4 inch installed4 inch  with ventWe have been getting a lot of orders for our XL units, mostly from St Louis and Chicago areas. These will fit the old fashioned 4 inch vents with 5 inch flashing. Xl units are custom made due to their size and non-standard vent heights found in old homes. So we need the height of the vent on the low side and high side before we can make it. Here are some pictures of a short vent we made an XL unit for.