What Size Generator for Space Heater (1,500W)? (Startup vs. Running Watts)
1,500W = 12.5A — dangerously close to a 15A circuit limit and the most common cause of generator overload in winter.
Wattage at a Glance
Danger Zone — Simultaneous Heater Overload
Two 1,500W heaters alone consume 3,000W — the most common cause of winter generator overloads
Quick Reference
- Running Watts
- 1,500W (12.5A at 120V)
- Starting Surge
- None (resistive only)
- Minimum Generator
- 2,000W
- Two Heaters
- 3,000W — leaves no room for other appliances on 3,500W generator
- Alternative
- Propane catalytic heater — no electricity required
Space Heaters: The Most Common Cause of Generator Overload in Winter Outages
A standard 1,500W portable space heater is a purely resistive load: no motor, no compressor, no surge. It draws exactly 1,500W (12.5A at 120V) from the moment it's switched on to the moment it's switched off. The load is perfectly constant and completely predictable — which makes space heaters easy to plan for in isolation.
The problem is that 1,500W represents 12.5 amps on a 120V circuit, which is 83% of a 15A household circuit's capacity and 100% of a small 1,500W generator's running output. Add a second space heater, a lamp, a phone charger, and a refrigerator, and the total far exceeds what small generators can deliver. Space heaters are the single most common cause of generator overload trips during winter storms, according to generator service centers.
The math compounds quickly: two 1,500W heaters (3,000W) plus a refrigerator (150W running, 800W surge) plus a coffee maker (1,000W) equals 4,150W running and a 5,650W surge — exceeding most 5,000W generators when all are running simultaneously. The discipline required is treating each space heater as consuming its full wattage for the entire time it is on, and budgeting your generator capacity accordingly.
Energy efficiency perspective: a 1,500W space heater running for 8 hours consumes 12 kWh. On a generator burning 0.5 gallons per hour at moderate load, that's 4 gallons of gasoline per heater per night — at $3.50/gallon, roughly $14 per night per heater, plus the generator's noise and CO risk. For multi-day outages, propane-fueled alternatives (catalytic heaters, Mr. Heater Big Buddy) generate heat without any electricity and are far more fuel-efficient for heating purposes.
Recommended Generators for This Load
Prices and availability are accurate as of March 23, 2026 and are subject to change.
3,500W running
Champion 3500W Dual Fuel
$529 – $619
Runs a single space heater plus a refrigerator and lights — appropriate for one-room heating during an outage.
Check Current Price on Amazon2,000W starting
WEN 56200i (2,000W Inverter)
$399 – $459
Handles a single space heater alone — use low (750W) setting to preserve headroom for other loads.
Check Current Price on AmazonAs an Amazon Associate, GeneratorPicker earns from qualifying purchases.
Frequently Asked Questions
Can I run two space heaters on one generator?
Only on a generator rated at 4,000W+ running capacity, and with nothing else connected. Two 1,500W heaters draw 3,000W continuously — that's the full running output of most 3,000W generators, leaving zero headroom for a refrigerator, lights, or anything else.
Is a space heater the most efficient way to heat during an outage?
Not really. A propane catalytic heater (like the Mr. Heater Big Buddy) generates the same BTU output with no electricity at all — just propane. For multi-day winter outages, a propane heater is dramatically more fuel-efficient than running a gasoline generator to power an electric space heater.
Running multiple appliances at once?
Use our free wattage calculator to add up all your loads and find the exact generator size you need.
Calculate My Total Wattage