Can anyone help me with this please? 

"I want you to know" versus "I wanted you to know." 

Are they both grammatically correct and pretty much one and the same? I understand the difference of tense forms want/wanted, so please no lesson needed on that. I am sending a letter to a friend and I would like to thank him for all of his help. So should I use "I want you to know how much I appreciate your help" or "I wanted you to know how much I appreciate your help"? Insight needed please.