The collector panels are usually mounted on a nearby roof, or ground-mounted on a tilted rack. Due to the low temperature difference between the air and the water, the panels are often formed collectors or unglazed flat plate collectors. A simple rule-of-thumb for the required panel area needed is 50% of the pool's surface area. This is for areas where pools are used in the summer season only. Adding solar collectors to a conventional outdoor pool, in a cold climate, can typically extend the pool's comfortable usage by months and more if an insulating pool cover is used. When sized at 100% coverage most solar hot water systems are capable of heating a pool anywhere from as little as 4 °C for a wind-exposed pool, to as much as 10 °C for a wind-sheltered pool covered consistently with a solar pool blanket.