Most modern fridges have this feature. It is to prevent moisture condensing on the evaporator (cooling) coils. If you allow room air to keep circulating over the evaporator coils, they will deposit the humidity they are carrying thereby building up ice.
Once that happens, since ice is a bad conductor of heat (hence igloos), heat transfer is hampered, and the coils need to be defrosted for the fridge to work well again. Old fridges did have this problem .
Is this the normal temperature for a fridge in the US? Mine is set at 3 C (37.4 F)
It sounds like introducing more humidity might be more of a problem than letting out some cold air.
There are giant refrigerators at grocery stores and such that are designed to run without doors at all. At our local store, the milk is kept in coolers with doors, but dairy products are kept in refrigerators with no doors.
I’ve always figured that if it was so awful to leave the door open, grocery stores (which must have cooling costs far in excess of mine) would be more careful with keeping the groceries cold.
Interestingly, frozen items are all in coolers with doors. However, some frozen meets are in deep-well freezers. I assume these are efficient because the frozen product is kept at the bottom of the cold air. Since cold air sinks, the energy loss is not very great.
My grocery store was renovated in the middle of the pandemic, and most of the new refrigerated cases have doors now (though not as hefty and or well-sealed as the frozen food section or the milk cabinets which are just open to a big refrigerated room behind that have racks for the product rolled up to the doors). So things like pre-packaged salads, fresh cut fruit, bagged coleslaw, packaged vegetables, vegetable dips, various cheeses, meat substitutes, pickles, etc. that used to be in open refrigerated cases are now behind doors. Fresh produce, fresh meat, and the artisanal cheeses are still in the open, but I suspect their time will come as energy codes get more stringent.
I’m sure the stores have analyzed the reduction in sales that comes from having items behind doors and weighed that against the energy costs. That’s one reason for the more strict codes. Also, big box type stores with very few windows and a lot of interior volume tend to be more air conditioner dominated that heating dominated. In other words, the internal heat load from customers, lighting, and equipment, combined with a relatively tight building envelope, means that they could be running the air conditioning even when it’s well below freezing outside. Since most grocery store equipment has the heat-rejecting condensers outside (save for those occasional small things like the drink coolers at the checkout counters, or a randomly placed Esther Price chocolates display), then the cold air “leaking” out of the open produce cabinets and such are just providing extra air conditioning to the spaces that already need it. To a point anyway.
We just recently purchased a new fridge. It’s some highly recommended by Consumer Reports LG thing.
But it’s a door-in-door.
This lends some interesting perspective. The door-in-door was intended to allow quicker access to high-volume items (like beverages) without having to let any of the cold air from the main compartment of the fridge.
The reality of these door-in-door refrigerators is THE IN-DOOR COMPARTMENT IS NOT SUFFICIENT FOOD SAFE AS THE TEMP ROUTINELY RUNS AROUND 47.5F.
This is bewildering to me, as the configuration of the fridge leaves NO POSSIBLE PLACE to store MILK other than inside the in-door compartment, where is it is NOT FOOD SAFE.
If I open in the in-door compartment long enough to fill up a soda, the temp quickly escalates to 50F in just a few minutes.
So at least with “fancy new fridges,” you lose temps pretty quickly if the door is open.
Cold, dry air is being continuously replaced by warm, moist air, which comes in, dumps latent heat, cools, drops out and so on. Can warm up the box and the goods pretty damed fast; that’s why God gave us coffin freezers.
What temp do you have the fridge set for? I set mine for 34. I used to have an LG fridge with the door-in-door and never had a problem with warm milk. (At least not until the compressor failed) But I will say that 47 degrees is ridiculously dangerous.
Those coolers have an air curtain that separates the cold air in the cooler from the room air. They’re not as efficient as coolers with doors, but sales from them with no visual barriers are better than coolers with doors, so on balance, they cost less to run.
Fridge is set to 35 (34 is max low). I have a thermometer in the in-door compartment and I keep it at the top, which is the warmest portion of the entire refrigerator.
The coldest at the bottom of the interior door compartment is only about 8 degrees cooler.
This seems to be a problem with all door-in-door units at large.
Worse: that particular beeping is rare enough that dogs don’t know what it’s for, and just start barking like crazy.
Or is it just my dog who does that? 
A similar argument was made for through-the-door ice and water dispensers. The problem is that the savings from not opening the freezer to get ice is more than offset by the poor thermal performance of the little plastic flap in the door, which is an issue 24/7/365.
It really seems like this should be common knowledge, or something advertised. I would 100% not have gotten such a dumb, fancy thing had I known the drawbacks of the in-door compartments.
I think I assumed 50F for round numbers, but it could be changed for lower temperatures in home refrigerators. 3C will change the results by 50% (24C-3C)/(24C-10C) = 1.5 (50% more)
So a refrigerator set for 3C (37.4 F) will change above calcs as
9> So the electrical energy consumed over the 3 minute period is 1.5 * 1083600/4 = 406350 J = 0.11 kWh
10> 1 kWh in the US is about 10c. So 0.11 kWh is about 1c. So you waste about 1c in electricity if you leave the fridge open for 3 mins.
So we get the same round about numbers.
Either that or until the temperature equalizes, whichever come first.
Interesting. Do you have a Maxwell’s Demon living in your fridge to stop the cold air escaping?
As opposed to 26.53p per Kilowatt hour here. Around 30.7 US cents