cfm calc

[kool it man]

I've got a fielpiece atachment (anemometer head) and this reads feet/minute, meters/second , or knots.

It has a vane probe to take the reading.

what i'm wondering is how to read a supply or return grill with it to get cfm?

I assume you take a reading and get the area of the grill
then what...:confused: ?

[cxagent]

to get cfm
take a reading in feet per minute
then multiply that reading by the duct size in feet.

For example -
reading inside a 12" x 18" duct gives 300 ft/min

duct size in feet = (12"/12"per foot) = 1 foot
(18"/12"per foot) = 1.5 feet

300 ft/min * 1 ft * 1.5 ft

450 cubic feet per minute

[commissioning authority]

Gentlemen

Take multiple readings across the opening and average them then use that ft per minute on your duct calculator for the duct size and it will give you cfm

[kool it man]

thanks for the replys

I'll start doing using the info...:)

[Carnak]

Kool It

You can try to get an average velocity out of the grille, but you need to know the free area of the grille. Using the duct area will give you a high reading.

[kool it man]

Originally posted by Carnak
Kool It

You can try to get an average velocity out of the grille, but you need to know the free area of the grille. Using the duct area will give you a high reading.

this sounds like what I'm looking for,

after I get an average reading in ft/min do i tmes this by square ft of free area.

all I'm looking for is an approximate reading when I'm looking for cooling or heating problems.

[ricm]

Here's the formula's I use... with success.

http://ww2.imagewiz.net/images/hvac/144533_cfm.jpg

Hope this helps...

[ricm]

sorry about pic size.