If your fish house is in your garage or adjacent to the house, and you have gas or oil fired central heating, then why not put in a radiator? I would not recommend running the central heating just to heat the fish house. But in the winter months you will be heating the house anyway. So the fish house will be heated for free! If you are thinking about using this method there are a couple of things to think about; - The fish house needs to be fairly close to the boiler or another radiator. - You should...