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I am a student who studies in a different city than my home so I go home almost every weekend or second weekend. I recently brought a room sized fridge and to save electricity costs, whenever I go home, I turn off the fridge which is usually for two-three days and in case of extra vacations, more. Recently somebody told me that that isn't healthy for the fridge and the compressor will get inefficient if you keep doing this so you should just keep it on. Now my question is, if I turn it off for 2-4 days, will the compressor or fridge in any capacity be messed up? Or work less efficient? Or will there be any issue?

Thanks in advance.

isherwood
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khawajayy
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    Do you empty the fridge of perishable food when you leave it off? – Jim Stewart Jun 19 '19 at 12:25
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    Check your fridge's energy rating or look it up with EnergyStar to get an idea of the power cost. You may be surprised at how low it is. I have a small fridge in my basement, I just looked it up. The estimated cost to run it is $27 **per year.** Turning it off for a day or two once a week may only save you a few dollars a year. – dwizum Jun 19 '19 at 20:17
  • Hello, and welcome to Home Improvement. Good question; keep 'em coming. – Daniel Griscom Jun 19 '19 at 23:16
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    @dwizum It may not save you anything. Consider: the cost to keep it at a low temperature versus the cost of cooling it back down from room temperature, which implies a lot of continuous running. – user207421 Jun 20 '19 at 01:09
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    I read `room sized fridge`, you mean *full* sized? I... can't imagine you needed a fridge the size of a room... – Nelson Jun 20 '19 at 02:42
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    @Nelson I had the same initial reaction to "room sized fridge" but figured OP meant *dorm* room sized, aka mini-fridge or beer fridge. Khawajayy, can you clarify? – A C Jun 20 '19 at 03:01
  • Technically no, biologically, probably yes. – Dr_Bunsen Jun 20 '19 at 09:47
  • Your savings are likely marginal. – copper.hat Jun 20 '19 at 13:24
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    @user207421 I don't see why the cost of cooling it back down from room temperature would be higher than the cost of continuously running it. That doesn't make any sense from a physics point of view, because any energy that we need to put in to bring the temperature back down, is energy that we didn't have to replenish while the fridge was turned off. – Tom van der Zanden Jun 20 '19 at 14:48
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    @TomvanderZanden You need to open the door when you turn off the fridge. This means all the air and fridge parts that are normally cooled warm up to ambient temperature. Then when you turn if back on, all of that needs to be cooled down again. So there is a fixed extra cost to turning it off. While running on the other hand it only needs to get the warmth that creeps in through the insulation out again. So the larger and better insulated it is, the less you should turn it off. – Nobody Jun 20 '19 at 19:35
  • If you follow the answers and leave it on, adding a few bottles of water will help you save just that extra little bit of electricity/money. Since water requires more energy to heat or cool, once cold, they will help keep the internal temp cooler, longer without the need for the compressor to run. Having a couple of liter bottles of water in there all the time will help save money this way all year long. – coblr Jun 20 '19 at 19:46
  • @TomvanderZanden That's only true if the process is 100% efficient. – user207421 Jun 21 '19 at 03:16
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    @user207421 I'm not sure what you mean by that. Most refrigerators are more than 100% efficient, in the sense that they can move more than 1 Joule of heat for every 1 Joule of energy input. The total amount of heat the refrigerator must move when it remains on the entire time is greater than the total amount of heat that must be moved to bring it back down after it has been left off for a while (unless, as Nobody correctly points out, the door is left open when the refrigerator is off). Refrigerators are usually specified to move a certain amount of heat for a certain amount of energy input. – Tom van der Zanden Jun 21 '19 at 07:54
  • @TomvanderZanden It's another 'case' of efficiency: we're comparing two scenarios and efficiency is efficiency across scenarios, not efficiency of fridge itself: case1: fridge on 24/2days with no door opening (starting temp 4° T afrer 2 days 4°), case2: fridge off 24/2 days starting temp 4° T after 2 days: 22°, in this case to store food safely we must cool down 22° to 4°. Case 1 suppose we use 1 kWh, case 2 suppose we use 1,2kWh: case 2 is 20% less efficient than case 1, even if the fridge itself is 200% energy efficient. – DDS Jun 23 '19 at 10:48

11 Answers11

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Someone will close the door and...

