How Many Watts Does a Box Fan Use? Running Watts, Amps and Daily kWh
By Seamless Home Team, Home services operations · October 19, 2026 · Updated October 19, 2026
Quick answer
A 20-inch box fan typically draws about 55 to 100 watts. Lasko's published specifications list 56–83 W (0.5–0.7 A) for its Cool Colors B20308, 65–90 W (0.6–1 A) for the Pro Power B20548 and 73–102 W (0.6–0.9 A) for the Power Plus B20801, all at 120 volts. Virginia Cooperative Extension's appliance table, which has no separate box-fan line, puts its closest category — window fans — at 55 to 250 watts. Daily energy is watts × hours ÷ 1,000, so as an illustration an 83-watt fan running 8 hours uses about 0.66 kWh a day.
A box fan is one of the cheapest ways to move air in a house, and one of the smallest loads you can plug into an outlet. "How many watts" has a short answer and a few useful ones:
| Figure | Roughly | Where it comes from | What it is for |
|---|---|---|---|
| Running watts | about 55–100 W | manufacturer spec tables | Circuit and backup sizing |
| Current at 120 V | under 1 A | spec tables; watts ÷ volts | The outlet circuit it shares |
| Energy per day | depends on hours | watts × hours ÷ 1,000 | The bill |
The ranges are typical, not a specification. The rating label or manual for your fan describes it better than any chart.
Running watts: about 55 to 100 for a 20-inch fan
Manufacturer spec tables are the most direct source. Lasko publishes these figures for three of its 20-inch, 3-speed box fans, all at 120 volts:
| Model | Power | Current | Airflow (as published) |
|---|---|---|---|
| Lasko Cool Colors B20308 | 56–83 W | 0.5–0.7 A | up to 1,725 CFM |
| Lasko Pro Power B20548 | 65–90 W | 0.6–1 A | up to 2,000 CFM |
| Lasko Power Plus B20801 | 73–102 W | 0.6–0.9 A | — |
Each figure is a range rather than one number because a 3-speed motor draws different power on each setting. Other brands and sizes will differ; the label on the fan is the authority.
Virginia Cooperative Extension's appliance wattage table has no separate line for box fans. Its closest category, the window fan, is listed at 55 to 250 watts; the box fans above sit inside that range. For scale, the same table lists a ceiling fan at 65 to 175 watts, a whole-house fan at 240 to 750 watts and a portable heater at 750 to 1,500 watts — which is why a fan and a space heater on the same circuit behave so differently.
Energy per day: watts × hours
Virginia Cooperative Extension's formula is the standard one: wattage × hours used per day ÷ 1,000 = daily kWh. Multiply by days of use and your utility's rate for the cost. Its own worked example uses a window fan: 200 watts × 4 hours a day × 120 days a year ÷ 1,000 = 96 kWh a year.
As an illustration only, an 83-watt box fan running 8 hours a day uses about 0.66 kWh — about 20 kWh over a 30-day month. At 16 cents per kWh, that is a little over $3 for the month. On a lower speed, or for fewer hours, it is less. The watts to kWh calculator does the arithmetic for any wattage and running time.
Amps: under 1 on a 120-volt outlet
Lasko's tables put all three models under 1 amp at 120 volts. You can check any fan the same way: 83 watts ÷ 120 volts is about 0.69 amps, and the watts to amps calculator converts either way.
A box fan plugs into an ordinary receptacle that shares a circuit with other loads, so the fan itself is rarely what trips a breaker. Virginia Cooperative Extension notes that when you measure a motor with a clamp ammeter, the reading on start-up can be about three times the running current — brief, but worth remembering when several motors start at once on a battery.
Box fan, ceiling fan or window AC
A fan moves air; it does not cool it. Where a box fan helps is moving air across the people in a room. For the comparison loads:
- A ceiling fan sits in a similar range — 65 to 175 watts in the extension table — and is wired to a lighting circuit rather than plugged in.
- A window air conditioner actually removes heat, and draws several hundred watts to about a thousand or more to do it.
For the whole-house picture, see how many watts a house uses.
Box fans on a home battery
For backup power, a box fan is among the easiest loads to keep:
- It is small. Roughly 55 to 100 watts against a battery inverter rated in kilowatts.
- It is useful when the big load is not. Central air conditioning is often too large to back up; a fan keeps a bedroom tolerable on a summer outage night for a fraction of the energy.
- It goes where the outlet is. Whether it runs in an outage depends on which receptacle circuits move to the critical-load panel.
Refrigeration, heating controls, networking and medical equipment usually come first, as what a critical load panel is explains. The critical load panel planner tests a list of circuits against an inverter's continuous and surge ratings.
Getting your own number
- The rating label or manual — watts or amps for your fan.
- Your speed setting — high draws the most.
- Your hours — how long it actually runs.
- Your electric bill — the rate per kWh to multiply by.
When fans and other small loads are part of a battery backup or electrical upgrade, their circuits are listed and checked during design on the home battery and backup projects Seamless Home coordinates — get a free estimate to start. Coverage is confirmed per service area rather than promised as blanket availability.
Frequently asked questions
How many watts does a box fan use?
Typically about 55 to 100 watts for a 20-inch model. Lasko's spec tables list 56–83 W for the B20308, 65–90 W for the B20548 and 73–102 W for the B20801. The figure for your fan is on its rating label or in its manual, and it varies with the speed setting.
How many amps does a box fan use?
Under 1 amp for the models above: Lasko lists 0.5–0.7 A, 0.6–1 A and 0.6–0.9 A at 120 volts. You can also divide watts by volts — 83 watts ÷ 120 volts is about 0.69 amps.
How much does it cost to run a box fan?
Multiply watts by hours, divide by 1,000 for kWh, and multiply by your rate. As an illustration only, an 83-watt fan running 8 hours a day uses about 0.66 kWh, or about 20 kWh over a 30-day month; at 16 cents per kWh that is a little over $3 for the month.
Is a box fan cheaper to run than a ceiling fan?
They are in the same range. Virginia Cooperative Extension lists ceiling fans at 65–175 watts and window fans at 55–250 watts; the box fans above sit at roughly 56–102 watts. Hours of use and speed setting matter more than the type.
Can a home battery run a box fan?
Easily, in most designs. At well under 150 watts, a box fan is one of the smallest motor loads in a house. Whether it runs in an outage depends on whether its outlet's circuit is on the battery's critical-load panel.