Can the collectors also be used to heat a spa?
Solar pool heaters are a great way to heat both pools and spas. They are easy to maintain and provide free heat after the initial installation cost. The collectors can be mounted anywhere where they receive direct sunlight for as much of the day as possible. Using a solar blanket at night and when the pool is not in use is also a great way to preserve the heat that you gather during the day.
Yes, but you will need a backup heater for evening use to. Those pools with an attached spa and spillway are well suited to a solar collector. Most have valving allowing you to send the heated water directly to the spa while spilling over and heating the pool. In this situation, the spa will always be the warmest part of the pool.