Nominal Sizes

Every manufacturer uses nominal sizes.  Nominal sizes are typically a whole number rounded up from the “actual” size.   In sizing custom-size filters for exhaust frames, it is important to understand the difference.

EXAMPLE

18S:  18″x30′ Standard Accordion
Nominal height (or width): 18″
Actual height:  17.5625″

AFX:  I can’t make an exact 18” or 20” without extreme waste.  The base paper width for this size is 35.25 ” (39.25″ for 20″).  Saw kerf is .125” or (35.25-.125)/2 = 17.5625.  If I cut 18” from 35.25, I’d throw away the other 17.25” (double the cost).

All filters require +/- 0.125″ variance. 

 NOMINAL   ACTUAL 
1M 39.25″
36″ 35.25″
20″ 19.625″
18″ 17.625″
24″ 23.75″
29″ 28.75″

Due to historical numbering, these sizes are “nominal” by sku (1MS, 36S, … 2972S).  All other custom size skus are actual (+/- 0.125″ variance).  If you require an “actual” size, send the inside dimensions of your frame.  AFX will provide the appropriate size/part number.  

Do you need a custom size? 

Measure the inside of your exhaust frame for length and width (or height).  Send us your actual inside dimensions and we will provide the manufacturer part number!

Request quote

Custom Size Accordion