"You don't know that heaven exists; per Scripture, you can't know that. You have been told that heaven exists and you believe that you have not been lied to. That is clearly your choice to believe that way, but you can't rationally expect everyone else to believe without evidence. Threatening a non-believer with hell is the equivalent of threatening any rational adult with the boogeyman." -Michael Lamb

Our belief in the existence of Heaven isn't simply based on a trust that we have been told the truth. The trust we have in God isn't like the blind trust believers have in books or the words of professors--when it comes to baseless and unscientific Darwinian evolution.  Faith in God is not believing without evidence. It is based on evidence. This is the teaching of the Bible and the experience of those who obey its words:

“He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son. And this is the testimony: that God has given us eternal life, and this life is in His Son. He who has the Son has life; he who does not have the Son of God does not have life. These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God” (1 John 5:10-13).

What you don't have knowledge about is that this knowledge is more than an intellectual belief. God "seals" the sinner that obeys the gospel with the Holy Spirit so that he has “the witness in himself.” This is the new birth of which Jesus spoke in John chapter 3. Without it you will not enter Heaven. So we can “know.” Now you know.