I was shocked the other day when I took the vent cover off of, what I thought was a heat register in my living room. I figured that I should vacuum out the vents before I turned on the heat for the first time. I was current to the apartment plus this would be the first winter season season living there. Imagine my surprise when I realized that there was no duct labor there. It was genuinely open to the other side of the wall where there was an identical vent cover. I thought at first that someone just put them there for decorative purposes however when I asked the condo owner about them he explained that the vest covers plus pass through were to allow for freezing air return. The heat came from the vents in the ceiling plus it was drawn down by the freezing air returns. The air was then sucked back into the heater to be warmed again. This natural flow of moderate plus cool air allowed for even heating. Years ago, before Heating, Ventilation plus A/C systems were installed, they used floor vents plus wall vents to circulate the moderate air throughout the house. It is still used in multiple areas where it is impossible to install current equipment. Warm air rises, cool air falls, it is just the nature of things plus if you can use this process to supply you an even moderate temperature, this is all the better. If you have efficient, “drafting”, as it is called, you can definitely save a lot on your utility bills too.