Why does tank water heater have 2times+ longer warranty than the
tankless water heater?
Will the tankless gas heaters be worth it in terms of save money
because off long term efficiency when I already have a solar water
On Tue, 23 Aug 2011 22:25:41 -0700 (PDT), rishi khanna
You just answered your question by being intelligent enough to ask
it. The tank has a longer warranty because it will last longer - and
your solar water heater will increase the efficiency of the tank
More to the point.
The tankless has a crazy amount of BTU capacity. It has to, because it
doesn't have much internal water capacity so it doesn't have much time
to heat incoming water before it leaves the unit on it's way to your
shower. You often need to supply a larger gas pipe to the unit - larger
than even your furnace needs.
Combine that with all sorts of electronic burner and combustion controls
and sensors, ignitors, computer controller, etc, and you've got a pile
of electronics and wires that have $$$ written all over them.
I don't know why anyone would want a friggin blast furnace in their home
just to heat water, when a conventional tank is so cheap and reliable.
Anyone who can't afford a few hundred bucks to buy one instead of paying
$300 a year to rent it is crazy.
The only real advantage to tankless is they take up less space.
They are slightly more energy efficient but not enough to ever pay for
FWIW, last spring I replaced my natural gas water heater with another tank model.
Tankless also offer an unlimited quantity of hot water. You can't
run out as you can with a tank type. That can be a factor for
I'd also check into what gas line capacity the tankless requires.
Whole house ones typically need a larger line run, which could
cost as much or more than the unit. However, in this case with
a solar pre-heater, the tankless could probably be smaller, so
a smaller gas line, ie the existing one, might suffice.
As for the warranty, the tankless has a 12 year warranty of
the heat exchanger, 5 years on parts, 1 on labor. The tank type
has a 12 year warranty on the tank and parts and 1 year on
labor. So the main difference is that the tank type has
coverage of parts other than the tank for years 6 through 12.
For actual longevity you might check Consumer Reports and
see what data they have.
i replaced my water heater last summer.
upgraded from a 50 gallon 75,000 BTU model to a 75 gallon 75,000 BTU
buy a higher BTU model for essentially endless hot water. hgher BTU
has shorter warranties but produces far more capacity..
theres lots of tankless downsides will post them tonight
1) Natural gas prices have been very low the past few years, and there's
no indication that's going to change in the next few years. Anything
you spend to reduce natural gas usage will have a proportionately small
return on investment given low gas prices.
2) Conventional hot-water tanks are pretty efficient from a
standing-loss standpoint, and what little heat they do radiate can be
reduced by a relatively cheap external insulation blanket. On the other
hand, the radiant heat loss from the tank is captured inside your house,
the advantage of which is proportional to your northern geographic
location (or as a function of altitude).
3) heat loss from a conventional tank flue is minimal if you have a
power-vented system (when the fan isin't turning, it's acting like a
baffle preventing air flow through the flue). I suppose a
power-operated shutter could be added to completely close the flue and
prevent heat loss when the burner is not on.
4) efficiency of heat transfer is inversely proportional to the heat
gradient. The burner of an on-demand heater needs to put out 10's of
thousands, even 100+ thousand BTU in order to heat incoming water during
the water's short residency time inside the heater for the water to
reach conventional hot-water temperature (typically 140 to 160 f). The
more north you are, the colder your incoming water supply will be, and
the more capacity (in BTU) the burners will need to be to bring the
water up to the desired temperature. Exhaust heat loss from these units
is significant while they are operating, and during their off-cycle as
they cool down they can't dump much heat energy into the water because
there isin't much water stored in the unit.
Conversely, the burner of a conventional water tank is capable of much
less BTU heating, and the heat from the burner has more time to come
into contact with the internal tank surface and transfer it's heat into
the water. The exhaust gas temperature in the flue of a conventional
heater can be so cool as to require a small electric blower to properly
exhaust the gas out the flue. This is an indication that most of the
combustion heat is being transfered into the water and not being
exhausted out the chimney.
In other words, perhaps 50% of the combustion heat of an on-demand
heater is actually being transfered to the incoming cold water and the
other 50% is being lost in the exhaust, while 80% of the combustion heat
is absorbed by the water in a conventional tank. The difference is that
an on-demand heater is on perhaps 30 to 90 minutes per day, while a
conventional tank might be on for 4 hours a day. But remember that when
a conventional tank is on, it's burners are using a much smaller amount
of gas compared to the on-demand heater.
5) the efficient use of an on-demand heater is challenged by short
hot-water usage events. In most houses, the hot water lines are
minimally insulated and thus the water in them quickly drops to room
temperature. Anyone turning on a hot-water tap in an upstairs bathroom
will notice it take 10 to 30 seconds to actually get hot water. It
doesn't matter what type of heater you have (assuming the heater is in
the basement). A short hot-water use event (say, washing your hands)
will end up dumping a lot of waste heat out the exhaust when an
on-demand heater is signalled to turn on and then soon after turned off
to heat the water for that short-use event.
