A pool is a great place to relax, cool off, and enjoy quiet time, especially when it's in your own back yard. However, when is the best time to replace that pool liner? Experts say it's best to schedule the appointment in February, then have the replacement done in April. This is because the warm days help the pool professionals create a vacuum, and the cool nights help create a seal that holds the vacuum in place. If this seal never happens, the liner will come off when the weather grows significantly warmer. It's important to have a warm day, combined with a cool night, to allow the seal to place properly.