You probably won't notice a drafty door until the weather becomes cold. But if you wait until the weather becomes cold. But if wait until then to replace  mangled weather stripping, your fingers are likely to become numb in the process. So set aside a pleasant September or October day to do the job.

Felt or foam weather stripping is inexpensive and easy to apply, but it doesn't last long. You're better off going with vinyl, silicone or metal. The U.S. Department of Energy has an online chart that compares the options. Please refer to: www.energysavings.gov