I have bought a sonic humidifier that has a 1 litre capacity and takes about a day to emit this moisture into the air. I want to know roughly how much effect this might have.

I'm going to ignore effects of sources/sinks/storage like showers/cooking/washing/ventilation.

If we imagine a starting point of 20C and 25% RH, then this is about 4 g/m^3.

Now let's imagine instantaneously and evenly adding all that 1 litre (1000 g) of water into the air in my flat (72 m^2 and about 3m tall, so volume of about 216m^3). This would be adding 1000/216 = 4.6 g/m^3.

So we would be roughly doubling the moisture content, and

**. This would be a great result.**__the RH would increase to about 50%__*Future blog update...estimate the effect of time on this scenario by looking at the rate at which the humidifier works and the rate of ventilation in/out of the flat...*