6) because of the very high heating capability (BTU capacity) of
on-demand heaters, the extreme thermal cycling of their internal
components will age the unit much faster than a conventional water
heater, and they do or will require more maintainence and repair vs a
conventional water heater (they have control devices, electronics, etc,
that are not present in conventional heaters, and as we all know -
electronics and HVAC equipment really don't tend to co-exist very well
for the long term).
7) on-demand heaters have electrical or electronic controls that require
a source of AC current. Thus they will not function during a power
failure. Anyone living in a northern climate that is subject to
sporadic winter power failures will not appreciate the lack of hot water
during extended outages.
No home owner that has a working conventional gas water heater will ever
live long enough to recoup the savings from replacing his existing
working heater with an on-demand unit - and it's not a given that there
will actually be any measureable savings in gas use.
What has been observed is that the behavior of occupants change in terms
of how they use hot water when a conventional heater is replaced with an
on-demand heater, and that change usually results in less hot water use
(shorter showers, changes in shower heads, installation of low-flush
toilets, etc, insulating hot-water supply lines inside the house) so
it's not always clear where the savings come from and why.
Replacing an old / leaking conventional water heater is very easy for
most novice home owners / handymen, and at a cost of only a few hundred
dollars, the cost/reward ratio is still heavily in favor of replacing a
old conventional water heater with a new conventional unit.
You will get more bang-for-the-buck by
1) putting an insulating blanket around your existing or new
conventional water heater
2) insulating as much of the hot water supply lines inside your house as
you can reach
3) use a low-flow shower head
On-demand water heaters are basically a crock of shit designed to give
plumbing and HVAC companies a very lucrative new revenue stream.
Your post was one of the most comprehensive and accurate summaries I've ever
read on tankless heaters. Well done. While I wouldn't call them a crock, I would
agree that there are only a few scenarios where they make sense.
If anyone is interested in more detail, Dr. William Hoover, former engineer for
State Water Heater, wrote a paper on the topic called "What's the Big Deal About
Tankless Water Heaters?". You can find it all around the net, but here's one
Except for the part about low-flush toilets reducing hot water
usage... I've never flushed with hot water. The only people I know of
who might flush with hot water are the ultra-eccentric, ultra-rich,
and they really don't give a damn about saving energy.
Some of the measurements done on homes that have replaced conventional
hot-water heaters with on-demand (tankless) heaters have also measured
the changes in total water usage. The theory being that some water
savings can be attributed to placing on-demand heaters closer to sinks
and kitchens where you won't waste as much water waiting for hot water
to come out of the fawcet.
Those measurements of water savings can be confounded by other changes
performed at the same time, such as replacing conventional toilets with
low-flush versions (which of course has nothing to do with hot water
usage or the type of water heater).
One would think that those that did the study would have
kept other things constant. Seems mighty strange that
installing a tankless would drive people to replace toilets.
You have a link to that study?
True if it's a powered vent model. If it's not, a lot of the
heat loss is up the flue when the unit is off.
It's not just radiant, it's all the heat that is captured. And in
cases, it's captured not in the living space, but goes to waste
in an unheated basement or garage. And if the water heater
is in the living space, then while it helps in winter, it also
increases the cooling cost in summer.
The above is so totally wrong, it's laughable.. If that were true,
would be far less efficient that tank type. In fact, it's the other
"Gas tankless water heaters, which use high-powered burners
to quickly heat water as it runs through a heat exchanger,
were 22 percent more energy efficient on average than the
gas-fired storage-tank models in our tests. That translates
into a savings of around $70 to $80 per year, based on 2008
national energy costs."
Who should we believe? You or folks who have done
It's not clear to me that they are more complicated than
a direct vent high efficiency tank type.
Thanks for taking the time to reply to HG's items (4) & (5).....saved
me having to.
His post started out ok by veered of in the middle... :(
I was originally enamored with tankless but the high tankless unit
costs & the fact that my tank style water heaters last 20+ years kinda
made it a no brainer. In the mild SoCal climate the tank pilot keeps
the water hot..... I more or less have an "on demand" water heater
anyway, main burner only fires with usage and I never run out.
Tankless CAN make sense but its all about usage and objectives......
endless hot water to fill a large jacuzzi tub >>>>> good
endless hot water for a house full of teenagers >>>>> maybe not so
One of the major considerations when thinking about going to tankless is
energy supply. They will require a large electrical feed, or some type of
gas. If that is not present, then the cost of the run (particularly for
electric) can be substantial. Easy for new construction, not so easy for a
retrofit, unless you are lucky, and are close to a source.
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