What it draws
Box Fan
A fan is the most useful comfort load per watt-hour in the house during a warm outage. It does not cool a room, it moves air across skin, and that distinction is what makes it affordable on a battery when air conditioning is not.
Typical draw, and the number that actually applies
A household box fan commonly draws somewhere between 40 and 100 W depending on size and speed setting. The label on the fan gives the figure for yours, and the lowest speed setting draws considerably less than the highest.
Read the nameplate. It is usually a sticker on the back, inside a door, or on the power adapter, and the figure printed there is a maximum for that specific unit rather than a typical reading. Any range on this page is a starting point for arithmetic, not a substitute for that label.
- Running watts used here
- 60 W
- Duty share applied
- Continuous
- Average draw for the estimate
- 60 W
Hours from a 1024 Wh battery
Estimated hours from the reference battery at 60 W average draw. An estimate, not a guarantee.
The arithmetic, in full
hours = (rated Wh x 0.85) / average watts
average watts = 60 W running x 1, continuous = 60 W
= (1024 x 0.85) / 60 W = 870 Wh / 60 W
The estimate below assumes a fan running continuously at a middle speed setting. Running it on low, or running it only in the room people are actually in, stretches the result considerably.
The derate of 0.85 covers inverter conversion loss and the share of rated capacity a pack will not hand back. It is one planning figure applied to every unit on this site, not a measurement of any particular model.
Starting surge
A fan motor draws more current for the moment it comes up to speed than it does while running. The spike is far smaller than a compressor's, but it is the reason a fan is classified as a motor load rather than a resistive one.
Duty cycle
This load draws continuously while it is switched on, so no duty share is applied and the average draw is the running draw. Switching it off is the only thing that reduces it.
How to get by without powering it
Every watt-hour you do not spend is one you still have. These are the moves that cost nothing.
- Open windows on opposite sides of the house after the outside air has cooled, and let the pressure difference do the work for nothing.
- Close blinds and curtains on the sunny side during the day. Keeping heat out costs no watt-hours at all.
- Move to the lowest floor. Basements and ground floors stay meaningfully cooler than upper ones.
- Run the fan only where somebody is sitting, and on the lowest setting that helps.
Where this sits in the sequence
This load becomes realistic at stage 3, and not before. Read that stage including the part about what it does not cover, because the limits are the useful half.
Related gear
Products live on the gear pages rather than here, because the decision on this page is about arithmetic and the decision there is about hardware.