But still, it is unfair that the other house mates should have to stump up for gas, that is being used for the times when they are out of the house. I wouldn't keep the gas on all day to keep myself warm and then expect the others to pay for it, that's just wrong.
Can your work from home friend not put on some extra jumpers, hoodie etc. to keep warm? Or at the very, very least turn the temperature on your heating down a few degrees to try save some money. I would have thought between say 15-18C would be a sufficient temperature.