You can list your unit on there, as well as do background and credit checks and collect rent.In addition to asking a local realtor for the rental rates, you can look at the rents of similar properties in the area, which you can find on places like Zillow and Apartments.com

Additionally I invest purely for cashflow.

What is relatively new is the “mortgage stress test” where banks shall add an additional 2% on the top of the landing rate to make sure people can truly afford it.

In addition to what's been said above, the invoice should clearly state the address where the work was done and your company's name.

We were at a loss for how to get cash to purchase additional property, and are considering taking out a mortgage on the duplex.

Plus don’t forget closing costs on each not to mention most properties need at least a little work and additional cap ex to turn into performing assets.

@Nadir M.Two additional thoughts:1) A central boiler is a cost trap for owners.

In addition you'll have to make the monthly interest only payments.

There is additional reserve requirements when buying more than 1 unit, so get up to speed on those so you are prepared to have those in place at the time of closing your loan. 

These are professionals with additional training and a stricter code of ethics.