Basically they save floor space and deliver an endless supply of hot
water...until they break.
Will they save you money? No!
Our son put a Bosch tankless heater in his home when they built it
almost 5 years ago. He is rural and uses propane and he is more than
convinced it is saving him a lot energy money.
But it ain't all good. In the past few months the holding tank sprung
a leak (not the tankless heaters fault), then a valve problem. About
two weeks ago it started leaking a little and he called a plumber
friend. The plumber told him on the phone it was likely an O-Ring
that he could fix himself but Scott was too busy to work on it and
told the plumber to come on out. Good thing because the heat
exchanger had sprung and serious leak and they had to replace the
entire heater. Fortunately he was about two months inside of his
warrant period and he got a new heater with a new warranty for cost of
labor. He says he would probably put one in again but he isn't quite
as sold on them.
Another thing we noticed when we visited was noise. He has it in a
long closet next to the guest bedroom and when that thing comes on it
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.
Tankless units have 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
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 a conventional gas
water heater instead of paying $200 - $300 a year to rent it is crazy.
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.
It was cut and pasted from another ng.
You didn't really think HG wrote this did you?
1) The cost numbers are pretty high
2) There was also a recent price drop of nearly 50% for tankless heaters.
3) Regular chimney vented tankless are no different to install than tank
heaters and are an easy DIY
2) If you're going from a chimney vented tank to a condensing tankless,
them you have the added cost of the intake and exhaust pipes, which should
be of equal length.
Also doable as a DIY
Notice also that the tankless, albeit not showing a measured efficiency near
it's rating, still rated higher than a tank heater.
I had a 40 gallon chimney vented tank heater feeding the whole house.
I added a condensing type equivalent tankless, for $500. feeds directly the
kitchen and basement laundry room, and bath and shower that are under the
Then tank heater feeds the 1st floor WC & sink and the upstairs bathroom
with tub & shower. which are vertically above it.
The tankless also feeds the water heater when demand from the heater has
gone past 20 gallons. No more running out of hot water upstairs....
Total Natgas consumption is down.
When the hot water tank goes, it will be replaced with a tankless too.
On Sat, 5 May 2012 20:04:29 -0500, "Attila.Iskander"
Using a 5 gallon "point of use" tank will give you ALL of the upside,
without the downside. Use the big tank for large demands, and the POU
for instant hot water. Main tank serves taps close to the tank and
provides large capacity to those served by POU.
On 5/5/2012 9:49 PM, email@example.com wrote:
Exactly. My washer is the farthest from the water heater, so there sits
an electric 10 gal unit ontop the washer. Fed by the hot line from the
main tank. Also there is a utility sink between the washer and dryer
fed by that ten gal unit. No waiting.
remove the "not" from my address to email
...and aggravation. Our new house has the water heater in the garage, at the
far corner of the house from the master bath, about 100' of pipe. It takes
seemingly forever in the morning for the shower to get hot.
In this house, the water heater is in the attic. The pipes to the kitchen go
down two floors, under the slab, and over to the kitchen. The water to the
dishwasher never gets hot.
At least the new house has an unfinished basement so a small point-of-use
water heater would be trivial to install. Definitely a possibility.
i was not interested in energy savings. I was interested in having
appropriate hot water in the washer and dishwasher. My gas bill never
reaches the minimum with a conventional 40 gallon tank and the stove
running on gas. The 1500 watts on the point of use tank is a moot point
because it is fed with water that is 5 or 10 degrees hotter than it's
set point. It rarely pulls any current.
remove the "not" from my address to email
But it's a reservoir-type of water-heater, correct? There
must be some energy use to keep the reservoir hot. I'm just
wondering if it's an overall savings, or close enough to
make me want to install here. If it turns out to be an
energy loss by a substantial amount, I might give it a pass.
On Sun, 06 May 2012 19:47:42 -0700, "Malcom \"Mal\" Reynolds"
Which, if you READ my post, it has no need of doing with a 40
(canadian) or 50 (US) gallon gas water heater backing it up. And the
50 gallon water heater standby losses are VERY negligible (about 50
therms per year installed in heated envelope of house) and are only an
issue at all for the roughly 4-5 months where it is warm enough that a
little heat added to the house is not welcome.
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