I have air cond. Running but son says even if he keeps his window open when it is running, it will not effect the elec. Bill. Is this true? Same with heater being run, he will keep open his window , stating it won't effect the elec. Bill

Close the vent in his room and then his door. He'll find out. Yes, it certainly will affect heating and cooling costs BUT, if the outside air is less than the set point, he may actually cool the house.

Of course it is, if window is open the air will run harder and longer trying to cool outside, same with the heat, with window open it will use a lot more electric

Son is seriously WRONG, as was explained. It will certainly increase your heating and cooling bills. Block off the air vents to his room and make sure he keeps door closed.. but even that will raise your bills because interior walls are never insulated.

I'd nail his windows closed if he refused to listen.

Also make sure you block any draft that may go under the door. Keep track of your bills, and send him his share.

My guess is the son is another young Einstein (I'm being sarcastic) with all the answers and no job or income and doesn't know the value of money yet since its not his. I think keeping track and sending him a bill of his share is a WONDERFUL idea even if you know he has zero income to pay it NOW, but explain you expect to be paid (even if you really might not). Would give him something to think about. If he's getting an allowance...tell him its all going towards the utility bill instead...won't take long for him to get the point I bet.

Kids say the darned'st things? If you have an Alarm System, you can have it shut off AC if a door or window is opened more than 5 minutes(or any time you like). He will likely keep the door/window closed? Does his room have a Smell to it?