How the figure is calculated
The two markets publish different numbers, so the calculator uses whichever exists. US models from the ENERGY STAR list have an annual kWh figure, but the hours behind it are not published, so we show the yearly cost as-is and do not invent an hourly rate. British models from Meaco publish rated input power instead, so we multiply watts by your hours and by a duty cycle, because the compressor stops once the humidity target is reached.
The duty cycle starts at 100 %, the maximum, and stays visible so you can set it.
What drives the cost
Capacity and efficiency: a 50-pint Frigidaire FHDD5033Y1 is listed at 520 kWh a year against 249 kWh for the 20-pint Midea MAD20S1QWT. Room humidity and temperature decide how long the compressor runs, and the humidistat setting decides when it stops.
Worked example
US: the Frigidaire FHDD3534Y1 (35.85 pints/day) is listed at 379 kWh a year, which at 18.31¢/kWh is $69.39. The large FHDD5033Y1 is $95.21 a year.
GB: the MeacoDry Arete One 20L draws 216 W, so an hour costs 5.69p at 26.32p/kWh. Eight hours a day is 45.48p, or £13.64 over 30 days at full power; if the compressor runs 70 % of the time, that drops to £9.55.
Running it efficiently
Set the humidistat to around 50 to 60 percent rather than continuous, close windows, and empty or drain the tank so it does not stop. Drying laundry indoors with a dehumidifier is usually far cheaper per load than a vented tumble dryer.
Questions
Why do US models show a yearly figure but not an hourly one?
ENERGY STAR publishes annual kWh without the hours behind it, so dividing it into hours would mean making a number up.
Can I use my own dehumidifier?
Yes. Type its wattage from the label and the hours you run it.
Is the standing charge included?
No, only the energy used. Standing charges are the same whether it runs or not.