<snipped to conserve bandwidth & cut down on quoted posted clutter>
I am glad you really want to understand, and I'm happy to oblige. Let's
work through this...
No, I'm *not* basing this totally on the energy guide (based on standard
U.S. Government tests) label, but I believe that is a good starting
point. A therm is a therm (approximately the heat energy of 100,000 BTU
http://en.wikipedia.org/wiki/Therm), and the sum quantity of therms
consumed in a hot water heating event relates to the total cost of
heating that water. A poorly designed heating device will consume more
therms to heat (and store, in the case of tank-type heaters) that water
than a well designed heating device.
The Bosch 2400 E uses 177 therms per year, according to the energy guide
that came with it. You can get more information on this model at:
After reviewing the Bosch efficiency factor specifications, you may want
to compare the estimated therm usage and/or efficiency factors of
tank-type heaters so that you can compare "apples to apples". Please
note that I am not advocating Bosch over any other brand; Bosch just
happens to be the brand that I purchased. There are several tankless
choices available in the marketplace, and one should shop wisely &
compare efficiencies, performance, features, warranty terms, options
No, I do not have a National Bureau of Standards lab here in my home to
measure this level of detail. But I do not need one either. The
efficiency factor of the Bosch 2400E is .80%, and the efficiency factor
of the Whirlpool 50 Gallon Flame Lock™ Natural Gas Water Heater is .58%.
(you can verify this by comparing heaters on the lowes.com website). An
efficiency factor of 1.0% would be a perfect, lossless conversion of all
BTU input to hot water output. Anything less than that represents some
loss of efficiency. The lower the number, the greater the loss. That
having been established, it all comes down to how much money one is
willing to spend in order to own a higher-efficiency water heater.
Again, please review my previous post. There is only one variable, the
$0.91/therm price of gas. Everything else is a fixed cost. Water inlet
temperature, thermostat settings, etc. would be the same if I ran both
tankless and tanker in a side-by-side comparison in real time, and one
would prove to be more efficient, and more economical to operate than
the other in the long run. It's all about the efficiency of the device,
and how much one is willing to spend to buy it.
I hope this helps.
Michael Thomas, Paragon Property Services,
Not sure if you caught the original thread (which I wrote) from which
firstname.lastname@example.org is quoting ... the question was why Bosch states in the
installation instructions that "The 2400 E is not approved or designed
for solar/preheat backup or high temperature booster use". I hadn't
planned on using it as such, but I was disappointed that a) the heater
cannot be used in a Solar hot water system e.g. be fed solar pre-heated
water, and b) I didn't learn this until after the purchase was made and
the box opened.
My thoughts were that it really *cannot* be used this way because
something will break, or else it is a corporate disclaimer to relieve
them of any liability if their heater is used in a solar heating system.
The latter I understand, but I can remember once upon a time installing
Paloma tankless heaters as part of a fresh-water solar hot water system.
The Paloma would get its water from a large storage tank of solar heated
water; if the water temperature was greater than the heater's thermostat
setting, the water would pass on through and the heater would remain off.
Do you know why this heater cannot be used in a solar preheat system?
Nit pick point well taken. I don't think I'd ever recommend electric,
other than to say it is an option and the product is available that way.
If you were *really* off the beaten path -- no natural gas lines nearby,
no propane available -- then electric might be the only option.
Especially if it were only for occasional use, as in a summer cabin in
the middle of nowhere. Most people I know who are heating *anything*
with electricity tend to spend more to heat it than they would have with
That said, tank-type electric water heaters get by with less standby
loss than gas units, since they have no flue to allow heat to escape.
Tankless have been in use in Europe and Asia for many years, where they are
generally considered to be low-end appliances. They're used because they're
easier to install in apartments than a central tank, and because they have
little or no footprint in space-limited apartments. (many apartments may
only be 600-700 sq ft, so even the tank's footprint is significant.) In Asia
where I've lived, one of the marks of a higher-end apartment is that it uses
tanks instead of tankless.
I've used them in several apartments and always found them somewhat finicky
and less satisfactory than tanked units.