It will fill the fridge's internal spaces with mold

Air holds moisture. Warm air is capable of holding more moisture than cold air. Everytime you open the fridge door, you let in room air. This contains more moisture than air can possibly hold at refrigerator temperatures, which means condensation occurs inside the fridge. When it occurs on the coils, it is visible as frost.

Those panels that line the fridge interior are not airtight. Air also circulates behind them and condenses there.

The upshot is, a fridge has a lot of water or ice inside it, in all sorts of inaccessible nooks and crannies. When you shut off, the interior warms to room temperature, a sealed space with more condensed water than the air can possibly hold. It hits 100% humidity and you have a petri dish for mold.

The only cure is to leave the door open enough that air circulates freely, which keeps the humidity same as ambient. However, this doesn't work. Humans have embedded programming to close any refrigerator door on sight. The entire species has 18 years of full-immersion psychological conditioning starting nearly from birth to close refrigerator doors.

Why the mold is bad

I learned this by repeatedly cleaning mold off a fridge we ran when needed. It seems a simple fix; clean off the surfaces and you're all good. However, those are not the only surfaces. There is also the backside of those surfaces, the machinery including evaporator coil, and electricals. You cannot reach those to clean them. And to be clear, the interior lining of fridges are decorative, not hermetic seals.

Exactly the same black mess is happening in the inaccessible locations, in roughly same proportion, since the humid air is convecting all over the fridge. If it happens repeatedly, the mold gets thicker since you're not cleaning it.

Obviously that can affect machinery, but this reserve of mold spores can also get on food.

