I agree that the energy used does not depend on the voltage. However, it will
change the calculation of the energy used. The parameters that were used in
the calculations were measured except for voltage.
As you say, the voltage will change the duty cycle of the heater, keeping the
energy use relatively constant (neglecting line losses). Thus low voltages
will lead to high duty cycles (and vice versa), so the particular duty cycle
measured is associated with a particular line voltage. That line voltage was
presumed, not measured.
I did not monitor the line voltage continuously during the experiment, but I
did measure it with a Fluke digital voltmeter. It was right on 240.0 volts.

Phil Sherrod wrote:

On 30-Mar-2004, "BruceR" wrote:


How was I swindled by buying tankless heaters?


There's nothing wrong with a tankless water heater, and they do have the
advantage of providing an unlimited amount of hot water.

The "swindle" (maybe that is too strong of a word) is by salesmen who claim
that the tankless heaters save a great deal of energy and power cost. A
tankless heater cannot save more than the heat lost from a standard tank type
heater. As my measurements show, this is pretty small, typically $4/month.
But you won't get a full $4/month in savings because each time you use hot
water it has to heat up the metal heating unit which then radiates (loses) that
heat when you stop using the water. My guess is that a tankless heater saves
about $2/month in energy loss. So if you have a savings of $24/year and a
tankless heater costs an extra $480 dollars (pretty typical), the payback time
is about 20 years (assuming it lasts that long).

There is another reason to use a tankless heater. If you have a long
run from your whole-house water heater, you will use up the capacity of
the pipe run before you get hot water at the tap. That amount of water
is wasted as well as the energy needed to heat it. If you don't have
the space, a tankless heater will provide instant hot water. If you
have the space a small conventional tank will do just as well.

I went a different route and it works quite nicely. I plumbed a return
path back to the bottom of the whole house water heater. As long as the
return run is everywhere lower than the supply, water will continue to
circulate by gravity. Of course, I insulated both runs and since we
live in a climate not needing AC, the energy loss is negligable.

On 30-Mar-2004, "daestrom" wrote:

Exactly right. This is the same as 'setback' thermostats. There *is* a
savings, but it is difficult to calculate/predict the results.

I agree. However, the temperature drop in a house over an 8 hour period could
easily reach 25 degrees (assuming sub-freezing temperatures outside), and the
energy cost from heat loss of a whole house is much greater than the cost of
heat loss from a water heater.

On 30-Mar-2004, (m Ransley) wrote:

Well Phil your calculations on tankless vs tank are not quite accurate.
You also forgot that Tanks unless flushed regularly loose efficiency
every year. I just had a tank replaced in a bldg it had over One Foot
of scale- crap in it after 17 yrs. Now that reduced efficiency apx 20
-25 %

17 years is a pretty long life for a water heater.

Scale reduces the volume of the tank, it does not reduce efficiency nor does it
increase power usage. The scale will be at the same temperature as the water,
so it will radiate heat at the same rate. With a smaller effective tank, you
will be able to use less water before it starts getting cold, but the energy
required to heat whatever quantity you use will be exactly the same.

Tankless don't have these problems , they
don't scale. they remain at their rated as long as the burner is clean.
and last 2 to 3 x longer.

Your tank heater lasted 17 years, so you expect the tankless heater to last 34
to 51 years??

For figures on savings you are wrong. I know people that say the same
as me 25- 50 % in costs of operation. saving 15 - 40 a month.
There are allot of people with tankless , they are how you should base
your opinions. Real world everyday use. Not guesstimates.

The whole point of my analysis was to avoid "guestimates". What guess are you
saying I made? Rather than guessing, I took accurate measurements that show the
total energy cost due to heat loss is about $4/month. If you are saving more
than that you are either (1) using less hot water or (2) using a cheaper source
of energy such as gas.

On 30-Mar-2004, Islander wrote:

There is another reason to use a tankless heater. If you have a long
run from your whole-house water heater, you will use up the capacity of
the pipe run before you get hot water at the tap. That amount of water
is wasted as well as the energy needed to heat it. If you don't have
the space, a tankless heater will provide instant hot water. If you
have the space a small conventional tank will do just as well.

Yes, I agree with all of that. I my case, I could locate the tank in the crawl
space directly under the two bathrooms that it serves.

One other consideration on tankless heaters: Since they have to fully heat the
cold water as it is flowing, they have to use much more power while they are on
than a conventional tank heater which has a reservoir of hot water. My heater
draws about 18 amps at 240 volts. A tankless water heater may draw 50 amps or
more at 240 volts. That means that you have to run a much heavier wire, and,
unless you have a high capacity service panel, it may use up a signifcant
portion of your total power capacity.

