Frank, you've heard this before. This is a very, very, very basic bit of thermodynamics. ALL matter radiates ALL the time in ALL directions. As its temperature changes, the frequency range and intensity of its radiation changes, but even at one centigrade degree above absolute zero, matter radiates. SSDD's contention that matter does not radiate towards warmer matter, 16 ways from Sunday, is nonsense .
The inside of your house may be a snug 78F, but when you open that door, radiation from all the matter outside will come in the house. It will add a relatively small amount of heat to the interior. Unfortunately, the interior of the house is simultaneously exposed to the cold outside and its radiation (at higher frequencies and at greater intensity) will leave the house through the open door. Before you opened that door, that same radiation would have hit the inside of the door and remained in the house. The door, presumably at a temperature close to 78F, is also radiating back into the house. Now, with the door open, the radiation from the interior is escaping and instead of that relatively warm door radiating back into the room, we have the sub-freezing exterior sending it meager radiation in. The net result, ignoring any air movement through the door, is that the room will cool. It is pouring its own heat outside through the open door and receiving a much lesser amount coming in from the cold surfaces in the front yard.
Got it?