Thank you! Yes, I am using transient calculation and I've noticed it takes some time to run. I have tried the Patch option but it didn't seem like the water cooled down at all, I could only notice the changes in the temperature of the tank around the water as it got heated by the water. So I wasn't sure whether this option was a correct way to do it. But in general the Patch option gives a certain domain an initial temperature (and not a static temperature), is that correct? Then it would be what I need. If I can tell correctly, I cannot give different temperatures to different parts of the model in the standard initialisation.