Based on comps, improvements, and regional strength, I believe several of the properties have doubled in value in the 4 or 5 years that I have owned them.Not wanting to sell, my thought is to have them reappraised and pull equity.   

I had fully renovated it before the first tenant, but never had a chance to do much work since then. 

Even if you decide to switch the nature of the heating system, you should, and still may well be required, to perform this analysis.A detailed heat-loss model will also help you prioritize and plan improvements to the building envelope - such as air sealing and insulation.A few missing bits of information,  which may assist the BP community to provide you with some helpful ideas, include:size and organisation of the building: SFH, duplex, triplex, etc.

But I listen to the podcasts every chance I get.

These ad sales are purchased mainly by real estate agents, mortgage professionals, and others who hold an interest in the home buying, selling, and improvement process.

I think it was Jim Carrey who said to Lauren Holly "Oh I get it; you're telling me there's a chance".

To me it is going to most likely be next to impossible for you to do what you want to do unless you are willing to live on VERY little BUT if I was to advise someone trying to do this I would say FLIP as fast s you can until you build up enough to buy multi families Or start and run a successful business The chance of the business failing is huge.

Another example would be if John never sold the inherited house but used joint funds to make improvements.

Do you by chance have any recommendations for NPN funds or a syndication sponsor?

Try to focus on a target area and get to know it very very well to minimize the chances of buying the wrong deal.