You can fit the production unit inside the house, they are not that big. Leave your tank outside. It has to be pretty damn cold to freeze 1000+L of water. So cold in fact that if you have a 1 tonne block of ice in your back garden you are not likely to go out cleaning windows anyway.
My tank is outside, the only time it has ever frozen was on the 8th of January 2010 when it dropped below -20 here.