However, markings on the heat unit were incorrect - turned out the York Furnace was actually an oil heater.

check out the high cost items, too - age of roof, heating/cooling systems.$2,875 Rents x 12 = $34,500 Incomeminus (Taxes Insurance Maintenance Vacancy PM)- $5,500 - $1,200 - $4,800 ($100 per door per mo) - $3,450 (10% vac) - $3,450 (10% PM)= $16,100 Net Incomenow you just need to subtract your (Mortgage x 12 months) to see what's leftoverassume $200k purchase price, 40% down, 5% 30-year = $644.19 x 12 = $7,730.28or about $697.48 cashflow per month

.,  Heat map with percentages? 

LOL  so we move  to places that are more affordable you think anyone want to live in Texas with that heat and humidity after living in San Deigo heck no but they go there because 350 to 500k buys you a super duper home.. and over a million basically a mansion.However those who own 750k homes that rent them for 3k that's not the best use of those assets either right ?

I don't know the details of yours....Things to consider...Frame to accommodate install of windows, run another line of current HVAC system to provide heat/cooling, install a few outlets, lights if needed, exterior cladding to match or coordinate to existing cladding.

We are working to add air conditioner or heat pump to 15 new 14'x56' homes in SC. 

A point of reference, a few years ago a Philly fireman lost his life due to a rowhome fire caused by the heat lamps and illegal wiring in the basement where tenants were growing pot.

Central air through out and zone heat.

There is a large 3 stall heated garage.

I'm personally handy around houses so I used ~$6,000 and some elbow grease to repair a water damaged garage (posts, sheathing, shingles, exterior paint), upgrade to vinyl windows(entry level), painted every wall, removed nicely perfumed carpet and refurbished hardwood floors, replaced kitchen counters and appliances, installed heating duct to 2nd floor. ~2 years later insulated attic with blown in.