Du Pont calls Hytrel, has survived a million cycles in lab tests.

The FlexDampers themselves have been successfully tested through hundreds of thousands of cycles. Unlike a balloon, they do not stretch when inflated. The air fills the space between inner and outer membranes.

With the Airzone system, you can separately heat and cool anywhere from two zones on up. Enerzone sells two- and three-zone systems off the shelf (which you can combine to serve four or five zones). For larger installations, the company custom makes a single panel containing the necessary solenoid valves.

The Airzone air pump is electrically connected to the heating and cooling system and turns on any time it does (in response to a thermostat, as usual). The pump has a suction port and a pressure port, both of which are attached to the solenoid valves. The valves can send pressure through the air lines to inflate the dampers, or suction to deflate them. "Since the pump stays energized, if there's a leak in a damper it is transparent to the system," Tartaglino points out. Enough air is pumped to keep even a leaky damper inflated. A pressure-relief and a vacuum-relief valve in the solenoid panel bleed off excess air.

 Zoning a forced-air system can cause a couple of problems-both solvable. It may increase the noise at registers. "When you shut off half the ductwork, you're moving basically the same amount of air through a smaller volume so you may get increased noise," Tartaglino points out. The solution? Install a bypass-a duct with a barometric damper to connect the supply and return plenums directly. Then excess air can be routed there. A bypass duct can also solve another potential problem: too little airflow over a furnace's heat exchanger or an air conditioner's evaporator coil.  

Deflated, a FlexDamper lies flat around the inside periphery of the duct (top photo). When it inflates (second photo), it seals the duct. For complete sealing, a triangular foam insert fills the center. A typical Airzone installation (diagram) consists of two or more thermostats (regular or programmable-one for each zone), the control panel containing all the electric or electronic circuitry (electronic controls are used with heat pumps or more complex installations), and the panel that holds the solenoid valves (one for each zone), with the air-pump box beside it. Plastic tubing connects air pump to solenoids and solenoids to FlexDampers. Wiring from thermostats to the control panel is 24V AC. FlexDampers come in round and rectangular shapes to fit 5to 14-inch ducts. Custom sizes are also available.

"With a two- or three-zone system we've never found it to be necessary," Tartaglino states, "but with more it could be." If you do not use the triangular sealing inserts in the center of the dampers, the slight bleed-through should eliminate the need for a bypass in most systems.

If your system includes a heat pump or air conditioner, a wise precaution is to install an evaporator coil temperature-limit switch. This optional device keeps the evaporator coil from freezing: It opens all dampers and turns off the compressor any time the coil temperature drops too low.

 Installing FlexDampers can be a cramped, dusty job, but compared with installing conventional dampers, it's a breeze. I installed two large FlexDampers by cutting an access hole in my furnace's supply plenum and inserting the sleeves into the ducts from there. I used, and strongly recommend, the optional plenum access door Enerzone sells. With it, you cut a hole in the plenum to match the size of the door frame (it comes in several sizes), then install the door. Once that's done you can easily get into the supply plenum without worrying about raw metal edges.

I got by with two FlexDampers because my ducting starts as trunk lines (large ducts from which smaller ducts branch). And I did not zone my entire house. If installing the dampers from the plenum won't do the job, you can install them from the outlet end of the duct by removing the register. Indeed, you can install a FlexDamper anywhere along a duct.

Once the FlexDampers are in place, you run tubing from them to the solenoid valves, one line for each zone. Then you connect the thermostat wiring to the control panel.

 I've had my present condensing oil furnace only two years, so I don't have a long record of energy use,  but we did use less oil last winter than the year before: Corrected for weather variations, it comes to 1.04 gallons per degree day this year compared with 1.19 gallons per degree day last year (though I can't be sure the difference was all due to the dampers). The biggest benefit has been comfort: Last winter we could go into our north-facing room, turn up the thermostat, and within a few minutes the room would be toasty warm. And we didn't have to overheat the rest of the house. This summer, the air conditioner cooled the room just as quickly.

 Reprinted with permission from Popular Science