Temperature Controlled Motorized Furnace Vent

During the winter, our bedroom can get very warm. Inevitably, we end up closing both vents in the room and then several hours later open the vents because we are freezing. I decided to automate this process.

Originally I had envisioned having a small temperature sensor across the room which would relay open and close commands wirelessly to the motorized vent. Given the unreliable results from the light switch controlled outlet project, I abandoned that idea. Instead, I decided to put the temperature sensor on the same board as the vent motor controller.

I purchased a Vent-Miser programmable vent. These vents have a programmable timer and will open and close the vent depending on the time of day. All I cared was that it was a motor controlled vent.

The motor is controlled with a PIC16F1824 micro-controller and the temperature is read using one of the analog to digital inputs fed by a TC1047A temperature to voltage converter. The PIC spends most of the time asleep allowing it to conserve energy. Once a minute it wakes from sleep, takes a temperature reading and decides whether or not to open the vent. With the temperature sensor inside of the furnace register, there are some wild temperature swings when the furnace is on. To compensate for this, the PIC looks for the minimum temperature over a ten minute period. Then, depending on the minimum temperature, it makes a decision about whether or not the vent should be open. Currently, if the temperature is over 73 degrees it will close the vent and if it is under 70 degrees it will open the vent. This was done to prevent the vent from opening and closing sporadically due to noise on the temperature sensor.

The entire circuit is powered by a 9V battery. Using very imprecise measurements, I estimate a lifetime of just over two years. This of course depends highly on how often the vent opens and closes.


If you would like detailed schematics or code, please let me know and I will post them as well.

17 thoughts on “Temperature Controlled Motorized Furnace Vent

  1. Hi,
    I’m very interested in your vent controller. Would you be so kind as to share your schematics and code.

    I’m looking to control temperature in a similar way to you.

    Many thanks


  2. You estimated the lifetime of a 9v battery being used in your device and not the device lifetime itself, right?
    I guess 2 years is pretty good and you can always get rechargeable batteries for an almost unending usage.
    I’d be very interested in something like this, but is it possible to control a ceiling fan that way?
    I mean, my wife loves to sleep with the ceiling fan turned on, but I can’t just stand it. Is there any way to turn it off when the room temperature reaches certain levels?

    I’d be very interested in your device schematics as well!
    Great idea and thanks a lot!


    • Alfred,

      Correct, the estimated lifetime is for the battery, not the device. To control a ceiling fan, I would suggest looking at using an Arduino with a relay shield on it. Since the fan is already being powered by 120V, you might as well tap into that and not use a battery. Plus, with a mechanical relay, batteries would not last very long at all.

    • With z-wave home automation you can automate your ceiling fan without altering the manual functionality. You will need a z-wave controller like MicasaVerde’s Vera Lite, a z-wave switch and a z-wave temperature sensor. You will still be able to turn it on off manually. But system will turn it off when certain temp is reached or it will turn on off all night long when temperatures reached.

      With z-wave you may only need to replace the batteries on temperature sensor.

  3. aso interested in your scematics and code. have a problem room. can it be programmed to close at a high temp limit and open at low temp limit if the electroinics were extended to the wall and only ran wires to the motor on the vent?

  4. Hi Jason

    Nice work. I am looking to do exactly the same – just discovered and ordered a few Vent-Misers…

    +1 for posting the code and schematic, if you don’t mind. (Or PM me what you have if that’s easier … this looks like a nice holiday break project :)

  5. Hi, I’ve ordered a couple of vent misers to repurpose for a homemade HVAC zoning project. I haven’t been able to see a vent miser in person, and it will still be some time before I receive mine. I put together some registers with a bracket and servo before i discovered this product. I was wondering about the interface to the motor control. Do you drive the motors directly? How do you know when it has reached end of travel etc…. if you send me your schematics & code I could figure it out, or if you rather explain it to me I would appreciate either. Its starting to heat up down here in Texas and I want to have all the parts I need when the vent misers arrive to just hook it up and start tweaking the system.


    • Faisal,

      I am directly controlling the motor with a simple transistor based H-bridge. There’s no feedback on it yet, so I’ve timed how long it takes to open/close and added a little extra time….Definitely crude, but it works and the motor/gears don’t seem to mind. If you add some feedback let me know.

  6. Hi I am trying to control the temperature in a natural underground wine cellar by closing some vents to regulate temperature. Your application looks excellent. I am not an electronics expert but would love to find out more. I have a soldering iron and can get relevant vents in UK so would be grateful for schematic or any advise. Thanks

  7. I found this site after finding these vents. I want to integrate these with a zwave type relay. I am wondering how these work. Are they normally open and then when voltage is applied they close? Or does the controller spin the motor one way to open and the opposite to close? Vent Miser would be awesome if they just integrated a zwave controller instead of the timer.

    • Hi,

      It’s just a DC motor that opens and closes the vent. A positive voltage opens the vent and a negative voltage closes it. I used an H bridge to apply the voltages.

  8. I am in the process of finalizing a new similar product and would like to speak to you with regard to your knowledge in this application.

    713 203-0358

  9. Hi there,
    How has this ended up working for you? I would be very interested in the detailed schematics if you’d be up for it.

    Thank you,

  10. A very nice project you have there Jason. I was searching for a controllable motorized vent and found your project. I definitely want to attempt building one, if you don’t mind sharing your schematics and code, it would be greatly appreciated. Please PM if you feel that’s more appropriate. Thanks a lot.

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