Reddit mentions of Honeywell R8845U1003 Relay Switch

It's possible with a little work. https://smile.amazon.com/Honeywell-R8845U-1003-Universal-Switching-Transformer/dp/B000LDBP9Q/ref=pd_rhf_eetyp_s_vtp_ses_clicks_1_1?_encoding=UTF8&pd_rd_i=B000LDBP9Q&pd_rd_r=2WWZCVT64DV8MC1AP15R&pd_rd_w=m5yx6&pd_rd_wg=VCXOJ&pf_rd_i=desktop-rhf&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=05d75987-58ed-4d36-bbfa-515cd87e4ee3&pf_rd_r=2WWZCVT64DV8MC1AP15R&pf_rd_s=desktop-rhf&pf_rd_t=40701&psc=1&refRID=2WWZCVT64DV8MC1AP15R

I'm in a similar situation and have been brainstorming about it for awhile. You have two options:

1. Ditch your current wireless system and run a wire to a converter that changes the millivolt signal to 24V.
   
   https://www.instructables.com/id/Nest-Thermostat-With-Gas-Fireplace-or-Other-Milliv/
   
   https://www.amazon.com/dp/B000LDBP9Q/?coliid=I28F84ZZZ5MVLS&colid=2UT1TBBXYOV2A&psc=0&ref_=lv_ov_lig_dp_it
   
   
2. Build your own wireless transmitter using Arduino and Raspberry Pi/Google Things/etc. I'm trying this option because my current remote has some unique settings. Here's the tutorial on how to get/transmit the wireless signal:
   
   https://arduinobasics.blogspot.com/2014/06/433-mhz-rf-module-with-arduino-tutorial.html
   
   ​
   
   Hopefully I'll be successful and post my results, but more likely I'll give up on being able to adjust flame height via my voice and just go with option 1. Good luck!

I have a gas (millivolt) furnace and no 24v wiring in my house.

It’s a bit ugly, but I have this plugged into a wall outlet, which steps down voltage to 24v for a Nest Thermostat. It also has millivolt leads to connect to the switch terminals on your furnace. It was designed specifically for this sort of application.

Works perfectly so long as you don’t lose power, which happens to me frequently in the winter. My current solution to that is just a piece of wire I manually use to jump the furnace switch when I need heat. I’ll eventually replace it with a zwave thermostat that has a backup battery.