Venstar T5800 API Setup

Before you can start using the Venstar’s API there’s some things you have to do.  But before you even think about using the API you ought to get the Venstar just connected normally.

The wiring for it is beyond the scope of this web site, but the main requirement is that you must supply a constant 24vac to it.  Many older furnaces simply had two wires that went from the furnace to the thermostat and shorting them out was what turned the furnace on.  There’s a good amount of online guidance concerning this, or get a professional.

Once you have it connected to the furnace you can then connect it to your wifi network.  Once you install the wifi key you will have to go to: menu->accessories.  There are 3 screens in accessories that are important to you.  First is the setup screen.  Here you will choose which wifi network the Venstar will connect to after it finishes scanning the neighborhood.  I assume one of those networks found will be your own.  If there’s a password you would enter it here.

Once you are connected you might want to take an hour or so and create your Skyport account and get a feeling for all the good stuff there.  Returning to our setup, still under accessories, next go to the accessory information screen.  There you’ll find the DHCP-provided IP address the Venstar got when it joined the wifi network.  Write this information down, as you will be reusing everything but the IP address itself.  You will want to change this address to a fixed one, as it will be hard-coded in your Perl program.  You do this by going to menu->accessories->setup.  At this point the Venstar rescans for networks.  Wait until it finishes, then select the one you want.  It will force you to re-enter the password.  After that you can select manual setup and enter the ip address.  Change the last digit to something outside of the router’s DHCP range (which start at 100 and run up from there), i.e.  The other addresses should be copied from the original DHCP information you copied down from above.

The third accessories screen that we care about is to enable the API itself.  The entry toggles between enabled and not.  Obviously you want it enabled.

Assuming your HCA computer is on the same subnet with the Venstar (which is the typical situation in 95% of all homes, and which is required for using the API) you should then be able to ping the Venstar’s address from HCA.  Further, you should be able to point your web browser to the Venstar and start exercising the API.  As an example, my Venstar is at  If I type in “” into my web browser’s url window (not to be confused with the search window, but in some browsers they are the same) I get a JSON response.  JSON is a series of text fields formatted in a certain way.  Microsoft’s Internet Explorer will ask you what you want to do with the JSON and you can simply open it with your favorite text editor (Notetab++ is mine).  This is a very useful way to see what the Venstar is sending you.  Once you get to this point we can then look more closely at the API itself.

As In Various and Sundry