But don't forget that you have expenses like maintenance, taxes, insurance, heat, hot water, electricity, management, etc. 

Building is 1968- will have to find out about lead paintPitched Asphalt Shingle Roof with aluminum gutters, Ill have to double check but think its 5 to 7 years old.Separate meter for electric but owner pays for heat (Oil-- not sure conversion gas is worth it but option is there)Good question about wiring, i would've never thought of that..I would assume I want it to breakers..

Had to replace a frost-proof sillcock.Even some years back when we had a serious drought, the water was still good - little bit of sulfur smell in the heated water, but that's it.

We split it by number of bedrooms rather than square footage.The only push back we've gotten is on heating bills in units with poor heat distribution/insulation.Remind tenants that they are splitting all the base charges which is an overall savings for them compared to separate utilities.

If I could add to what John Leavelle said  ; it could cost as much as $60,000 to do a full Rehab here in the Philadelphia Area        My Friend Sean just did a Rehab in the Port Richmond Area Close to Fishtown and he it was $60,000        Sean has done many flips and I thought he went as "Budget" as you possibly can , for an example ; he paid $7,000 for a brand new HVAC  (Heat & Air Conditioning)  with new duct work , where that would have been double in the open retail market       Good luck with the project & feel free to reach out to me if you need any help or have questions SincerelyRick      

I used a private lender because this property was a "3 Season" cottage on a lake and didn't have heat or insulation, and therefore wouldn't qualify for a conventional mortgage.

A good example is a 2 family with structural, electrical and plumbing issues on a home that is 100 years old and needs lots of work but the seller was hoping to get 190,000 and currently includes heat, hot water and electric and is only getting 1100 for the side that is rented. 

We had high velocity heating and cooling (connected with our tankless hot water heater in basement and its own AC since we had 3 zones) and ducting in an 1860 Victorian I owned.

And you have 2 or more of everything:  heating systems, electrical boxes, kitchens, etc

gas water heater dryer and central heat ok.