Harper - Reinstate Monica
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    +1 I was going to write something similar (though not quite as detailed) but you beat me to it. The other point I was going to add is that a refrigerator can take many hours (manuals typically say "24 hours" but I suspect that is boilerplate copied for the last 50 years) to cool down. They take a long time because the compressor/etc. are designed "just barely big enough" to keep the price down (and enhance manufacturer profits). So when you turn it on & put in the milk you just bought, it will spoil quickly because of the delay cooling down, negating the small electricity savings. – manassehkatz-Moving 2 Codidact Jun 19 '19 at 14:16
  • There are fridges which are used infrequently, like in campervans / RVs, perhaps they have been designed to avoid this problem. Also just as a general principle mold requires food (I mean mold food, not human food) and many of the internal materials of the fridge are plastic or metal which would not be edible by mold. Maybe some dust or other contaminants would suffice, however. – StayOnTarget Jun 19 '19 at 19:08
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    @DaveInCaz Generally, camper/RV fridges aren't designed to avoid the listed problems. Like almost any fridge/freezer, RV fridges take time to cool down to operating temperature or dry out after being turned off. It's desirable to turn one on considerably before wanting to use it and to leave the door(s) propped open (i.e. unable to be closed) for an extended time after turning it off to prevent mold (and wipe the inside down after any ice melts to help dry it out). Any refrigerator/freezer will accumulate dirt/dust/particles during normal use, which mold can use for food. – Makyen Jun 19 '19 at 22:39
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    I usually hang a towel over the open fridge door to indicate that it is to be left open. If that does not work, a notice or sign might. – Andrew Savinykh Jun 20 '19 at 00:22
  • Panic at the disco .... havent you ever heard of,closing the *** ***** door? **** ends up in divorce even before you say I do! But in all seriousness, to give this full credit for the answer it should talk about the compressor and efficiency too. – noybman Jun 20 '19 at 01:33
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    As often as I have seen refrigerators left open, I question that “embedded programming” thing. But it doesn’t matter if no one is there to see it and close it, which seems to be the situation OP is in. – WGroleau Jun 20 '19 at 05:50
  • That bolded text with the big font at the start seems to implicate that it would be turning off that cause mold to grow. But you say it yourself later: it's not the turning off, but neglecting to leave the door open that's the actual problem. The (possible) conditioning might affect how well one succeeds in avoiding that, but it's not a given. Some of us have also been taught to leave fridge doors open if they're turned off. – ilkkachu Jun 20 '19 at 07:12
  • This answer is confusing. They ask about turning it off and your answer mentions opening the door and letting warmer air in. Why would the fridge reach 100% humidity if it is turned off? Is it turning it off that creates mold? Having a leaky fridge? Leaving the door closed when it's turned off? – Emobe Jun 20 '19 at 10:18
  • @Emobe perhaps because answering so the the OP can keep their fridge in good condition is part of what we like to do on here... So it **is** relevant , as you will note by the number of upvotes... – Solar Mike Jun 20 '19 at 12:13
  • @emobe the answer goes into detail about where the moisure comes from. Repeated exposure to outside warm air allows condensation to freeze in nooks and crannies in the fridge/freezer, which turns back to water upon warming. The answer does jump to mold - and explains the causal relationship properly. – Saiboogu Jun 20 '19 at 12:34
  • @ilkkachu but we are grossly outnumbered.... – Harper - Reinstate Monica Jun 20 '19 at 14:52
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    @manassehkatz: "Just barely big enough" compressor is not about cutting corners to save money. You **always want** a compressor that's just barely big enough for the cooling task at hand, because otherwise it will run with a very very short duty cycle and will not remove any significant amount of moisture before the desired temperature is reached. Yielding, once again, mold. – R.. GitHub STOP HELPING ICE Jun 21 '19 at 04:56
  • @R.. I would argue that there is a "good range" - might be 'x' HP (or BTU or however you want to measure it) to 'x' * 1.25 (making up numbers here), where if you go greater than 'x' * 1.25 then cycle time will be too short and you go less than 'x' then cycle time will be too long - and that cost-sensitive manufacturers (and *all* manufacturers are cost-sensitive, but manufacturers of "small fridges" (cheap foreign boxes) are far more cons-sensitive than manufacturers of "big fridges" (Whirlpool, GE, etc.) and therefore get as close to 'x' as they possibly can "barely big enough". – manassehkatz-Moving 2 Codidact Jun 21 '19 at 05:04
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    To prevent the door being closed. Write "DO NOT CLOSE" on a piece of cardboard a bit larger than fits in the fridge, so it sticks out - then leave the cardboard in the fridge, preventing the door from being closed. It worked perfectly for many years at my previous workplace. For better results, glue together 3-4 layers of cardboard, for a thicker sign, forcing the door more open. – Gertsen Jun 21 '19 at 12:34
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    Pull the electrical cord and leave it hanging over the door, both making it impossible to shut close without removing the cord and as an indication that it isn't functioning. If this doesn't help in your environment then, well, leave it on. :-) – Gábor Jun 21 '19 at 15:05
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    @manassehkatz I think what you're having in mind is "freezing capacity", and indeed larger compressor means larger freezing capacity. It's yet another parameter that's listed in the manual. Eg. my 8-year old 275l (195l cooler + 80l freezer) is rated 6kg/24h, but today 3.5kg/24h is more popular in that size. If someone cooks and freezes it a lot, they need more. If all one does is bring frozen pizza and ice cream from a store, they need less. BTW, smaller compressor also means more room in a given body, so that might be another factor. – Agent_L Jun 22 '19 at 07:47
  • Can you clarify, is mold damaging to the interior of the fridge or just something gross you will have to start cleaning out if you don't leave the door open? While it is a good point, I'm not sure how an aside about mold has more up votes than an actual answer to the headline question that also mentioned mold before this answer was written... – statueuphemism Jun 23 '19 at 11:07
  • @statueuphemism okay. But it's not an "aside" just because It comes from left field. It's the direct answer. – Harper - Reinstate Monica Jun 23 '19 at 14:28
  • @Harper I agree that your edit directly answers the question of how the mold is actually damaging and not just an inconvenience that needs to be cleaned up every once in a while. – statueuphemism Jun 23 '19 at 15:35
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You're probably not saving any meaningful amount of electricity by turning it off for just 2-3 days. Sure, it won't use any for those days, but the temperature inside will raise to room temperature. After you turn it on again, it will have to work for many hours to cool down again. This could cause abnormal wear on the compressor, because it's designed to be frequently turned on and off by the thermostat just to keep the temp level, and not to work for several hours in a row to cool the whole thing down from room temp. However, this effect is probably insignificant.

