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Flushing toilet and the shower



 
 
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  #1  
Old July 12th 05, 05:15 AM
[email protected]
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Default Flushing toilet and the shower

This is something that's been bugging for a long time.

Lots of times on TV, there's a person in the shower, someone comes and
flushes the toilet and the person in the shower starts screaming and
freaking out.

Why does the person in the shower react that way? Is this some special
reaction that was invented for TV purposes or something? I decided to
take a hot shower and have a relative flush the toilet and the only
thing that happened was the water pressure dropped slightly, no big
deal. Nothing else happened. So why do all these people on TV freak
out?
I probably wouldn't normally post such a silly question but that new
commercial I keep seeing about flushing the toilet while someone's in
the shower is starting to irritate me. I just don't get it.

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  #2  
Old July 12th 05, 12:40 PM
Jonathan Kamens
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If the temperature of your shower water doesn't change when someone
flushes the toilet in your bathroom, your shower has a
pressure-balanced valve. This means that when you set the water
temperature, what you're setting is the proportion of hot water to
cold. When someone flushes the toilet, part of the cold water pressure
is diverted to refilling the toilet, so the amount of cold water going
into the shower drops, but the valve automatically makes a
corresponding drop in the amount of hot water so the temperature of the
water coming out of the shower head remains the same.

In contrast, with old-style shower fixtures, when someone flushes the
toilet, the amount of cold water going into the shower drops but the
amount of hot water doesn't, hence the scalding.

Most new construction nowadays uses pressure-balanced valves. It's
even required by code in some places, for safety reasons, i.e., to
prevent the scalding that's made fun of in the commercials.

A step up from pressure-balanced valves is temperature valves. You
tell them what temperature you want the water and they adjust the
proportion of hot to cold automatically to reach that temperature.
  #5  
Old July 12th 05, 04:29 PM
Matt
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We do not have pressure valves on our shower and yet we don't have the
problem. Further this shouldn't be an issue. Hot water only flows
out of the tank when cold water is flowing in. If you flush the
toilet, overall water pressure should be reduced. If your house water
input is strong enough when you flush the toilet, you should have a
surplus of water to continue the cold stream to the shower AND the
toilet. However, if your water pressure is too low, when you flush the
toilet it will divide the water in half, and you'll end up with hot
water and not enough cold to counter it. The solution is to increase
the feed pipes going to your bathroom.

Alternately (and I like this solution).. I turn the heat on my hot water
heater down to the point where I only need to use hot water (not cold
water) during a shower. Not only does this eliminate the ability to
scald the person, but you also use less gas/electric to heat the water,
as it is not scalding temperature. If you need to add water to cool it
down.. it is too hot!

wrote:
This is something that's been bugging for a long time.

Lots of times on TV, there's a person in the shower, someone comes and
flushes the toilet and the person in the shower starts screaming and
freaking out.

Why does the person in the shower react that way? Is this some special
reaction that was invented for TV purposes or something? I decided to
take a hot shower and have a relative flush the toilet and the only
thing that happened was the water pressure dropped slightly, no big
deal. Nothing else happened. So why do all these people on TV freak
out?
I probably wouldn't normally post such a silly question but that new
commercial I keep seeing about flushing the toilet while someone's in
the shower is starting to irritate me. I just don't get it.

  #6  
Old July 12th 05, 05:59 PM
Jonathan Kamens
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You're right that if there is sufficient water pressure and
the cold-water feed pipe to the bathroom is large enough,
flushing the toilet won't cause the temperature in the shower
to change noticeably. Another thing that would prevent the
problem, in the absence of pressure valves, is a separate
feed pipe to the shower which some houses have.

However, that's not a really useful answer for someone who
*does* have the problem of the shower temperature changing
when someone uses the cold water. Putting in a larger feed
pipe to the bathroom is an expensive operation. Increasing
the water pressure, if the pressure is low in the whole house,
is even more expensive. Installing a pressure valve in the
shower is a much less expensive way to solve the problem.

As for keeping the hot water heater temperature low enough
that you can shower with only hot water, you're right that
that saves money and reduces the risk of scalding, but this
has several disadvantages:

* It makes your dishwasher (if you have one) work much
harder and/or not get your dishes as clean.

* Your clothes washer (if you have one) may not get your
clothes as clean (if your washer does automatic temperature
control, this will probably only be true on the "hot"
setting).

* Your hot water will get used up more quickly if there are
periods of the day when you're using a lot of hot water.
  #7  
Old July 12th 05, 06:39 PM
Ian
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The two answers sound right to me.
There used to be another reason -
some 2 or 3 decades ago, in Britain anyway, there were shower units
that heated the cold intake as it passed through/across some kind of
electric element situated behind the main panel: I had one myself
installed to replace the bathtub. You pulled a cord with a red ball on it and
the one with a black ball to switch off. There must have been a
control to adjust hot and cold flow, but I don't remember it.
Anyway, if someone ran a cold tap in any other room, the resulting
drop in pressure would cause the heating device to automatically
switch off as a safety feature, so you were standing suddenly under a
spray of freezing cold water ..... great fun.

--
Ian
Ft Worth, TX
  #8  
Old July 12th 05, 09:56 PM
Matt
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* Your hot water will get used up more quickly if there are
periods of the day when you're using a lot of hot water.


While I agree with most of your points on hot water.. will it really?
I mean since it's not heating it nearly as hot could it actually get it
"hot" quicker as there isn't as much overhead?
  #9  
Old July 12th 05, 11:44 PM
Jonathan Kamens
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Matt writes:
* Your hot water will get used up more quickly if there are
periods of the day when you're using a lot of hot water.


While I agree with most of your points on hot water.. will it really?
I mean since it's not heating it nearly as hot could it actually get it
"hot" quicker as there isn't as much overhead?


Some tank water heaters have pretty good recovery time, but I can
assure you from personal experience than a couple people taking showers
plus the dishwasher and maybe the clothes-washer running around the
same time can easily exhaust a 40-gallon tank, and that's when the
water's set to 120 degrees, which is the most common recommendation for
safety and energy efficiency.

A shower uses about 2 gallons per minute. If your hot water is set to
120 degrees and you shower at 100 degrees, probably about 2/3 of the
water you're using is hot water, so you're using 1.66 gallons of hot
water per minute. That's 100 gallons of hot water per hour, which is
higher than the recovery rate of the best tank water heaters. Add in
baths, which use a more water than showers, and appliances, and you
can easily use up your hot water. If your heater is set lower, it'll
get used up faster.

We've got a 40-gallon tank. I'm hoping that it wears out and we have
to replace it before two of my four kids get old enough to decide they
need to shower every morning like I do :-).
 




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