Alcan Window Channel Balance

Many thanks for writing in to us. Most Alcan windows use the Series 380 Channel Balance. This balance has a bottom nylon shoe with a 1" depth, or 'heel-to-toe' measurement. It appears you will need the S380-30, but the stamp code of 2900 is a bit unusual, as it is not from any sort of rating system we use. Is it the same stamp code on the other balance from this window? In any event, it would be best to weigh your window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option on the product page.