I have a small problem when our heating or AC system comes on, the hot and cold air blows through all of the vents except one. How do I rectify this.
There are two ways to solve this problem. The easiest and cost free way is to simply partially close down all the other vents to force the air to flow more readily to the starving register. This is a primitive but effective way to, as they say in the biz, balance the system. This is a common way to make seasonal changes in a two floor house with a single zone. In the winter months, you want more heat downstairs, but it tends to rise upstairs. By partially closing the upstairs registers, the downstairs registers blow more heated air, which eventually rises upstairs anyway. In the summer, the reverse is done. The upstairs registers are left open wide, while the downstairs ones are partially closed. Of course, you will have to fine tune this method through trial and error to get the best seasonal balance.
The other way, which would require more work and expense, would be to install a boosting fan for that register. These are designed to turn on when they sense air movement or a temperature change. They can be installed as part of the heating system, and are tied into the central unit. There is another type that I have seen available in some mail order catalogues and home stores. It is installed in place of the register, has a temperature sensitive switch and receives power from a nearby outlet. Taken from Naural Handyman