You may consider speaking with a free-lance computer programmer...could save you some money and you can make updates as your success grows...adding filtering features etc...

There are two thermostats, two air-conditioners, and two furnaces. 

Most tenants only experience with HVAC is the thermostat and when it fails to work.  

Hello,I recently purchased a duplex and realized (...) that there is a single gas line and a single thermostat.

Everything Ken said plus plaster walls, no insulation, higher electric bills, walls sweating when its humid in florida and the resident leaves front door open, damp smelly houses, Pealing paint, wood rot, old windows, crawl space under the home, bdrm and closet doors that don't close properly, electric locks that the old front door doesn't like as the door is not aligned correctly, Cyrstal knobs that fall off, old thermostats with 2 lines but my new thermostat needs 3 lines, critters in the fireplace....

As a professional programmer, I just can't place any trust in ANY online auction system, just like I would rather sit a a poker table than in front a poker slot machine.I was going to cite some examples, but having raised the question of manipulation should be sufficient to cause a moment of reflection before you dive into the deep end of the pool.Your experiences?

There are available thermostats which will control both the furnace and heat pump (or air conditioner) allowing the heat pump to provide cooling and stage 1 heating.

I never even thought about doing digital locks or thermostats before, but I'm sure it makes it a lot easier. 

We had programmers that added code so we could do our own photo uploading and hosting.

I'm a full-time programmer living in San Francisco, CA.