Our Zoned Systems Provide 5-Star Service From Your Air Conditioning System

Our Zoned Systems Provide 5-Star Service From Your Air Conditioning System

In this writer’s opinion, there is a wide level of competency in heating and air conditioning service providers exhibited in our industry. First, there is a “Chuck in a truck” level that can’t be depended on to show up, nor can one say the probability of repairing a problem is high and usually accompanied with Chuck is little concern for customer service. And the level of proficiency increases to a service provider that has the education, training, and experience to recognize which heating and air conditioning challenges to pursue based on that education, training, experience, and motivation to provide the best level of service possible.

For anyone considering a zoning application, I highly recommend selecting a heating and air conditioning service provider like Tri-County Mechanical that exhibits the highest level of professionalism AND seeks to provide the highest level of service possible.  The highest probability for a great zoning installation begins with a heating and air conditioning service provider that is motivated to provide excellent customer service, installation experience, and possess knowledge akin to a doctorate degree in heating and air conditioning.


The initial and foremost step in installing a zone system is the determination of the heating and cooling requirements for the dwelling. Those in our industry call it a load calculation. For a zone application, not only are the requirements for the dwelling needed, the cooling and heating requirements for each room must be determined and grouped together for each section of the dwelling that is to be “zoned”.

The requirements of each room are summed together to get the requirements for each zone. The requirements for each zone is summed together to arrive at the total requirements for the dwelling. A critical portion of the zone calculation not only includes requirements for each room and zone but air flows for each room and zone. Cooling and heating requirements predicate the capacity. Air flows per room for each zone predicate duct system designs.

Scenarios for zoning that make sense

  1. Let’s start with what our heating and air conditioning mechanical code requires. Multi-level homes require at least 1 thermostat on each level. Anything more than that is considered homeowner preference.
  2. When the percentage of glass (windows) in one area of the home exceeds the percentage of glass in the other areas of the home. A common example is a sun room that is designed to be the main living area in a home.
  3. Some single level homes are so large that it is NOT possible for a single thermostat to maintain comfort throughout the home.
  4. Homeowners that desire to maintain different (NOT extreme) temperatures in different areas of their home for comfort or usage patterns in their home. One common example is a room over the garage. Another example is a master bedroom suite that the owner desires different temperature settings (at night) than the rest of the home. Or guest bedrooms that are sporadically utilized.

Scenario for zoning that DOES NOT make sense – the thought that an existing duct system can be incorporated into a well performing component of a zoned system application.

Zoning can be achieved 1 of 2 methods.  (Probably not within Chuck’s level of expertise)

1.  Structures that have separate heating and air conditioning systems that have installed capacities equivalent to the heating and cooling requirements for each zone provide the “simple” approach to zoning. Nothing is different in the installation and operation of the systems is different than what is experienced in single level dwelling with one system. There is just more than one system. The key to the relationship of 1 thermostat to 1 system.


​When 1 of the systems required is so large that 2 smaller systems could be substituted in its place.  The benefits of utilizing one large system versus 2 smaller systems are lower initial costs and lower maintenance costs. Considering these criteria, 1 system will cost less than 2 systems. However, the utilization of 2 systems that equate to the equivalent capacity of the larger system provide:


  • Greater comfort. (Two thermostats provide increased comfort in 2 spaces instead of 1, i.e., decreased temperature swing in the conditioned space, for instance, the master bedroom AND the main living area) and
  • Greater efficiency (Two systems provide increased efficiency by conditioning the zone that needs conditioning instead of conditioning the entire dwelling when a single zone needs conditioning.
  • 1 large duct system is significantly less efficient that 2 smaller duct systems because 1 large system has greater duct losses than 2 smaller duct systems).
  • If 2 smaller systems are utilized, there is protection from a system failure (if one system fails, there still will be cooling/heating in a portion of the dwelling).

Stepping back and considering the benefits received (2 systems versus 1 system), the utilization of 2 systems may be the best alternative.


2.  Multiple thermostats connected to 1 heating and air conditioning system. Zone controlled system provide optimum comfort in the areas conditioned.  The greater the number of thermostats, the greater the comfort but more complex to deliver that comfort. The more complicated design requirements translate to greater required space for air flow paths.

