Air Flow From A/C vents differs from room to room

Old 09-02-02, 07:45 PM
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Air Flow From A/C vents differs from room to room

I have a one story 2400sq. ft. home. It is six years old, and the problem that I am having is that three of the rooms in the house do not get anywhere close to the same temperature as the rest of the house. My bedroom and the living room will freeze you out, while my two daughters rooms stay a constant 10 degrees warmer than the rest of the house. Does anyone have any suggestions or solutions as to what may be the problem, and if so what I may be able to do to correct it.

Thank You
Old 09-02-02, 08:28 PM
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This is why I got out of doing most homes. I only do custom homes and commercial now. The proper way to heat and cool a home is to do a room by room load calculation. By doing this, a good program will tell you how many cfm's are needed for each room, the size duct needed to supply the air, and what tonnage is needed for the equipment. This should be done for every home. I have seen a lot of builders and contractors only do this once for each model home they build. Then they just change the address, so they can get permits. However, this should be done every time, because if the house is on different sides of the street, the load is a lot different because the sun hits the house differently. Anyway, after this is done, the duct should have dampers installed for every drop. By doing this, you can measure the amount of air and open or close the damper until the right amount of air comes out. The remaining air continues down the duct for use somewhere else. Most contractors do not install dampers in homes. By not doing this, the air comes out of the vents closest to the air handler, and by the time it gets to the end of the trunk lines there is not enough air left. Even if these steps are followed, sometimes there are hot spots. This is because an air conditioning system is contolled by the thermostat. The system ONLY KNOWS what the temperature is at the thermostat and not any where else. Once it satisfy's the t-stat, the system shuts down. Leaving the fan in the on position can help some, because air is being continuously pulled across the t-stat, mixing the warm air with the cold. There are contols that can be added called zoning. A good zone system has electric dampers and t-stats in different zones of the house. Each t-stat is capable of bringing on the system. The zones that don't need cooling, don't open, causing more air to travel to the areas that need it and satisfy the demand quicker. You could try closing the dampers in the grilles(if they have them). This would also force more air to other areas. However closing dampers at the grilles makes the grille more noiser. The dampers I was talking about are installed in the trunk line in the attic. This way, if they're closed, they are still quiet. I would also check to see if you have any dampers installed that made be closed for the bedrooms. Do the kids keep their doors closed? If so, is there a way for the air to return out of the bedrooms? A 1" gap under the door should do for most bedrooms. If not and the doors are kept closed, this would cause the rooms to heat up some. You can only blow so much air in a bottle! Inspect the ducts and make sure there are no dampers closed and that the duct system is still sealed. No air leaks.
Old 09-03-02, 04:36 PM
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good advice

from noiminal. i personally tend to stay away from motorized dampers as they will fail over time, and the manual ones allow the homeowner greater control over individual rooms. i recently removed a two zone system and redesigned the duct to work in the homeowner's opinion"better than it ever did before"

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