Aprilaire Thermostat 8800 any MODBUS experts?

integrating the Aprilaire communicating Thermostat into Home assistant

anybody up for the challange as this is a full featured thermostat with multi heat and cool zones also humidity sensor and indoor and outdoor temp sensor it can provide lots of data to homeassistant as well be controlled remotely rs485 protocol from the T stat

I’m also interested. I have Aprilaire 6000 series zone control wifi thermostats.

I noticed the only platform that has an Aprilaire integration is Homeseer. Would be awesome if this could be integrated into Home Assistant.

toss a vote on this

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Done. Thanks for requesting. Really hope I can get an integration for this.

for anybody that is willing to build this integration I have successfully accessed the thermostats via com port and can query status and make changes to the the thermostats I successfully used a 485/422 to 232 adapter and a 485/422 to ip to virtual com I ordered a 485/422 to usb adapter as well an 232 to usb adapter I also have a pdf file that has all the commands that apply to the thermostat

A query type command has the following syntax:
An assignment type command has the following syntax:
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+1 I’m currently using HomeSeer for precisely this reason.

Homeseer app does not work with the 8800

This seems to be the relevant documentation needed to integrate the serial command protocol of the 8800:


yup I have that and used it to control my thermostats in terminal to verify they work as intended just no clue how to integrate it into Home assistant

I’ve also voted for this as I am totally frustrated with Aprilaire and their lack of support. Even getting this into Google Home has been nothing short of a headache. Additionally, the fiasco with their cloud issues due to an employee uploading incorrect version numbers have me wishing I went another route with my system.

I had an HVAC pro come out and issued a quote of $2k just to move to the Nest learning thermostat. This is due to the proprietary nature of the Aprilaire system and the dampers used to control the zones.

I am just using the aprilaire thermostats but from what I read most of the stuff is basically on and off controlled exactly what parts is you HVAC tech referring to?


The board is the Aprilaire 6404 3-Zone control board and the 6823 dampers (x3). Obviously, I am not going to do the swap on a brand new HVAC system… I was just hoping the Nest Learning could connect and control the Aprilaire components.

the 6823 use 24v AC to close and a spring to hold open nothing proprietary about that and easy enough to control

and the installation manual for the 6404 does not show anything too weird
if it were me I would be getting a nest and replacing one of the thermostats and see for myself but I suspect the tech was trying to up sell you on stuff you don’t need

ok I used this 422/485 to USB adapter on my Home Assistant computer

USB Serial Adapter

and am able to control it through my remote desktop into Debain 11 OS

I installed modbus into Homeassistant how do I send a command to it via homeassistant to confirm that it can talk to my thermostats?

Okay I managed to build thermostats in Home Assistant but still have not figured out how to get the modbus language in Home assistant to talk to the Thermostats

Definitely would like to see this! Might make sense to write something up on a Raspberry Pi or something in Python and leverage PyModbus. Just a thought.

I have a 6045M installed by my builder, Meritage, who for some reason could not be bothered to install a standard smart thermostat.

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agreed I don’t have any python skills so it is still beyond my realm just want to be able to control them in Home assistant, toss a vote on this

Where did you find the model number? I know mine is a zone controlled 6000 series but I couldn’t find the model in the thermostat UI.

FYI, Meritage installed mine too. They installed some obscure iDevice switches as well but luckily I was able to get those integrated into home assistant.

Had a sticker on the back, the board also has it silk screened on it and when I send a id inquiry to them they respond with model # and firmware version.

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I do have a extra thermostat that I can setup and allow access to anybody that is willing to tackle this project :slight_smile:

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