Blocking a Vent Taboo

Old 07-08-08, 07:26 PM
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Blocking a Vent Taboo

I've gathered that it is frowned upon to block a vent, but is this different?

Our house was built in 1960 and the duct work was sized for a swamp cooler system. The air conditioning was added later, either 84 or 94 by the model number, and the house cools very unevenly. The living room and family room, with giant vents, cool nicely but the bedrooms receive little airflow. An A/C specialist was out today and he said that the main problem results from the ducts not being sized to the A/C, and that new ducts needed to be installed at around $2,500.

Can I just block one of those giant vents in the living room/kitchen area to send more flow in the other direction? He measured the room and the duct and said the vent was too big, but not to block it. I don't understand why not, and haven't found the internet to be much help. Can anyone point me in the right direction?

We are poor college students living in ARIZONA. Thanks so much!
Old 07-09-08, 07:24 AM
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The problem might be that if you close off the larger vents, the blower motor will have more resistance to force the air down to the bedrooms. So it will have to work harder, and shorten it's lifetime. If it's really bad, I suppose it could heat up and potentially be dangerous.

However, a blower motor costs about $100, if you install it yourself. If you replace it every year, figure 21 years vs new ducts. (I don't know if you'd have to)

If it were me, I'd see if closing those vents actually makes the other rooms cooler. If it did, I'd go with that solution, and plan on changing out my motor sometime in the future. either myself, or asking a handyman to do the work. (of course, if you do that, your AC/HEAT system will probably not be under warranty)

If it doesn't actually help, new ducts might be your solution.
Or, sticking a window unit in your bedroom for $200.
Old 07-09-08, 10:45 AM
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Visualize yourself being entered to run a Marathon. On the day of the race you have stuffed-up sinus passages but you still want to run the race. Then just before the starter fires his pistol someone slaps a piece of duct tape across your mouth.

This is what blocking vents in an HVAC system is akin to. You MUST have a certain airflow throughout the system to achieve optimum performance. Far too many residential systems are built with minimum, or below minimum ductwork and they simply cannot "breathe" well enough to perform adequately. Adding even more resistance by blocking off vents, either supply or returns, WILL cause far more problems than it will cure.

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