If you have a furnace and air conditioniner in one unit it doesn't matter because the thermostat acts like a switch.

There are alternate options to transfer air to/from bedrooms, but those get somewhat complicated.The cassette fan coils are ugly and take up wall space, You also need a thermostat for each one so you have to plan for labor for that wiring.In my experience the Japanese products (mitsubishi, fujitsu, daikin, etc.) are better technology than the American manufacturers (trane, lenox, etc.).

The rationale for considering the Nest Protect is the ability to be notified on my cell phone when an alarm is triggered, the ability to pinpoint exactly which alarm went off (location and whether it was smoke or CO), the ability for the alarm to turn off the forced air furnace (already has a smart thermostat) when it detects smoke or CO, and the ability to turn off the alarm from my cell phone once I know it's all clear.I don't currently get many nuisance alarm complaints at this tri-plex. 

You have to constantly market, answer inquiries, process payments, move tenants in, handle questions about how to operate the TV remote/furnace/air conditioner/thermostat/etc., move tenants out, coordinate cleanings, pay lodging taxes, change your insurance, furnish the property, stock consumables, and more.

Those costs add up quick if you leave a toilet running, or if the hose is left on, or if your contractors feels like setting the thermostat to 70 when its a 110 in the summer for the whole week while you are not there. 

It may just be the thermostat, condenser unit going bad (coils leaking, etc), perhaps its out of freon, or maybe even bad fuse or solenoid.  

I rent a duplex to two groups of two tenants, so you`d think among the 4 of them, somebody could be home for a new AC unit to be installed.When they first notified me of the problem, I asked them to check the breaker, make sure the thermostat was set correctly, check if the unit was coming on at all etc and to let me know their findings.I heard nothing for ten days and figured it was working, but sure enough, when I contacted them to make sure, it wasn`t.I made an appointment for a tech to come out the next day, but none of them were available and couldn`t agree on a day they`d be home until several days later.When the tech came out, he got the AC working, but barely and it wasn`t worth fixing.I told the tenants I`d have a new one put in ASAP and scheduled an estimate for the next day.None of them could be home the next day, but I felt bad for them and their pets, so I offered to be there for the estimate.  

Don’t give her special treatment(that means don’t give in) and tell her if she’d like to request to do these upgrades herself(installing a nest or smart thermostat isn’t hard) she can pay for it but if she takes it when she leaves she needs to restore the house back to normal.

If it's electric, sometimes the heating elements or thermostats burn out; they cost a little more but all the hardware stores have them.

PLEASE provide me with tipsHow to check if the cleaning crew did their job properly from a remote location, I was thinking of having them take a live video before payment...which remote door locks and thermostats are most reliable?