My home was built in the early 50s, heating was a wall furnace between the front room and the hallway, in the sixties a large family room was built on the back of the house, it too was heated by a wall furnace. In the 70s the home owners installed a pellet stove in the family room as well as a whole house swamp cooler, they installed a large air return in a skylight wall that with the use of a bypass would heat the entire house with the cheaper pellets vs gas. The swamp cooler vwas disconnected before I bought the house in 2010. By 2018 I decided to refi my loan and install a split system with individual room control. The open doorway between cyhe front room and the kitchen was a vacuum for what ever the air temperature in the family room was. By placing these vinyl strips on the kitchen doorway the temperature differential between the 2 rooms was quelled