FCC Multiple Module Certification Strategy

[awef]

I'm curious if anyone has experience certifying devices which span several rooms.  An example is a smart home with a thermostat in a different room.

I imagine if I have an Arduino-like device in Room 1, and a thermocouple in another room, it would be simple.  Just certify this arduino-clone and be done.  The thermocouple has no brains, no clock.

Okay lets add a brain to that thermocouple and put it on an RS485 bus.  So now there's effectively 2 arduino like things A) the main brain, B) the smart thermostat.

Lets say my target is to sell a solution where there's a smart thermostat in a variable number of rooms, say 1-5 rooms. 

For the sake of simplicity, let's just say there's no significant EMI emissions regardless of # of main brains and smart thermostats.


So could I save money by seeking just a single certification for both the A) main brain and B) the smart thermostat?  I suppose why not right? It's just a single system with long wires.  Put it all in the chamber and plot the graphs and be done!


Okay but then someone wants to order an extra smart thermostat for a new room.  Would i have trouble marketing/selling it since... that smart thermostat no longer is bundled with the main brain?

What if someone likes my main brain, but needs qty 0 of the smart thermostat... why? because they're a cool hacker and just like my PCB or ... maybe their original PCB broke.  Flooding of the basement where they have their main brain. 

So I'm thinking... would I really want to double my certification costs and separate these devices?  Or could I get one certification that covers multiple parts and save money? 

Let me know what you think No need to be a lawyer... just want your thoughts especially if you have been involved in something similar.  We're asking some professionals as well but ... nobody knows everything right?