Heloc for down payment

[Jeremy Gerondal]

Hi! I am a beginner investor. I have a paid for property with rental income, I was looking to do a heloc on, to use as a down payment for a mortgage. 
2 questions: 

1- Would I have to draw the funds and season them in my bank account for however long is required by the lender since it is a transparent secured source? 

2- Would the balance affect my DTI and thus the max amount I can borrow? Or would lender use the monthly payment (max or average)? In the second case, since the rental income are likely to negate the heloc monthly payment, would it affect my DTI and loan ability?

Thank you in advance!