I've used the Bigger Pockets calculator do look at the numbers but I think I still need some encouragement to actually go for it.

This is a very "back of the envelope" calculation. 

@Bjorn Ahlblad it is a little hard to calculate the average, which is what got me thinking about posting the question.

I would use a simple depreciation calculation by looking up the average lifetime of your HVAC system and dividing the cost of the system by it.

Biggerpockets also has a calculator you can use to analyze deals and I highly recommend you start this as soon as possible, even if you are not ready to buy.

View report*This link comes directly from our calculators, based on information input by the member who posted.I already own this home in another state that my parents live in.

Any payments on the balance remaining from the original loan must be included in the debt-to-income ratio calculation for the refinance transaction."

With that info, you should be able to use the Bigger Pockets calculator to start running numbers.

*This link comes directly from our calculators, based on information input by the member who posted.

They calculate your expectant DTI in consideration of you using 100% of your HELOC.