Registers (vents in your rooms) have louvers (adjustable arms) to direct the air into your rooms. You should not use the louvers to completely close the registers. This will make your system less efficient. The louvers are their so that you are able to adjust the air flow to avoid drafts. You should keep the registers as open as possible though.
Louvers are designed to adjust your registers, however, once you find you are comfortable with the air flow, you should not keep adjusting them. Indian Air Trane Comfort Specialists can help you find the right adjustment.
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