However, for rentals, you do need to have someone monitor and add water to the system.   

I also monitor Colorado.gov for state issues and every Realtor associations.

If they're relatively small, open concept and 1 story then you could do a vented gas rinnai monitor heater.Or if it's more cut up and you've got high ceilings then you could run a forced air furnace with the duct work at the top of the ceiling w/ a drop ceiling below to hide the duct work.

I acquired a property in Illinois that had higher levels of radon and it was as simple as putting down sensors to monitor. 

I don't want to rely on guests to monitor the levels.

Great 👍 Hopefully Karla is still monitoring this post 2 years later …?

I think that is always recommended and it is something I do.My inspector has uncovered things they werent aware of and has also alerted me to issues to monitor to make sure they are rehabbed properly (for instance ensuring that the electrical scope included adding additional circuits because the current number was deficient).

Both can be remotely controlled/monitored.

It's not completely passive as you have some work to do in finding operators, learning about asset classes, etc - but once you make the investment you have nothing to do but monitor the ACH's into your account (Hopefully) and read reports.I have done both active and passive investing and had great results with both - you just need to decide which route you want to go and then commit to it.Good luck!

While it sounds amazing to have 20 doors rented out, you also have 20 different families to contend with, potentially several property managers, the tax returns and monitoring the cash flow and expenses, plus overhead of physically owning the real estate (mortgage, repairs etc).I wanted to have time and geographical freedom, which is something I feel most investors want - but it often gets covered up with "financial freedom".