You’re replying to somebody from the UK. They want it warmer than 18C inside. In winter it is typically much colder than this outside so they’re saying their heating won’t get the house warmer than this even if windows are only cracked open.
> The minimum house temperature your home should be kept at to avoid damp, mould and condensation is 18°C, according to health and energy experts.
That article and the supposed experts are idiotic. Condensation is a function of relative temperatures and humidities. If your house is warmer than outdoors, then you're not going to get condensation from outdoor air.
The outdoor air isn't really relevant, the issue is human activity (breathing, showering, laundry, etc.) raising the indoor humidity when combined with low indoor temperatures causing surfaces to approach the dew point. Particularly external walls or windows that will be a lower temperature than the room as a whole.
At 70% RH and 15C air temperatures, the dew point is 10C - which could easily be achieved along the exterior walls of an older more poorly insulated house.
Spindly old grandmothers can crank the thermostat. Everybody else who cranks it then proceeds to whine about the cost and air quality is being an idiot. Put on a sweater.
