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HVAC Zone Controls & Zoning Dampers

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Upgrading thermostats; solving a "common" problem

HVAC Contractors, Support, homeownerszoning supplyComment

So, maybe you have decided to upgrade to a Wifi thermostat, or even just a standard "programmable" thermostat... only, you come to discover that your old thermostat has one less wire connected to it than the new thermostat needs.   This is usually the "24VAC Common" wire sometimes just called "C" or "24C".   This means that your old thermostat was either mechanical, power stealing, or battery operated... which isn't a problem if you don't want a modern thermostat.  MOST modern thermostats (especially WiFi) need a "C" wire from the 24V transformer to power the thermostat... this means getting a "C" wire to the thermostat.

This isn't a new problem, it started showing up in the 1980s with the first programmable thermostats... over the years, I have suggested and used several different methods to overcome this issue both with zoning and with typical single thermostat applications.  Until recently, I couldn't really recommend anything other than running a new wire... and running a new wire isn't always possible.

METHODS to add "C" Wire

  1. Run another wire to the thermostat
    The most straightforward and full-proof method is obvious: run another wire.  If possible, this is ALWAYS your best solution.
  2. Power thermostat from separate transformer
    Don't use this method... it is risky and not all thermostats support the ability to separate the "R" from the equipment transformer.
  3. Use the "G" wire for "C"
    This method DOES work but it limits the functionality of your thermostat control.  (ie. you will not be able to independently control fan from the thermostat)  The reason this works, is that the equipment automatically turns the fan on during a heating or cooling call, so the "G" wire controlling the fan from the thermostat is only necessary to turn the fan on by itself.  You will NOT be able to turn fan on from the thermostat by itself with this method.
    NOTE: This works with MOST equipment, but you should check or test before employing this method. (#3)
  4. ADD-A-WIRE Device
    It is the BEST method and really the only method I would use if a wire cannot be run.  This is a relatively new concept to me... it has been around for a few years at least but we just started recommending it within the last 2 years.    Several companies have started offering an "ADD-A-WIRE" device that allows the addition of a "COMMON" wire.  These devices range from $15 - $40 and are very simple to wire (you have to be able to get to your equipment furnace/blower). 
lux addawire.JPG

How an ADD-A-WIRE Device works:

venstar addawire.JPG

It will come in 2 pieces, one is a small box with several connections labled "R", "C", "Y", "G", "W".  You will follow the included wiring instructions to connect this box at your indoor HVAC equipment.  The other piece that comes with the ADD-A-WIRE is a wiring connector with 3 leads, this connects at the back of your thermostat as shown in the wiring instructions.
Once these two pieces are wired properly you will have the "C" you need for any thermostat... it's almost like magic (electrical engineering magic).

NOTE: Make sure all wiring is done with the power to the HVAC equipment OFF at the breaker.

A few different models to choose from (prices on amazon at time of writing)  There are many others available but they all do the same thing (NOTE: we are not compensated by any of these companies or any others for our opinions):

For more information about specific use with zoning and zone control systems such as SmartZone... contact us

Another thing to consider:  The ecobee3 and ecobee3 LITE both come with an "ADD-A-WIRE" type device.  So, if you are thinking about a WiFi thermostat and are afraid you will need to add a wire... keep the ecobee in mind.  See our WiFi stat roundup for more info

2016 USER QUESTIONS - SmartZone Advanced

Support, homeownerszoning supplyComment
Photo by BackyardProduction/iStock / Getty Images

QUESTION: I have two 9580 thermostats one in the office, the other in the main hangar bay (two zones).  When heating both zones or only the hangar, I need the furnace to go full blower with normal scheduling through stages 1 and 2.  When servicing only the small office area, I don't want the system to advance from stage 1.  Unfortunately, the office is so small and the modulating schedule of the furnace is still too much airflow for the office (the zone bypass when servicing the office is the main hangar modulating damper that is controlled via SPC (excess dumps into hangar)).  This damper will be wide open during call for hangar heat.  The main damper control logic is managed through a 3PDT  24 Vac relay. So, I need to block out stage 2 from only 1 zone (office).  The zone ramping schedule of the 9580 works well with the 100k modulating furnace control board, and would like to keep that capability. 

ANSWER: Configure the zone 1 thermostat connector STAT TYPE to G2 (conventional gas/electric) or H2 (heat pump) to allow the thermostat to control staging and use the hangar thermostat on zone 1. Wire only the stage 1 circuits (Y1 and W1) on the office thermostat to the zone 2 thermostat connector (Also connect R, C and G wires). Set dipswitch 4 to the LOCKOUT position. This will configure the zone controller to allow 2nd stage only when the hangar thermostat calls for 2nd stage regardless of whether the office thermostat is calling. When the office thermostat is calling and the hangar thermostat is not, SmartZone will not allow 2nd stage to operate.


