C.F.M. per TON as to Duct Sizes
TURTLE
This is turtle.
Manual D for ducting but I have Manual T / for Turtle. The duct is for
flex with only 1 box length runs. Sheetmetal should be done with Manual
D . These calculations was used before Dealer knew anything about
Manual j or Manual D . This was when you had a HVAC Engineer hire by
the Warehouse and he came out and size the unit and done duct
calculation for you. this was in the 1950's. These was the ruff
estimate given to All the Dumb --- Dealers at that time.
Discharge Duct sizes per CFM Flex.
4" 40 cfm
5" 60 cfm
6" 100 cfm
7" 150 cfm
8" 200 cfm
9" 300 cfm
10" 400 cfm
12" 600 cfm
14" 900 cfm
16" 1,400 cfm
18" 1,800 cfm
20" 2,300 cfm
Return Duct sizes Per CFM Flex .
12" 800 cfm
14" 1,200 cfm
16" 1,500 cfm
18" 2,000 cfm
20" 2,400 cfm
Tonage Per CFM
5 ton 2,000 cfm
4 ton 1,600 cfm
3.5 ton 1,400 cfm
3 ton 1,200 cfm
2.5 ton 1,000 cfm
2 ton 800 cfm
1.5 ton 600 cfm
Calculations are ruff and can change as job application may change.
TURTLE
Just Thinking Again Sorry .
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TURTLE
johnl45
TURTLE wrote in message <93nrg1$2u2$1...@nnrp1.deja.com>...
Abby Normal
a manual D but a Btu is a Btu and a Cfm is a CFM
Residentially for supply branches feeding grilles diffusers and registers I
would max out at 600 feet per minute
Therefore with a four inch supply, I would use it for up to 40 to 50 CFM
A 5 inch is good for 80 cfm
A 6 inch say 100 to 120 CFM
An 8 inch say 200 CFM
A 10 inch say 320 CFM
Off the cuff, for quick estimating purposes, I would size supply triunklines
lines for 900 fpm and return trunks for say 750 fpm. The supply ducts would
usually end up with similar dimensions sized by a guy with a Trane
Ductilator with the 0.08" or 0.09" per 100 foot setting worn out.
These numbers worked well in residential estimates. What do your manuals say
for residential sizing?
In the old days, my father based it all on tables for a 90 degree
temperature rise and his theory of " equal area return air"
TURTLE
--
This is turtle.
Yea they do , but this is for the None Manual D owners. I personally
like this one sheet guide and not have to start reading manual D when I
can hang this one sheet guide on the wall to look up and get all my
information. Also if one of my tech or competitors wants to borrow my
Manual D . I print them out a one sheet guide and give it to them. Your
not borrowing my stuff.
TURTLE
Everyday is my first day in the business.
Got my e-mail address back as above .
Gary E
small.
I use:
14" 800 cfm
16" 1000
18" 1200
20" 1600
Of course I've seen 14" returns work on 5 ton systems for years too but
that still doesn't make them right..
johnl45
Gary E wrote in message <3A5FE5AC...@gte.net>...
Darryn
>I use the same discharge sizes but I think the return sizes are a little
>small.
>I use:
>14" 800 cfm
>16" 1000
>18" 1200
>20" 1600
>Of course I've seen 14" returns work on 5 ton systems for years too but
>that still doesn't make them right..
>
>
I tend to agree on the retrurns mostly I size for 3.5 m/sec velocity
on returns which equates to Garys figures
But for supply Turtles supply rules of thumb are not bad but I often
select the main branch for about 5 m/sec and then drop down a bit on
the branch takeoffs
Sorry for the SI units its sunday and I couldnt be bothered
calculating into Imperial for you guys on the other side
My devalued Aussie $0.02 worth
Darryn
poppy...@my-deja.com
"johnl45" <loca...@ameritech.net> wrote:
> Your velocity would still be too high 14 X 8 @ 800cfm = 1113 fpm.
>
Since the turtle started out with flex duct we have been discussing
round flexduct. Therefore 14" equals 1.07 sq ft and Garys fpm would be
less than 800 which is exactly how I design returns.
Vic Plank
Lancaster PA
johnl45
400 fpm with a maximum of 700 fpm. I size up to reduce noise.
poppy...@my-deja.com wrote in message <93seeg$eei$1...@nnrp1.deja.com>...
poppy...@my-deja.com
"johnl45" <loca...@ameritech.net> wrote:
> I stand corrected, but even with round flex the recommend velocity is
only
> 400 fpm with a maximum of 700 fpm. I size up to reduce noise.
>
> poppy...@my-deja.com wrote in message
<93seeg$eei$1...@nnrp1.deja.com>...
> >In article <04186.18683$3M.5...@nntp0.chicago.il.ameritech.net>,
> > "johnl45" <loca...@ameritech.net> wrote:
> >> Your velocity would still be too high 14 X 8 @ 800cfm = 1113 fpm.
> >>
John:
I only use flex in 5' sections other than that it is spiral pipe and
then the 800 fpm for returns and 1000 fpm for supplies works very well.
But then again all I do is commercial and industrial work with high
ceiling and plenty of room for the sound to dissappate. When sound
from the HVAC is a concern sound attentuators are used.
Vic Plank
Lancaster PA