Register                
Results 1 to 4 of 4

Thread: AUX Heat On Venstar Wifi (T7850)?

  1. #1
    Junior Member

    User Info Menu

    AUX Heat On Venstar Wifi (T7850)?

    Hello. I have, and am pretty happy with, a Venstar T7850. I use it with a typical heat pump backed by an electric furnace (heat strips). Everything seems to be working right in terms of furnace control. But I am a bit confused about AUX heat.

    I am told by Venstar tech support that any time the heat strips are engaged (be it because the heat pump is locked out at cold temps or if the difference between setpoint and current temp is too great for the heat pump alone to meet the need) that the thermostat should display "AUX". However, I have never seen that happen.

    Yesterday morning, our heat pump was locked out because the outside temp (we have a wired sensor) was below our lockout point of 25. Of course, the electric furnace did run. But I never saw "AUX" displayed when, based upon the tech support statement, I should have seen it.

    I have a program that polls the thermostat's local API every few minutes and records the runtime stats in a database. These stats include the number of AUX heat run minutes for the day at that time. During the entire morning that value remained 0.

    I will say that I do, on occasion, see the runtime stats include non-zero AUX heat runtime minutes. I did so yesterday afternoon for example. But at that time, the heat pump was NOT locked out as the temp outside managed to get above 25. In this case, looking at my recorded data from the thermostat, I could see that these AUX minutes occurred between 1pm and 1:09 pm when the setpoint was set to 64 and the room temp had somehow dropped to 61.

    I am not quite sure how this large a gap occurred. I set my 1st deadband at 2 degrees so I would have thought that the heat pump would have been engaged when the inside temp dropped to 62. I guess it is possible that the temperature drop could have occurred during a period wherein the heat pump was disallowed from running due to cycles per hour (set to 3) or minimum compressor time off (set to 5).

    However the gap occurred, in this case the inside temp managed to fall such that the thermostat decided it had to engage the electric furnace to meet the short term demand. I do find this a bit strange as I have my second deadband set to 2 degrees and the second 2 degrees/2 minutes off the first deadband. So I would have thought the temperature would have to drop by 4 degrees below the setpoint for the AUX to be engaged. And none of my readings recorded show a difference greater than 3 degrees during the period in question. I suppose it is possible that it did so between the times of two successive polls.

    So I am hoping that someone here can help my understand all of this non-intuitive (at least to me) behavior? I guess I (and maybe Venstar tech support too?) could be confused by the meaning of "AUX". Could it be that AUX is only used/recorded/displayed when the thermostat sees too large a difference between the setpoint and the current inside temperature?

    Thanks in advance for your help.

  2. #2
    Administrator

    User Info Menu

    Quote Originally Posted by whitedavidp View Post
    Yesterday morning, our heat pump was locked out because the outside temp (we have a wired sensor) was below our lockout point of 25. Of course, the electric furnace did run. But I never saw "AUX" displayed when, based upon the tech support statement, I should have seen it.
    Is the wired outdoor sensor connected to your Venstar T7850 or is the wired outdoor sensor just connected to the thermostat wiring at the heat pump?

  3. #3
    Junior Member

    User Info Menu

    Quote Originally Posted by Thermostat View Post
    Is the wired outdoor sensor connected to your Venstar T7850 or is the wired outdoor sensor just connected to the thermostat wiring at the heat pump?
    Hello and thanks.

    I cannot say 100% about any connections elsewhere, but I am 100% sure that there are two wires from the outdoor sensor to the T7850. They were previously wired to the Honeywell TH8000 that was in use. And that thermostat always seemed to display outdoor temps and AUX properly (or at least when I expected it to do so). I spent alot of time mapping the wiring from the TH8000 to the T7850 and am pretty darn sure that is correct. The outdoor temp displays properly (or close enough) all the time.

    And when the primary heat source (heat pump) is locked out at 25 the secondary heat gets engaged. I can feel heat coming from the registers and can see that the heat pump fan is NOT running. It just does not seem to: (a) display that AUX is in use anywhere on the tstat nor does it (b) record the runtime usage as AUX usage rather than "normal heating" in the data returned by a query of its local API. It seems that this difference is NOT discernible on their Skyport web interface either.

    As I described, I DO sometimes see some AUX heat time accumulate and display in response to my queries via the local API. But this never happens during heat pump lockout and appears to be only when the delta between indoor temp and setpoint is larger than 2 degrees. I cannot say for sure that AUX is not displayed in that circumstance on the tstat. I need to test that. But if so, I have to wonder if I just do not understand Venstar's interpretation of AUX (and their tech support does not either) or there might be some issue in their onboard logic.

    Cheers

  4. #4
    Junior Member

    User Info Menu

    I can confirm that I see Aux Heating displayed on my T7850 ONLY when the difference between setpoint and current room temp exceeds my 2 degree 1st deadband. I can further confirm that I never see this during heat pump lockout.

    Thanks



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •