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What Size Generator Do I Need for Halloween Decorations?

For most home displays, a 2,000-watt inverter generator is more than enough. Lights, a couple of inflatables, and a few spotlights together rarely add up to even 500 watts. The one thing that changes the answer is a fog machine: its heater alone can pull 1,000 watts or more, and once that is in the mix you want a 3,000-to-3,500-watt unit. The method is the same either way. Add up the running watts of everything you plan to plug in, leave headroom for the motors that surge at startup, and never load the generator past about 80 percent of its rating for hours at a time. Before any of that, though, the number that matters most is not watts. It is where you put the generator, because a portable generator makes carbon monoxide, and that is what actually hurts people.

The whole job starts with one total: the watts of your entire display. Add every item's nameplate wattage with the Electrical Load Calculator, then match a generator to that number with the headroom below. Not sure what each prop draws? The spotlight and inflatable guides below break down the common ones.

Carbon monoxide first, watts second

A generator burns fuel and produces carbon monoxide, a gas you cannot see or smell. The U.S. Consumer Product Safety Commission links portable generators to close to 100 carbon-monoxide deaths in the country every year (CPSC, 2024 report on non-fire CO deaths tied to consumer products). Every one of those is preventable with the same few rules:

  • Run it outdoors only, well away from the house. CPSC guidance is at least 20 feet from the home with the exhaust pointed away from doors, windows, and vents. Never in a garage, a shed, or under an overhang, even with the door open.
  • Put a working CO alarm inside. One with a battery backup, near the sleeping areas.
  • Never back-feed the house. Do not run a cord from the generator into a wall outlet to power the home's circuits. It can push live voltage back onto the utility line and kill a lineman, and it bypasses every protection in the panel. Powering the display means plugging the display's cords straight into the generator, nothing else.
  • Keep it dry. Operate the generator under an open, ventilated canopy made for the purpose, on dry ground, and keep your hands dry when you touch it.

For most yards, the honest question is whether you need a generator at all. If a regular outlet reaches the display and the load fits the circuit, an extension cord is safer and simpler. A generator earns its place when the display is far from any outlet, or when it is big enough to overload the circuits you have.

Add up the running watts

Start by listing every item and its wattage, printed on the label or the adapter. A modest yard might look like this:

6 LED spotlights × 20 W = 120 W

Light strings, total ≈ 100 W

2 inflatable blowers × 80 W = 160 W

Running total = 120 + 100 + 160 = 380 W

At 120 volts that whole display is only 380 ÷ 120, or about 3.2 amps. That is why a small 2,000-watt generator is overkill in the best way; it never breaks a sweat. Now add a fog machine, and the picture changes:

Previous running total = 380 W

1,000 W fog machine heater = 1,000 W

New running total = 1,380 W

That 1,380 watts is 1,380 ÷ 120, or about 11.5 amps, which is nearly the entire 12-amp working limit of a single 15-amp household circuit. That is exactly the point where people reach for a generator or a second circuit. Inflatable and inflatable-blower running watts here reflect typical 2025 homeowner figures; a fog machine's rating is printed on the unit and varies widely, so use yours.

Add headroom for surge, then derate

Two adjustments turn a running total into a generator size. First, the motors. An inflatable's blower draws roughly 50 percent more for the moment it spins up than it does once it is running, so the generator has to clear a brief peak above the running total:

Blower surge on 160 W of motors ≈ 160 W × 0.5 = 80 W extra

Momentary peak (with fog machine) ≈ 1,380 + 80 = 1,460 W

Second, a generator should not run at its full rating for hours. Keep it at or under 80 percent, the same headroom rule the NEC uses for any continuous load. So the generator's rated running watts should cover the running total with that margin:

1,380 W ÷ 0.80 = 1,725 W minimum rated

A 2,000-watt generator technically covers 1,380 running watts, but it would sit at 69 percent and has little room when the fog heater cycles on hard, so a 3,000-to-3,500-watt unit is the comfortable choice for a display with a fogger. Without the fog machine, the same yard's 380 watts needs only 380 ÷ 0.80, about 475 watts of rated capacity, which any portable generator on the shelf beats several times over. Match the generator to the load, and add up the load with the Electrical Load Calculator rather than guessing.

The cord from the generator still matters

A generator has to sit well away from the house, which means a long cord out to it, and a long cord loses voltage the same way any run does. Use an outdoor-rated cord, size it for the total load and the distance, and keep the display on GFCI protection; a generator does not remove the shock hazard of a wet connection in the yard. The Extension Cord Voltage Drop Calculator checks that the cord to or from the generator holds voltage.

The short version

  • Most displays: a 2,000-watt generator is plenty. Lights, spotlights, and inflatables rarely total 500 watts.
  • Add a fog machine: step up to 3,000 to 3,500 watts. The heater alone can pull 1,000 watts or more.
  • Size it from the running total. Add the nameplate watts, divide by 0.80 for headroom, and clear the motor startup surge.
  • Carbon monoxide is the real hazard. Outdoors only, at least 20 feet from the house, exhaust pointed away, CO alarm inside.
  • Never back-feed the house wiring. Plug the display straight into the generator.

NEC reference

NEC 2020. The 80 percent headroom used here mirrors the National Electrical Code (NEC) continuous-load rule in 210.20(A) and 210.19(A); a continuous load is one expected to run three hours or more per the Article 100 definition. Outdoor receptacles and cord-connected equipment at a dwelling fall under the GFCI requirement of NEC 210.8(A). Connecting a generator to a home's wiring is permitted only through listed transfer equipment under NEC Article 702 for an optional standby system, which is why back-feeding a wall outlet is both unsafe and against code; powering a display directly off the generator's own outlets does not involve the house wiring at all. Watts equal volts times amps is the power relationship, not a code value. The generator carbon-monoxide figure and the 20-foot placement guidance are from U.S. Consumer Product Safety Commission materials (CPSC, 2024); the wattage and surge figures are typical 2025 homeowner values, and your equipment's printed ratings govern.

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.

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NEC Code Quickstart

This guide covers one calculation. NEC Code Quickstart walks all twelve exam calculations start to finish, each with a worked example and the exact code reference: ampacity and derating, breaker sizing, voltage drop, box and conduit fill, grounding, dwelling load, range and dryer demand, motor circuits, and transformer current. Written for the 2023 NEC with notes for the 2026 edition.

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