As someone who manage/repair his own and clients properties here in DC , I can tell you that your cashflow is not great if you focus only on your cashflow, but that is reality for most of DC market as home prices are high, but you have very low mortgage rate ( read free money ), also your rental property attracts best tenants = easy to manage, small vacancy rate..also it is probably all brick home, with small yard so it is low maintenance. where roof and AC are the biggest expenses, and you already paid for HVAC.( I dont know why did you pay $5K for HVAC if you have America Shied Insurance...) Also you are cashing on steady appreciation in DC market as @Mark Holencik already did calculation for you.
When you get those cheaper suburban houses, you will probably have bigger cashflow, but also higher maintenance cost, probably lower income tenants, and I dont know about appreciation as I dont know that market. So depending on what are your plans/goal make sure to include other factors in your analysis when getting your new rental and not just cash flow numbers.
I would go with ELOC as @Damien Hall said and test your new area first, and if you are doing well and making more money , then dump DC property, but until then I would keep it and enjoy easy appreciation in your DC house.
Hope that helps.