Does it really need stainless to the weather cap? I've had the same
flue on my tank type for 10 years since I moved in, and I'm pretty sure
it has been there much much longer than that. I could see a couple of
sections near the heater needing to be SS, & maybe I'm fussing about
nothing, the whole thing can't be much more than 10'. If it is so hot
on the stack that stainless is required, how close can it come to wood?
Will it be necessary to sawzall the ceiling and roof and put in metal?
If you have the installation instructions, you should not take it upon
yourself to re-engineer and re-design the installation just because you
don't understand all the design and engineering the factory put into it.
Proper design not only ensures satisfactory operation, but a reasonable
expectancy of long life and safe operation under normal and many abnormal
Follow the instructions and feel confident that it is done properly, will
work and last a long time, will not cause a fire or other problem, and will
not be a problem in a sale or other unexpected situation.
In general, stainless flues are not specified because of intense heat but to
prevent corrosion (rust-out). Each type of appliance and flue design has
certain specified clearances from wood or other combustibles to prevent
fire. If you have never ever seen a malfunctioning appliance over-firing
with a red hot flue thru the ceiling you may not fully appreciate the value
of a proper installation.
You asked about common sense in the situation. To me, common sense says to
follow the manufacturer's instructions. Five years from now, it will be a
bigger PITA to change the piping than to spend a few dollars now to do it
Common sense question WHY A TANKLESS????
They arent as good as a tank type having troubles with low flow no heat
high flow not hot enough, require larger gas line since their BTU is so
Besides during the heating season they energy the lose goes to heat
your home, that cuts energy savings by half around here.
finally they cost so much their payback period based on high efficency
exceeds the probable life of the tankless:(
so why are you making this expensive downgrade?
I would never go back from my properly sized Takagi gas unit (a max
235,000 BTU Mobius TM1 ) to a conventional tank type heater - nor
would my spouse let me.
The Takagi does exactly what we require.
When the house is empty, it just sits there, burning no gas at all.
If we are entertaining a house full of guests, it fires up on demand
and produces water at the temperature we want, in whatever quantity is
required - up to sufficient quantity to run a dishwasher , a clothes
washer, two showers, and provide water at the taps at the same time -
continuously for hours if required.
That's what we paid for.
And that's what we got.
We love it.
We also use tankless units extensively in rehab rental units - in our
case the increase in rental square footage resulting from the reduced
utility area footprint alters the "typical" payback calculations.
Paragon Hone Inspection, LLC
Most gas/propane fired tankless unit produce a HOT exhaust, and the WH
manufactures generally spec a UL listed cat III system - in the US
the choices I'm aware of are FasNSeal, Z-VentIII and Saf-T Vent - and
than it be installed "per manufacturer's instructions".
So you need to read *both* manufacturer's instructions, and then follow
For example the SS pipe specified for most tankless heaters is 2x wall
material, but still requires clearance to combustibles - FasNSeal for
instance requires 12" at the top, 8" to the side and 4" below a
horizontal run, and even then if it's other than a one or two unit
residence they specified a non-combustible enclosure.
In addition, these are engineered systems, so to maintain their
ratings each manufacturer is going to require that in so fas as
possilbe the entire system be composed of exclusively of their
components, and installed per their instructions, and ther only
exceptons they allow will be BFPs, wall caps, ect. specified by the
appliance manufactuer for use with cat III systems.
Other frequent problems I encounter in tankless retrofits:
- Insufficient combustion air: many tankless WHs are rated at 180,000
input BTU or above, which is more that most GFAFs, often no provision
is made to insure increased combustion airflow, resulting in a
negatively pressurized utility area (sometimes, an entire house) which
can result in back drafting of exhaust vents, etc.
- Insufficient gas supply: most take type units are fed by a .50"
line for at least part of the run, most tankless units REQUIRE a .75"
line all the way to the unit or they may not operate at full output. In
addition, depending on the run and other appliances attached, it may be
necessary to replumb the entire supply system, upgrade the gas meter,
This is not a just a "theoretical" problem, either. The *majority*
of service calls by Takagi for "defective" newly installed units
are the result of an undersized gas supplies, and in the last year I've
had to upgrade the newly installed gas meter on a building feeding a
Takagi tankless WH and a GFAF because the gas company disregarded our
specifications and installed a "standard" sized meter undersized for
the actual requirement, and on another project the plumbers had to tear
out and ungraded the entire length of newly installed gas supply line
because they had failed to size it based on the fact that it would be
feeding multiple tankless heaters.