I called last week to inquire about using this zone controller in a hangar that had a small office area and a large bay. I advised the call taker that I had Honeywell 9580. I also asked about the capability of the zone controller to handle the smaller office area’s lower CFM requirement and whether or not I could defeat the step-up from W1/Y1 to W2/Y2. I was told that the controller can be set up to defeat the stage step-ups.

After reading the manual, I found that there are no multi-stage inputs on the controller board from thermostats. So, basically, the capabilities of the Honeywell 9580 are wasted. Also, the stage defeat is for the whole system, not zone-specific as I need. It would be pointless to defeat stage increases while heating/cooling a large hangar space

ANSWER: The SmartZone controller typically controls staging based on the total system conditions which is the most efficient way to operate a multi-zoned multi-staged hvac system. However, the zone1 thermostat connector on SmartZone can be configured to allow the thermostat to control staging (refer to the top of page 10 of the installation manual). When the zone1 thermostat is configured for staging the ability to lockout 2nd stage with only 1 zone calling is disabled. With the thermostat controlling staging your ability to limit staging will be determined by the features of your Honeywell 9580 instead of the SmartZone control.


I have a honeywell mastertrol2 mm2, i wanted to update my thermostats but my zone controller has separate b and o wires going to thermostats . Will updating my zone controller to a smart zone 2 help this problem?

ANSWER: Updating your zone controller to a SmartZone 2 zone controller will allow you to use any 24VAC thermostat. SmartZone controls are designed to be universally compatible with 24VAC thermostats including WI-FI models used to control your thermostat remotely through the internet on your smart phone or tablet. You should be able to connect any 24VAC thermostat to a SmartZone control without any problems.


Do you have a digital thermostat that you recommend or sell to go with SmartZone?
From ecobee.com

From ecobee.com

ANSWER: ZoningSupply does not carry thermostats, however, SmartZone controllers are compatible with any 24VAC powered 5 or 6 wire thermostat. Popular brands our customers install with SmartZone include Honeywell, ICM, Braeburn, Nest, Ecobee, Aprilaire, Lux, Lyric,  and MANY others. We suggest you avoid using low priced 'power stealing' thermostats as they may cause intermittent issues if your utility power fluctuates. Power stealing thermostats are typically low priced and can be identified by the lack of a C (common) terminal on the thermostat wall mounting plate.
If you are looking for a WiFi thermostat check out this other article:

http://zoningsupply.com/blog/best-wifi-thermostat-for-zoning

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Best damper motor (actuator) on the market... we tested them all.

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Well, maybe not technically ALL of them but dozens and even more than in this photo.

We narrowed down by specs that would work for us first.  Between 30 and 60 second travel time, 90 deg rotation, at least 1.5nM torque, lower than 3.5VA power consumption, 24Vac operation, clutch free movement, minimum open/close, range of 3/8" to 1/2" shaft and more.  Once we narrowed down to here we still had about 6 or 8 motors and we tested the top 5 for full 10 year accelerated life and field testing.  Some we even used in production for a while.  We are now confident when we proclaim that the Belimo motor that is made for ecojay and we sell with SmartZone wins in all categories... reliability, noise & installation/setup.

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Zoned climate control in your car… why not your home?

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dual climate control

For many years, lots of car manufacturers have been putting separate passenger/driver/rear climate controls in cars.  In such a small space, this could be seen a “silly” feature because the passenger & driver are in very close quarters.  In most homes, however, heating and air conditioning systems still tend to have only ONE climate zone (one thermostat).  Dual or multiple climate zones for a home makes much more since than in a car but is not nearly as often implemented.  With SmartZone most existing heating & air conditioning equipment can be upgraded to have multiple climate controls (thermostats) in different areas.  You could have a thermostat in the kitchen, bedroom and living room… comfort everywhere.  Additionally, with SmartZone, areas that are not being used can be turned OFF to save energy.  All the parts you need shipped for free from ZoningSupply.com Zoning experts standing by to answer any questions you have or help with system design.

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Light switches don’t save energy… turning the light switch OFF saves energy

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Zoning Return on Investment – Payback?

There is no short answer to this question with Zone Control.  Energy CAN be saved with zoning but it is also capable of increasing the comfort of a home.  Because of this, a zoning system can both save and cost energy depending on how the homeowner uses it.  User habits of operating the system primarily determine how much energy will be used or saved.