💧What does a dehumidifier cost to run?

Per hour, no — 300 W is a third of a window air conditioner and a fifth of a space heater. Per season, it is one of the larger items in a house, because it runs for months rather than hours. The honest comparison is annual: 650 kWh for a basement unit is more than a modern fridge uses in a year.

No. Pints describe water removed per day under a standard test; watts describe electricity. Larger-capacity units do draw more — roughly 250 to 350 W for a 30-pint machine and 500 to 700 W for a 50-pint — but a bigger unit that reaches the target humidity faster and then cycles off can cost less to run than a small one working continuously.

Set a humidistat to 50% and let it decide. Continuous running takes the room drier than it needs to be and burns hours for nothing; on the other hand, switching it off entirely lets moisture build back up and the machine then works hard to catch up. Cycling on a setpoint is both cheaper and better for the room.

It draws more watts but works at low temperatures where a compressor model struggles. In a heated room a compressor unit wins on electricity; in a cold garage or an unheated basement in winter, the desiccant model may extract more water per kilowatt-hour simply because the compressor one is barely working. Check the room temperature before choosing.

In winter, yes — everything a dehumidifier consumes ends up as heat in the room, plus the latent heat released as vapour condenses, so it is a small electric heater with a useful side effect. In summer that heat is unwelcome and works against any air conditioning in the same space.

Fix the moisture at source before buying more capacity: gutters and downpipes, a bathroom fan that actually vents outside, drying laundry outdoors, and sealing a damp floor. A dehumidifier managing a leak runs forever; one managing ordinary humidity cycles a few hours a day.