Standard size is 220mm x 207mm The telescopic section extends up to 384mm. Internally the baffles acts as stiffeners to make a more rigid construction and reduce back draughts . This reduces the free area to 19,800mm² . This means the CAVHEXT9 can be used with all our 9×9 inch cast iron air bricks without reducing the free area with one exception. When used with the MAX9 air brick, the maximum free area from this air brick will be 19,800mm2 and not 28,000mm2
