I get the whole "come home to a warm fire" advert thingie, but it's terribly expensive. A 40 K bag of coal in my area is €20.00 and lasts about 3 days if used sparingly. Duncan Stewart had a guy on who said 70% of the heat went up the chimney. I lit one over Xmas & new year week, and then blocked up the chimneys with my own homemade version of a chimney bag. I made it with a strong plastic bag and left-over attic insulation. Works fine and saved me the €35 those things cost in the shops. I also noticed during the arctic weather, that the cold coming down the chimney was something else. The heating was on full blast until I blocked it up.