Winterizing an indoor pool
We have an indoor pool which even though we live on a lake in Ontario Canada my wife uses the pool year around which she finds therapeutic for her aches and pains. Because of the high and getting higher cost of oil which we use to heat the pool, we are planning on shutting down the pool from this fall through to next spring. Our concern is will the water freeze if we turn off the heater for the winter considering that the pool is indoors and the only heat would be from the ground that the pool sits in and heat from the sun that comes in through three very large windows and two glass sliding patio doors. One end of the pool room consists of large granite boulders which hold heat when the room is warm from the sun and helps to heat the room when the sun goes down. Also the winter can go down to 20 degrees below zero. If necessary I can keep the heater on to keep the water a few degrees above zero. Since moving water will not freeze I can also keep the circulating pump on and/or get a bubbling machine which some people use in winter to keep the water from freezing around their docks. The representative of the company that services the pool feels confident that all things considered the pool won't freeze if left to its own devices but some more opinions would be appreciated. I'd hate to find out the hard way that he's wrong.