Copyright RetroZone inc.2012 



SECTION 7 Planning and Pre-wiring Information




With an Airzone system directing the flow of air exactly where and when you need it, energy is not wasted over-heating or cooling an area that is already satisfied or unoccupied.  Fuel savings of 10 to 30 percent or more are possible, depending on how the Airzone System is used or "managed."



Three different types of zone control with Airzone give you three different levels of capabilities.

Primary Zones- (Airzone Systems with control panels) A primary zone is a zone with a thermostat that not only controls Flexdampers but also controls the operation of the HVAC System, and is totally automatic.  When a primary zone thermostat calls for air, the Flexdampers serving this zone will open, Flexdampers serving other zones will close, and the HVAC system will operate.

Slave Zones- (SPP panels with no Control Panels) Slave zones are used to simply open and close certain ducts, such as those serving an unused guest bedroom.  While slave zones can be controlled by a toggle switch or thermostat, only the Flexdamper(s) are controlled:  The HVAC unit is not brought on or off.  Airzone’s SPP Panel, on its own, is an example of a slave zone.

Combination Primary/Slave Zones:  Suppose you wanted to zone a home into three primary zones with a SPP and control panel, and also wanted to control a seldom used utility and guest bedroom. Use a SPP-3/control panel combo tied with an SPP-2 for this control.  Order the SPP-2 without a pump.

Why not use an expanded SPP-3/control panel combo for five primary zones of control?  Besides greater cost, if the utility room were set up as a primary zone, it could be the only zone calling for air - forcing you to use some type of static pressure relief system.  On the other hand, if this area were a small office where temperature was critical, a primary zone would be the way to go.




ALL SYSTEMS - Designing a zoning system into a home or office is easy, if a few basics are understood.  The zoning system should always allow a certain amount of airflow over the coil or heat exchanger of the HVAC system, so the Airzone system should never be installed in such a way as to restrict a significant amount of the total airflow going through the HVAC furnace/evaporator coil.


As an Airzone System begins to close dampers, the air velocity and static pressure will increase, and more air will be moved through the remaining open ducts.  This occurs up to the point that the HVAC fan capacity is exceeded and the amount of airflow is reduced.  At that point, simply use one of several static pressure control systems or methods offered by Retrozone, Inc.


Where to mount the Airzone Panel:  The Airzone Panel(s) can be mounted by the HVAC unit, or remotely if desired, as long as the panel(s) are easily accessible.  Avoid bedroom closets or locations where the minor noise of the Airzone Panel could be a problem.


Where to mount thermostats: Thermostat placement is critical to maximize the benefits of zoning.  Thermostats should be placed at a central location in each zone, on an interior wall. Avoid placement where lamps, sunlight, or other artificial heat loads can affect the thermostat.



The Airzone System can often eliminate the need for two or more separate HVAC systems, while at the same time offering more zones of control.  Because the Airzone System manages airflow so efficiently, you can use a smaller HVAC system with no loss of comfort and big gains in energy savings. In fact, the Airzone System works best with a properly sized or slightly undersized unit.

On installations where the duct system is being designed to use zoning, the size of the ducts can be slightly increased to enhance the zoning performance.  When designing the duct system for zoning, caution should be used to avoid two extremes:  First, over sizing the ducts to a point that, when all Flexdampers are open, air velocity (how fast the air is moving through the duct) falls to a point that air is not properly circulated in the duct.  Second, under sizing the ducts to a point where too much airflow is restricted when only one zone is calling for air.

For an Airzone System of three zones or less, each zone's duct(s) should be sized to handle 60 to 70 percent of the total airflow.  This will enable an installer to avoid using any kind of static pressure relief system, since both extremes mentioned above will be avoided.  Instead, static pressure and air velocity will vary as zone dampers open and close.  Call a Retrozone expert for more information.


New Construction - Designing the duct system layout.

Designing a duct system to include an Airzone System can be easier than designing a single zone duct system.  Why?  A conventional single zone system must have the duct sizes carefully calculated to the load on each room or zone.  Even so, this method of duct sizing cannot compensate for sun load and other changing variables.

An Airzone System automatically controls the airflow to each zone, making the size of the duct serving the area less critical.  The ducts should be sized larger than ducts in a single zone system so that each zone can receive enough air to quickly satisfy.

 Two and three (and sometime four) zone systems using the Airzone System can be designed with no static pressure control systems.  Airzone Systems using more zones will typically need one of the static pressure control systems.


Planning the layout of the duct system in new construction requires not only attention to the floor plan of the home, but also how the homeowner will be using the home.  Making each room a zone can be impractical because of the expense; instead the home should be divided into areas or zones that are used typically at the same time.  An easy example is a home that has all the living areas on one end, and the sleeping areas on the other.  The designer might make this a two zone application - living and sleeping.

The duct system should be designed so that the ducts serving each zone are accessible for easy Flexdamper installation.


Checklist for installing an Airzone System in new construction:

A.   Design duct system so that each duct is accessible for Flexdamper installation and service.  All ducts from each zone should connect together and then home run back to the plenum, so that each zone has only one or two ducts, thus needing only one or two Flexdampers.  Where the capacity of a 12 inch or larger duct is needed for a given zone, consider using two smaller Flexdampers/ducts per zone, since response time will be faster.