Therefore, when we upgraded our present house we installed a second hot
water tank that services only the master bedroom, with the other tank
serving only the kitchen and other bathrooms. The MBR has about 650 sq ft,
and we put the hot water tank in a small closet in the adjacent guest
bedroom. We get almost instant hot water, the temperature and water volume
never vary, and the unit is out of sight.
After experiencing tankless units of several different types, I wouldn't
consider one for my home. Regards --
ONE MOMENT PLEASE!!! The owner's manual for my Bosch 2400E states that
"The 2400 E is not approved or designed for solar/preheat backup or high
temperature booster use". Why this is so, I know not -- and no
explanation is given in the manual. This is too bad because if I decide
to install solar collectors at a later date, I won't be able to feed
solar pre-heated water to the Bosch unit I just shelled out $998 for.
Also, I did not know about this until after buying the unit & reading
Once upon a time, I worked for a company doing solar hot water system
installations. At the time, a popular setup was to run stored solar
heated water through a Paloma tankless. If the inlet temperature was
greater than the Paloma's thermostat setting, the heater remained off.
Same thing if a swimming pool was involved.
Perhaps someone will comment here as to why the Bosch 2400E is not
approved or designed to be fed pre-heated water.
[also, I'm going to start a new thread on a technical question I have
about my particular heater -- look for "Bosch 2400 E" in the subject line]
If your water heater location only gets a little bit below freezing,
some makes of tankless heater have freeze protection built in. (It's a
heat exchanger, after all -- just run the heater a bit when ambient
temperatures drop below freezing.)
My Takagi also has a remote sensor available for the ambient temperature
circuit -- that's used when the heater is installed indoors, but with a
short flue to sub-freezing weather, so that the freeze protection will
keep the exchanger warm despite subzero backflow in the flue.
Completely draining the heater is typically quick and easy for a
tankless setup, they're normally plumbed with draining and backflushing
in mind. For a summer cabin, I'd say completely draining the plumbing
off-season would be a good idea no matter what type of water heater you
have. A friend's summer home even has an air-compressor port on the
highest line in the house, so you can open one fixture at a time to blow
out any water trapped in low spots.
email@example.com is Joshua Putnam
Robert Allison wrote:
> I don't sell them. I am a general contractor. They are just one of
> new popular items since people have become aware of them and how much
> energy use they can save. I haven't seen any of my customers complain
> about them. The last one that I installed cost $845, the install was
> 300 dollars and she got a 200 dollar rebate from the city.
> I have one, with two baths, a kitchen, dishwasher and wife and 2 kids.
> Haven't run out of hot water since I put it in. I got a Rinnai and it
> has been performing for 5 years now. I cannot compare energy savings
> head to head, because I went from an electric water heater, to a gas
> tankless, but my electric bill went down by $45 dollars a month (It
> averages about 250-300 per month).
> You seem to be trying to convince people that they are spawn from hell
> and I am just trying to present the honest facts. I think you are the
> one who is biased. It makes no difference to me what the homeowner
> wants to install, I make money on the whole job, not just one part.
Greetings, Mr. Robert Allison General Contractor, and welcome to this
very interesting discussion about tank-type vs. tankless water heaters!
I'm moving your valuable contribution to an appropriately re-named
thread so that we can stay organized -- I hope you will follow it here.
The thread started out as rinnai vs. rheem tankless, but soon morphed
into a general tank-type vs. tankless water heater discussion. Then I
joined in, and renamed the thread as such. I won't ramble on about stuff
that I already covered. Hopefully you have picked up enough information
from the various posts in this thread.
Now then. You say that you have installed tankless heaters for your
clients, and they haven't complained about them. Plus, you own one
yourself. This is a good thing IMHO for this discussion group. I
recently installed a Bosch 2400E (natural gas) in my home a few weeks
ago, and have been mostly satisfied with the unit, as well as my own
installation. A dozen or more copper sweat-soldered joints and no leaks.
Anyway, I have a question that I hope you or someone else reading this
post can answer.
