Nest Thermostat - Always Wrong

01grander

I hope this community is nicer than some others, I posted elsewhere and they were very condescending. I had a new hvac installed and I’ve had various issues but the issue I have now is that the nest thermostats are always horribly off, and they aren’t near a window, getting direct sunlight or have an air vent pointed at them.

I have two, so I just have to wonder if it’s the actual thermostats but these existed before my new system and the variance just didn’t seem to exist before. I’ll be downstairs and it’ll show 71 but my probe shows 74-75.

I went with a 2 stage Rheem, and it seems to be working but it’s worse than my old system and not sure if it’s just because of the thermostats but they worked ok on my last system.

Should I invest in nest sensors to supplement? Or switch over to Ecobee? I am also concerned that they are wired differently, one has the red wire in Rh and the other has Rc.

Any suggestions?

109A_5

Home owners seem to love the NEST since they have convinced themselves they need the features, marketing genius. HVAC pros seem hate NESTs since they seem very problematic in various ways.

In your case maybe the hole in the wall behind the thermostat where the wires come through is allowing a draft and skewing the temperature the thermostat detects.

Additionally since they are a learning thermostat and you changed the HVAC equipment it may have to relearn or be reset so it can relearn the characteristics of the new HVAC equipment.

ratio

What did you have before?

There are a few environmental things that will cause a modern digital thermostat to read wrong, and some internal programming/design decisions that may result in some unexpected results, but by and large they are accurate.

I'd check for a draft behind it like @109A_5 mentioned first of all.

01grander

https://forum.heatinghelp.com/discussion/comment/1905339#Comment_1905339

I did turn off the learning portion, I hate variability, just wanted control. I have dogs so I didn’t want them being uncomfortable. Is Ecobee any better with the hole affecting temp?

01grander

I had these same nest thermostats, the hvac was a heat pump rheem but single stage, I was told 2 stage would be better overall but idk. Do I just put some insulation around the hole or some spray foam?

Jamie Hall

Got to admit that I don't love Nests — for a variety of reasons — but generally speaking inaccuracy isn't one of the reasons. With a two stage system — heat only? Or is it two stage heat and cool? You do have to be rather careful to get the wiring correct — but again, inaccuracy isn't a result of that, either.

One major question to help us go a little further, perhaps. Do they maintain a reasonably steady temperature, even if it is not the correct one? Or do they let the temperature vary a good deal —more than a few degrees? Particularly if there is more variability than wanted, check the programming to make sure that all the program choices (there are a lot of them) correspond correctly to your actual new system

pecmsg

loose the NEST!

EBEBRATT-Ed

@01grander

Most on here play nice.

1 Check for a hole behind the thermostat is #1

Then the wiring needs to be checked but we need to know what you have for equipment first Model # and serial #. Then we can help.

How are they controlling two stages with a NEST?

We need a more complete picture of what you have for thermostats and equipment.

hot_rod

pull it away from the wall see if it reads the same as as any other thermometer you have handy, to place next to it.

109A_5

Maybe with the new HVAC equipment install the C wire was not connected or not connected correctly to the HVAC equipment.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1905380#Comment_1905380

or a loose connection causing some heat build up?

109A_5

https://forum.heatinghelp.com/discussion/comment/1905382#Comment_1905382

Sure certainly possible. I'm thinking since the NESTs preexisted the present HVAC equipment they may have not been touched.

So if the temperature offset of both NESTs started with the install of the new HVAC equipment (so the connections that got touched are there at the HVAC equipment) so that may be the common denominator.

Or if there is only one temperature probe as the second opinion maybe it changed and the NESTs are actually fine.

HVACNUT

What "probe"? You have a thermometer that reads a different temperature than the thermostats? Both thermostats?

The original heat pump was single stage. The new heat pump is 2 stage. Do the Nests have Y2 terminals? Are wires connected to Y2? Is Y2 jumped to Y1 somewhere?