- No backflow preventer in freezing climates - many tankless units
require a backflow preventer to reduce the risks of freezing the coils.
Sone units (for example some Takagis) have a built-in in coil heater,
but this is NOT designed or intened to take the place of a BFP.
So you really have to plan such installations correctly, and then check
cafrefully to make sure they are in fact installed as planned.
Paragon Hone Inspection, LLC
nearly all reports from tankless owners are negative, open a kitchen
faucet a little no hot water ever.....
it appears some peoples usage patterns fit a tankless.
in so far as rental units, the added costs for gas lines etc must wipe
out any energy savings for many years.
beyond which during the winter a standard hot water tanks heat loss
helps heat your home........
of course during a power failure the ONLY showers a tankless owner gets
is a cold one, unless it has a battery backup......
With the current terrorism issues a tank type heater is a excellent
source of emergency drinking water
I found the opposite when I was looking at going tankless, almost
everyone who had a properly-sized heater raved about it. The complaints
I've seen are mostly people whose heaters are so small they shouldn't
expect better than lukewarm water anyway.
I've certainly enjoyed the switch -- plenty of hot water, fast. Enough
that I can run the dishwasher and the laundry while I'm taking a shower
and not worry about exceeding the capacity of the heater. I don't think
I'd ever go back to a tank, unless I had enough spare room for a *huge*
firstname.lastname@example.org is Joshua Putnam
happy it worked for you.......
in cold climates a tankless may have trouble heating the water enough
when incoming water temp is low....
honestly it doesnt matter what heater anyone buys, doesnt effect me in
just feel bad for folks trying to do something good, then finding out
it was poor investment...... provided worse service than original
or their teenagers now freed of running out of hot water remain in
i should look for a old discussion of this, and all the problems people
The upshot of the whole issue (the thread is filled with quite a bit
of scientific nonsense[+]) is that _if_ a properly sized tank-type
water heater will do the job satisfactorily in _your_ home,
the break-even cost point for a tankless (if it even exists with
your situation) is so far out in the future, it can be more-or-less
But there are situations where tankless truly are superior. Those
are where the hot water line length from where you have to put a tank
to the fixtures is excessively long, and you lose a lot of heat (and
have unacceptable to _you_ wait times) waiting for the hot water to
arrive. That's where point-of-use and/or tankless stand out.
Another situation is where the current HWT is undersized, and you
don't have room for a larger one and/or the appropriately sized
tankless could usefully supplement it at a reasonable install
Most houses these days are set up so that the HWT tank is placed
more or less a minimum distance from the fixtures. Eg: bathrooms
and kitchens clustered around where the HWT is. Eg: stacked bathrooms
in multi-floor homes etc. Costs less in terms of plumbing, particularly
[I have a large two story. The plumbing is arranged such that
all hot water requirements is along a 20' horizontal line. All of
the plumbing is contained in about 10% of the house's overall
footprint. One corner, and about halfway down one side. That's
it. Except for the cold feed from the well, which is at the opposite
corner. No hot water flow path is more than about 20' long.]
But if you have a strange house - eg: sprawling single story homes with
bathrooms/kitchen[s] strewn randomly around, sometimes one (or even
more) tankless units really help.
A friend of mine had one such strange house. The hot water line to
one of the bathrooms was well over 100' long. Seemed to take forever
for the hot water to arrive. That would have been perfect for
a tankless. Instead, he happened to have a small 3 gallon tank-type
120V water heater sitting idle. So we installed it in the bathroom,
fed from the hot water side of the main HWT. Instant hot water, and
if you were taking a shower and were going to exhaust the teensy
3 gal tank, by the time it started to matter, the line from the main
HWT to the bathroom HWT had warmed up and you were getting hot water
heated by the main.
Efficiency wise, it wasn't too great, because you ended up losing
a _lot_ of heat in the 100' line. But the 3gal HWT was free. And
at the time tankless wasn't really available. These days I'd
install a tankless instead.