After installing my tankless heater, I discovered one thing the old
storage tank hot water heater was very good at: trickling a flow of hot
water into a sink. Tankless water heaters have trouble here, because
they depend upon a pressure drop to fire the heater. If that drop is
less than what the tankless sensor can detect (because so little hot
water is being demanded at any given moment), then no hot water. Or as I
have observed with my new tankless heater, after running full hot water
for a minute or so, and then turning down the hot mix down to below the
sensor threshold, the tap flows a combination of
hot-then-cold-then-hot-again kind of "checkerboard" hot water into the
sink. I know what's going on -- the tankless pressure or flow sensor is
reacting to my hot water demand and turning the burner on, off, and back
on again as I manipulate the sink hot and cold valves. So, the hot water
plumbing is delivering hot, then cold, then hot again water. That all
makes sense to me, but I want to improve on that if I can.
I know that tankless water heaters depend upon an inlet-outlet pressure
differential to trigger the burner (natural gas, in my case). I recall
reading that my Bosch 2400E has a pressure or flow sensor which detects
a 0.8 PSI water inlet/outlet differential. I have performance-tested my
home plumbing for any hot water "crossovers", and found none.
SO HERE COMES THE $64 QUESTION: Is there a way to adjust this pressure
sensor if it is adjustable, or to swap it out for a sensor of a
different, lower pressure differential value if it isn't adjustable; or,
is there any way to adjust the pressure parameters in the Bosch's
on-board computer/processor to lower the burner turn-on threshold so
that I can trickle some instantaneous hot water?
I hope all of that makes sense ... if not, someone please hammer on me
and I'll re-write my rather long-winded question into a shorter-winded
and more concise question if I can.
I have no idea. That would be a question for the Bosch
company or a company that repairs Bosch equipment. I know
that there are different thresholds on different units, but I
have never attempted to adjust the threshold (nor have I had a
need to do so).
I am sure that it is possible, but I can't answer your questions.
with input water at 70 degrees you have it easy. our incoming water in
late winter has been 39 degrees.......
its like taking water out of the fridge.
as to adjusting a tankless for low flow.
its probably impossible for a trickle.
combo of detection ability and the possiblity of overheating water and
possible tankless damage.....
imagine a trickle flow going out of tankless, the tankless burner
might turn that trickle flow into steam. imagine steam boiling
splashing out of a faucet while your washing your hands.
Yikes! No doubt! 39 is some cold water. Perhaps you could store this 39
degree water in large insulated tanks & use it for cooling during the
summer months LOL!
BTW, tankless mfrs. such as Bosch and Takagi (and I'm sure many others
but I don't know it for a fact) make higher-output tankless models to
deal with extra-cold inlet water. Check their website documentation on
this feature for more information.
this can be done, but...
Right you are: at the point of trickling use -- at the kitchen sink,
mainly -- the sink outlet temperature tends to be either hot or cold;
very tricky to maintain "warm" at low tankless flow rates. I believe
this to be the Achilles' Heel of tankless design. It has proven
especially frustrating to maintain a low flow of warm water because just
when I think I have the mixture right, the heater shuts down (without my
knowledge, as it makes virtually *no* sound when it is running & heating
water), but I don't realize that it has shut down until its charge of
cold water eventually makes it to the sink. The natural instinct at that
moment is for me to compensate by increasing the sink's hot water tap
sufficient to exceed the threshold of the heater's pressure drop sensor
(causing the burner to commence heating), but as the water in the
tankless' heat exchanger is at that point thoroughly cold, there will be
a delay until the hot water appears -- despite my compensating, the
water grows colder until the heated charge makes its way through the
plumbing. Then it becomes too hot, and so I back off on the hot water,
causing the pressure drop sensor to signal the burner to shut off, and
the cycle repeats in a slow motion too hot/too cold loop. I have found a
"magic spot" position for the sink tap (I have a Moen Extensa type
single-stalk valve) to entice the warm water to come out, but that spot
is very flow dependent.
I am pondering the idea of installing the tiniest possible electric
tank-type heater, say a 5-gallon unit or less (if less than that is
made), directly under the sink to help compensate both for the
temperature time lag caused by the tankless heater, as well as perhaps
buffering the too hot/too cold temperature loop. I realize I would be
compromising the energy savings brought about by the tankless heater,
but it may be a possible solution.
