Conventional Systems All conventional solar water heaters used in areas that freeze suffer the limitation that if the water is left in the tubes during freezing conditions, the water in the tubes freezes with the result that the tubes burst. Many draining solutions have been tried with good effect and most of these appliances are equipped with frost plugs that prevent damage to the system if it has not been drained.

Vacuum Tube systems Draining solutions and frost plugs are not an option with the vacuum tube models. Happily, there is no need of them since water in the tubes does not freeze readily. Water keeps circulating as long as the temperature remains above 3.98 degrees Celsius because it's density is changing.

Remember that the vacuum tube converts light to heat and sufficient light will arrive, even on a cloudy day to compensate for the losses when there is no light. The upshot of this process is that all water in the entire system must fall below 3.98 degrees Celsius before any damage can be done.

Pumped systems simply pump warm water through the manifold, which prevents damage from occurring. Thermosyphon systems have very well insulated tanks containing several hundred litres of water, consequently, it takes a great deal of cold to freeze the contents.

Fortunately, few people live in the areas where light is not available for long periods of time and they do not use solar hot water.