To be honest the best way to stay warm for the least amount of money in winter is to sit around the house in a onesie and buy a large thick rug for the lounge. Supplement this with a 1kw panel heater (depending on size of room) and this works quite well.
Calor gas heaters produce moisture which promotes mould (i had this problem last year), unless you have a window open which lets in the cold air defeating the purpose of having the fire in the first place.
Using air con seems a flawed way of heating as well as heat rises and that source of heat is near the roof. I tried it and the air at head hight was warm but legs and feet were cold. Maybe the newer air con models are better than what i currently have.
Pellet/log burners are an expensive initial outlay and for the sake of 2-3 months a year, it it really worth it?