Dehumidifier size calculator
Answer four quick questions about your home, damp and washing to see what size dehumidifier you need (12L, 16L, 20L or desiccant), which models to shortlist and what it costs to run.
By Matthew Smart · Rates correct as of 5 October 2026
How to use it
- 1Pick the size of the home (or the part of it) you want to treat.
- 2Be honest about the damp: condensation on windows is light, a musty smell or wet sills every morning is regular, and black mould or damp patches is severe.
- 3Tell it how often you dry washing indoors and how warm the room is in winter. Temperature decides whether you need a compressor or a desiccant model.
Dehumidifier size calculator
Answer four questions about your home. The calculator suggests a capacity and type, names the models I would shortlist, and shows what that size costs to run at your tariff.
Compressor dehumidifiers lose efficiency as the room cools; desiccant models keep working down to about 1°C.
Pre-filled with the Ofgem Energy Price Cap unit rate for 1 October – 31 December 2026. Change it to the rate on your own bill.
Your estimate
- Recommended size
- 20L
- TypeCheapest to run in a heated home
- Compressor
- Model to shortlistor the Pro Breeze OmniDry 20L
- MeacoDry Arete One 20L
- Running cost, per dayAbout 230W for 6 hours
- 36.3p
- Running cost, per winter1 October – 31 March, at full power
- £66.11
Compressor dehumidifier
Sizing follows the rules of thumb in my dehumidifier size guide. Running cost assumes typical wattage for the suggested size, at full power for 6 hours a day, at 26.32p per kWh (Ofgem Energy Price Cap, 1 October – 31 December 2026). Real costs are usually lower because compressor models cycle off at your target humidity.
A starting point, not a survey
This uses the same rules of thumb as my size guide. It cannot see your walls. If damp is coming from a leak, a failed gutter, rising damp or a blocked air brick, no dehumidifier will cure it, so fix the source first. If you sit between two sizes, go up one: a bigger machine reaches your target humidity sooner and then idles.
Rates correct as of 5 October 2026. Updated each time the price cap changes.
Our top dehumidifiers right now
Cheaper to run usually means lower-powered, not worse. These are the models that scored highest in our dehumidifiers line-up.
1MeacoDry Arete One 20L
2Pro Breeze OmniDry 20L
3Duux Bora Smart 20L
Written by
Matthew Smart — Founder & Editor20+ years working in home and garden maintenance Exeter, Devon, UK
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