Getting multiple Nest thermostats working in the same house


Living in a country where it is possible to spend in excess of $1000 a month on electricity I want to do everything I can to minimize my power consumption. With this in mind, and the fact that the average temperature in the Cayman Islands is 80+ a learning thermostat that says it can save me money is something I would be very interested in. When we bought our new house at the beginning of the year I decided it would be the perfect opportunity to save some money and get my geek on!

I am not going to go over everything the Nest thermostats can do and why they would appeal, check out their website if you don’t already know what they are.

Single Nest Setup

Our house has a multi-zone A/C system. One main zone for the open plan downstairs area including my office, a second one downstairs for the kids bedrooms and then the third one is for the master suite that takes up the whole of the upstairs.

Due to the cost of the device ($250), plus shipping and duty fees (about another $80) I was hesitant to pull the trigger on three of these at the same time so went for just one to start with and put it in the main living area as that is where we would see the biggest savings.

The installation was simple enough [picture gallery], just 3 wires and 2 screws, all handled by the nice screwdriver supplied in the box.

The setup of the device was just as hassle free, once it is connected to the wifi network and then your Nest account it pretty much goes about its business for the first few days while you adjust it and it learns what you want the temps to be over the course of the first week or so.

Once the initial learning period is over it will set its own schedule and you should just be able to leave it. I found this wasn’t quite ideal. It might be fine for most people where electricity isn’t quite as expensive as it is here, but after looking at the schedule it had devised I went in and tweeked it a bit. For example the bedrooms don’t need to be cooled from 5pm through to the following 7am, we get home get changed in the room and then we aren’t back in there until between 9 and 10, so I adjusted it to cool for a bit around 5, and then not come on fully until it is time for bed and then to go a bit higher during the night when we are asleep and won’t notice it.

At the end of the first month we had saved about $70 on our bill, which was just over 20%! That is a pretty large saving, and the device would pay for itself over the course of less than 6 months.

The fact that I set the schedule up myself does negate some of the main reasons for getting one of these devices. However, trying to get a thermostat that looks as nice, is as easily adjusted using the web interface or smartphone/tablet app, and can handle schedule with as many changes as you want in a day is nigh on impossible for the same money. Most thermostats give you 4 changes of temperature a day and then give you a setting for Monday-Friday and another one for the weekend. That’s fine, but we have a schedule where I know, for example, that I will be home on a Wednesday lunchtime so I can have the system cool for that, but the rest of the week it is set to ‘away’ mode from 8am – 5pm.

Multi-Nest setup

With the success of the first device a few months later we decided to complete the system and get the other two devices we needed. We weren’t expecting the same level of savings as the rooms that were being cooled were much smaller and has less requirements for changes through the week.

The devices were just as easily installed and everything seemed fine, until the end of the first week. When checking the Nest app on my phone I saw the question mark [image required] for both of the new thermostat’s. Checking both them and the troubleshooting guides I found they had disconnected from the wifi as the battery was low. But why would the battery be low? They were setup the same as the other devices.

As a test I reconnected the old thermostats and the cooling worked perfectly. I charged the Nest’s with a USB charger and plugged them back in. A week later the same problem, low batteries and disconnections from the wifi.

This time I checked the technical info tab of the Nest settings page and saw that the wifi signal strength was hovering around 40%, which according to the Nest website, could cause the devices to not turn off when they should as they are hunting for the wifi and thus drains the battery.

To fix this problem I broke out an old router I had lying around which has the DD-WRT [link] firmware on it so I could boost the power. This also meant I could create my own wireless network for the Nest’s so there would not be any interference. Before I had chance to see if this fixed the problem I ran into more problems.

I cannot blame the Nest’s specifically for this, but both of the systems that the new devices were connected to blew their capacitors in the air handling unit and stopped working. One I could believe was coincidence, but both of them going with a couple of days of each other with the new devices hooked up?

So after a hefty repair bill I finally was able to check if the Nest’s would work with the boosted signal from the DD-WRT. The answer was no, the signal was reading 50-60% on both of the new devices, but they would still drop connection to the Nest website after a few minutes. They would reconnect as soon as you touched them, but 15-20 minutes later they would show as offline.

This seems to be a reasonably common problem on the Nest forums where users have single units that work fine and then when they add a second they have problems with connections dropping. Again, it is something that you can’t say is definitely a problem with the Nest, but more than 1 or 2 people have the same issue so maybe there is more to it?

The eventual fix to get them online constantly was to set IP reservations for them in the DHCP setup of my router. As soon as I did that they connected and have now stayed connected with no issues for over a week now.


It was a very stressful couple of weeks when I was trying to sort the new thermostats as it is such a large investment when you are putting in more than one of these that you don’t want to think you have wasted your money. There was a point when I was looking at the repair bill for the two air handlers that I considered selling them on and just going with a simpler system. To be honest, if the units had cost me less money I may well have just given up.

But, I didn’t, and now that the system is nearly working perfectly (more on why it’s not 100% shortly), I am glad I made it work.

Just in the last few days there have been a couple of occasions when the convenience really helped. One of our sons came down with a fever one night and was roasting, we wanted to turn the AC down as over night it is set to 81, the problem is the thermostat is in his big brothers room and we didn’t want the risk of waking them both up, so I was able to just use my phone to drop the temperature and make my son more comfortable.

The other instance was when we went away, and I could just set the devices to Away from my phone, and then see that none of them came on the entire time we were away, and before boarding the plane home I could set them back to normal operation so the house was cool when we arrived back. The last thing you want to come home to after 20 hours travelling with 2 small kids is a house that is roasting, and the other option is to leave the system running when we aren’t there. I am not that rich!

The final piece of the puzzle

The last thing that I need to get working is to make the Nest think it is outside the US and get the right weather information for our location. There is a hack I can use on my Synology NAS that should make it work via DNS, but I haven’t had chance to try it out yet.

Update It’s now been 3 weeks and I have been seeing the odd disconnect when I go into the app on my phone. Again it is only ever the two newer devices that drop out. It’s not as bad as it was, but most days one or other of them seem to drop out for half an hour or so.