Attic Insulation on Rental - Install or not?

[Bret Weigel]

Hi all, I had some tenants move in last month to a 3/2 SFR (I just closed on the property a month prior) and I really like them a lot. Good people. Anyways, the first day in, we realized the hot water heater needed replacing. The second day in, they realized that the house was not cooling to the temperature they had the thermostat set at (mind you we're experiencing a 100+ degree heat wave this summer and summers here are always hot); however, the house felt cool and the HVAC folks checked the unit and everything was running accordingly.
Long story short, I told them that I'd look at insulation in the attic as a possible solution. I received a quote and was wondering, since the equipment itself works fine, and adding the insulation will reduce their utility bills by 15-18%/month, does it make sense to ask them what they'd like to do (i.e. ask for some help in the bill) since it's not absolutely necessary to the house? Or what is my approach? 

Thank you.