Nest Thermostat Additional Temp Sensors

(Jon Allsebrook) #1

Hi All,

Ok so got one of these awesome devices at the weekend (I have been putting it off for a long time as wasn't sure I could do the install but it was very simple!) and its working really well.

What I can't do is get it integrated into ST using either method provided by the community.

When I do get it integrated (I may wait for official integration) is it possible to get it to perform certain actions based on temp sensors I have elsewhere? Our main bedroom for some reason becomes the coolest/warmest room when the system is running and the thermostat is sat in the dining room where the temp stays higher than elsewhere. What I am thinking is that I could use a temp sensor in the bedroom to control the thermostat during certain times or would this cause issues generally?


(Brian Steere) #2

That's certainly possible, but it would involve creating custom SmartApps to handle the logic. There isn't anything built in that can do that.

(Jon Allsebrook) #3

Hmmm just had a brainwave... I could use IFTTT to turn the thermostat on/off when an ST sensor goes above/below a certain temperature?

(Patrick Stuart [@pstuart]) #4

I've been tracking the accuracy of the ST multi sensor thermistors and they are all over the place.

I did modify the default device to allow for a calibration factor +/- but that still isn't enough.

You could do this, but you run the risk of using a very cheap thermistor to set the temp of your HVAC and could potentially freeze up an AC, blow a fan motor, etc.

Maybe you could mitigate this risk using the law of averages. If you had say, 5 sensors throughout the house, you could pick one for the target and then use the min and ave temps from the other 5 to alert you of a potential problem before it gets too bad.

Also, hoping one day ST will allow devices to actively poll a zigbee device and get the latest temp rather then waiting for the next poll interval. This would allow us to really test the accuracy of these thermistors and how wild they are reading.

(Acastal) #5

I think the "Keep Me Cozy II" smart app will do what you want.

(Jon Allsebrook) #6

Thanks for your reply @pstuart. I literally put an ST Multi next to the Nest this morning to run some comparisons and I am seeing a big difference in the temp reported by the nest and that of the ST Multi. As of now I have the nest reporting 73 and the ST Multi reporting 68. Thats a big difference and should I trust that the Nest is more accurate than the ST Multi and look at calibrating the ST Multi?

(Patrick Stuart [@pstuart]) #7

Which nest reading are you using? The one from the nest display itself, the website or anyone's Nest device other than mine?

All the nest devices here had a horrible truncation bug, they all converted a double value to an int before rounding.

So if the nest was reading 74.9 the device would truncate that to 74 when the nest website or actual device would read 75.

My version fixes that...

The same issue exists with the ST Multi temp reading and I fixed that as well in my version of the device.

I still wouldn't trust the ST Multi temp readings to run a tstat remotely from, the poll interval is fixed at 2 minutes. You don't want to be triggering your AC on and off every 2 minutes because you got one reading at 77 and then 73 the next 2 minutes.

In order to do it properly you need to add some smoothing or timer to run the ac until a setpoint as been reached.

Ultimately, the Nest really can't work off a remote sensor, because it will run to a temp and stop. You would have to overshoot the temp you want... For example you send the nest the command to cool to 73 degrees. That is the temp the nest will read.

So, if your remote sensor is reading 75 and you want it to cool to 73, you would need to get the current reading off the nest (not impossible) and do the math to set the nest to 71 instead. Then in theory, your remote sensor would eventually read 73 and the nest could read 71.

Unfortunately, temp sensors are not created equal, and turning on and off HVAC systems 15-50 times a day is not good for the motors, etc.

(Jon Allsebrook) #8

@pstuart The nest reading is from the Nest App and the Nest itself as I can't actually get the integration with ST to work so right now its a moot point smile

From reading what you say I think I am going to leave using the additional sensor as a control out of things and just be happy where it is at. Especially as there is such a difference in the temps the devices are reporting. The Nest is actually learning the schedule pretty quickly so using that and some additional scheduling I should be able to cover things off.

Thanks for your input really helped!

(Patrick Stuart [@pstuart]) #9

Why can't you get the nest working on ST? Have you tried my Nest device code?

Just edit the preferences for your serial number (all caps) username and password after you create the custom device type in the ide and add a new device in devices and choose the new nest device at the bottom of the list.

Should work fine.


This worked like a charm, much appreciated! Now to see how I can tie it all together with my various bits and pieces.

(Steven Weinstein) #11

Anyone get this idea working? I really could use this.

(Colin Mc Hugo) #12

Hi Guys,

I am a little behind in this conversation but i have a similar issue. I dont have any thermostat (only non smart) in my apartment. My bedroom is always getting cold throughout the night which makes me have very broken sleep (covers on, covers off etc) so i would like to get a smart thermostat that would heat the bedroom (which is colder than most rooms due to patio doors i got installed a few years back) but i would be afraid that if i do this the whole apartment would be very warm and the bedroom would just be average. Would i be better off getting some silent fan heater in the room and hook it up to a smart wall socket and IFFT when the temperature goes below a certain value? Also can you tell me does the standard door censors monitor the temperature or do i need another device? thanks again much appreciated. Colin

(Paul Barden) #13

Hi all.

I can't find the same topic so I have revived this thread.

I just bought 2 3rd gen nests for upstairs and downstairs zones and I would like to take advantage of my smart things motion in other rooms.

I'd like to average these temps with the temp of the best itself to control the heating.

Has this since been accomplished by anyone??.

Thanks in advance.strong text

(Isaac Dressman) #14

Is this not a thing?

Seems like this is a core value of nest, that it is IoT enabled...

(Matt) #15

Download best manager. It lets you use remote temp sensors and all kinds of other automations.