I always find it quite suspicious that if someone has a formula that can identify homes that will double in value, get zero-cash down financing, and multiply your money at an unlimited rate that they would ever freely share that information for any amount of money, lol.

I would think some type of sealant on the inside walls and a good de-humidifier along with double checking the downspouts on the house would be sufficient. 

I went down to the crawlspace just to double check, and found a lot of water.

It probably would not have mattered much if he paid double or triple when you factor his appreciation for decades.

You are looking at double that.Some possible reasons:- Inefficient heating system- Leaky building - old windows and no attic insulation- Tenants leave windows/storms openTo me, the heating expense problem is a huge plus for your investment.

It had a double up impact. 

One bath is in the finished basement (mostly finished, not laundry area), oversize 1 car garage, separate tool shed, privacy fenced back yard, central a/c with gas forced air heat, newer roof, vinyl siding, new-ish double pane windows.  

He manages our 2 double sided units (all rented).

On the flip side you'll want to figure that you are getting to double dip appreciation and income while the reverse is going on.  

The cost with install will probably be double the old unit.If you have an old water heater now is the time to replace it while the hot stack are still available!