Is it better to line dry inside or outside a house? On a winter night (so no radiation from the sun), my house is 10°C warmer than outside. Both temperatures are above freezing. I measured the humidity and found out it to be the same both outside and inside.

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*Is it true that it is better to line dry the clothes inside the house?


*Humidity will raise inside the house eventually. At which humidity % it is better to move the clothes outside?


*If there is a blowing wind outside, will it make the process of drying faster?
 A: In general, evaporating water out of clothes happens faster when it is warmer, when the relative humidity is lower, and when the air is moving.
In the wintertime, the relative humidity inside a heated house is usually quite low (this is why your skin gets dried-out and crinkly in winter) so the best place to dry clothes in the wintertime is indoors, in a heated room, above a heater vent which is discharging warm air into the room.
A: You note that relative humidity is the same outside and inside, which means that you are really asking whether the 10C temperature difference in favour of inside outweighs the fact that humidity inside will increase as linen is drying.
The answer will depend on several other variables:

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*how much water do you need to evaporate?

*how large is the room?

*how well is it ventilated?

*what is the drying constant of your linen?

Based on the first two, you could calculate an increase of the relative humidity in the absence of ventilation. At 20C, 1% relative humidity corresponds to 0.17 g/m³ of water. So one thing you can do is find out whether there'll be a significant increase in the humidity level of the room.
Then, you're left with many questions to actually get to the dynamics of drying. First, you have to wonder whether the humidity will be homogeneous in the room or not. Experimentally, I can tell you it's not, as my linen dries slower indoors when not spaced enough. [And so, yes, a wind outside speeds up the drying.]
Then also, you have to know how good is your linen at drying, which, to be calculated and not experimentally measured, would include getting to the typical pore size (possibly with two different scales, the weaving scale and the fibre scale). You could also get it experimentally. This would allow you to use Dalton's law to estimate evaporation rate with the different partial pressures outdoors and indoors.
All this being said, with a 10C difference and same relative humidity, I'd dry my linen outdoors. In general, I'd dry linen indoors only when relative humidity is very significantly lower there, or it freezes outside (*), or possibly if I have very little to dry and can spread it well apart.
(*) ...which turn out to be often both true or both false, as @nielsnielsen mentions, simply because saturating water pressure increases with temperature, so outside cold air is low in absolute humidity (it has condensated out) and gets also low in relative humidity when you heat it up indoors.