On 30-Mar-2004, "News" wrote:

Tankless take up far less space than a large cylinder, one its main
advantages. I have seen these used in commercial kitchen on faucets where
they are on for the best part of an hour. They can deliver 12 litres per
minute continuously and never run out. That is 720 litres per hour (190.2
US gallons per hour) running out of the tap. 190 gallons? that is quite a
size of storage cylinder you would need when a small white box on the wall
does it without taking up all that space.

Agreed. That is the primary advantage of tankless heaters.

What I disagree with is the assertion made by others that they save significant
money over a tank heater.

On 30-Mar-2004, "News" wrote:

Did you calculate whether more energy will be used
to re-heat from cold when only having the water on when you need it? A
quick recovery water heater may be very efficient as the larger power input
is used for a much shorter time. When you need the hot water it will be
ready quite quickly and no hanging around. I have seen electic water heater
cylinders on push timer switches set for say 2 hours. Then you can't leave
them on 24/7. If you need hot water, push the switch; 15 minutes maximum
later, you have a full cylinder of hot water.

Based on my measurements, I believe the savings will be very small, no more
than $4/month (probably more like $2/month). And you have the inconvenience of
having to push the button 15 minutes before you want hot water.

$48 a year extra for
each household per year is a lot of collective energy. Energy that is
running out and pollutes when used.

That's a valid point. But remember that replacing a few 100 watt light bulbs
with the new florescent replacements will probably save more energy than is
lost by an electric water heater. The point of all this is that the energy
loss from an idle water heater is pretty small.

On 30-Mar-2004, Mick wrote:

This assumes that the water in the heater is cooling down to ambient
every day.

I never made that assumption, but maybe someone else did.

The only point I made related to ambient temperature is that the energy loss is
directly proportional to the temperature differential between the water and the
ambient air temperature. All of my measurements were made with the water at a
stable temperature (within thermostat limits).

"Phil Sherrod" wrote in message
...

On 30-Mar-2004, "News" wrote:

Using high efficiency condensing water heaters will bring different
results.
The lower the return temperature the more efficient they are. If you
allow
a tank of water to cool and you re-heat it with a condensing water
heater
the re-heat is very efficient in fuel use.

I've never seen a water heater that was designed to condense water on the
outside. In fact, I can't understand how that could possibly happen since
the
shell of the water heater will be hotter than the surrounding air.

In the European market they are common. A condensing boiler is a separate
unit heating the water of a storage cylinder. Condensing boilers, or water
heaters, extract latent heat from the exhaust gasses. The lower the return
temperature the more efficient they are. A cylinder of hot water cooled
right down will have a lowish return temperature for a large part of the
re-heat. This is efficient. Just topping up the hot water when the odd
sink of water is drawn-off, as the cylinder stat has dropped a few degrees
is less efficient when using a condensing water heater, although still more
efficient than not using one.

I don't particularly like this company's products, but a decent
explanation.:

http://www.ravenheat.co.uk/productsCSIPRIMARY.htm

"Phil Sherrod" wrote in message
...

On 30-Mar-2004, "News" wrote:

Tankless take up far less space than a large cylinder, one its main
advantages. I have seen these used in commercial kitchen on faucets
where
they are on for the best part of an hour. They can deliver 12 litres
per
minute continuously and never run out. That is 720 litres per hour
(190.2
US gallons per hour) running out of the tap. 190 gallons? that is quite
a
size of storage cylinder you would need when a small white box on the
wall
does it without taking up all that space.

Agreed. That is the primary advantage of tankless heaters.

What I disagree with is the assertion made by others that they save
significant
money over a tank heater.

Condensing versions do. See:
http://www.ravenheat.co.uk/productsCSI85.htm

Once again I am not drawn to this company's products, but the explanation is
OK. This is a European "combi" a white box on the wall that supplies
infinitely continuous hot water and can heat the house too with no large
storage tanks or cylinders. The European's are far in advance of the USA in
this market. The USA has only recently adopted "tankless" water heaters
(instantaneous in the UK). These have bee around since the 1920-30s. The
USA is ahead in forced air systems, which I tend to like when design
correctly, but most in the UK hate because we tried to fit them and didn't
have a clue.

The power used is equal to the power required to replace the lost heat.

Same thing with heating houses. The heat needed to maintain temp is equal to
the heat lost.

Lowering the temp in the house (or the water heater) saves energy because
there is less temp differential between the house/ heater and the
surroundings.

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"Phil Sherrod" wrote in message
...
I recently installed an electric water heater to service a guest bedroom
located far from the central water heater. Since water will be drawn from
this
heater only when guests are visiting, I plan to leave it turned off to save
power.

