How to control a furnace fan wirelessly - design suggestions?

HI, everyone, I’m wondering if you can give me some design suggestions for my project. My goal is to turn on the furnace fan in my house when the temperature of the upper level is more than 3 or 4 degrees different from the lower level (and then turn it off again when the temps agree). My original plan was to use an electric imp on both the upper and lower level of the house, sense and transmit the temperatures to online data storage, then send an HTTP message back to one of the imps when the temperature difference reached 3 or 4 degrees and the imp could turn the furnace fan on/off via a relay. So far, I’ve been able to send data to Sparkfun Data, Thingspeak, and Wolfram, but I haven’t figured out to detect the temperature difference and send a message back. Does anyone have suggestions about how to do that? Or is this design way too complicated for what I want to do? It’s not very practical to run a direct wire connection from the upper level to the lower level of the house, so that’s why I am trying to do it wirelessly. Thanks in advance for any suggestions.

Just an idea for you …

You can use two imps and the imps can communicate with each other through their associated agents. Each agent has its own URL, and each one can POST to the other.

So one imp is the “master”. It knows the setpoint, the temp at its location, controls the furnace hardware, and handles the online data storage. The other imp is simply sensing the temp at the ‘other’ location. When the master imp needs to know the temp from the other, it requests (asks the agent) for its temp. You probably only need to sample the temp every 30 or 60 seconds?

If you don’t want to use online data storage, you do not even need a website. The agent can host its own website that you access via the agent’s URL. If you have your own personal website (like GoDaddy or Host Monster), you can do anything you want. In this case, you would have your own MySQLi database, and use PHP scripting.

The idea of using the imp to turn the fan on or off in parallel with the existing furnace control is a good plan. I would never rely on any ‘remote controller’ to have total control over something as critical as a furnace. There are too many points of failure. Even using a “Nest” is a bit over the top. The old clunky Honeywell controls are the most reliable.

thanks, mlseim, I hadn’t realized that the imps could communicate with each other. That makes much more sense. I’ll head that direction. Thanks again.