By not opening the door when you're gone, you're already saving electricity. The most work the fridge has to do is to cool down all the warm products you put in and all the warm air you let in. If you're not there to open it, it's a bit electricity saved already.

The most significant part had already been covered in other answers: turning a fridge off is a multi-hour effort that involves removing food, having the frost thaw and cleaning up resulting water. Turning it on again is also non-trivial, as it requires drying it thoroughly to prevent immediate frosting. Thawing and refreezing without all this effort will damage the fridge, through mold and ice damage. The whole cleaning is well worth it when you leave for few months, but not for few days.

If you want to optimize the fridge, make sure that the hot part (usually at the back or built into the sides) has room and unobstructed airflow. Small fridges are convenient to be stuffed in cramped spaces, like under desks. Simmering in a pocket of hot air greatly increases power consumption. Observe when the compressor is running and after a while (eg when it stops) use your hand to check if the air around the element feels warm (not the element itself, it's supposed to be very warm to touch). It should not: all the air warmed up by fridge should convect away freely. In a nice, cool environment, the fridge has much less work to do. Less work = less electricity.

You can observe how often and for how long does the compressor turn on when the fridge is not opened. It should barely work at all. If the compressor is on most of the time, then it means that the insulation or seals are damaged and the best course of action is to either repair the seals or get a new fridge.

The rule of thumb that one should follow in all areas of life is to first measure the actual costs before trying to cut them. In programming we call it "premature optimization". The problem with it is that it yields insignificant savings while detracting your attention from areas that actually need improvement. Get a kill-a-watt to measure how much running the fridge actually costs you. If the fridge is very old and leaky, you could find out that moving towards more expensive non-perishable food can be financed by ditching the worn-out electricity hog entirely.

I hope your fridge has an actual compressor. Peltier-baser solid-state portable fridges are ridiculously inefficient and IMHO not worth using at all.

Agent_L
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    "The rule of thumb that one should follow in all areas of life is to first measure the actual costs before trying to cut them." Excellent! Put that at the top! – FreeMan Jun 21 '19 at 15:09
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A fridge keeps a steady temperature by turning the compressor on and off. The only difference is that you exchange a few on/off cycles with one longer on-cycle when you get back. I would say that does not negatively affect fridge lifetime, and might even improve lifetime because the total on-time is reduced as well as the number of cycles.

The only thing I can recommend from experience is that you should always leave the fridge open when you turn it off. Leaving it closed will lead to mould formation.

