Adjusting Your HVAC Vents (Heating and Cooling)

Each Summer and Winter, most of us have to adjust our HVAC systems to keep our homes at a comfortable temperature. Here are some tips on how to make these adjustments:

In this example you can see two damper levers (the back and front of the
house) while the "secret hidden damper lever" to the third floor is behind
the curved duct in the middle (up and behind the wooden joist), and requires
a stepladder to reach. The vertical duct on the left is for the return air flow.

1. Each of us has three damper levers controlling the airflow to different parts of the house: 
1. One goes to the front section of the house (second floor above the garage)
2. Another lever controls airflow to the back of the house (first and second floors)
3. The final lever -- and the hardest to reach -- controls airflow to the third floor
2. The basic principle is that because warm air rises, you'll want to increase air flow to the top of the house (third floor) during the cooling season (Summer) while increasing the relative amounts of air to the lower floors during the heating season (Winter).
3. Note that it isn't always obvious which direction on the lever is fully closed and which is fully open, though usually "open" is when the lever runs in the same direction as the duct, and "closed" is when it is perpendicular to the duct. (It depends on how they installed the damper.) You may need to determine this by moving the lever all the way to one end and testing whether air is coming out of the vents with the fan on.
4. Your dampers should have three natural positions: closed, open, and halfway in between. The damper position will be unstable if you try to place it at another point even if you tighten the wing nut down to hold it in place.
5. The HVAC vendors don't recommend shutting the vents and registers (in the ceilings and floors) completely as they say it strains the HVAC system, but you can also adjust the airflow coming out of the registers to fine-tune the amount of air coming out.
6. Otherwise, you should make sure to change the air filters on a regular basis.

Suggested procedure in Summer (thanks to Jim's post on Facebook):

1. The downstairs and second floor dampers (levers) are a quarter of the way open.
2. The third floor damper, the hardest to get to, is open all the way.
3. Set your fan to ON and let it run continuously for 3 to 4 days to equalize the house.

During the Winter you'll want to reverse this procedure. Partially close the third floor damper while opening at least the first floor damper all the way. As mentioned above, you can fine-tune the temperature by also changing how much the registers in the ceilings and floors are open.

Amy also posted much more extensive information to Facebook in January of a year ago at the start of Winter.