Closing Furnace intake ducts


Old 04-01-07, 08:57 PM
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Question Closing Furnace intake ducts

I live in a 3 story house. 2 furnace air intake ducts on the main floor, one on the top floor and one on the lower level. I', remodelling the lower level and adding electric baseboard heaters. Is it OK to close the air intake ducts to the furnace and the 4 'out' ducts on this floor? Does the furnace 'need' the air intake? Will it mess up the furnace if I close the air intake on the lower level?

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Old 04-01-07, 09:57 PM
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You dont say what kind of duct work you have on them. Try this Turn the blower on and block the cold air return you want to take out. See if the furnace get the air it needs. See how hard it is to open the blower door on the furnace. if its hard then you need more air . if it comes open easy then it OK.
Old 04-02-07, 05:27 PM
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Closing ducts

The way ED mentioned is one way do test but a far better way is with a pair of thermometers. All furnaces have a temperature rise spec. It is usually somewhere between 55 & 70. The spec on your furnace might be on the data plate for the furnace or in the installation & operation manual if you have it. To perform the test all you need is two thermometers (preferably long stem) known to read the same.
Close off the ducts in question.
Turn the thermostat all the way up.
Insert one thermometer in the return as close to the furnace as possible & the other into the supply either just after the first turn in the duct or, if you have A/C, just beyond the A/C coil.
Allow the furnace to run at least 10-15 minutes & monitor the temperatures.
The temperature difference should not exceed the temperature rise spec for the furnace. If it does, try opening the return you closed.
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