Does efficient dryer use require me to dry a new load immediately after removing the first load?
December 19, 2010 10:49 AM   Subscribe

There seems abundant advice to fill your clothes dryer with a wet load immediately after you pull dry clothes out in order to take advantage of the heat already in the dryer. How much electricity does this save on average?

It would be great to know the average savings in kWh in order to calculate the total yearly savings.
posted by reeddavid to Home & Garden (10 answers total) 4 users marked this as a favorite
I don't know if this is true anymore. Most modern dryers have a cool-down cycle they run before stopping.
posted by chairface at 10:58 AM on December 19, 2010

There's way more thermal mass in the cold, wet clothes you put in the dryer than either the few interior bits of sheet-metal that get heated incidentally or the small volume of warm air that remains inside it between loads. I'd guess any savings are inconsequential. But to really be sure would require an actual experiment. Maybe send a letter to Consumer Reports and ask if their labs have ever studied this?
posted by RogerB at 11:05 AM on December 19, 2010 [3 favorites]

If you have electric heat and an electric dryer (or gas heat and a gas dryer), it's doubtful that it saves nearly as much energy as you might expect. A good chunk of the heat in the dryer will be released through the walls of the dryer as it cools down; it'll warm up the room some, and that will (in principle) cause the furnace to run less. Some heat will be lost through the external vent, but if that energy loss is a significant amount then you should look into a heat keeper.
posted by Johnny Assay at 11:25 AM on December 19, 2010

Agreeing w/all of the above. Savings is probably on the order of a few bucks a year, at most.
posted by jon1270 at 11:32 AM on December 19, 2010

You will be saving, I would guess, if anything at all (see Johnny Assay's comment) far far less than 1% of the energy needed for one cycle. So I can't give you a kWh figure, but a very generous assumption would be 0.5% of the total electricity cost of your dryer over the year.

If you want to save energy, wash your clothes only when they really need to be cleaned (not after every single wear, and jeans almost never) and then hang your clothes to dry. This will have a much, much larger affect on your energy consumption.
posted by molecicco at 12:16 PM on December 19, 2010

Negligible savings at best. There will be some heat retained in the material of the drum itself and an insignificant amount in the air in the dryer. The best reason to quickly remove your just dried load is to prevent wrinkles not to save energy by immediately inserting a wet load. If you want to get technical you could do some calculations. The heat stored is the delta T times the mass times the heat capacity. Assume a 10 lb steel mass for the drum and a few parts in the heat path from the burner and also assume a fairly hot drum of 120 degrees. The heat capacity of steel is about .12 btu/lb F. Thus the heat stored is about (120-70)*10*.12=60 btu. Even at relatively high gas cost at $15/1000cf (1 MMbtu) you get about .09 cents saved. Even if my assumptions are wildly off the savings remain puny. You want Kwh, which equals about 3400 btu so each load would save about .018 Kwh which at 12 cents per Kwh is about .21 cents. I did these pretty fast so I could have screwed up a unit conversion or something.)
posted by caddis at 6:38 PM on December 19, 2010

During the winter, a far more economical answer is to disconnect the exhaust tube (cap it!!!), and tie/duct-tape a large muslin bag over the exhaust. The bag will catch the lint particles, and you'll recapture the moist heat in your house. I use a 3' x 4" diameter "sock" for the filter, and it doesn't nearly clog up over one winter (but do check it).

The lint is not only an annoying source of dust, but a fire hazard if it shares the room with the furnace or gas water heater, so do bag it.
posted by IAmBroom at 7:04 PM on December 19, 2010

Venting a conventional dryer into your living space is very much against code and probably not a good idea. The theory is that in winter you need to add both heat and moisture for comfort. An electric dryer vent has both. (So does a gas dryer but it has one more bonus, carbon monoxide - do not ever try such a foolhardy stunt with a gas dryer.) A dryer exhausts a tremendous amount of moisture, even in the dry depth of winter your house may not be able to comfortably accept all this moisture. You do not want to promote mold growth. The bigger danger is fire. You will be exhausting your dryer over a ball of old dryer lint - not safe. I suppose the risk is diminished if you clean it regularly etc. but dryer fires are no joke. There are dryers designed to be vented indoors but they condense the water vapor and safely trap the lint. I am not sure if they are available in the States but they are not uncommon in Europe.
posted by caddis at 8:58 PM on December 19, 2010

Energy Star recommendations for dryers.
posted by dhartung at 9:51 PM on December 19, 2010

As has been said - it depends on the dryer and location of the dryer. The best way to save money when drying clothes is to hang them on a washline. We never use our dryer in the summer months.
posted by JJ86 at 6:43 AM on December 20, 2010

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