I don't think this is a possibility. I know that the heater has an
outlet temperature sensor, and that a modulating valve can adjust the
heat exchanger BTU input. At any rate, the heater has a 12-year warranty.
I don't think any well-known manufacturer would allow their tankless
heater to turn into a steam cleaner...
As another poster pointed out, most recently manufactured "whole house"
tankless heaters are made with modulated heat output, so that the
thermostat's setting takes priority if at all possible.
[to the "top posting" and "bottom posting" advocates, I have
deliberately "middle posted" here because it seemed like the logical
thing to do, more like a conversation -- maxodyne.]
tankless manufacturers recommend 2 tankless in series, for super cold
input temperatures. modulating gas valves are a improvement, but may
not have and doont appear to have the range of trickle to full on. if
at least one of them did no doubt it would be advertised.
so you went tankless but are now thinking of installing a small
electric tank under your sink? electric water heating costs way more
than gas, still has standby losses, a new something to
putting aside the endless hot water, was the tankless worth it?
I believe that it was in my case. I needed to do something because the
tanker was leaking. I realized that there were choices, and I made one.
No, I'm not going to install an electric pre-heater, I was only
*pondering*, both for myself and to see what others might say.
The difficult tankless trickling kind of bothers me ... but running out
of tanker hot water, or having to plan my shower around others' showers,
or the dishwasher, or the washing machine etc. also kinda bothered me.
As I learned to live with the tanker's idiosyncracies, so shall I learn
to live with those of the tankless. But really, other than high initial
cost and very low hot water flow issues, there are no other drawbacks to
my tankless conversion IMHO.
As I mentioned in a previous post, my two children are still living at
home while going to college -- but not for much longer. In a couple or
so years, it will just be me. That tankless heater will be spending a
lot more time in the off mode than it currently is. I believe I will
begin to *really* save on the gas bill then, especially if the price of
gas goes up -- and I have no doubt that it will.
I really do not like wasting things either, and the tankless is more
efficient than the tanker, period. It uses less energy and takes up less
well honestly I might add a tankless here, when we get a new furnace.
currently we have a 75K BTU tank type heater, its over 7 years old.
now when a new furnace goes in the furnace will get moved, its in the
middle of our basement and kinda in the way. all the gas lines will be
changed. our furnace was installed in 1965 and wastes lots of
so i would like to add a tankless as a preheater, upgrade to a 75
gallon 40K BTU tank, this will get me a 12 year warranty tank, and
what should be endless hot water. with no trickle or other troubles.
other than initial cost the tankless wouldnt cost anything to operate
since either way the water must be heated.... frankly i dont mind the
standby losses, in the winter it helps keep my basement warm. its also
does your tankless need power line voltage to operate? a power failure
at the wrong time could leave you with a cold shower:(
This sounds like an excellent plan -- I had considered similar before
the tanker began leaking. I figured as old as it was, it was gonna go
someday; had my tankless already been installed upstream, it would have
done the preheat (and eliminated that doggone tankless very low flow
issue) although standby losses on the tanker would still be an issue
(see next paragraph). Then, when the tanker went, I would be left with
an already installed tankless.
I on the other hand *do* mind the standby loss. Not so much in the
winter, as the tanker was (and the tankless is) in the laundry room
which is adjacent to the kitchen, and some heat is added. Note that
there remains a true "total standby loss" at all times of heat radiating
from the storage tank up through the flue. Not sure how to calculate
that, though. Anyway, I live in southern California where it gets hot
enough for several months during the summer that I run my central air
conditioner -- which is also cooling the tanker's standby losses. Again,
not sure how to calculate the cost of that.
I had considered this issue when comparing tankless heaters. Bosch does
make a model that generates its own power from the water flow --
probably some kind of impeller wheel generator, although I don't know
for certain -- but the model so equipped was not available in the BTU
capacity that I wanted. The self-generating model is the Aquastar 1600
if you are interested. I noticed that other mfrs make tankless heaters
that use batteries to ignite the burner & maintain their settings. The
2400E that I installed *could* be plugged into a UPS (Uninterruptible
Power Supply) that are commonly used to provide short-duration power to
computers during a power outage. The standy current for the 2400E is 40
milliamps; however, it also uses a fan to force positive flue
ventilation which needs less than or equal to 2.5 amps (these amperage
figures are from the installation manual). The UPS would probably
provide backup power for a good long while though, so long as hot water
was used judiciously.
