Air conds are provided by you?
Anyway, you did a very big mistake here.
If I were you, I'll measure each appliance's maximum draw(set to lowest and blower speed at max) for 2 hours and take measurement. Like if 2 hours using 2 units, then 4 air conds will use 8 units for 2 hours. 1 day would be 48 units. 30 days will be 1440 units. The water heater, WM and others. Get the average out and calculate.
Then from there you set a price of a room rental, this can avoid your problem.

That's actually a very good suggestion and perspective supersound! I shall definitely consider this.

Always try to think what your tenant will do(is not their property, so they won't other to take care).

That is so true! Part of me is hesitant to rent out this particular house as I've spent quite a bit of money on it (as i was staying there before this).         

For me, I'll just sell and keep the money in banks for FD. Sometimes the yield are better. But provided you don't use that money.

The thought did occur to me, but i keep reminding myself that what i make now will not be the same in value in 10, 20 and 30 years, given the awesome inflation wave coming to this country.