Two things come up again and again in a UK flat: whether the damp you can see is going to turn into mould, and whether the way you dry your washing is quietly costing a fortune. Both are answerable with arithmetic rather than opinion, so we built a tool for each. They are free, they need no sign-up, and nothing you type is sent anywhere — the sums run in your own browser.
Why we built these rather than writing another article
Most advice about damp and drying costs is generic, because it has to be — a guide cannot know how cold your walls are or what you pay per unit. A calculator can. Put your own readings in and the answer is specific to your flat, which is the only answer that is actually useful.
Both tools show their working. The condensation checker uses the Magnus formula for dew point, the standard approximation used in meteorology and building physics, and compares it against the surface temperature you supply. The cost calculator uses nothing more exotic than watts × hours × unit rate, with the current Ofgem price cap rate as a starting point that you can overwrite.
Once you have your number
Both calculators point at the same two fixes. If drying is the problem, a heated airer and a dehumidifier working together cost a fraction of a tumble dryer. If condensation is the problem, pulling the humidity down is what stops it forming on the glass.
Best heated clothes airers
Best dehumidifiers for drying clothes
Best dehumidifiers for UK flats
Best hygrometers for monitoring humidity
Using these on your own site
Journalists, landlords, letting agents, tenant advisers and community groups are welcome to link to either tool, quote the figures they produce, or point residents at them. No permission needed and no attribution required, though a link back is always appreciated. If you want a figure checked or need something explained before you publish, get in touch and we will help.