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FREQUENTLY ASKED QUESTIONS

1. What material is required to zone a standard system?
2. What should we know to select a pressure relief damper with an SMZ, RED series panel
   or a JTZ-HP?
3. When we zone an existing ventilation system, should we try to have about the same amount of CFM in each zone?
4. Working in new construction, when a zoning system is going to be installed, should I consider it before
   I design the ventilation system?
5. Is it possible to order some sizes of zone dampers, even if they are not in the DuroZone catalogue?
6. Is it preferable to use Multi-Size (MS) or Multi-Blade (MB) dampers?

1.  What material is required to zone a standard system?

In general you need:
- A control panel                               
- A thermostat per zone                   
- A pressure relief damper               
- A motorized damper per zone     
- A transformer                                 

2.  What should we know to select a pressure relief damper with an SMZ, RED series panel or a JTZ-HP?

1. Ask for the total CFM of the system.
2. What is the approximate CFM of the smallest zone?
3. Take the total CFM of the system and subtract the CFM from the smallest zone.
4. Size the by-pass to the difference.

This pressure surplus can be sent to the mechanical room, to a false ceiling, a basement, etc.  However, it is essential that this excess pressure be dumped into an area covered by the zoning system to prevent the building or house from being in a negative pressure.

The by-passed air can also be ducted back to the return. The pressure relief damper is installed on the side of the supply duct before the first zone. Next you install a duct from the pressure relief damper to the return duct, as far away as possible from the equipment. This should be done far enough down the line to ensure that the dumped air is tempered to reduce any chance of damage to the compressor, the furnace fan or it's heat exchanger, etc. If the air is by-passed right at the unit, install sensor controls. It is always possible to install some probes or safety features if you consider it necessary.

Zoning a Retrofit System

Generally, in retrofit your duct sizing options are few. Plan on installing a by-pass damper in all retrofit applications.

3.  When we zone an existing ventilation system, should we try to have about the same amount of CFM in each zone?

Yes. The best situation would be to obtain a balanced distribution of the total pressure of the system. An even distribution of the air will give better results and an easier installation. You should install a pressure relief damper.

Zoning a New System

4.  Working in new construction, when a zoning system is going to be installed, should I consider it before I design the ventilation system?

Yes. The goal is to keep a constant velocity whether one zone or all zones are in demand.

Two or three zone systems:

1. Size each zone to take between 60 to 70% of the system's total CFM.
2. Be sure to have, in each zone, a minimum of six supply ducts of six inches diameter or equivalent.
3. A pressure relief damper is optional, but preferable.

 Systems of four zones and more:

1. Size your ducts normally and increase by 25%.
2. Install a pressure relief damper.

Questions on Zone Dampers

5.  Is it possible to order some sizes of zone dampers, even if they are not in the DuroZone catalogue?

Yes, custom sizes of Multi-Blade dampers (MB) are available.

6.  Is it preferable to use Multi-Size (MS) or Multi-Blade (MB) dampers?

Usually both will work; each one has its own advantages:
Multi-Size Dampers:
- Price more attractive.
- Since each Multi-Size has 2 or 3 adjustments, a small inventory covers many sizes.
- Motor always on the side of the damper.
Multi-Blade Dampers:
- Possibility of having the motor on the side or on the bottom of the damper.
- Larger sizes available.