Tenant compains about not enought heat!

[Sarah Byun]

We have a 3 unit property in Montgomery County, PA.  It's been just less than one year since we purchase this property.  The previous owner had not taken care of the property well and had the first floor tenant control the thermometer for the all 3 units.  It was the oil heating system which was costing over $10K a year!  The heater got broken over the summer so we decided to replace (make an investment)  to replace the oil heater to gas heater.  We have the Nest thermometer installed so we can control the heat and we have set it to 73 degrees.  Then, I get a call from my 1st floor complaining that the heater is not working and that it is too cold.  My 2nd and 3rd floor tenants has no problem and they have additional portable heater running to keep themselves warm. 

We are ready to renew the lease and will be increasing our rent due to management cost, taxes etc.  1st floor tenant has been there for over 12 years and never got a increase in her rent and complains about almost everything.  (Want to color the front door for the holiday, the sink is keep getting clogged).  We don't want to lose a long term tenant but, what will be the best way to handle this situation.  Many experience landlords, please share your experiences.