On waiting for warm water

07 Nov 2005

Got questions about the environment? Ask Umbra.

Dear Umbra,

You know how, when you turn on the hot water in an old building, it usually takes a while for it to kick in? Well, my question is, if I turn on the tap full blast, will the hot water come sooner? Is it the amount of water you let run, or the amount of time you leave the tap running? I've talked to my landlord, but in the meantime, can I save water by letting it run slowly?

Sincerely,
(No) Hot (water) and bothered

Ask Umbra continues below

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Dearest Silly Pun,

You know I love to share my water-heater knowledge.

There is a water heater in your building, connected to your faucets by yards and yards of pipe. The heater, most likely a tank-style heater, keeps its electric elements or gas burner busy throughout the long days and nights. The water in the heater is hot 24/7, and ready to rush through the floors and walls to your faucet. After you use hot water and turn off the faucet, the eager water is stopped short and left to wait in the pipes until it is once again called into duty. As the water stands and waits, its heat is eventually lost to the pipes and their surrounding air. When you once again turn on the faucet, the first water to pour out is that which was once hot and has now become cold. So you need to run it until you've bypassed the stale water, and fresh hot water has once again reached your apartment from the bowels of the building.

That is why it takes a while. Pipes are always filled with water, and operate on that system we might have learned about in physics class -- a sort of pressure system where you are basically drawing up the new hot water by releasing the ex-hot water. As you may see, there probably isn't much your landlord can do to shorten your wait. Pipe insulating tubes might help, as they delay heat loss, but the amount of exposed pipe available to an insulator is likely quite wee.

I don't think you can do anything to change the amount of water wasted in any given hot-water demand moment, whether you run it fast or slow. Just run it till it's hot -- and if you are super-industrious, collect it in a bucket and use it for something. Watering plants, or dousing attacking Mongol hordes.

Conduitly,
Umbra

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (2 comments)

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Umbra, Umbra, Umbra

11/7/5 2 Umbra, Umbra, Umbra,
Girl,
U gotta get to thinking better on this... now let's see, are there typically any tanks near the shower where you can store the water until it can be used (say for flushing solids down the sewer pipe, maybe)? Consider using gallon milk jugs, filled with the cold shower water, then pour them into the toilet tank right after a flush, or just water the plants.

There are also domestic hot water recirculation pumps that keep the warm water slowly circulating which can save some water and energy in some cases, but be sure to include a night and weekend timer to turn the pump OFF when it is not being used.

With natural gas prices doing a x1.5$ this winter I am using my water heater a la Mexicana, that is I turn it way down after my shower and laundry, then strike it up about an hour before I will need it again. This limits the standby losses, and I only pay for what I use. One could argue that since my tank is inside the house, that the lost tank heat goes into heating my house, but I use a set-back thermostat, so that is less the case. Also the standby flue losses from a hot tank (water and room air) can be significant. Hot air will gravitate up and outta the house 24/7 unless you install a code-approved automatic flue damper.
Bests,
j'Deen
NRG Engr.

by JamesDeen at 3:55 PM on 07 Nov 2005

hot water waste

I learned from an unemployed friend to turn the water heater off , except for one hour before a shower. Amazingly, most people think this wastes heat because "you have to heat that cold water again"... Even a Physics graduate told nme this!
- moral: the unemployed know more about practical thermodynamics than graduates?

[to convince any silly graduates: say, "If I'm going away for 5 years, should I leave the water heater on? How about 5 days?
- the actual reasoning is this: waste energy is that which escapes from hot water, the hotter the more waste heat escapes (4th power?)]

http://gbruno.tblog.com/ http://www.flickr.com/photos/98865429@N00/

by gbruno at 6:20 PM on 15 Nov 2005

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On waiting for warm water