We sent an HVAC tech out as soon as she called with no heat on the second floor (1st floor did have heat).

Current boilers are30+ years old for the radiator heat. 

I get to know of problems at times before the tenant notifies me, e.g. an alert saying "The systems has been calling for heat, but the temperature has dropped by 5 degrees", or summer time, "The system has been calling for cool in the last hr but temperature has risen by 3 degrees", or "High humidity detected" is often a sign of a non-cooling system.

Where would your tenant place the litter boxes and how would he empty them (we had one couple who completely clogged a sewer line tossing litter down a sink...not a toilet).Finally chasing fleas and worrying about litters of kittens (or females in heat) are not fun things. 

It shrinks rapidly in heat. 

updated appliances, pulled up linoleum and refinished floors, added electric panels in units, and added instant hot heat/hot water for units Lessons learned?

I'm currently in the process of getting a home with window units that only cool with no heat.

Just replacing a 3 ton HVAC gas heat no duct work,  No more then $4500. 

We had to change the entire entire heating and air conditioning  and heat ducts to get enough room to do the re-framing.

Purchase price: $424,900 Cash invested: $84,980 I bought this property mostly renovated in 2015 in the heat of Calgary's real estate market but I knew this was a good deal and good long term hold property, I made an offer only a few hours after the property was listed on the MLX and ended up in a bidding war with 3 other buyers which I won by having the most flexible terms (apparently I was not the highest offer).