Here’s how I’m currently thinking about it:The interest rate on my existing property is 3.5%, so I’d like to maintain that rate rather than refinancing the entire loan.

The first house that I bought was 17 years old, 3 br, 1.5 bath, brick ranch house with hardwood floors, Andersen windows, ceramic tile baths, gas heat and a brand new roof. 

@Jason Piccolo or @Ram Go, what is the loan balance, interest rate, and when does the loan mature?  

You've probably heard of big Landlords losing property, but only because they were flagrantly violating Fair Housing, running a slum, or otherwise violating the law in an egregious manner.

The modeling of this is actually pretty easy (see link: 42-unit proforma sample), but my model treats the pre-refi loan as I/O, but that can be updated based on your deal.

@Angelica Byrnecan you just save up enough until you are able to house hack? 

But to answer your question, House canary is good for rent rates, zillow is a good tool for property data and for seeing what is for rent for how much, sales comps etc. 

If you Bank/Lender does not allow it you can refinace the mortgage into a DSCR or true Portfolio loan program. 

It's growing rapidly and price of labor/ housing is dirt cheap.

Perhaps you have coverage for the replacement value BUT the insurance company when calculating the replacement property uses modern building materials like drywall but your original house had plaster which is much more expensive.