Quote:
Originally Posted by Dave Lane
Well they are wrong or they are taking a simplistic view in a very small house. Assuming you have plenty of ducts shutting off a room or two that are not being used will not hurt your system. Too little airflow can cause the coil to not get warm enough from the passing air which can be a problem.
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If you shut off more than 10% of the airflow it will void your warranty. And it will take life off your system. The average a customer gets charged when I have to change out a blower motor is $400.
If you have a 3 ton system. That equates to 1200 cfm's of air. The average bedroom will have a 6 or 7 inch piece of duct that feeds the register that you see in your floor. A duct calculator figured at .10 static pressure will tell you that a piece of 6" duct will flow about 100 cfm. A piece of 7" duct about 150 cfm.
So you can only safely shut off 1 register in your home if you have a 3 ton system.
Now there are exceptions. A variable speed blower will ramp up to make the difference up. If you have a zoned system the extra air will be put into the "dump" zone.