Thermostat in the cloud


With my ever-loving wife, “Charlotte” (not her real name), on sabbatical, it has become an increasing challenge to maintain a comfortable, yet energy efficient temperature in the house amid her comings and goings and various sabbatications.

BAYweb has a convenient and powerful way to control the temperature using a web browser from anywhere in the world. You log on to their website ( to see the current temperature in the house and adjust it as needed. The service is free but you have to buy and install their control module and thermostat. In our case, the cost of the hardware was offset in less than a year with reduced energy costs by adjusting the temp when we weren’t home.

Of course you can manually set back your old-fashioned thermostat before you leave on vacation and reset it when you return but the BAYweb system has these advantages:

  1. If you forgot to set back the thermostat before you ran out the door for your vacation you can do it from your motel or even your smartphone at the rest area.
  2. A few hours before you return from vacation you can turn the temp back to normal and the house will be comfortable when you walk in the door.
  3. You can monitor the temperature while you are away. One guy was away during the winter and noticed that his house was getting too cold and got the heating repair company to fix his furnace before the pipes froze.
  4. You can view charts and reports of energy usage and temperatures.

Our house has separate systems for upstairs and downstairs so I bought two pairs of thermostats and control modules. The basic idea is to replace your current wall thermostat with the new one and splice the control module into the wire that runs between the thermostat and the air handler. (The air handler is the unit in your attic or basement that blows the heated or cooled air. See “The return should suck more.” The heat pump or air conditioner compressor is the noisy unit outside.)

A few years ago I had installed this system at another house and put the control modules in the attic next to the air handlers. (Air handlers shouldn’t be located in an uninsulated attic but that is a topic for another post.) The module has some indicator LEDs that are sometimes helpful to see, which means a trip into a hot attic.

Control modules mounted on a panel in the basement next to the electric panel
Control modules mounted on a panel in the basement next to the electric panel

For this new project I decided to mount the control modules on a panel in the basement, which is much more accessible and visible. This was right across from the downstairs air handler but three stories below the upstairs air handler in the attic.

Two spools of thermostat wire hanging in the attic
Two spools of thermostat wire hanging in the attic

I put two spools of thermostat wire (5-strand and 7-strand) on a piece of PVC pipe in the attic and pulled the wire down to the module in the basement. The 5-strand wire connected the new thermostat (which requires only 4 wires) to the control module. The 7-strand wire connected the control module to the air handler in the attic. Rather than cut the old t-stat wire and splice both ends to the new wires, I disconnected the old wire from the terminals in the air handler and connected the new 7-strand wire directly to the terminals.

Junction box for thermostat wire splice in attic
Junction box for thermostat wire splice in attic

Then I spliced the disconnected end of the old wire to the new 5-strand wire that was heading down to the basement.

The wire strands are 18 gauge, which is pretty small. My wire stripper had only 12 gauge and 14 gauge slots. You know how wire cutting pliers get little nicks from cutting really hard wire? It turns out that those nicks can be the right size for stripping small wires.

The key to HVAC wiring is knowing your colors. This is where your kindergarten education comes in really handy. You connect the red wire to the terminal labeled “R” and the green wire to the terminal labeled “G” and the white wire to “W” and the yellow wire to “Y.”

Terminals in the air handler. Notice the letters next to the terminals.
Terminals in the air handler. Notice the letters next to the terminals.

Perhaps you are noticing a pattern. Perhaps you have a future in becoming an HVAC technician.


The control module has to have a network connection so that the BAYweb servers can talk to it. Unfortunately, they currently don’t do Wi-Fi so you have to connect an Ethernet cable. Even more unfortunate, my router was two stories up in my office and I wasn’t crazy about drilling more holes in the walls.

So how do we make something wired wireless? The typical router takes a wired connection and beams out a wireless (Wi-Fi) signal. I needed to go the other way: receive a Wi-Fi signal and convert it to Ethernet. This relatively unknown feature is called “client bridge mode.”

Google located what I needed: a ZyXEL 3-in-1 Wireless N Pocket Travel Router, Access Point, and Ethernet Client (MWR102). This thing is smaller than a deck of cards and costs under $25. The user manual doesn’t describe how to put it in client bridge mode but if you dig enough on the web you can find it. You configure it using your PC and then take it wherever you want, which in my case was the board where the control modules are mounted in the basement.

ethernet crimping
Crimper for attaching an Ethernet connector

Ethernet cables come in various sizes but I wanted a very short one for connecting the control module to the ZyXEL. I’ve always enjoyed making my own using a crimper tool. In this case, I needed two short Ethernet cables for the two modules so I took a 4′ pre-made cable and cut it off about 8″ from each end. Each piece had one connector and needed another one on the other end. I used the tool to strip off the outer jacket and then line up the little colored wire strands in order: white/orange, orange, white/green, blue, white/blue, green, white/brown, and brown. Kindergarten education scores another one! I made sure the wires were pushed in the connector all the way before crimping it because otherwise the wires won’t connect. Don’t ask me how I know this.control modules annotated

old thermostat
Old thermostat with leaking batteries

The next step is to replace the old thermostat with the new one. The batteries in the old thermostat had leaked and the flaky battery ooze was not encouraging. The new BAYweb thermostat does not require batteries so that is a plus.

new thermostat wiring
Same-colored wires twisted together with wire nuts in the new thermostat
new thermostat
New BAYweb thermostat

After twisting the wires together with wire nuts, I screwed the thermostat to the wall and turned on the power to the air handler.

The last step is to tell the BAYweb website about the new thermostat and set the temperature.

I’m not sure what the “BAY” in BAYweb means so since I use it to make the house comfortable for my ever-loving wife, we call it Charlotte’s web.

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