For the registered 120 V, non-motor space-heater example in the BGT 1.2.2 dataset, the running planning value is 1,500 W (range 750–1,500 W). Starting demand is also 1,500 W (range 750–1,500 W).

These are low-confidence planning values, not specifications for every space heater. The registered range does not identify 750 W as a particular heat setting or operating mode. For your heater, use its nameplate rating whenever available.

One 1,500 W space heater: generator check

For one registered heater and no other loads, the calculation gives 1,875 W running, 1,500 W starting. Under this tool's assumptions, a generator would need to meet both stated capabilities.

The decisive constraint is the heater's sustained 1,500 W running demand. This calculation divides that demand by 0.80 to produce the 1,875 W running-capability result. That is an assumption for this specific calculation, not a universal sizing rule for every generator or load.

Treat the heater as an essential load only if electric heat is part of your outage plan. Lights, a refrigerator, chargers, and other loads must be included in a separate whole-load calculation if they will run at the same time. Do not assume they fit within this one-appliance result.

What the wattage range includes

This page covers one dataset entry: a 120 V, non-motor space heater represented by 1,500 W (range 750–1,500 W) for running demand and 1,500 W (range 750–1,500 W) for starting demand.

For this registered variant, the running and starting ranges are equal, so the calculation does not add a separate motor-start surge. That does not establish that every product sold as a space heater behaves the same way.

The range can support preliminary planning when the exact unit is unknown. It does not tell us which value applies to a specific heater, thermostat state, or control setting. Those details remain unknown without model-specific information.

What the sizing result does not confirm

The one-appliance result is a capacity-planning envelope, not approval of a particular heater and generator combination. It does not verify:

  • The generator's outlet type or receptacle rating
  • Cord suitability or connection method
  • Voltage regulation or waveform quality
  • Grounding or transfer equipment
  • Heater-manufacturer restrictions
  • Fuel use or runtime
  • Capacity for other loads running at the same time

Before using a specific combination, compare the heater's nameplate with the generator's continuous-power rating, voltage, applicable outlet information, and manufacturer instructions. Permanent connections to home wiring are outside this lookup and should be addressed using appropriate installation guidance and a qualified electrician.

Watts are not daily energy use

Watts describe power—the rate at which the heater uses electricity while operating. Daily energy depends on both power and operating time and is expressed in watt-hours (Wh) or kilowatt-hours (kWh).

This page does not supply operating hours, thermostat duty cycle, measured consumption, or daily energy. Because a thermostatically controlled heater may cycle on and off, its running wattage cannot be presented as daily energy by itself. No Wh/day or kWh/day figure is calculated here.

How to check your heater's actual rating

  1. Turn the heater off and unplug it before moving it to inspect the label.
  2. Find the electrical label or nameplate. Check the back, bottom, cord area, or model-specific manual.
  3. Look for watts marked W. Use that rating instead of the generic planning value when sizing your load.
  4. Record the model number and voltage. These details help distinguish your heater from products with different settings or electrical requirements.
  5. If the label lists only volts and amps, do not treat either number as watts. Use a calculator that supports the appropriate conversion or obtain the wattage from the model documentation. This page does not perform that conversion.
  6. If no rating can be found, keep it unknown. Unknown does not mean 0 W. You may use this page's low-confidence range for preliminary planning, but not as confirmation that a particular generator is compatible.

Next step for your backup-power plan

If the heater will run with other essentials, enter all loads that must run at the same time in the Generator Size Calculator for Home. Keep optional loads separate so you can decide which appliances may need to take turns.

For an explanation of the two generator power ratings, see Running Watts vs Starting Watts: What Your Generator Needs.