You're as cold as ice

August 18, 2008 7:17 AM

Is it cheaper to buy or make 10 pounds of ice cubes?

Here are the factors: I am in Chicago, fresh water is cheap, electricity not as cheap, I have a standard refrigerator. I started thinking about the value of my time in making the (ever depleted) ice bin.

Thoughts?

posted by zerobyproxy to food & drink (14 answers total)

Depends. If you're just sitting around, swapping out ice trays every few hours while you watch movies/read/whatever, it's not a big increased cost.

My major concern would be having the room to store 10 pounds of ice cubes, assuming you need them all at once; my own fridge is mostly full of food, without room for huge amounts of ice.
posted by Tomorrowful at 7:25 AM on August 18, 2008

Assuming you will be running the freezer anyway, it's cheaper to make the ice cubes. Your freezer will actually be more efficient the more full of ice it is. Don't forget to factor in any time/costs associated with going out to buy the ice.

How much time does is take you to make ice that you think it is a factor? Protip: you don't have to watch it freeze.
posted by mikepop at 7:27 AM on August 18, 2008 [3 favorites]

You could make bigger blocks, then chip them down with an ice pick.
posted by StickyCarpet at 7:28 AM on August 18, 2008

You could get a refrigerator with an automatic ice maker - figure that cost as contrasted with your cost of time + the energy lost every time you open the freezer door to make ice.

Also, you have significant time/effort involved with purchasing and lugging around ice. And you have no idea what kind of water goes into it.
posted by amtho at 7:35 AM on August 18, 2008

If it helps, I find that store bought ice usually tastes better.
posted by electroboy at 8:19 AM on August 18, 2008

considering the cost of ice at my old chicago corner shop I guesstimate you will save $0.002 for every hour invested, making this a grand savings of $0.52.

in other words: this is a minimal investment not worth fretting about.
posted by krautland at 8:20 AM on August 18, 2008

If you're always running out of ice, you should probably just buy it, given that you want ice and seem to have developed no habit of keeping yourself stocked.
posted by shownomercy at 8:29 AM on August 18, 2008

Making ice using your freezer will probably cause it to run more (because you'll be putting room-temperature water in there and freezing it), but short of putting a Kill-a-watt on it, I don't know of a good way to measure the increased cost. I suspect it'll be minimal, because I believe your fridge's compressor (in a typical household) runs most often to keep the fridge at normal temperature because of people opening the door, not to chill the freezer. However I don't know of any hard evidence for that, or really even any good way to measure it.

This assumes you're making ice in your freezer that's turned on and cold anyway; if you're planning on plugging in a chest freezer (or something) solely for the purpose of making some ice, it's probably much more expensive. In that case, you have the total cost of running the freezer to account for, and not just the marginal cost of the additional electricity required to freeze the water.

I would suspect that home-made ice would be cheaper just given all the costs that bought ice needs to cover -- not just water and electricity to make the ice, but also transportation costs to bring the ice to the store where you buy it, the deliveryman's time, ice company profit, store profit, packaging, etc. You're buying a lot more than just frozen water. Also, you need to factor in the gasoline spent driving to the store to buy it.

However, if you make it at home I think the biggest 'costs' are going to be your time and all the space in your freezer that the ice-making project is going to take up. Although it would be possible to figure out the exact cost of the energy required to freeze 10 lbs of water, I'm not sure that would really be a significant part of a rational buy vs make decision.

(Personally, I'd buy it, unless you had an automatic ice maker and an empty freezer and can just let the icemaker work and dump it into a bin as it goes. Anything else is too much of a PITA. Also, store-bought ice does taste better in drinks.)

Just out of curiosity, I looked up the energy required to freeze 10 lbs of water. Assumptions are that the water starts out at 60F/289K, and ends up frozen as ice at 0F/255K.

This has to be considered in three parts; the chill from 289K to the freezing point at 273K, the actual freezing, and then the cooling from the freezing point down to 255K.

