Sunday, November 25, 2012

The Nest Thermostat

I recently bought a Nest thermostat. The idea is that it saves energy by being smarter. I also suspect people (including me) buy them because they're cool :-) One of the Nest founders was former VP in charge of iPods at Apple. The clean design, packaging, and user interface are reminiscent of an Apple product.

I'm mostly going to talk about an installation issue I had. For more of a general overview check out Scott Hanselman's Nest review.

I wanted to buy one when they first came out a year ago but they weren't available in Canada. Later, I used their compatibility checker which said it wouldn't work on my system. When the second generation Nest came out, I checked the compatibility again and this time it said it would work. At first I thought this was a result of improvements in the second generation, but I think it might have been my mistake the first time around - I may have entered all the connections that my current thermostat had, instead of just the ones that actually had wires connected.

Nest offers the option of having them arrange a local installer, but the instructions looked straightforward, so I just ordered the device.

It was easy to install. They even supply a screw driver, and the device has a level built in so you get it straight. I had to use the optional backplate to cover up the mess behind the old thermostat since I didn't want to get into filling and painting. Which is too bad, because it would look even slicker without the backplate.

The setup process was straightforward and I didn't have any trouble getting it to connect to my home wifi. (Other than the awkwardness of entering a long password without a keyboard.)

I had to shake my head when the first thing it did was start downloading updates. I get tired of every computerized device I own having to endlessly download updates. Actually, it's not the updates I mind, it's bothering me with them. Just handle them invisibly behind the scenes.

One tip - set the display brightness to auto rather than the default medium. This adjusts the brightness depending on the ambient light, making it less blinding at night.

Everything seemed to work fine and I patted myself on the back, prematurely as it turned out. I noticed that it seemed to have trouble turning off the furnace after it got to the correct temperature. It would cut in and out for quite a while before finally stopping. I emailed Nest but it was the weekend and I didn't hear back. The second night it crashed and rebooted. And in the morning the display would not turn on automatically when you approached.

I did some research on the web and found that the display won't come on automatically if the battery gets low. I also found other people had similar problems with cycling on and off. I learnt more than I really wanted to know about "power stealing". (Old style thermostat wiring was not designed for smart devices that require their own non-trivial amounts of power.) I ended up having to remove the Nest from the wall (it just pops off the base) and charge it with a USB cable.

Finally, I broke down and phoned Nest. (I hate phoning for customer support since it's usually such a frustrating process.) I got through fairly quickly to someone who was quite knowledgeable.  He had me check a bunch of things and play with the wires. The Nest has a bunch of helpful debugging information under Settings > Technical Info, including the battery voltage, and the input voltage and current. My battery was showing about 3.7 volts. The input voltage is a little misleading. These are 24 volt systems and mine were around 26 or 27, so I assumed I was good. But according to the rep, you have to divide by 1.4 and the result should be around 24 volts. Which means the Nest should show around 30, in which case mine were too low. I assume this is something to do with AC versus DC and how the Nest measures it. But given that the Nest is obviously computerized, I don't understand why they don't just divide by 1.4 before displaying the voltages. My input current was 20ma but he didn't say if that was good or bad.

It also seems strange that the customer support guy had to get me to manually read this information from the Nest. The device is already sending a bunch of information back to them (e.g. for the web interface) so why doesn't it send the technical info as well, so they don't have to get the user to give it to them.

The end result was that Nest said the problem was that the voltage coming from my furnace was too low and I'd have to get someone to check the furnace. I tried the company that installed the furnace (Greggs), but they couldn't come out for a week. I could have put back the old thermostat and waited, but that wasn't appealing!

I contacted Brent Veitch from Rock Paper Sun (the folks who did my solar panels) to see if he knew anyone who might be able to come and look at it. He offered to come himself although he's not a furnace specialist. Coincidentally he had just heard about the Nest recently so he was interested to see it.

I told Brent about Shelley asking "Why does the furnace keep cutting in and out?". He said, "Just tell her it's because you replaced a perfectly good thermostat with an expensive new toy". Ouch! Shelley laughed.

It turned out the problem wasn't really with the furnace. It just wasn't designed for the power stealing the Nest was doing. Ideally, there should be another C wire that could supply power, but the old wiring in our house didn't include it, and it would have been a major undertaking to run new wiring.

Brent had already talked to Nest and they had suggested adding a resister at the furnace end between the C wire and the Y wire (air conditioning) that was being used to "steal" power. They suggested 220 ohms but I believe he eventually went with 270 ohms. (Note: it needs to be a high power resister e.g. 5 W) That seemed to do the trick. The furnace now shuts off properly. The only question is whether this will cause any problems turning on the air conditioning. But considering we haven't used it for two years, I'm not too worried. (The battery voltage now shows about 3.9 V, the input voltage about 29, and the input current 40ma)

Although Nest's telephone support was quite good, they seem to be in a bit of denial about this issue (or at least deliberately vague). There's no mention anywhere about the resister fix. They do mention the power stealing and C wire issue but only in general terms. I'm not sure what percentage of installs have this problem, perhaps it's rare. And if you paid someone to install it, presumably they would deal with it. I can understand they don't want to broadcast their problems, but better to have information about how to fix it than try to pretend it doesn't exist.

Since then, the Nest has been working great. It's very cool that I can view and control it from the web or from an app on my iPhone or iPad (they also have an Android app). It's fun to be able to turn the heat up from my iPhone when I'm on the way home so the house is warm when I get there. (Although I'm sure the novelty will wear off quickly.)

In theory, the Nest will automatically learn your schedule based on manually turning it up and down, but I was too impatient to wait for it and manually set up my own schedule. (Based on the first couple of days, the learning did appear to be working.) I sure like being able to edit the schedule from my computer instead of the painful scheduling interface on our old "smart" thermostat.

Another nice feature is that it will automatically detect when no one is home and turn down the heat. I was a little skeptical of this feature, but after a week or so of "learning" it seems to be fairly accurately detecting when we're away from the house. It's somewhat conservative so if you just go out for a short time it won't kick in. But that's probably best, and you wouldn't save much energy anyway. (Even without this feature, if you forget to turn the thermostat down when you go out you can always do it from your phone.)

As much as I like the Nest, the initial problems made me a little nervous. A thermostat is a pretty critical piece of equipment in Saskatchewan winters. But since resolving the power issue it has worked flawlessly so I'm feeling better about it.

If you want help installing a Nest, give Rock Paper Sun a call. (They've also applied to be one of Nest's official local installers.)

Also check out Scott Hanselman's Nest review with more photos and screenshots. He had no problems at all with his install. (I notice from his photos that he did have a C wire - perhaps a newer house.)


  1. Great story!! You and your toys :-) I'm just enough of a Luddite to not have a cell phone so I guess I won't be wanting one of these thermostats either :-) However, at our place, unless the thermostat could split wood and light the fire, it's of limited usefulness! The only time our thermostat and heating operate is when we're not home and then all it has to do is keep the house at a constant +7C.