B. Up-size the ducts according to the guidelines in this section and the Manual J guidelines.  It is very important to have plenty of duct capacity into each zone so that zone may satisfy quickly, should it be the only zone calling.  Don't worry about a zone getting to much air; the Airzone system will automatically control that.

C. Run all thermostat wire during the construction phase. Run 8 conductor, 22 gauge thermostat wire, or call for specific details for your system.  Be sure to locate thermostats central to each zone.

D. Depending on the duct layout and the mounting location of the Airzone System Panel, run tubing during construction.

E. Do not oversize the HVAC system - bigger is not better with zoning.  Consult Manual J for details. 



The Airzone System was especially designed for existing applications where the ducts are already in place, since Flexdampers can be installed easily in existing ducts.  The Airzone System can correct many existing system problems.  See "Correcting Problems in Existing Systems" for details.

Try to divide the home into two or more general zones of use.  Also inspect the duct layout to determine how the home can be divided.  Several ducts can be tied together to create one zone.

Attempt to limit the number of primary zones to six or less.

Each zone will need a thermostat centrally located within that zone.

Experience has shown that most duct systems can be divided into two equal zones (and sometimes three) and need no static pressure relief system.



As mentioned earlier, some care must be taken to insure that an adequate amount of airflow continues to pass through the HVAC system to insure proper operation.

While restricting too much airflow can cause several HVAC problems, these problems are easy to deal with or solve using various Retrozone products and design techniques.

Problems with restricting too much airflow are rare for the following reasons:  When only one zone is calling (the most restrictive mode) that thermostat is satisfied very quickly, before problems such as coil icing can occur.

With Airzone Systems, many options and safeties exist to control these potential concerns. Install the Airzone System according to the instructions.  Should you have a problem, use one of the solutions below for correction.


A. ECL switch - Two and three zone new construction /  retrofit applications typically need nothing more than Airzone's inexpensive ECL switch installed on the suction line of the evaporator coil to monitor against coil freeze up.

If refrigerant temperature drops too low, all Flexdampers will open.  The ECL switch is recommended for all systems except heat pumps.  Heat Pumps should use a control panel that accepts duct sensors for hi/lo protection. 


B. Dump Zones - If too much airflow restriction is suspected, simply remove a Flexdamper from a duct serving a common area like a hallway where temperature control is not critical.  This "wild duct" is open all the time, and relieves system pressure.


C. Barometric relief damper - This Retrozone product is installed in a duct between your supply air plenum and return air plenum, and opens automatically to relieve pressure as zones close off.


D. Static Pressure Control System - Similar to the barometric damper, the Static Pressure Control System provides static pressure control for commercial installations over 5 tons, and is available in all duct sizes.


E. Controlled Damper Leakage - Round and Rectangular Flexdampers can be installed to leak 10% or more to reduce system pressure.



Fact 1:  The most efficient HVAC unit is one that is sized correctly to the load on a home or office.

Fact 2: Many HVAC units are oversized for the home or office.


Over-sizing your HVAC system may sound like a great idea - plenty of capacity to keep you warm or cool.  But the truth is that an oversized unit actually decreases your comfort AND wastes energy at the same time.  An Airzone System, by eliminating over cooled and over heated areas, stretches the capacity of the unit.  Further, when unused zones are shut down, even a severely undersized HVAC unit (not recommended) has the ability to provide total comfort in the zones that are being used.


Almost everyone has some type of a problem with comfort in their home, as well as a desire to save energy.  Airzone Sysems can be used to correct many types of comfort and/or energy problems:


A. Undersized HVAC System - Review the '"Sizing the HVAC Unit Correctly" Section above to understand why Airzone Sysems can turn the undersized unit into a highly efficient and comfortable unit.

Without zoning, most HVAC systems have to be sized for "design conditions," meaning the hottest and coldest days of the year.  However, these peak temperature extremes account for only about 5% of the year.  The rest of the time, energy and comfort are wasted through cycling losses and poor humidity control.

With Airzone, a smaller HVAC unit can be used for better comfort and energy savings. What about the 5% of hottest and coldest days?  Remember, with an Airzone System, no energy is wasted overheating and overcooling the areas you are using, so you get more mileage from the capacity you do have.  Second, you can always setback areas not in use, and achieve total comfort in the occupied zones.

The other 95% of the year is rewarded with significant gains in energy savings and comfort.  Call Retrozone, Inc. for more information on this subject.


B. Hot and Cold Spots - Using multiple thermostats and multiple zones of control, Airzone puts air exactly where it’s needed, by "borrowing" the air from unoccupied or satisfied areas.


C. Poorly Designed Duct Systems:  Airzone can correct many duct design flaws since Airzone forces the air to go exactly where it’s needed.

The key to solving HVAC problems with Airzone is common sense and a thorough understanding of how Airzone operates.  For more Information on how Airzone can be used to correct a problem duct system, call the Retrozone Factory.

Copyright RetroZone 2013

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