More than one thermostat for one zone?


Senior Member
I had a general question: The house I bought is an older one and the heat was run as one big one (and apparently it is a real pain to change that). I am having central air put in and it will also be one zone.

I currently have a HAI thermostat installed and connected to the elk.

My question: Is it possible to hook more than one thermostat up so I can have controls upstairs and downstairs?

I realize I could put a keypad and use that, but I'm not sure the WAF will be there for a hallway installation.

Could also try and go down some type of touchscreen (ala IVB using CQC or one of the other packages such as Mainlobby) as part of the next phase of integration, but was wondering if it is possible to hook more than one thermostat to a single zone setup (and connect it to the elk).
The M1 can control upto 4 HAI Thermostats using a M1XSP or 16 RCS and 16 Aprilaire Thermostats. Generally one thermostat per HVAC system.

Using multiple thermostats into one HVAC unit may be a problem. You can use the ELK Touchscreen or ELKRM software from differenct locations to control one thermostat.
You could use a selector switch to select between two dumb thermostats, but you could have user confusion if the switch was selecting the "wrong" thermstat at the time.

Electronic thermostats probably don't like to be switched around that way.
WayneW said:
You could use a selector switch to select between two dumb thermostats, but you could have user confusion if the switch was selecting the "wrong" thermstat at the time.

Electronic thermostats probably don't like to be switched around that way.
Can you think of a manufacture which makes these switches? I would love to install a 2nd dumb thermostat in my master bedroom for night time use.
You could use 3 or more double pole, double throw relays to switch between two thermostats.

Set up your M1 with Rules to automatically switch between the thermostats at certain times of the day or control the relays with Tasks or Telephone remote control from the bedside.

Good idea! :D
Not having done this myself, but the theory sounds good... you just needs a SPDT switch with the center switch connected to the HVAC unit and each side connected to a thermostat. The wire you want to mess with is the one supplying power to the thermostat, usually brown or red. Then all the thermostat outputs (green, yellow, etc) would just be wired in parallel at the HVAC unit, since only one of the thermostats would have power to feed the output. Again, I wouldn't try this with an electronic thermostat, but I think it would work with a dumb mechanical thermostat, which is usually just a temperature switch and a couple mode switches.
WayneW said:
...but should work fine with electronic thermostats.
with the exception that some of the lower end/lower cost electronic thermostats (like I have for my unfinnished basement) get power from the zone controller (24 v) I dont know as I want to be switching power to it on and off every day.

others just have a switching relay to the zone controller and a few AA batteries to power it
I have a cheap digital thermostat, I will have to keep my eyes open for another cheap model, I would love to try this.
Well central air is in (so much more comfortable) and an idea occurred to me. What if I put another HAI thermostat and wrote some kind of rule so that when it changed heat, it would set the other thermostat (which controls heat) to the new value. Another rule would cover the heating thermostat having the cooling value set (it would relay the value to the cooling thermostat).

This is more of a problem solving exercise at this point. It would be preferable to running wire from the boiler to the new tstat (which would result in removing the lower tstat) and it would let me have thermostat based control from two locations.

I was looking at the rule options and I am not sure if this is possible though, but I am not clear how some of the custom settings and such work, so I figured I would throw it out there.

If this does work, it seems like a great approach. My next problem would be do I take another look at Aprilaire or RCS before investing further in HAI.

Is it possible to write rules like this with variables?
I was looking at this further and researching custom values and the like

It seems if I set a rule (nice to have functionality possibly included below, it seems what is supported is close to this, and I may be misunderstanding custom settings so maybe something like this could work)

THEN SET ACTStatCounter (Counter 1) TO COOLING TEMP OF ACStat (TStat 1)

THEN SET HeatTStatCounter (Counter 2) TO HEATING TEMP OF Heat Stat (TStat 2)
THEN SET Heat Stat (TStat 2) COOLING DESIRED TEMP TO HeatTStatCounter (Counter 2)

Or at least something like that. Anyone seen anything like the above work? I was playing around and could get close, but I think perhaps the above functionality is not supported currently.

It seems if I were to be within a range of degrees for heating and cooling, which seems plausible, I could write it out (IF 70 degrees then set 70 degrees). It would eat up some rule space but since there are probably only a small number of temperatures I need (granted someone will break this) this might work as well.

Spanky > Thank you. Granted the touch screen would solve this, my problem is two fold 1. Putting touch screens in place of thermostats is a bit pricy. 2. I still need thermostats and it may be difficult to tell people that this one only does heat, go upstairs, or vice versa.

I do expect to have some kind of enhanced support at somepoint (touchscreen, etc) but I'd like to have a thermostat on each floor, and since I only have one large zone for heating and cooling...

A touch screen would be real nice... unfortunate it would need to be prioritized a few projects down the road. I'm also starting to wonder if control via media center might make sense as that seems to be taking over the existing tv's. Means it needs to be on and in wide usage throughout the house, which for now is only 2 tv's.
I was giving this more and I think there is another option (I don't want to switch control from one to the other based on time of day):

If I implement something like CQC or other automation software, it can check, say once a minute (or even a bit longer) and if the desired temp has changed, set the other thermostats value to the new value. The same process would be employed for the other stat as well.

I still need to get a wire to the control wire from the thermostat, but I can actually link in close to the panel for that which makes it easier. Plus in the end I get the multiple thermostats without time restrictions (other than not immediate settings changes, but I can deal with that I think if it is a minute variation).
the only thing to think about is which thermostat has "master control" so you dont change ona and your wife dosent change the other and end up in an endless loop...