
Since the portable space heater draws a constant 1,500 W whenever it is operating, you can accurately predict generator fuel consumption. At typical generator fuel efficiencies, running the portable space heater continuously adds approximately 0.1 gallons of gasoline per hour to your fuel consumption. If the portable space heater operates intermittently (like a thermostat-controlled heater), the actual fuel impact will be lower.
For sensitive electronic components within the portable space heater, an inverter generator provides the cleanest power output. However, most resistive appliances work fine on conventional generators as well. If you are running the portable space heater along with sensitive electronics like computers, the inverter generator protects all connected devices.
Portable Space Heater Wattage Compared to Similar Appliances
The following table compares the portable space heater to other appliances in the hvac & climate category. Understanding relative power requirements helps you make informed decisions about which appliances to prioritize on your generator and where you might find opportunities to reduce your total load.
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Portable Space Heater (this appliance) | 1,500 W | — |
| Central Air Conditioner (3-Ton) | 3,500 W | 4,500 W |
| Window AC Unit (5,000 BTU) | 500 W | 600 W |
| Window AC Unit (10,000 BTU) | 1,200 W | 1,500 W |
| Furnace Blower Fan | 800 W | 1,300 W |
| Whole House Fan | 500 W | 800 W |
| Dehumidifier | 650 W | 800 W |
Frequently Asked Questions
How many watts does a portable space heater use?
A portable space heater uses approximately 1500 watts of continuous (running) power during normal operation. As a resistive load with no motor, it has no starting surge above its running wattage.
What size generator do I need to run a portable space heater?
To run a portable space heater by itself, you need a generator rated for at least 1,875 W (2 kW), which includes a 25% safety margin above the running wattage of 1500W. However, most people run additional appliances alongside the portable space heater, so your actual generator needs will be higher. Use our calculator to add your other appliances and get a comprehensive recommendation.
Can I run a portable space heater on an inverter generator?
Yes, a portable space heater runs perfectly well on an inverter generator. As a resistive load with no motor starting surge, it is one of the easiest appliances to power with any generator type. The clean sine wave output of an inverter generator is a bonus for any electronic components.