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Heating / Air Conditioning

Ductwork

Your heating / cooling system is a "reducing trunk system" engineered to deliver the right volume of air to each register in your home by reducing the diameter of the duct as the system branches.

Reducing Trunk System

Your system has two types of ducts;

The trunk duct runs perpendicular to the floor joists. One duct runs to the front of your home and another runs to the rear of your home. These large ducts are fully exposed beneath the floor joists in your basement and are wrapped with foil faced insulation.
The branch ducts run from the trunk ducts to the individual registers in your floors. These ducts run between the joists, are wrapped with foil faced insulation and are generally hidden under the fiberglass floor insulation between the floor joists. Every register has its own individual branch duct.

Both types of ducts have internal dampers that control the flow of air thru the system. (The registers in the floor also provide some control over air flow but are primarily designed for fine tuning.)

Trunk Ducts - The trunk ducts have a single damper (although you might have two) that controls air flow to the front of your home. The trunk duct damper is located near the furnace.
Branch Ducts - Every branch duct has a damper located near where the branch diverges from the trunk duct. The branch duct dampers are sometimes hidden under the fiberglass floor insulation between the floor joists so you may have to dig it out to access the control handle. The images below show the two types of dampers in the closed position.


Trunk Duct Damper	Branch Duct Damper

HINT: It's a good idea to find and label all of your branch ducts and their dampers. The heating contractor has been known to occasionally forget to install a damper.

Adjustments

Depending on how you use your home, you may want to balance the system by adjusting the dampers. Your heating balance may be different from your cooling balance so note the location of the damper control handle.

NOTE: When you purchased your home, it was delivered with all of the dampers in the fully open position. According to customer service, you can have your system balanced once for free.

Both types of dampers have a wing nut that is loosened to make adjustments and then tightened to hold the adjustment in place.

Trunk Duct - The trunk duct damper has OPEN, 1/4, 1/2, 3/4 and SHUT markings.
Branch Ducts - The control handles on the branch duct damper are set parallel to the duct for the open position or perpendicular to the duct for the closed position.

An adjustment somewhere between open and closed is also possible on both types of dampers.

HINT: Let's say that the trunk duct that runs to the front of your house has six branch ducts (dining room, living room, foyer, den, guest bath, guest bedroom). If you close the ducts in the three enclosed spaces (den, guest bath, guest bedroom), you would also set the trunk duct damper to about the 1/2 mark (it actually depends on the relative volumes of the heated / unheated space).