It is a pet peeve of mine when anybody leaves the refrigerator door open much longer than necessary. My husband claims that as long as the food doesn’t get too warm it doesn’t matter how long he leaves the door open (in winter) because the extra energy expenditure needed to re-cool the air inside the fridge results in warmer air in the kitchen, thus less need of our (electric) heating. While I understand his point, it seems to defy logic. Is he actually right?
He’s right that it results in warmer air in the house, but he’s wrong that that air is heated more effeciently than the central heater does, as that’s what it’s designed to do.
He’s right if your home uses electric heaters, and not heat pump or gas.
But even then, tell him it’s even more efficient to set the refrigerator’s thermostat slightly higher (less cold) and only open it for a short time.
But that’s just my point - he claims that it’s not any more effecient. I just don’t understand how leaving the door open (thus warming the fridge AND cooling the room) doesn’t waste energy.
On second thought, I think he is right (and I was wrong) - if you make the refrigerator work harder, the extra energy ends up as heat in the kitchen, which means less load for the heater.
But the caveat I stated above stands - it’s only true if it’s electric heat, and not a heat pump. Most home A/C’s use either a heat pump or a gas furnace, both of which are more efficient than electric heat (or a refrigerator).
Blue Mood is in the UK, where most homes have a boiler (furnace) powered by gas or oil, with pumped, water-filled radiators, controlled by a single thermostat. The likelihood of the extra heat output of the fridge making a measurable impact on the ambient temperature of the room where the thermostat resides (thermostats rarely being located in the kitchen for obvious reasons) is very low. The fridge will merely pump harder, based on its thermostat, to cool a space that now includes the kitchen, raising the kitchen temperature by a fraction of a degree.
Tell your husband to stop wasting leccy.
(But this does raise a pet peeve of mine: we spend money heating our houses, then spend more cooling a cubic metre of them down. Why not build the fridge into the external wall and use the winter temperature to keep food cool, for a minimum of energy usage?! Should I patent this?)
A small quibble on the definition of efficiency. A resistance electric heater is always 100% efficient. Every joule of electricity ends up as heat. A gas furnace can not be this efficient, as hot flue gas has to exit the building. You can use the heat in the flue gas to warm incoming combustion air, but there’s a point of diminishing returns on that, and heat is going to escape up the chimney. Typical oil or gas fired furnaces are around 80% efficient, though there are some high efficiency condensing types that can be higher.
Now economic efficiency is another thing. If a BTU costs more when purchased as electricity than it costs as natural gas you may find it useful to use the less efficient heating source.
According to some DOE cites I found on an oil company web site found here, (I know, but there’s probably no outright lies) the cost per BTU of natural gas was at the time around $4.25 cheaper per million BTU than electricity, but after the relative efficiencies of the systems are taken into account natural gas only works out to be around $0.35 cheaper.
Energy prices are extremely volitile. I work in an industry that generates its own electricity and steam from a variety of sources, including waste wood, oil, natural gas, coal, and recovery boilers used to fire byproducts of the pulping process. Those BTU bandits over on the power side do practically hour by hour comparisons and models to find out which source of energy is cheaper at any given time. Check with **Una Persson ** to see how complicated this can be.
YMMV depending on energy prices. You may also want to consider whether your refrigerator will last as long when used in this manner, because it sure isn’t designed for continuous use as a room heater.
Only if you have a time machine - what you just described is a larder.
What’s the difference between a pantry and a larder? My late granddad had a larder, but it was internal to the house.
My idea is something a bit more high-tech, with a solar-powered dehumidifier, flaps (madam!) that open and close based on temperature, and a fridge-style cooling unit for the warmer months.
Larder and pantry are more or less synonyms, but pantries sometimes incorporate storage for cookware, whereas larders are usually for the storage of food only. There are also contexts in which a pantry is actually a small self-contained kitchen.
Some of what you’re proposing does sound novel, but the idea of a closet vented to the outdoors isn’t a new one. The larders in some older houses are built that way - thick walls, and a louvred or gauze-glazed window to the outside (on a north-facing wall).
I was going to suggest it might be more efficient installing a fridge with the pipes run through a wall to the radiator coils fitted on the external wall - certainly it would cool quicker that way, in winter, as fridges are all about achieving a given temperature difference between the coils and the inside. But… you’d be throwing away heat that would otherwise warm the room, which is desirable in winter (and of course is what all of this is about). I can’t quite work out whether it would be a saving to have the fridge working less hard by dumping its heat outdoors, or by allowing that heat to warm the room a tiny bit, at the expense of running the fridge harder and for longer.
Then what do you do in the summer, when the wall is hot? Perhaps you could design this as slide-out modules - switch out the fridge and pop in an oven module? 
In a modern house, you’d have insulated cavity walls, and thick, insulated, movable flaps (madam!).
ETA: “pop in an oven module?” That’s a very good idea, too. Have the oven on an external wall too to save a few degrees of heating. Except with a British summer that wouldn’t really make a difference… 
This comes back to the same question as above about how you get your heat and what the energy prices are. Then, too, a heating system installed for use as a heating system will hopefully put the heat more where you want it and less where it doesn’t matter as much, which a resistance heater plopped into the middle of your kitchen probably won’t do. So all told, it’s almost certainly more energy-efficient to take advantage of the cold outside, if the construction cost isn’t an issue.