Why is a tank water heater better than a tankless? There is another thread
on this subject but I got there late. Many poster favored a tank water
heater but there no explanations of why.
Background: We want to replace a tankless water heater because the pilot
light goes out daily and cannot get it fixed. We have conflicting
recommendations between another tankless and a water heater with a 40 gal.
The house is in Costa Rica. The water heater is in the garage which is
about 30 ft from the house. A propane tank feeds it. The water is hard and
sandy - all the shower heads and aerators were clogged when we took
occupancy. The house will be unoccupied for months at a time (will that
create a bacteria problem with a tank?). Their are only two of us but when
we have guests the demands on the system might be heavy. The house has
three very large bathtubs we jokingly refer to as mini-pools. Fuel and
electricity are much more expensive in CR.
In your case, you want LOW TECH because of the location (Costa Rica).
I would think that maybe electric heater might be more ergonomic, given
that the temperature of the incoming water would be relatively warm,
hence you don't need to mix it with overly hot water for, say, a shower.
Even washing your hands wouldn't really call for heated water in a
tropical location like that - yes?
An electric 40 gallon tank, set to 120F, would probably work pretty
good. Paint it black and locate it outside in the sun!
Go electric. Save the propane for the barbeque.
Many of the points below are based on the ergonomics and economics of a
middle-class household in US/Canada - not a transiently-used vacation
house in an equatorial / tropical country, and more importantly is based
on natural gas supplied by pipe (not propane stored on location in a
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.
On May 22, 7:47 am, email@example.com wrote:
One thing lacking here is actual cost. None of us
know what the costs of the alternatives are in CostaRica,
nor the cost of the fuels for those recommending going
electric versus propane, etc.
Another factor is the poster mentioned filling 3 large
tubs. I can tell you that a 50gal won't fill a good size
jacuzzi type tub to the desired temp. Here they put
in two tank types for houses that have such a tub.
So, depending on how large those tubs really are
and the probability they need to be filled at the same
time, etc would weigh into the decision.
As would servicing, ie is there a company that knows
tankless? Maybe not since they can't seem to keep a
pilot light going. Wonder how old the current tankless is?
Seems odd to have to chuck it if all that's wrong is the
pilot light issue.
What's the basis for draining it? I would tend to think
draining could be worse. It puts air into the tank and
air, plus wet and steel equals rust. Personally, I'd just
shut if off.
On Tue, 22 May 2012 08:50:41 -0700 (PDT), " firstname.lastname@example.org"
A lined tank (most today ARE) won't rust - and being empty they don't
get "skunky" Up here freezing is also an issue - which it is NOT in
As for cost - I don't know about Costa Rica, but here - and many other
places, 2 50 gallon tanks are less expensive than one tankless.
Tankless = technonlgy - which in many parts of the world translates
directly to trouble and expense if, not when, a problem arizes. The
KISS principal. Use the simplest device you can get away with - if
something does not exist, it cannot fail.
On Tue, 22 May 2012 08:50:41 -0700 (PDT), " email@example.com"
You're right I think that after a few days, ithe water would be too
cold for at least the legionairre and some other stuff to grow. Even
in CR, I think. Especially if he's in the mountains, with the
orchids and quetsals (the birds). . I was there in 1971. Didn't see
any orchids or quetzals, though. I visited a Quaker colony in the
mountains made up of consicentious objectors to war, in this case
WWI, who left the US during WWI when the US didn't recognize
conscientious objection. I'm sure they're still there and they still
speak English most of the time. It was iirc, cool compared to the
plateau, which is cool compared to the coastal areas. Most people
live on the plateau, although Blacks were not allowed to until maybe
the 1960's. They had to stay in the coastal areas. Of course I
don't know that the OP lives with the Quakers or even in the mountains
OTOH, I"ve only cut open one water heater, and it was some sort of
heavy but still flexible vinyl or something non-metal inside, maybe
3/16" thick. It was translucent, almost white. I don't think the
drip tube rusts either. The drain valve that came with it is
I cut open a tank once. the anodes were lose in the botom, 6 inches of
i cut it open where the leak was, and had a patch welded in. it got
used for collecting over flow water from a cistern to use for
irrigating plants. i was pretty pround of my invention for my mom i
was just out of high school.
i was back at that now vacant lot, its wierd, utility pole cut clear
of power lines, sidewalks till intact, slab where shed was......
the mobile home long gone, neighbor bought the land after it became a
i was 17 when mom lived there now i am 55 and mom long dead........
i woner if whats left of that tank is still at top of hill? but didnt
want to walk thru the beds of poision ivy to find out.... once was
Upon pressuring the water system in the house, check for leaks immedicately.
When done with leak testing, turn the water off to the water heater, drain
cleaning out all the dirt in the tank. If the water was chlorinated, then the
tank not like to built up bacteria. If the water drain is green, then you need
to put a gallon of beach in the tank, fill the tank and let it set for a few
hours. Make sure the heater section if off when ever you drain the tank. Turn
the water and force flushing of the junk in the bottom of the tank out. Remove
any screen at the house faucets and open the valves to clean out the water lines.
I had slim coming in off the street water and stopped that problem by installing
a whole house filter which includes the water heater. But the buildup in the
water heater required me to remove the drain valve to clean the tank out with a
garden hose attached going outside. With the bottom of the water heater
cleaned, the water heater worked better. Cleaning out the water heater is a one
or two year repeat job pending on the water and piping type.
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