Sanchises
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    For a REALLLLLLLLLLLLY old fridge, one might argue that a warm compressor wont seize like a cold one would. They'd probably be right, but besides this (*which is silly), @Sanchises answer makes all the sense in the world. A fridge that is off (and modern) shouldn't be hurt by not running. You might want to consider turning its temp down (or up to be precise), so that it spends less energy keeping cool and then you can leave things in it that dont spoil at cooler (vs colder) temps. Then you can enjoy a cold beer that much faster when you come back. – noybman Jun 20 '19 at 01:29
  • and ... If it's a kerosene fridge it won't have a compressor at all. – mckenzm Jun 20 '19 at 05:33
  • @statueuphemism The best voted answer have a point that there might be no savings (although I would argue it probably does) - and it might be a point that people feel easier voting on. – Sanchises Jun 23 '19 at 18:57
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It's hard on the compressor because a fridge is designed to have a few number of room temperature to preset temperature cool-downs but it will maintain that temperature for several years. When it has to do this major cool-down, it runs constantly for several hours until the air inside is at the preset temperature. It would shorten the lifespan of the fridge, and it's not really saving you any money.

Sometimes those things we think are saving us a little money will cost us big money in the end.

Mr. Anderson
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Turning off the fridge for 2 or 3 days every week or two weeks is not normally done and could have unexpected consequences, but even a small fridge generates some heat which would raise the temperature of the room if the room is not ventilated or even air conditioned. Presumably the room a/c is not on when you are gone, or is it?

All things considered I would leave the refrigerator on when you are gone.

Jim Stewart
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You need to open the door when you turn off the fridge. This means all the air and fridge parts that are normally cooled warm up to ambient temperature. Then when you turn if back on, all of that needs to be cooled down again. So there is a fixed extra cost to turning it off. While running on the other hand it only needs to get the warmth that creeps in through the insulation out again. So the larger and better insulated it is, the less you should turn it off.

It's unclear in the question, but if it's a mini fridge suitable for a dorm room, then likely it's small and not well insulated, so maybe it pays off to shut it off for 2 days or more. On the other hand if it's a standard full sized fridge, then it's very unlikely to pay off. If it's really a room sized fridge, you can be very sure it won't pay off.

The only way to know for sure, for your fridge and the spot where you installed it (that matters) is to use a cheap power meter and compare. They are like $20 you need to compare your power bill first to decide whether that's worth it.

Nobody
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In addition to the other answers already posted, you may want to use a thermal mass (e.g. bottles of water) to take up the space in the refrigerator not used by perishable goods that you actually want there.

When you open the door during normal use (or someone opens the door while you're gone), the chilled part of the fridge exchanges relatively quickly with warmer room air, and the fridge is closer to the starting-over point than it would be if there were bottles of cold water in there. This also applies to the air that leaks in/out due to imperfections in the seals around the door etc.

If you regularly fill up the fridge right when you come back, this may not be worth it, as the fridge does have to do more work to cool down the bottle of water than just air. However, if you are regularly under-utilizing the space capacity and want to do something easy to improve efficiency, there's an idea. It also helps (slightly) with preparedness for water service outages.

WBT
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I should also check the manual that came with your fridge. I recently purchased a fridge and it comes with a 'vacation' mode. This essentially tells the fridge that you've taken anything really perishable out and it can go into an 'energy saver' mode and not have to keep everything quite as cold as it otherwise would.

Paddy
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If it is a an energy efficient refrigerator ,I was told by an appliance repair man that there are issues with some getting them to restart after being disconnected.

Cottages on cape cod
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The maximum electrical and mechanical stress on the compressor occurs when it switches on. The motor has a current spike until it starts moving and the compressor has to work hard to bring the system up to pressure.

Eliminating a few days worth of start cycles will not damage the compressor as long as the fridge is not tipped or moved immediately before restarting. This can cause a liquid lock in the gas part of the system which can damage the compressor.

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It may be damaging your food (fridge take about 4h to go from 22° to 4°, more if being filled with room temp. stuff), also a fridge need relatively more energy to go cold from ambient temperature than to stay cold once cool.

If you have an 'average' empty fridge you could improve energy efficiency and also temperature 'constantness' filling the space you don't use with bottle of beverages, once cooled bottles will keep the cold in, if fridge is empty, cold air will escape as you open the door and the compressor will have to cool all the air every time you open the door.

DDS
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