The house on the corner who have ducted heating (we had a squiz when it was for sale), have just had their gas bottle removed. I guess they worked out it was too expensive, and have gone back to wood. i don't know them well enough to ask how much it cost.

if you can find out how many litres of gas your unit costs per hour, you could do a rough calculation by asking how much your local gas provider charges per litre and estimate how often you would have it on