Duct Questions


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Old 11-11-12, 05:48 PM
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Duct Questions

Iím designing a duct system for a wood furnace I am putting in my home, and I have a few questions.

The furnace will have its own ductwork, which will be flexible, and will be temporary (I am finishing the basement next year, relocating the existing furnace and replacing the duct), so being 100% perfect isnít my main goal, but I would like to make it as efficient as possible without hiring a contractor.

I have already done the calculations for room loads, so I know what I need to supply. The part Iím having trouble with is duct sizing Ė static pressure, air speed and when to reduce the trunk to be specific.


What is the maximum static pressure goal for a heating system?

How is system static pressure calculated? Is each section of the trunk and branches added together, is the largest value used, or is there another way?

When would the trunk be reduced in size? Iím guessing after the volume of air in the trunk has been reduced enough to warrant the next duct size down. Example: 700CFM is flowing through a 14Ē duct and 250CFM has been bled off in to branches. At that point the trunk would be reduced to 12Ē.

If the velocity of the air is greater than 600-700FPM, what else will be affected besides noise level?

I have also read that cold air returns should not be placed in bathrooms or kitchens. Why is this, other than the obvious odor distribution through the house?

Thanks for any help you can give!
 
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Old 11-11-12, 06:35 PM
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It has been too long since I did any duct design to help you with most of your questions but this one I can answer.

I have also read that cold air returns should not be placed in bathrooms or kitchens. Why is this, other than the obvious odor distribution through the house?
Of course I don't need to answer as you have already figured it out.
 
 

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