Or another example: a kitchen doesn't really use a lot of hot water
compared to a bathroom or clothes washer. If the kitchen is a long
way away from the rest of the plumbing, a small tankless really
As someone previously opined, there is NO UNIVERSAL solution
for ideal water heating. It depends on your circumstances
[+] For example, the comment about "efficiency loss of 28% while
tank is idle". That's 28% of almost nothing (because modern
tanks are so well insulated). In operation, the efficiency is
the same. You're going to spend hundreds (if not a thousand or
more) for something that at most saves about the same amount of
power as turning off a 60W lightbulb? Even environmentally, that
makes no sense. If it's the only reason you're doing it, it's
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
In houses without basements, like 99.999% of all homes here in Southeast
Texas, the water heater goes OUTSIDE the conditioned space. This is a
CODE requirement. It is NO help in heating the house in the winter.
There is NO universal solution for domestic hot water.
1. Available energy sources
2. Hot water demand in the house
3. Code requirements for gas powered appliances, electric too
4. Cost of equipment and installation
5. Temperature of incoming water
6. Quality of incoming water
All these factors and more affect the decision on which system to purchase.
In some cases, an electric tankless will make the most sense for
households that can drain an 80 gallon normal tank.
In some cases, a natural gas or propane tankless will make the most
sense, again for households that use ALOT of hot water.
In other cases, a conventional electric, natural gas or propane tank
will solve the problem
In other cases, solar panels will supplement the existing tank
In other cases, geothermal heat pump will supplement or replace the
conventional tank (still retain conventional tank as a backup, but turn
Bottom Line, there is NO UNIVERSAL solution for domestic hot water.
An excellent debate, and now I'm if anything, more undecided. My
original thought was this: We are on propane, our only cold weather is
normally November through March, and there are many 70 degree + days
even then. To fill my tank at the end of summer last was over $300 it
had been topped off in April. That means that the clothes dryer and hot
water tank used all that, there is a gas range, but that was used
minimally as we ate a lot of wraps and things like that through the
summer. The tank (30 gal) is less than 4 years old and the house was
re-plumbed for propane at the same time (3/4 black iron pipe). I feel I
can do the install for < $1200 for a 240 sized unit even with the
stainless exhaust. the closet is very centrally located, new insulated
runs are planned (for later) to the bathroom and kitchen/ laundry room.
I feel if it would save $10 a month it wouldn't take long to recover
the original investment especially with a $300 tax credit. That would
take 7.5 years. Optimally it would pay back faster. Normally there are
just 2 people in the house, we are retired, so we are there all day, I
realize every hand washing is going to fire the tank, that in itself
may be the deal killer.
check tankless warranty, typically not 10 years and payback often takes
that long... make certain your existing propane tank lines and
regulator can supply the tankless big consumption....
you will save the regular tanks standby losses, what about adding a
water heater blanket to reduce standby losses even more?
It sounds like your current tank is inside your heated space? in the
winter the stanby is no loss.......
so you figure payback at 7.5 years?
Somehow I doubt that, The installer made a big deal out of making the
closet air tight and installing an air intake into the attic, claiming
it would never pass inspection the way it was; (louvered door, only the
exhaust pipe going into the attic). Actually, my first choice would be
to install solar with a small tankless backup, but I may need to win
the lotto first. Shame to waste 30 100 degree + days a year and still
be paying for water heating.
you can do nearly anything, trouble is cost vs benefits.
heck cover a few acres with solar panels, spend a couple million and go
payback? never panels will be worn out long before you get 2 million of
electricity from the install.......
now super insulating your home, solar hot water, some things have a
payback within a reasonable time......
hows your home insulated? might be a better way to spend the bucks?
>hows your home insulated? might be a better way to spend the bucks?
R16 in the walls, tinted double glazed windows with an inch between the
panes, attic is the weak spot, but I'm holding off till I get the
wiring all the way I want it. It has blown cellulose level with the
rafters with some r-13 on top, I want attic blanket to replace the
r-13, but will just tear it up running wires if I do it now. It is
miles from where I found it, but in the 50's insulation wasn't a big
deal in Texas. Our inclimate weather is summer heat, any benefit on the
heating side is a minor thing, but something that cuts the AC use is a
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