Multi-zone HVAC


Active Member
It’s been dawning on me recently that I need to automate the HVAC system in my town house.

As things stand now I have a typical 1 zone HVAC system with the thermostat in the living room on the first floor and have to control heating and cooling by manually opening and closing vents as the seasons change.

I’m running into a problem where I either need to turn off the heating and cooling and open all the windows or keep all the windows closed and run the heating and cooling.

I need to figure out how to setup a 2-zone (upstairs and downstairs) or 3-zone (each bedroom upstairs and the entire downstairs) HVAC system that will let me open and close windows at my leisure and still allow the other sections of the house to remain at a comfortable temperature.

I’ve gone ahead and ordered 1 of these ceiling registers from AutomatedOutlet to play with but I’m trying to figure out the best way to control a whole system of registers.

My first issue is getting temperature sensors into each zone. I can’t really run wires from both the upstairs and downstairs to a single place. I can get both the upstairs zones to one place upstairs and the downstairs already has a thermostat. I looked for wireless temp sensors at AO and SmartHome but didn’t see anything. Wireless would be ideal (I think) but I’m open to suggestions.

The second issue is how to control all this. I’m currently running an old standalone version of Housebot (1.61 to be precise) to automate my outside lights and a few indoor lights, nothing fancy. If I can continue to use Housebot, that’d be great but if not I’d like to stick to a computer based system and not a stand-alone controller. My beef with the stand alone controllers is that, while they are very nice, they have a lot of features I don’t think I need (security stuff specifically) and don’t particularly want to pay for.

And finally, I know that I’m going to need to replace the thermostat I currently have in my living room with one that can be controlled remotely. I’m just not sure which one. Again a wireless solution would be ideal for interacting with the thermostat but I’m not sure that something like that is available.

Ultimately this is the biggest home automation project I’ve decided to tackle and I’d like some pointers on where to begin.

If there’s anyone else here who has succeeded in making a retrofit multizone HVAC system on a multi-story building I’d like to hear how you did it and what you might have done differently. And of course, if there’s anyone who made the attempt and failed, I’d like to hear your stories as well.

Phew, this turned out to be a lot longer than I’d anticipated. Thanks for taking the time to read this guys and I look forward to your replies.
I need to figure out how to setup a 2-zone (upstairs and downstairs) or 3-zone (each bedroom upstairs and the entire downstairs) HVAC system that will let me open and close windows at my leisure and still allow the other sections of the house to remain at a comfortable temperature.

Did you mean vents or windows on opening and closing?

I think you want an HVAC specialist as if you are changing the zones there are all sorts of pressure calculations and such to setup the unit to run efficiently (and safely). I'm no expert here (and could be wrong) but I've read about considerations such as this. Perhaps if the unit is small its not as big of a deal, but something to check on.

You could always have someone come in and let you know what is involved (as they would have the expertise) and may be able to do it easier than you can.
Hi Mike,

Thanks for the info and note of concern. I'm not particularly worried about balancing the system, though. And here's why:

My town house is just around 1 1/2 years old. On each level, in addition to the registers, there are vents about 8-9" tall on wall by the floor that I believe are used to keep the pressures kosher when some of the vents are open while others are closed and the HVAC is running.

All I'm trying to do is automate something that I could otherwise do manually by going around each room and opening or closing the registers by hand.
Ahh understood.

To solve your temperature sensor issue, I believe it was mentioned that the Elk will have a tie in in the future to weather sensors. These are typically wireless and I would guess that you could put them in various rooms and then tie into some other HVAC control situation controlled by the computer.

This breaks your thought of avoiding a controller though. If you have some paint and spackle there might be some other options on the sensors (hard wire them, of course it may be harder to link them unless you use a controller or thermostats tied in for HVAC control, although you may want to see the difference in cost as you might get some better longer term options with a controller depending on if you need to buy a multi-zone hvac controller which may be a decent percentage of a controller price)...

Assuming you got the above figured out and replaced your registers with something like:

then couldn't you replace the switches with something automation friendly (Insteon?) and then pick a package that supports that protocol (support is sparse at the moment though).

I haven't done this however...
The register that you linked to is the same that I'm most likely going to use. I ordered one of the 100A models, which is the vent only, along with an Elk relay. It's the same hardware that Chakara did a review on here.

While I was laying in bed last night I was thinking about this a bit more and I don't think I can get away with just using a computer. In order to run the vent register control wires from a central location it's going to have to be near my furnace which is in a small closet in the garage. So my options are to either figure out how to put another computer in the closet (I'm up to 4 computers already for just myself) or a controller.

I'm thinking the controller would be a better route and if the Elk will allow that kind of wireless sensor that will probably be the easiest and best way to work this out.

I was thinking that I could rig something up using X-10 modules with those registers and just use the computer I already have controlling the lighting but I don't want something as unsecure and tempermental as X-10 controlling my HVAC.
I agree on X10, I have been planning on using the 2-way status capability and the reliability of Insteon relays for some similar types of automation I'm going to try. In the case of the Elk, its not out yet, but it is coming...

If you get something like the elk you could add security as well (they have wireless sensors if you can't run security wire).
There are a 2 flavors of Elk controllers on AO, the M1 and M1EZ8 both with prices. Assuming that there isn't another Elk controller due out, it looks like the M1EZ8 is what I would need.

I'm still not sure at this point how all this will tie into the HVAC system though. I don't need to be able to set different temperatures in the different zones, just monitor the temps and open/close the registers as needed. Because of that I only need a single thermistat to control the HVAC but how do I control a thermistat with a controller?

