So, I have connected 2 sensors and reading these for about 5 days now. One is outside the window (yellow) and another is connected to radiator (red). I made even a script that reads sensors every 10 minutes and sends reading over internet to public net and saves it to MySQL database. And using XML/SWF Charts, I can see live chart on readings. First problem I noticed right away is outside sensor. Currently here in Estonia, outside air temperature is around 10°C, but sometimes sun comes out and heats outside sensor up to about 25°C. That means that I have to find some better place for this sensor, where sun can't shine on it. Also, I think I should rewrite my script so that when reading outside sensor, then on saving it to database, It should save average value of current and last two readings.
Here is another chart, where temp1 is live reading of outside temperature and temp2 is average of last 3 readings. As you can see, temp2 is little bit smoother.
About my radiators, I found out that they are switched off for night. Every day 23:10, they are turned off and temperature starts to fall. And from 6:10 they are turned on and temperature rapidly raises. I am thinking that if I want some more energy efficiency, then I would also turn off radiators from 9:00 on working days and turn them on on 16:00, about hour before I'm home.