How much heat are you losing up your chimney? A typical house loses around 4% of household heat up chimneys, when the fire is not lit and the central heating is on. The Chimney Sheep is a plug made of thick sheep wool that fits into the chimney throat and prevents all that warm air from escaping, saving money on your heating bill and making your home more snug into the bargain.There are nine different sizes and these fit most UK chimneys. However chimneys vary such a lot that we also do made to measure Chimney Sheeps at cost effective prices.