We were called out to a house in Katy Texas, because a gas furnace was not operating right. We check out the furnace and it was kicking out on the high limit safety. We quickly diagnosed it as an air flow issue. We checked the air filters to make sure they were clean. Then we checked the static pressure and it was (1.10). The flex duct came from the return into the back end of the furnace. We recommended to the customer to add a plenum on the back end of the furnace giving us the space we needed to add a new return and tie in the existing return. We messured the static pressure and it was (.10). We checked the operation of the gas furnace and now it was not kicking out on high limit safety. More information on air flow can be found on my Air Flow Blog article.