If you could do it differently, owner occupied is easiest to get a HELOC on and has the lowest interest rates.  

I want to purchase an investment condo for $150,000.I want to get Heloc loan from my other investment condo for $50,000 and use it as downtown payment for this condo.Can I get a 30 year fixed conventional loan for $100,000 and use $50,000 for down payment from heloc?

The amount of equity I call pull is less than the cash I have but not significantly less.When doing this analysis it struck me that it may not be worth using a HELOC for the simple fact that the interest rate is ~9%* while the funds in my high yield account are only yielding ~5%*.

Did you ever find a solution for a 3rd position heloc?

You will owe exactly the same amount of taxes if you get a heloc or not. 

I also would not use your heloc unless you plan to cashout refi one of the properties once the rehab is complete - if you dont cashout refi one of them, you wont have any way of extracting the rehab funds to pay off the heloc. 

Is it foolish to consider using the HELOC for the down payment?

@Keith Angell I'd say you are on the right track with the HELOC. 

I like the idea of using a HELOC for value add projects where you can refi in 12 months to pay back your HELOC.

I do not have to much cash for a down payment but was thinking of doing a HELOC on one of the rentals to get more cash and go the BRRRR method.