I'm worried that during that because of that rehab period, my DC property could be considered my primary residence since I have a mortgage, and given the fact that I don't currently help pay my parents mortgage through rent and therefore can't validate me staying there.

I've started to lurk in the forums recently and its been pretty educational. 

My inquiry is based on the water and sewer bill we received for a time period where the bank owned the home, prior to us closing on it that was billed to us from the city after we closed.

Typical returns are 5-6% plus any capital gains upon exit with a 5-7 year hold period.

It's been very educational scrolling down every thread title updated in the prior few hours, and clicking on the ones that interest me, to read responses from others, to learn, and to reply if deemed relevant (with occasional humor thrown in).

I am currently learning real estate, reading books, and getting the education needed to implement my desired strategy.

We have began Youtube Video's providing home owners, buyers, and sellers educational pieces in all areas of Home life.

However mistakes here are costly.Getting the right education is the key to your success.

Read books to help educate yourself and change your mentality on money!    

So, my educated guess, is the current HVAC was installed in 2009 or 2010.As an aside, what a small world!