It also allows you to put a bigger chunk in, if you have enough income, and it allows you to put it in to a Roth plan so the earnings are tax free forever once you have the plan for 5 yrs. 

It will be my primary residence for about 1-2 yrs until I buy the next one therefore I am analyzing it as a rental.

She is the original owner of a little over 20 yrs but has been having issues with the bank and got a little behind on the payments.

Up here we we have long and serious winter, going from anything 20+ years old (75% efficiency) to a newer 85 - 95% efficient boiler would payback in 3-5-yrs

Within the past 3 years I did learn how to somewhat read the tempo of the NYC market and I've been spot on with calling what changes would happen for the past 2 yrs.

As long as you are in a position to take on the property when the renewal comes, you should be fine ... if the renewal is in 5-yrs, its not so bad, but if the Vendor only has 1-2 years left on the mortgage....

I was also a little bit confused by the varying rates you mentioned for 5 years and 7 years  with amortization over 20 yrs.

It's an old home, hell, the walls might not be insulated, so even if I were to spend 2-3k on a new, more efficient hvac (this one seems about 10 yrs old), it might just reduce the issue slightly.  

He worked for the government for 30 yrs.  

They lived there for about 11 yrs.