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Anonymous Poster

# Area Calculation of HVAC Duct Reducer

09/18/2010 4:02 PM

For calculating straight duct area we use 2l x (w+b).

But how to calculate area of duct reducer?

Can we use trapizium area formula i.e 1/2 x (Base + Top)xHeight. If we use this, for reducer, the formula will be

(a+b+c+d) x Length a - larger width b - smaller width, c- depth at larger side d- depth at smaller side L- length

In case of depths are same at both sides, then it is (a+b+2c) x L

Can some one tell me whether this basis is correct.

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#1

### Re: Area calculation of HVAC duct reducer

09/18/2010 5:21 PM

I think your math may not be correct in all cases.

Without the right kinds of drafting software, you can check your calculations by making isometric drawings, developing the true length lines, and then flat plane projections.

You will then be able to measure, scale, and calculate the area the sides of your reducer.

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Anonymous Poster
#8

### Re: Area calculation of HVAC duct reducer

12/13/2010 5:50 AM

this one i know can provide me formulla for HAVAC duct T-Elbow, Elbow and offset area calculation.

sh4uzujug@gmail.com

thanks and regards

shaukat ali

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#2

### Re: Area calculation of HVAC duct reducer

09/18/2010 7:00 PM

Whichever trapezoidal pieces are sloped in relation to the duct axis must have their altitudes measured as the slope distance, rather than simply l.

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#3

### Re: Area calculation of HVAC duct reducer

09/18/2010 11:11 PM

I am not sure WHY you are calculating area of sheet metal, but first let's go the the reducer.

For minimal pressure drop, the maximum angle of the reducer sides is 30 degrees from "straight". Assuming that angle, the area is easily calculated by the hypotenuse of the angle (2 times the "drop" distance) times the width of the duct at the end of the reducer. If you are using a "flatter" reducer, use the appropriate multiplier.

If the duct reduction is in both planes, use the mid-point width for each of the two (or three or four) "sloped" sides.

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Anonymous Poster
#4

### Re: Area Calculation of HVAC Duct Reducer

09/19/2010 4:58 PM
To find the area of a trapezoid, take the sum of its bases, multiply the sum by the height of the trapezoid, and then divide the result by 2, The formula for the area of a trapezoid is:
 or
 where is , is and is the height.
2
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#5

### Re: Area Calculation of HVAC Duct Reducer

09/20/2010 7:23 AM

That depends on the shape of your reducer, however I suspect you were trying to write "trapezoidal". In that case it is simply 1\2 height *(base1+base2). For total area of reducer multiply answer by 4.

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#6

### Re: Area Calculation of HVAC Duct Reducer

10/04/2010 11:02 AM

I have seen circular ducts.What is its advantage over rectangular duct?

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#7

### Re: Area Calculation of HVAC Duct Reducer

10/04/2010 2:02 PM

Circular ducts have the lowest pressure drop for the same volume of air flow AND the lowest cost per unit of air flow (least amount of surface area required PLUS higher "strength" due to circular shape so lower thickness required for same relative size ducts- rectangular ducts have force applied to flat surface so have greater tendency to bulge (or collapse if vacuum). Smaller surface area also means less insulation required.

Circular ducts also only have one joint, so easier to fabricate and seal from leakage AND the ducts can span a longer distance between hangers.

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