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How to Create Zones in a Forced-Air HVAC System

This Old House plumbing and heating expert Richard Trethewey shows how to control the temperature to every room of the house

In this video, This Old House plumbing and heating expert Richard Trethewey shows how to control the temperature to every room of the house.

Steps for creating zones in a forced-air HVAC system

  1. Use snips to cut a hole in side of furnace duct and fasten a male fitting.
  2. Attach to the male fitting a flexible duct, which is connected to an electric suction fan.
  3. Remove the grilles from all the registers throughout the house.
  4. Plug up the duct openings—except one—with a foam-rubber block placed inside a plastic trash bag.
  5. Turn on the suction fan to create negative pressure in the ductwork.
  6. Fashion a parachute from a plastic grocery bag and attach to it a spool of monofilament fishing line.
  7. Place the parachute into the one unplugged register. The negative pressure will suck the parachute and fishing line down to the furnace.
  8. Remove the flexible duct from the side of the furnace and pull out the parachute.
  9. Disconnect the parachute and attach the air tubing to the monofilament line.
  10. Go to the unplugged register and reel in the monofilament to pull the air tubing through the duct and into the register. Disconnect the monofilament.
  11. Unplug one of the other registers, and use its foam-rubber block to plug up the register that now has the air tubing in it.
  12. Repeat Steps 7 through 10 to pull a length of tubing from the furnace to every register throughout the house.
  13. At each register attach a pneumatic damper to the end of each length of tubing.
  14. Disconnect the suction fan, flexible duct and male fitting from the furnace. Seal the hole with a piece of sheet metal.
  15. Mount a manifold to the wall beside the furnace and then connect the ends air tubing ends to the ports on the manifold.
  16. Next to the manifold, mount an electric air pump. Connect the air pump to the manifold with two clear plastic tubes.
  17. Remove all foam-rubber blocks from the registers and reinstall the grilles.
  18. In each room with a register, install a battery-powered sensor, which allows you to control the room temperature.
  19. Mount to the wall in the kitchen or living room the main display panel, which grants you control over the temperature in every room from one location.


Foam-rubber blocks