But before shutting it down, I decided to take some measurements and
calculate
how much it costs to run an idle water heater.

The water heater is an electric GE Smar****er 40 gallon, “lowboy” (squat)
unit.
The plate on the unit says it draws 4500 watts, but my measurements show
that
it actually draws about 4320 watts (18 amps at 240 volts). The EPA
estimated
annual cost of operation is $401.

I used a Supco model DLAC recording clamp-on ammeter to record power
(amperage)
over a 3 day interval. During the same period, I used a Supco model DLT
recording thermometer to record the ambient air temperature in the crawl
space
where the water heater is located.

Here is a summary of my measurements:
Monitored interval: 3 days
Power draw when heating element is on: 4320 watts (18 amps at 240 volts)
Duty cycle when heater is running: 0.0161 (1.61%)
Average power used (heating watts times duty cycle): 69.55 watts
Temperature of hot water delivered: 114 degrees F.
Average temperature in crawl space during measurement period: 61 degrees F.
Temperature rise for water: 53 degrees F (114 - 61)

When the heater is on, it draws 4320 watts. However, the duty cycle
(proportion of time heating) is only 0.0161 (1.61%), so the average power
drawn
is 4320*0.0161=69.55 watts. (On average, the heating element is on 23
minutes/day.)

An average power usage of 69.55 watts over 24 hours works out to 1.669 KWH
(kilo-watt hours) per day.

The EPA average national power rate is 8 cents per KWH. So, using the EPA
power rate, the cost of keeping the idle water heater hot is 13.35 cents/day
or
$4.00/month or $48.73/year.

Here in Tennessee, we enjoy relatively cheap TVA power which costs 5.6
cents/KWH. Using that rate, the energy cost is 9.35 cents/day, $2.80/month
or
$34.13/year.

The EPA estimated annual cost of operation is $401 (assuming 8 cents/KWH).
So
the idle heat-loss cost of $48.73/year is about 12% of the total cost.

If you adapt these figures for another location, remember that the cost is
directly proportional to the temperature difference between the hot water
and
the surrounding room temperature, and you must adjust for your KWH power
cost.

Phil Sherrod
(phil.sherrod 'at' sandh.com)


Index: power, energy, cost, water heater, waterheater, KWH, energy use, cost
of
hot water, hot water cost, efficiency, power rate, electric water heater,

According to Phil Sherrod :

On 30-Mar-2004, "News" wrote:

Using high efficiency condensing water heaters will bring different results.
The lower the return temperature the more efficient they are. If you allow
a tank of water to cool and you re-heat it with a condensing water heater
the re-heat is very efficient in fuel use.

I've never seen a water heater that was designed to condense water on the
outside.

Gas "condensing water heaters" don't condense water vapor on the outside of the
heater.

They extract heat from the exhaust gasses to help heat up the tank.

They're called "condensing water heaters" because they're so good at it, much
of the water vapor in the flue gasses condenses out (which yields yet more
heat), and the flue vent doubles as a water drain. Usually plastic pipe.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to Phil Sherrod :

On 30-Mar-2004, (m Ransley) wrote:

Well Phil your calculations on tankless vs tank are not quite accurate.
You also forgot that Tanks unless flushed regularly loose efficiency
every year. I just had a tank replaced in a bldg it had over One Foot
of scale- crap in it after 17 yrs. Now that reduced efficiency apx 20
-25 %

17 years is a pretty long life for a water heater.

Scale reduces the volume of the tank, it does not reduce efficiency nor does it
increase power usage. The scale will be at the same temperature as the water,
so it will radiate heat at the same rate.

Not quite. Scale does not "circulate".

Thermal regulation will suffer, recovery time will suffer (possibly extremely),
more heat will be lost out of the tank due to overswings/higher delta-Ts,
insulative effects etc.

Scale will also shorten the lifetime of the elements - it sure did mine :-(.

For figures on savings you are wrong. I know people that say the same
as me 25- 50 % in costs of operation. saving 15 - 40 a month.
There are allot of people with tankless , they are how you should base
your opinions. Real world everyday use. Not guesstimates.

The whole point of my analysis was to avoid "guestimates". What guess are you
saying I made? Rather than guessing, I took accurate measurements that show the
total energy cost due to heat loss is about $4/month. If you are saving more
than that you are either (1) using less hot water or (2) using a cheaper source
of energy such as gas.

It's easy to contrive examples of where timers/demand heaters/etc will either
save you lots, save you insigificant amounts, or actually cost you more money.

There are LOTS of factors involved - duty cycles, temperature settings, usage
patterns, age, tank insulation quality, pipe insulation/size, tank size, energy
costs etc.

