We would love to do in such a way that it would improve his Debt-to-income ratio, which is a challenge for him at the moment, especially after having acquired this loan on the current $550k home in Denver.

Separating from the military is a challenging culture and social change that I understand very well as a veteran.

Couple challenges...1.

Being that you are a new investor, it may be challenging for you to get a business line of credit since you have no LLC history.  

Finding deals in the Denver metro area (I-25 corridor) has been a challenge for me.

(they somehow passed) The toughest challenge will be choosing your rums and pacing yourself on that. 

I appreciate your response and obviously want to challenge the idea that I have a case because I'm sure I'll run into these arguments.  

Now, I am up for bigger challenge.

Now, in my dotage(I'm 44;) I look at the portfolio and can clearly see that the theoretically lower cap rate properties have been substantial outperformers over the years on the metric of cash flow- so I'm pruning the challenging(and capturing the principal appreciation, *wink wink*) to replace it with the chill. 

Monitors are not bad (propane or ng) but keep in mind ... with any "single source" heating idea, there will be challenges (one room cold, the other too hot, etc.) -- You mentioned propane.