Wikipedia tells me that the specific heat of liquid water is 4.1813 J/(g K). 10 lbs of water is about 4536g, and 289 to 273K is 16K. Plug and chug and we get (16K * 4536g * 4.1813 (J/(g K))) = 303462 J.

To actually change the state of the liquid water to ice, you need to look at the enthalpy of formation of ice. Wikipedia claims it's 333.55 J/g (cited from the CRC Handbook). So 4536g * 333.55 J/g = 1512982 J.

But then we assume that you leave the ice in your freezer long enough for it to chill down to the ambient temperature, which is generally around 0F for a domestic freezer. This is another heat capacity issue. Water ice has a lower heat capacity than liquid water, allegedly around 2.050 J/(K g). As above: (18K * 4536g * 2.050 (J/(g K))) = 167378 J.

Total all that up, and you get 303462 + 1512982 + 167378 = 1983822 J. One kWh is 3.6 megajoules, so you're talking about approximately 0.55 kWh of energy.

That, of course, doesn't take into consideration the energy lost when you open the door, or to inefficiencies in the freezer's cooling system; it's purely the energy required to cool and freeze the water itself.

Anyway, that's just nerdery -- I don't think electricity is really that big a factor in the cost or decision.
posted by Kadin2048 at 9:04 AM on August 18, 2008

The reason your freezer keeps running out of ice is because the ice you make at home sucks. This is because the water you use to make ice at home has a significant quantity of gases and impurities mixed into it. This is why home-made ice has that white center (the white center is gas bubbles). Hard water (water with high mineral content) also makes for bad, poorly performing ice. This is why freezer ice melts fast in your drink, and why you keep having to refresh the ice in your glass.

Store bought ice, or restaurant ice, is made in special machines in which water is frozen in thin layers over a prolonged period of time, building up a solid, clear ice crystal. Furthermore, high quality ice machines (and good soda fountains) also include a water filter unit that filters the incoming water so that it is free of minerals. This makes for very high quality, long-lasting ice.

You can make clear ice cubes at home by boiling the water first to remove the gas in solution, and then letting it cool to room temperature. Then pour the water into trays and freeze it very slowly. The slower the freeze, the better. You can stage the freezing by placing the ice cube trays first in a refrigerator, to bring the temperature to the low 40s or high 30's, and then move the tray to the freezer.

So to answer your question, it is probably cheaper to make it at home, but the quality will be poor, and you will run out quicker. If you use a lot of ice in your home, or are fastidious about the cleanliness and taste of ice, you can get a small home ice maker.

FYI, for the ice nerd or burgeoning restaurateurs out there, the cleanest, longest-lasting, and most well-shaped ice I have ever had comes from the Scotsman Prodigy line of ice makers.
posted by Pastabagel at 9:04 AM on August 18, 2008 [7 favorites]

And though no one asked, this is the best soda fountain ever built by anyone anywhere in the history of the liquid refreshment, and also produces the best ice I have ever had from a soda fountain.
posted by Pastabagel at 9:12 AM on August 18, 2008

most likely cheaper to just make your own. i have 8 ice trays and a bin in my freezer as i use ice like it's going out of style. maybe do something like that if you only have 2 or 4 trays like most people.

also, bagged ice often has weird floaties and it skeeves me that i don't really know the source.
posted by misanthropicsarah at 9:17 AM on August 18, 2008

One other option to speed up the production of home icecubes- icebags. Filling them with filtered water, they are awesome compared to trays, in every way.
posted by ArkhanJG at 9:29 AM on August 18, 2008 [5 favorites]

Here in northwest Indiana you can buy an 8lb bag of ice for like $1.50, and a 22lb bag for $3.
posted by IndigoRain at 8:10 PM on August 18, 2008

Cheaper to make, *if* you have a good, efficient freezer. If you have a crappy freezer, it's a toss-up.
posted by Citrus at 7:03 AM on August 19, 2008