Where to find Manual J and Manual D?


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Old 03-29-05, 07:56 AM
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Question Where to find Manual J and Manual D?

I'd like to design the ductwork into my new addition, as I know I'll need to reserve space for plenums and incorporate penetrations for ducts into my joists, etc. I've got it estimated and laid out using generic rule-of-thumb calculations but I'd like to do it *right* and not just half-assed. I've seen frequent references to Manual J and Manual D for the calculations but haven't been able to find anything online about these methods other than people trying to sell software. Are there any resources online for the do-it-yourselfer that I could use to run the full calcs?
 
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Old 03-30-05, 03:09 AM
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If you do a search for SMACNA you will find the resources you are looking for.
 
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Old 04-02-05, 08:15 AM
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Go to the Air Conditioning Contractors of America store web site

http://www.accaconference.com/Mercha...ore_Code=ACCOA
 
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Old 04-02-05, 09:50 AM
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Damn, $125 for Manual J?? Seems a bit steep for a DIY Guess I might as well just use the same procedure 60% of HVAC contractors admit to using: guesstimates based on square footage and eyeball engineering.

Thanks, guys, you at least answered my question even if I didn't like the answer.
 
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Old 04-02-05, 10:16 AM
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Wink

Check there where you found the J and D. See if they have a duct calulater or go

http://www.constructionbook.com/xq/A...P=KNC-Overture
They have a J for $55.
You will need a ductulator for sure

ED
 
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Old 04-02-05, 10:16 AM
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Ha Ha Ha He He He LOL

Yup at that price it is a bit steep

What are you tring to do ?

I might be able to help in other ways
 
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Old 04-02-05, 10:22 AM
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Old 04-02-05, 12:39 PM
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Hey, found an online calculator! Seems to be exactly what I'm looking for I should be able to guesstimate BTU requirements based on square footage and # of windows, and use this link to calculate pressure drop and required duct size:

http://www.connel.com/freeware/airduct.shtml Looks like my calcs are holding true- 1200cfm off a 3-ton unit into three 12" ducts, split ultimately in 6" flex duct will maintain air flow at 500fpm. Pressure drop looks negligible over the worst-case 50' run. Would 0.0028psi be negligible static pressure drop? The table for my air handler doesn't even start until 0.10... ah, it doesn't say the units though! Would that be inches of H2O? 0.0028psi=0.15" H2O

I might be able to bum copies of Manual J and Manual D off the HVAC guys at the office, too...
 
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Old 04-02-05, 01:34 PM
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Better back check a 3 ton 1200 cfm a 12"is 500cfm 3 of them make 1500cfm where did you get that other 300cfm from.


ED
 
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Old 04-02-05, 07:27 PM
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? 400 cfm through a 12" duct = 500fpm, as does 100cfm through a 6" duct, which as I understand it, is a fairly quiet velocity and works out to nice round numbers for 4, 6, 8 & 12" ducts in 100cfm increments.

1200cfm is a rough estimate- this air handler will probably have more cfm through it, but I can't calculate it until the ducts are laid out and I can calculate the static pressure drop. This is all based off the instruction manual for my present air handler, of course... I'm assuming the new one will be similar since they're both 3-ton units, but it would be nice if it was a variable speed model.

Also, found this:
The basic structure of Manual J is:

Heat Gain (Btu/h) = HTM x Area

where HTM is a Heat Transfer Multiplier (in Btu/h/ft2). Area is the area of the building component (such as a wall).

The HTMs take into account orientation, shading, temperature difference, solar gain, thermal storage, diurnal temperature swing, construction, R-Values, and roof color.

Manual J is a simplified adaptation of more complex modeling, yet it does not make many of the gross assumptions that some other load calculation methods use. It estimates both the latent and sensible cooling loads (both are necessary to properly size a system).
 

Last edited by grover; 04-02-05 at 07:59 PM.
 

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