While I was in the installation manual, I found the heater specs &
modulation range in BTU: maximum input 175K, maximum output 143K,
minimum output 31K, recovery efficiency 86.5%. Temperature stability is
plus or minus 2 degrees Fahrenheit, although you can obviously toss that
figure out the window at very low flows.
I have experienced power outages with the old tanker, and it was rather
an unexpected joy to take a hot shower with candles and kerosene lamps
to light the way. Much more enjoyable than a "cold tankless" shower
would be for sure!!
One of the many good resources on the web for energy-conserving
appliances is realgoods.com. I noticed that they claim "Bosch sells more
than 1.5 million tankless water heaters each year", so there may reasons
why people are buying them. That's just the sales of Bosch; there are
many other brands...
well you could add a regular say 40 gallon tank, and just trurn it off
during the cooling season. in pittsburgh the AC season is very short,
so standby is trivial.
some tanks are forced vent with fan running only when burner is
active. this would elminate the loss up the flue, which ultimately
exhausts heated home air 24/7 forver.
that loss of heated air likely exceeds normal standby losses.
You are partly right -- the Bosch 2400E has vent assist during burn &
positive forced vent for 60 seconds after burner shutdown to clear flue
of any residual combustible gasses. However, this is a non-heat loss
issue to living space as the heater has a 3-inch air intake vent flange
which I have plumbed through ceiling to roof intake vent. So no heat
loss there either. Not sure if other tankless heaters do this though.
I use the small 170000btu battery ignition Bosch with incomming of
down to 35 at the coldest point, my main incomming is in a hill that
has lost dirt over the years so its getting shallower, I have never
needed to set it more than 75%-80% to get a hot shower. For tanks your
standby loss is up the chimney through the center of the tank which is
uninsulated, that is why tank have an Energy Factor of around 55-65,
this is a much more realistic rating than AFUE. So i dought you
benefit from heat loss into the home, rather you net loose through
chimney draw and heat comming out the center of the tank. Tankless
Energy Factor are near AFUE, mine is about 80. What I did was leave in
the old tank as a tempering tank, then the water goes to the tankless.
Some makes turn on at less a flow than mine but that is an issue, you
basicly turn it on or only down a bit, but why overheat water, set it
hot enough to take a hot water only shower, you will save $. The
biggest problem I would guess installers make is not testing supply
with a manometer with all competing gas apliances on so be sure 100%
tankless output can be reached on the coldest days, and not
calculating low winter mains supply on the coldest days. For single
use the 117000 btu is fine but if someone else needs HW while you
shower the 190,000 btu unit is needed. Two tankless together are for
apartment buildings, not regular homes.
Modern boilers have auto vent stack valves that close when the boiler
shuts off to help maintain the heat in the boiler, I have heard this
adds 2-5% in efficency, I do not believe water heater tanks use this.
This contributes to the low Energy Factor rating of tank water
heaters, which is a more realistic value of efficency. Tankless dont
have this issue. Europeans-NG importers have known this for years,
thats why most of Europe uses tankless, Research Energy Factor of Tank
water heaters and compare it to Tankless
Thank you, this is what I have been saying all along, that tankless are
more efficient than tank-type, period. But there are some in this thread
who will argue you every different which kind of way to justify their
stubborn decision to own tank-type heaters, sometimes even claiming that
tank-types are cheaper. I believe I will give up now on trying to
convince folks that tankless are cheaper in the long run.
Regarding your comment on most of Europe using tankless: from 1969 to
1970, I lived in a small town in Belgium. When I first got there, I
wondered what the white box was near the bathtub. As soon as I turned on
the hot water, I found out. It made a lot of noise, so I went to
investigate and determined it was an instaneous hot water heater. In
those days, they were quite primitive compared to today's instantaneous
heaters. This one had a pilot for ignition, so it did not use any
electricty. After this, I began to notice that -- as you pointed out --
almost all European homes had, and still have, tankless heaters. Must be
a reason, eh? $$$$
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