Copyright RetroZone inc.2012 


SECTION 1 The Round Flexdamper




Study all instructions carefully before beginning. Refer to Round Flexdamper assembly diagrams before beginning.


Round Flexdamper assembly diagrams

Tape Connection - On some larger Flexdampers, it may be necessary to use two or more lengths of tape to secure the ends together.  Once installed, the duct contains the Flexdamper and prevents the tape from pulling apart.

Try to keep the connect tape and Flexdamper warm during assembly to aid in good adhesion.  This special tape "sets" over time and provides a strong bond.The Nylon "T" connector taped to each Flexdamper should be removed and saved for splicing the Flexdamper tube into other Flexdamper tubes serving the same zone.





CAUTION Use only pure silicone adhesive.  Other adhesives may not meet UL or other safety requirements.

PLEASE READ!   Most Flexdampers when used in most horizontal ducts require no adhesive. The semi-rigid internal belt in the Flexdamper allows it to stand upright in the duct, while the tubing should be cut to a length that keeps the Flexdamper from sliding down the duct.

However, certain applications exist where a more secure bond to the duct is required, such as a vertical duct where the tubing, because of mounting needs, runs downward and does not support the Flexdamper.

Retrozone highly recommends the use of silicone adhesive on larger Flexdampers and Flexdampers mounted in vertical ducts.  In fact, since it is so easy to do, Retrozone recommends the "First Stage" adhesive mounting for all Flexdampers, to insure trouble-free operation.

Fig 1-11. Stage 1 adhesive mounting - Optional but recommended for all Flexdampers. Install air tubing on Flexdamper. Then place a liberal amount of silicone adhesive on the top, center taped joint of the Flexdamper. Install in duct.

Fig. 1-12 Stage 2 adhesive mounting - recommended for vertical, high velocity and other special applications.  Add two, 2 inch strips of connect tape to outside area of Flexdampers, centered between divider seals.  Apply adhesive to tape strips.  Apply silicone adhesive to top tape joint (same as Fig.1-11).

Install Flexdamper in duct.  Inflate Flexdamper orally or with the Airzone Panel (Fig 1-13) to allow the silicone to cure.  Flexdamper should now be supported by adhesive in two places evenly spaced around Flexdamper.


Fig 1-11,1-12,and 1-13

Fig.1-16 In-line installation. Useful in many applications using steel or rigid duct, including Northern homes where ducts are run under floor joists.

Carefully peel back insulation, uncovering a suitable amount of duct.  Drill a 3/8” hole to enable the use of tin snips.  (You may want to drill a second 3/8” hole about 18 inches upstream, if the air tube is to exit the duct).

Then, using tin snips, cut out a three-sided "half moon" piece of sheet metal large enough to easily fit one's hand and a rolled Flexdamper through.  The larger the duct, the larger the Flexdamper, so the larger the hole should be.

Bend back the sheet metal on the uncut axis.  Now, work through this opening to install the Flexdamper.  The Flexdamper may be tightly rolled to a small diameter, but try not to crease the internal belt.

Caution!  Wear gloves and long sleeves, and avoid snagging either yourself or the Flexdamper on the sharp sheet metal edges.

Hint:  You may find it easier to attach the connect tubing to the Flexdamper before you insert it through the hole.  If using optional silicone adhesive, try putting the adhesive on after the Flexdamper is in the duct.

After installation is complete, bend sheet metal back in place, and tape or caulk to insure an airtight seal. Tape insulation back in place.

Fig 1-16

Fig. 1-17 Splitter installation - In many installations, one large (trunk) duct will

split into two or more smaller (branch) ducts.  If the smaller ducts branching from the larger duct serve the same zone, then only one Flexdamper in the larger duct is needed.

However, if the branch ducts serve different zones, then a Flexdamper will need to be installed in each of these branch ducts.

Many different types of duct "splitters" exist- sheet metal, fiberboard, etc.