And typically, the air flow paths are in an attic that contains pre-engineered trusts where the space available is severely constrained. Another basic rule in designing zone systems is: the longer that air flow paths, the less effective zoned systems become because of the requirement for long duct runs. (minimal duct work leads to more efficient systems and greater comfort.) The greater the number of thermostats, the greater the dependency on electronic components to provide comfort, which translated means the more likely that a a single component in a zone in the system will not operate as planned (And there could be many components).


​A.  Let’s start with outdoor system (equipment) for the zone application. The poorest choice is a single stage system. The best choice is a variable speed system. A variable speed system costs significantly more than a single stage system. Variable speed systems can modulate down to 30-40% of total capacity. Single speed systems have only 1 speed (100% capacity). If using a single speed system, when only 1 zone needs conditioning, single speed systems have un-utilized capacity (air flow) that must be sent somewhere, usually through a bypass damper that sends the conditioned air back to the air handler OR back feeds the unneeded air into rooms that don’t need conditioning. (Either way…NOT A GOOD OPTION).

Another optimum design rule for zone applications is that the smallest zone utilized is capable of using all of the air when the variable speed system runs at its lowest capacity. Translated, a variable speed system provides for a design that allows the smallest zone to be 30 – 40% of total capacity capacity without producing EXCESS air.

​An additional equipment requirement is a variable speed air handler (blower). Variable speed air handlers are capable of generating higher fan pressures than standard air handlers and the increased air pressure from the blower is likely to be needed to push air through the longest duct run. (Variable speed air handlers are typically a required component with variable speed outdoor systems.)

​B.  The duct system will be described using a trunk and branch approach. Of course, a MAIN trunk will be required for the return and supply. The number of branch trunks (secondary ducts used to deliver and return air to and from the vents in each zone) needed will equal the number of thermostats / zones contained in the system. All zones require a return air flow path.


​Branch ducts will be sized based on the air flow requirements for each zone. Located in the branch supply trunk, a branch damper will be utilized where it connects to the main supply trunk. The dampers open or close depending on the need for conditioned air in the zone it serves. The motorized dampers receive the signal to open or close from the “brain” of the zone control system that is typically located near the air handler (in the attic).

​The brain, the zone control board, is connected to each branch damper, the air handler and each thermostat. It is the thermostat’s main responsibility to maintain detect temperature (and humidity) conditions and notify the zone control board (the brain) if conditioning is required.


In .the case that the heating and air conditioning system is producing MORE conditioned air than is needed, the dampers that control air flows to those zones that at the moment do not require conditioning, are opened slightly, to back-feed the excess conditioned air into one or more of the zones. (For Bryant’s and Trane’s zone control systems, the excess air (if there is any) is back-fed into the zone that the “brain” has determined will need conditioned air next. That’s pretty smart!)

All duct work that is utilized after each zone damper and to the supply vents in each zone are constructed just like a typical duct system. The branch return ducts are constructed just as a typical return duct path for air flow. For more info about the duct systems we construct, go​ here.

​C.  There will be ONE thermostat designated the master thermostat. All other thermostats will be considered “slaves”. The master thermostat will be capable of controlling all of the other thermostats.


Each slave thermostat has the capability to control its own zone. Typically, it is the master thermostat that is used to determine the humidity level for the entire dwelling. Note that an option exists that decreases the cost of a zone system slightly by utilizing sensors (temperature only and without a thermostat) in lieu of slave thermostats. All thermostats should be located near the return for each zone. Bryant and Trane zone thermostats have the Wi-Fi capabilities to enable connections to computers, phones and tablets.

If you are considering a zone application, we would welcome the opportunity to discuss with you the application that you desire, be provided with the specifics of your application and provide options based on our knowledge, experience, and the options available from our manufacturers.

​Since we desire to be as transparent as possible and I don’t like admitting this, but zone control systems can be complex. After the system is installed, it is unlikely that we will not have to come back and tweak the system a time or two. Complex zone systems are what they are, i.e., extensive duct work, much control wiring and with the realization that sometimes, mechanical devices and controls don’t work as expected. We are committed to prompt support and optimal performance of those systems we install!

If you desire to contact us, choose the method that is easiest for you to reach us.​

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Tri-County Mechanical Inc.

1041 Redi Mix Rd

Little River, SC 29566

Office: 843-773-2442

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