I had two 4 ton split systems completely replaced here in Las Vegas this spring. I was told by my installer (one that I found to be a company with years of service here and had an excellent reputation) that the XB13 condensers would be fine running to my new furnaces one a xb13 model and the other an upgraded furnace to 14 seer. My line sets are from around 1988 and are 3/8' and 3/4". The 13 seer condenser run to my upgraded attic furnace is maybe 25-30 feet, the 13 seer split to my upflow furnace is 50 feet. I did plenty of leg work before and they were convinced that it would be acceptable. After seeing this site I thought I'd ask for your opinion. If indeed this is going to be a future catastrophy what would be the best method to running new line sets? Any info would be wonderful. Thanks.