Similar to a plenum installation, often one duct can be removed to allow installation in the other ducts branching from the splitter.  Transitioning the air tubing from the Flexdampers through holes drilled in the splitter is often convenient.

Fig. 1-18 Register Installation - The register installation is often a good choice, since the Flexdamper can be installed by simply removing the register.  Read Section 6 on avoiding noise problems for register installations.

Working up through the register, first size the Flexdamper to the correct diameter (see Fig. 1-8). Since many register installations are in vertical duct, review adhesive mounting methods (Figs. 1-11 to 1-13)

Next, drill a 3/8” hole in the duct at least a foot or more upstream of where the Flexdamper will be located (not necessary if tube is to run inside of duct back to plenum).  With flexible type duct, reinforce both inner and outer membranes with connect tape before punching hole. Working from above the ceiling, run a length of tubing into duct and out through register.

Make sure area where Flexdamper will be mounted is free of sheet metal screws.  Attach end of air tube to the Flexdamper, apply silicone adhesive if applicable, then insert and install in duct.

Fig. 1-13  For all Flexdampers using silicone adhesive, especially vertical mounts:

If possible, immediately after installation inflate Flexdamper orally or with Airzone Control System and leave inflated (plug tube) for as long as possible to insure a good bond. 

Caution: Do not use compressed air or any source over 3 PSI.


Fig 1-11 to 1-13

HELPFUL HINT- Install Flexdampers needing adhesive mounting first to allow more curing time on the adhesive.

Fig.1-11 The tubing should be cut to a length that limits the Flexdamper from sliding down the duct. When doing a register or in line duct Installation, leave enough tubing upstream to move through an up and down arc as the Flexdamper inflates and deflates.




Study the "FLEXDAMPER INSTALLATION DIAGRAM" (Fig 1-15) carefully before attempting installation. Different methods of installation exist to install the Flexdamper, depending on the application.


General Notes, all Round Flexdampers:


The air tubing used with the energy saving Airzone System is very durable, but somewhat stiff.  When installing a Flexdamper, straighten the air tube or locate the Flexdamper in such a way that the air tube is not "fighting" the Flexdamper.

Round Flexdampers work great in steel or flexible duct.  Whenever transitioning a tube through flexible duct, reinforce the inside membrane with a patch of connect tape before punching hole.


Fig. 1-15 Plenum Installation - Note:  This type of installation is recommended for new construction applications.  Design the plenum so that all Flexdampers can be installed and serviced through an access door installed in the plenum.

Retrofit Plenum Installation:  Particularly useful in southern applications where ducts are often "homerun" to the plenum, installing the Flexdampers from inside the plenum can be fast and easy.  Should not enough room exist for an access door (or the distance from the access door to a duct(s) is too far), you may be able to remove just one (preferably larger) duct, and gain access to the inside of the plenum in this manner.


CAUTION! Be sure not to mount Flexdampers over sheet metal screws that are sometimes present in plenum starting collars.  While incredibly tough, the Flexdamper over time may develop a leak, which can diminish system performance.


Fig. 1-15a.  Flexdampers installed from the plenum and serving the same zone can be connected together inside the plenum, so that only one tube for each zone needs to be run through the plenum and to the energy saving Airzone System.  Make sure Flexdampers don't have enough tubing to slide down the duct.

Fig. 1-15b Drill a 3/8” hole in the plenum for each zone tube that needs to transition through the plenum.

Fig. 1-15c Plenum access door installed on plenum.


Fig 1-15

CAUTION! Especially when new, round Flexdampers can make a "popping" noise when inflating.  Locating the Flexdamper at the register, especially in steel duct, may cause a slight but objectionable noise in a bedroom area.  However, this typically is only a problem if the Flexdampers are moving during the night:  In homes where the sleeping area is one zone, and where the other zones will be set back at night, the Flexdampers will seldom actuate.  Avoid placing the Flexdamper at the register in a bedroom if you anticipate the Flexdamper repeatedly changing positions during the night.



Fig 1-16

Fig 1-17

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