Roth IRA distribution which consists of contributions to Roth IRA

I want to withdraw part of my contributions I made to Roth IRA over the last 10 years to put as a part of downpayment on a house I am buying. I made around $20,000 in contributions and I would like to withdraw $18,000. So, I am not withdrawing any earnings, just my contributions. 

Will the $18,000 distribution be included in my adjusted gross income (AGI)? I understand it won't be taxable (please confirm) since I am only withdrawing the contributions, not the earnings/income. But I also want to confirm if this amount will be included in my AGI. It is important for me to know/understand since I am on Obama plan for medical insurance and the premium assistance/recapture is based on the annual income when you file taxes.


Thank you!