If hell is temporary, heaven is also tempory. The New Testament use of the words eternal and everlasting makes it clear what they mean. Now consider how other verses use these words. God is everlasting. The Holy Spirit is eternal.
Redemption is eternal.
Salvation is eternal. The kingdom is an everlasting kingdom. The same words in both Greek and English are used to describe the future punishment of the wicked that are used to describe God, the Spirit, salvation, and the kingdom. To Make You Happy, Watchtower Bible and Tract Society of Pennsylvania, Inc., p. 92. Ibid., p. 97.