Worth leaving shower/bath water to cool down?

Question

Tendency here is to leave shower/bath water to cool down thus releasing its warmth to the bathroom. We always have the exhaust fan running while bathing of course to get rid of moisture.

And while we are in the bathroom (in centre of house, no windows) six

40 watts bulbs (total 240 watts) above the vanity mirror are on keeping the temperature comfortable so that relative humidity is not a problem.The mirror. for example, fogs over for five to six minutes and then clears by itself. There are no mould/mildew problems.

We have a fiberglass-shower tub unit. Hot water is heated electrically in basement below. A 500 watt baseboard bathroom electric heater rarely cuts in, the lights and other warmth keeping up the bathroom temperature.

At the end of a typical shower there is warm water in the tub about 4 inches deep, 15 to 18 inches wide and about 48 inches long. These are probably a bit overestimated; but to continue ............. that's 0.3 x 1.5 x 4 cu feet of water = 1.8 lets say 2 cubic feet of water?

Water weighs 'about' 60 pounds per cu foot. So 60 x 2 = approx. 120 pounds of soapy water at a temperature of around the human body; say

90 degrees F? . Leaving it to cool down for an hour or two, to say a room temperature of 70 degrees F releases 120 pounds times 20 degrees = 2400 BTUs of warmth.

One kilowatt/hr of electricity will produce 3300 BTUs of heat.

So 2400 BTU's of warmth requires 2400/3300 = 0.73 (approx three quarters of a kilowatt/hr).

Our electrcity costs, on average, ten (10) cents per k.watt/hr. So; by doing this am I saving some 7 to 8 cents per shower?

With an average of 1.5 persons in house one shower each per day = 365 x 1.5 x 0.08 = potential saving of $44 per year? Enough, maybe, for a magazine subscription?

Welcome comments, criticism, or advice whether I have dropped a decimal point (or other grievous error) in calcs.

And of course the above is probably a 'high' average. Many showers are quicker than that (less used water). While, for example washing one's hair couple of times a week, while showering takes an extra minute or so.

ransley · Accepted Answer

What is the actual temp of water in tub, its already cooled from air a alot, How much water does it take to clean the scum buildup every week. Turning down the thermostat water temp, insulating pipes, and low flow head will save alot more. Ng is cheaper than electric where I live.

Ed Pawlowski · Answer

Couple of comments.Yes, you are saving money by leaving the water to cool and give off the heat you paid for.  Rather than leave the exhaust fan on, leave the door open a few inches and you won't get the buildup of moisture and you won't have to blow out the heated air.  Neither of my bathrooms have vents and it has never been a problem if you open the door a bit.  If you are afraid of someone seeing you naked, run the fan.  Assuming the water is left, the next person taking a shower has to step into the dirty soapy mess?Next is the water in the tub.  We spend very little time cleaning the tub as all the dirt and soap are washed down the drain with little residue.  It seems to me that after sitting for a couple of hours, the soap scum and other assorted dirt is going to need cleaning.  That adds to both water use and the cost of cleaning solutions.  That, plus your time, detracts from the $44 a year.FWIW, my electric rate is 19¢, but my water is heated with oil.

sligoNoSPAMjoe · Answer

On Sun, 15 Feb 2009 06:32:38 -0800 (PST), terry wrote:	It depends on where you are, but where I am most of the wintercalls for running the humidifier to keep the humidity up to about 40%to avoid static problems and to make it more comfortable at a lowertemperature.  I suggest not running the exhaust fan during the heatingseason for most areas.  You will save even more that way. Just allowthe bath room to air out by opening the door, during or after eachshower.

aemeijers · Answer

Unless you are closing the drain, your drain is plugged. No way should 4 inches of water build up from a properly-installed and functioning shower. It should run out about as fast as it comes out of showerhead.

Phisherman · Answer

...My first thought was the energy saved by not allowing the heat downthe drain is offset by use of the exhaust fan.  Not using the fan is agood if your house is

Tony Hwang · Answer

Hi,If RH is 50% in my house in winter, all windows will fog up. See typicaloutside temp. is -20C range. It all depends.

Doug Miller · Answer

[snip]Never mind the energy issues -- you need to find out what's clogging your drain!!

Stormin Mormon · Answer

When possible, in the winter. I do leave my shower or tub water until the next shower, or tub. I figure I paid for the gas to heat the water, and those BTU I want to keep in my trailer.

h · Answer

And you spent way more than anything you saved using new hot water to clean the scum off the shower/tub walls and floor from leaving the standing water. Penny wise pound foolish.

Stormin Mormon · Answer

You mean a galon of water every week contains more BTU than 40 galons of hot water, every day? Amazing. I'm going to have to make this into a research project, and get published. Thanks for a great research paper subject, you goofball.

The Daring Dufas · Answer

Heck fire feller! Do wut we do down here in th South,take yall one bath a week.  FLNFTDD

Worth leaving shower/bath water to cool down?

Join the Discussion

Didn't find your answer?

Worth leaving shower/bath water to cool down?

Related discussions

How much water in a copper tube?

Well pump is leaking; what to do?

Water heating question: how to integrate hot water supply, radiant floor heat and solar? (2025 Update)

Join the Discussion

Didn't find your answer?