We have the Nest thermometer installed so we can control the heat and we have set it to 73 degrees. 

Ive heard good things about the nest thermostat too.

Make sure you carry good insurance, insulate the more risky properties into there own nest.

Basically, it's sugar and borax... doesn't kill immediately, so they take it back to the nest and feed it to the queen.I have taken out nests that must have had ants numbering in the hundreds of thousands (Argentine ants with linked colonies.

Or if you want to play it extra safe, you can always get into another business or just keep saving and hope you have a big enough nest egg by the time you're ready to retire :) 

I have heard go things about Nest as well but don't have one.

I save $$$ big $$$ every year because my lead tech takes the time to try to walk the resident/tenant through the problem they are having and resolve via phone if possible.My favorite hero call every time, is when it is 20 below and tenant calls with a furnace out issue, turns out it is simply the batteries in the thermostat, many people do not know that the thermostat in nearly all cases (except for a modern nest) are not direct connect/direct wire and are powered via battery.

BORAX - (look in the laundry soap aisle)sprinkle it where the ants are walking, they'll carry it back to the nest/colony. it works as a 'drying agent' so they ALL just wither up and die...

If not, possibly a bird nest is blocking it. 

I would focus on something like that up front so you make sure not to ruin Mom's nest egg.