Whether any specific measure will be worth the effort depends a lot more on
your unique circumstances than the technology per-se.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to News :

"Phil Sherrod" wrote in message
...

What I disagree with is the assertion made by others that they save
significant
money over a tank heater.

Condensing versions do. See:
http://www.ravenheat.co.uk/productsCSI85.htm

You've switched to an apples-versus-oranges comparison.

There are condensing versions of tank type water heaters too.

What Phil has done has shown that given _equivalent_ technology
the MOST that a tankless heater can possibly save you is about
$4/month (assuming electric in both cases) - the cost of running
an electric tank type heater without any demand for a month. Since
the technologies are equivalent, the cost of heating water you
actually _use_ have be the same[1].

The choice between tankless and tank-type should normally be made
on other factors - ie: speed of delivery ("instant"), physical
size, location, etc.

Here's another factor to consider:

Unless you're using gas, tankless heaters require much larger ampacity
circuits, which can be a problem w.r.t. peak loading.

Note especially: we have a new provincial initiative to use timers on
high load items to shift them off-peak, coupled with electric meters which
give you lower rates for off-peak usage.

It occured to me that it might be a good idea to put our HWT
on a timer so that it only runs at _night_, and operate off stored
heat during the day.

In a regimen like that, it may cost _significantly_ less to run a
tank-type heater, because the tankless puts most of its power
consumption during peak (higher cost) times of day.

[1] There's one significant difference between tank-type and tankless
which _will_ be somewhat of a factor in efficiency given the same
heating technology - the length of the plumbing. Since tankless
are smaller and tend to be put much closer to the point-of-use,
energy consumption to heat up the outlet pipes will be _much_ less
with tankless. If your pipes are uninsulated, this could be quite a bit
of money.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On 1-Apr-2004, (Chris Lewis) wrote:

Not quite. Scale does not "circulate".

Thermal regulation will suffer, recovery time will suffer (possibly
extremely),
more heat will be lost out of the tank due to overswings/higher delta-Ts,
insulative effects etc.

I would be really surprised if that has more than a 10% effect on heat loss
through the tank shell.

It's easy to contrive examples of where timers/demand heaters/etc will either
save you lots, save you insigificant amounts, or actually cost you more
money.

There are LOTS of factors involved - duty cycles, temperature settings, usage
patterns, age, tank insulation quality, pipe insulation/size, tank size,
energy
costs etc.

Whether any specific measure will be worth the effort depends a lot more on
your unique circumstances than the technology per-se.

I agree that there are lots of factors that offer potential savings. But my
figures were made with no additional insulation and no timer or other potential
energy saving device. So I believe the heat loss cost I measured is an upper
limit on how much can be saved by adding insulation, timers or any other type
of device. A perfect tank would have 0 (zero) energy loss through the shell.
That tank will cost $4/month less to operate. You can't do better than that.

Another person posted some industry data showing that an electric tankless
heater saves $2.30/month. That's almost exactly what you would expect from the
measurements I made -- the tankless heater saves about half of the heat loss.

"Robert L. Bass" wrote in message
...
Exactly right. This is the same as 'setback' thermostats.
There *is* a savings, but it is difficult to calculate/predict
the results...

There's yet another element which offsets any savings in winter. Heat
loss
from the hot water tank is heat gained for the house. Obviously this
isn't
a good thing during the air conditioning season, but for most folks here
that's a lot shorter than the heating season.

Also very true. Like I said, the calculation is 'difficult' :-)

daestrom

According to Phil Sherrod :

On 1-Apr-2004, (Chris Lewis) wrote:

Not quite. Scale does not "circulate".

Thermal regulation will suffer, recovery time will suffer (possibly
extremely),
more heat will be lost out of the tank due to overswings/higher delta-Ts,
insulative effects etc.

I would be really surprised if that has more than a 10% effect on heat loss
through the tank shell.

Depends on how well buried the bottom element is. When I pulled several gallons
of scale "slush" out of mine, I'm sure that it'd made quite a difference.

Whether any specific measure will be worth the effort depends a lot more on
your unique circumstances than the technology per-se.

I agree that there are lots of factors that offer potential savings. But my
figures were made with no additional insulation and no timer or other potential
energy saving device. So I believe the heat loss cost I measured is an upper
limit on how much can be saved by adding insulation, timers or any other type
of device.

That's what I've been saying - your number is the highest you could possibly save
given equivalent technology.

The only factor you didn't factor in is the output pipe length. Which means that
a HWT will expend a bit more power heating up the water you use than the
exact same tankless system, because the outlet pipe on tankless is usually
MUCH shorter.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

http://www.kahealani.com/articles/re...al_energy.html

--
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