Two thermostats, one system? Is it possible the zones are crossed in the panel? Up is controlling down and down is controlling up?

ratio

One additional thing to keep in mind: consumer grade temperature sensing is generally around ±2°. It ranges from expensive to Very Expensive to get better than that. Your Nest and your probe could be 4° apart from one extreme to the other & still be accurate and in calibration.

More importantly, how is the comfort? Without looking at the temperature, does it feel too warm or too cold? Change the setpoint a little. There's really no need for a temperature display on a heating/cooling thermostat in a house, the goal of these thermostats is to keep you comfortable, not keep the space at 72°. If you want to save energy, adjust things until you're uncomfortable, you'll save a lot more than a 2° setback.

01grander

https://forum.heatinghelp.com/discussion/comment/1905400#Comment_1905400

hello,

I have a Klein probe like this(it is surprisingly accurate):

I do have a y2 but for whatever reason they used two different ports on the two thermostats for rc and rh

I’ve had to use my room mini split since it gets closer to 75-76 when it’s set to 72 on the thermostat

I really appreciate all the comments, I’m a little busy but I’ll try to catch up later

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1905427#Comment_1905427

Looks like its wired for 2 stage. Where the R power lands on the thermostat won't affect temperature readout. Like @ratio said, be more concerned about your comfort level than the number on the thermostat. If you got 4 more of those digital thermometers, $20 says there would be at least a 2° difference between the lowest and highest readings. I'd probably take the thermostats and thermometer to the Office of Weights and Measures.

Have you put the probe of the thermometer in ice water to check its accuracy? Have you tried the same with the Nests? 🤪

109A_5

Personally I be curious about what changed (and when) to give you the temperature offset you see now.

01grander

https://forum.heatinghelp.com/discussion/comment/1905433#Comment_1905433

do you know why those two wires are different? They acted like it shouldn’t matter but I know I wired them the same when I installed the nest with my old system.

I know everything has variability, I just know my room is hotter than normal. I did close one vent in the common area so hopefully it’ll push more air to my room first and it’s helped get my room cooler. I think it was saturating the common area first and cutting off but definitely still off. May switch to Ecobee.

01grander

https://forum.heatinghelp.com/discussion/comment/1905443#Comment_1905443

I did go from 3 to 3.5 ton and 1 to 2 stage. With stage 1, I think there isn’t enough pressure to properly reach my room since it’s the furthest away(path of least resistance), I think most of it was dumping in the common area, I closed one of the two vents and it seemed to help.

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1905527#Comment_1905527

Just to clarify, this is one system with 2 zones, correct?

How was the decision made to go from 3 to 3.5 tons? Is there a barometric relief? Is the motor on the new system ECM? I think we're getting somewhere, but moving away from the thermostats.

Are you able to take pictures of the air handler and ductwork?

JohnNY

@01grander

I decided a few years go that I don't like the Nest and so I installed a comprehensive Ecobee system throughout my house with cameras, video doorbell, multiple room sensors, and security cameras.

Nothing worked right for very long and I found myself every few weeks cycling power and deleting and reinstalling the app to get it to work. Nest is not the problem. Technology is. It all sucks and I'm convinced that everything is made to work 85% of the time which is just enough so that you buy it but it just sometimes isn't going to work and you accept it as it is and still tell your friends it's great.

As far as the temperature being off, does it really matter? Different devices measure temperature differently and so results often vary. Europe has it right with the blue-to-red scale and Danfoss using snowflake/1 through 5 is even better. Don't let it drive you crazy.

SlamDunk

Wiring the Nest is straight forward. I hated it for the first two days because the wiring wasnt working. Youre kinda on your own with it. Non existent tech support.

Turns out the installer on the basic honeywell tstat had the wiring right but the guy in the basement had reversed two wires on the furnace. Once I corrected the wiring at the furnace, I havnt had a problem since. Kinda love it now.

The newest generation nest has remote sensors that average together to heat or cool the house evenly. The thermostat and remote sensor were dead on when in the same room. As far as accuracy? Who knows? I used to be a calibration tech. The cumulative tolerances between two thermocouples can be as much as four degrees and still be acceptable, as already mentioned. However, in my experience, devices are usually within 1 degree.