I see that the Elk M1EZ8 comes with a keypad, but it requres 4 wires and I don't have a way to run the control wires from my garage to where the touchpad would be replacing the thermistat. Unless there's a way to run the control of the HVAC to the controller (or something that can interface with the controller) then I could use the wires that already go from the furnace to the thermostat to link the keypad and the controller.

Also, and maybe you or someone else can answer this, but would I be able to use one of the Elk controllers to control the automated registers in conjunction with the wireless door/window sensors? For example, could the open status of a sensor override the HVAC control for that zone and keep the AC or heat from kicking on while the window is open?
For example, could the open status of a sensor override the HVAC control for that zone and keep the AC or heat from kicking on while the window is open?
Hmm. What if it is 50° outside and the window is open? B)
If I understand correctly you could do it like this:

1. Replace your existing thermostat with one controllable by the Elk (RCS, Hai and Aprilaire I believe are supported) you will need a serial expander to do this.
2. Put the controller in the garage (depending on the package it will come with a lockable cabinet)
3. Put the keypad in the garage (wiring issue solved) but this depends on how you enter the house and how the security will be setup. I am thinking of putting one controller by the garage, but others by the main door).

I believe the wiring of the keypad works similar to garage door openers, you can't just cut the wires and rub them together like days of old so even if the wiring to the keypad is exposed that might not be a major flaw (curious what others think). Perhaps there is a closet in the garage you can put the controller to put it out of view (then again if someone is in the garage, they have already breached the perimiter, which is something that the controller should already know).

I haven't heard of a new controller coming out (although someone joked about an Elk Platinum recently). Lots of expansions though (lcd touch screens, weather sensor tie in, Insteon support, etc).

Does this help?
TonyNo said:
Hmm. What if it is 50° outside and the window is open? B)
hehehe, if it's 50 degrees outside and I've got the window open, then I'm an idiot. But I'd rather be an idiot freezing his nards off than an idiot running the furnace with a window open when it's only 50 degrees outside. ;)
Mike said:
a whole bunch of good info
The location where this controller would end up is in a small closet in my garage that houses the furnace and the hot water heater. It's behind a set of doors and it would be easy enough to drill a hole in the wall to put the keypad above the light switch outside the closet.

I'm not thinking about security at this point though, just the HVAC capabilities.

I went ahead and looked at the different thermostats that you listed and I think the TR16 RS-485 Thermostat is what I would need? If I'm reading the description correctly I put the wall unit where my current thermostat is. I then use the wiring that connects the old thermostat to the furnace to connect the wall unit to the controller and I can connect the controller directly to the furnace.

So the setup would look something like:

Wall unit --> Elk Controller --> Thermistat Control Unit --> Furnace
|--> Automated Vent Registers
|--> Remote Temp Sensors for additional zones

Am I getting this right?

edit: the board doesn't seem to like leading spaces, but the lower section is supposed to be lined up with the Elk controller.
One line from the Elk Controller (the panel) will go to a keypad/touch screen
Another set of connections for the register and temp sensors (but the temp sensors based on wired use have to be on the first 16 zones but several you cannot use). The wireless connection and using weather sensors isn't out so anything there is speculative (although the concept makes sense).

You would need a serial expander to connect with the thermostat. Here is one consideration for the M1g versus the EZ8. The EZ8 allows one of these expanders, whereas the M1G allows for 7 (if I have my documentation straight).

Here is where that could be an issue: If I understand it correctly, Insteon support will be released as a serial expander connection. If you wish to use insteon and HVAC support for the RCS you would not have enough connections to do so.

On the thermostat itself, you may want to gather more opinions here. I had a HAI already installed (I was expecting at the time to install a HAI Omni II, but later got an Elk). I think Aprilaire was considered the best, followed by RCS, followed by HAI.

I've been considering something similar but am only using it for single zone heat (older house) currently. I was expecting:

M1G (corrected to show serial expanders properly on the data bus expander)
-Data bus expander-->
+Serial Expander-->HAI Thermostat
+Serial Expander-->Insteon Support
*Wireless Card

Note I think the serial expanders are chained when using an M1G (so it wouldn't be labeled quite like the above but text is not the best medium here).

Have to get some sleep, but figure out how you are going to use it as the above may sway you to the M1G (but I may also have gotten it wrong on how Insteon would be supported, I think there was a comment in a post here on it, maybe I can find it tomorrow).
Thanks for pointing out the potential problem with the EZ8s ability to expand. From just a cursory glance at the description on AO it looked like the only difference was the voice and phone capability.

I think I may have found a solution to my inability to run extra wires between the thermostat and the controller though. It seems that Elk is releasing a Z-Wave interface soon and Z-Wave just so happens to have a god awful, ugly thermostat that's designed to be controlled with a wireless Z-Wave controller.

I think I smell a solution here and I think it smells good.
Mike said:
You would need a serial expander to connect with the thermostat. Here is one consideration for the M1g versus the EZ8. The EZ8 allows one of these expanders, whereas the M1G allows for 7 (if I have my documentation straight).
Both the M1 and the EZ8 support up to 8 serial ports. I believe David stated that they were working on increasing the number supported, but I don't know if that would affect both or the M1 only.

The EZ8 does not have the first serial port included, as does the M1. So the M1 supports 7 expanders while the EZ8 supports 7 regular expanders and one special EZ8 expander.
Thank you for the correction Wayne. I went back to look where I saw that and I think I am misinterpreting part of the documentation, or the reference is incorrect. Now that you mention it I think Electron is using multiple serial expanders with the EZ8 currently if I remember his posts correctly.

Page 2 of the following PDF

Does this refer to something else when it says ports, or is it perhaps just wrong?


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