I installed one above the BBQ, so it lights up the grill when someone approaches.I installed electronic count down timers for the exhaust fans.  30 minutes in the baths, 4 hours in the kitchen. 

Art, I find it much better to build in to my profits one month vacancy each year to allow for some of the down time we may experience changing/evicting tenants if worst comes to worst. 

They'll survive and can heat water up in a pot on the stove,, showers well ya that's the breaks.if you want you can give a concession for the down time, it's just a part of ownership and some things are just not expected,, at least it's not 50 below and your worrying about frozen pipes,,If they ask say yes if they don't ,, don't worry..Important is you responded quickly and service is being completed.

Certainly you can make 15% on your active investments, but when you factor in downtime of your capital between deal and other constraints, I think 15% across an entire portfolio is tough.Certainly it can be done, but if it's integral to your plan, you need a different plan. 

I own a landscaping business in Illinois and in the winter down time I try and purchase a rental or two.

It drives calls to my phone and traffic to my site and I usually have a great time selling something he couldn't move.Also do some rentals in your down time.

Also to work harder on the pipeline so there is no downtime and continue to chug forward without missing a beat.

Taking over a vacant 4 unit that requires turnover expense in each one plus down time filling them back up versus buying that same building with even halfway decent tenants in each unit can skew your upfront capital needs by a huge amount. 

It is still appropriate to include some expense for utilities as you are factoring in 8% vacancy, so you would have utilities expense during turnover, downtime, etc. 

There doesn't appear to be much downtime but I've only been up and running for a couple months so don't take my word for it just yet.