Understanding Two Thermostats In One Unit

Understanding Two Thermostats In One Unit

You can control the temperature of the rest of the areas in your homes using a thermostat. Each unit has its own set of sensors linked to one thermostat. You need to program each thermostat separately when you install them. Each thermostat appears in the exact location on the wall and has the same type of switch. Armed with all this information, you can program each thermostat with its instructions, which are simple to follow.

The first step to installing your thermostats is to mark which terminals go with which switches. The terminals are small holes that you can see inside of each switch box. They are unique to each switch, so if you mark them now, it will be easier later on when we need to reference them again. Keep reading this article to learn more and avoid any problems or issues in your units.

Can You Have Two Thermostats and One Air Conditioner Unit?

You may connect multiple thermostat brands to the same HVAC device. Whether it be a ventilator, ac, boiler, or furnace, controlling the temperature in your home is not essential.

In principle, the problem with temperature can occur when there is inadequate space in a house. Even in big enough homes to circulate air well, insufficient air flow can result in uneven temperatures. 

Additionally, in larger dwellings, room air conditions are not evenly dispersed. Multiple thermostats can even out temperatures in different rooms if you install them, you may also place them in your basement. Installing multiple thermostats around the house can create heating and cooling zones.

In fact, you can use the thermostat settings to regulate the temperature and set it to your preferences. Each zone has a thermostat installed, but it is independent of other thermostats in the house. You can even have hot spots in a house with several floors and cold spots.

How to Install Multiple Thermostats?

Dampers, also known as zone dampers, are an efficient way to redirect cold or warm air using a single thermostat. A zone damper closes one channel in the ductwork and opens another part where cold or warm air is required, redirecting cold or warm air to where it is needed. Doing this increases the efficiency of the heating and cooling in your home.

How to Install Zone Dampers?

Homeowners may consider installing multiple thermostats if they have a large home or one with different levels. It can help them better control the temperature in various home areas and save money on their energy bills. Here are the things homeowners should know when to install multiple thermostats in their homes.


  • Draw a straightforward blueprint of your house. It doesn’t have to be precise. You only want to see the rooms and zones where you want independent thermostats. 
  • Make a superimposed diagram of your house’s duct system. 
  • Choose different colors to distinguish between lines representing the walls and rooms of your house and duct lines. You may use a different color to differentiate between lines representing the ducts and walls and the restrooms and corridors. 
  • Mark the air ducts with a marker that is heated and cooled.
  • Before installing the zone dampers, locate the air ducts’ branch points and the parts where they split into two paths, one leading to each thermostat. The rising warm air from the heater helps balance out the heat throughout the house and reduces the need for the thermostats to switch on and off.
  • If you want to install more than two thermostats, locate the sections of the air ducts where they split into branches that lead to zones where thermostats are located. 
  • Measure the length of the air ducts. Verify if two parts of the same size air ducts are divided. 
  • Purchase zone dampers that are the same size as the air ducts.

You may also call a professional installer and if you have question regarding the unit, you will easily know the answer. Keep in mind that some installations may have higher costs but they will do the job based on your expectations. 


Using tin snippers, cut a hole in the duct that is large enough to accommodate a damper. Some dampers are drop-in, whereas others are slide-in. If necessary, determine whether your damper is a slide-in or drop-in variety and choose the correct cut on the ducts. Secure each damper with screws and caulking.

Wiring the Damper and Zone Control Box

  • All dampers require two or three wires. The 18-gauge multi-strand thermostat wire should be stripped and connected to the damper wire connectors. Ensure that the wire locks are tightened with a screwdriver so the cables will not become dislodged.
  • Connect the opposite end of the wire to the zone control box. A zone control box usually controls two dampers. Connect the wires from each damper to the box’s ‘Damper 1’ and ‘Damper 2’ connectors, which have two screws each. Tighten the wires and ensure that they do not come loose. If necessary, you may install more than one thermostat or damper with a zone control box. You will locate the wiring connectors for the dampers you install on the box.
  • The zone control box connects to the HVAC unit with an equipment wire connection code. A zone control box should be installed near the HVAC but not beside it. 
  • Locate it on an air duct or wall near the HVAC. An 18-gauge 4-conductor wire must be stripped and connected as follows:
  1. White to ‘W’
  2. Red to ‘R’
  3. Green to ‘G’
  4. Yellow to ‘Y’
  • Connect the other end of the wire to the HVAC control board using the color code listed above.

Example of Two Thermostats Controlling One Zone

Two thermostats can control one HVAC systems zone, as the following example illustrates. In a house with two stories, the upstairs tend to get hotter than the ground floor in the summer. If no zoned HVAC system is installed or the system only has a single thermostat, the thermostat controls the temperature but cannot recognize that the upper floor is hotter than the lower floors. You could install a second thermostat without making zones in a two-story house. The second thermostat will turn on the blower fan when the temperature rises above a predetermined level. 

Because of this, the one-zone system can somewhat distinguish between zones. The air conditioning units will not turn on unless the main (downstairs) thermostat is set to 75 degrees when the temperature in the upper story rooms reaches 77 degrees. The blower fan will only turn on when the temperature rises above 77 degrees and will stay on to even out temperature differences. When the air conditioning system is turned on, the blower fan continues to run as required and not automatically, saving electricity.


With this compatibility, most people can choose from the largest variety of thermostats available on the market, including brands with the best security features, like Schlage and Honeywell. This blog post explored the option of using two thermostats in a multi-unit building to save energy and money.

While this can be a great way to reduce energy costs, it is not always feasible due to the extra work required to synchronize the thermostats properly. If you are considering this option for your building, be sure to take into account all of the associated costs and challenges. 


How to install the thermostats?

To install the thermostats, you will need to follow this process: 

  1. First, you will need to turn off the power on the unit you are working on. 
  2. Next, remove the old thermostat from the wall. 
  3. Once the old thermostat is removed, you will need to install a new thermostat. 
  4. To do this, you must connect the wires to the new thermostat. 
  5. Once the wires are connected, you will need to mount the new thermostat to the wall. 
  6. You will need to turn the power back on the unit.

Are Nest thermostats compatible with a zoned system?

Nest thermostats are not compatible with zoned systems. Zoned systems have been around for a while but are not as common as they once were. Some damper systems may require a power connector installed on the Nest thermostat to be compatible. When you’re not around, the Nest thermostats will use Eco mode in all zones to save energy.

Is it possible to replace only one thermostat with a Nest thermostat in a zone system?

It is possible to replace only one thermostat with a Nest thermostat in a zone system. It can be done by removing the old thermostat and wiring the new one in its area. The Nest thermostat will work with the existing zone system and provide accurate temperature control.