That is actually how tankless units are rated. :)
While well water is cold, that is not a unique
Tankless units are rated on their temperature rise/flow rate, (gallons per
minute). "Temperature rise" being the difference in temperature of the
water between input and output. The lower the flow rate, the more the water
can be heated.
That is how I understand it. Since the precious statement that I was
responding to did not indicate flow rate being a factor the broad brush
statement of only raising the temp X amount of degrees seemed pretty
problematic. I can absolutely understand raising the temp only x
degrees at full throttle at the faucet but at a lower flow rate I would
find it hard to believe that the temp would not rise.
One of the problems is that these things sense flow rate internally, so
a low flow rate can cause them to either shut down and/or lower the
Counter intuitive as it sounds, one of the cures for that problem that
is practiced widely is to turn on a second hot water faucet to keep the
sensor from lowering the temperature.
So much for being "green" and "conservation" minded... like many
"progressive" concepts which focus on feel good issues, the opposite
effect is often the ultimate consequence.
A common problem with tankless units though, because a "big enogh"
tankless unit would require more electrical power than the total
service available, and a big enough natural gas one would require a
larger meter/regulator, and often even a bigger supply line than the
gas co has installed for most residential services. I'd need to put
in a new underground electrical supply to install the recommended
electric tankless because I only have a 100 amp service, and I cannot
install more than 125 amps on the existing infrastructure. My current
gas meter would support the water heater with the furnace not running,
but would be borderline (at best) for sure if I also had a gas drier
or range running
That's going to be marginal.
Water coming out of the ground will be around 50F-54F
year around based on a lot of heat exchanger design
and development work I did many years ago.
A delta of 65F will give a discharge of 115F at 3.8 gpm.
115F is warm but definitely not hot which is about 130F.
I'll take your word on that, I always understood that they ran full bore
when the water was turned on, just like a tank type heater. I understood
that any flow rate above "x" ran the heater at full throttle and any below
"x" did not turn the heater on at all in the event of a dripping faucet.
Again ill take your word on that but it sounds like a faulty flow meter
Exactly. Take the whole state of California for instance. They are all
standing on shaky ground and the more they clean the air the drier it
becomes and is ripe for wild fires and preventing rain.
All units I've dealt with have multiple sensors, and a flow rate
restrictor, that use a microprocessor to adjust the heating ability to
both the flow rate, and temperature, of incoming water so that that it
matches the "set point" temperature (generally a setting that is user
Also have noted that many user complaints can be traced to the usual
reduced water pressure/flow rate on the output side of these units due
to the restriction, compared to the input, especially when used in
conjunction with modern "pressure" balanced fixtures.
So, yes, there is generally flow rate restriction available/involved
internally, and they don't necessarily run "full bore".
Therefore the basis of my original opinion - not for the faint of heart,
and certainly more expense to install and _maintain_.
The tank could be leaking from anywhere, water is going to show up at
the bottom because of that gravity thing. ;~) So check the inlet and
outlet pipes first. Gas water heaters tend to fail sooner than electric
because of the greater extreme heating conditions that the tank must
endure. The bottoms of the tanks are exposed to several hundreds of
degrees temperatures. Electrics don't get much hotter than the water
temperature at the faucet and the heating elements are in the water vs.
outside of the bottom of the tank.
Assuming gas, some units and or building codes require special venting
material. Apparently not any old vent will work in all cases. IIRC
Swingman had one installed in one of his homes that he built and the
vent material IIRC had to be stainless steel. And IIRC that ran about
$100 per foot.
So you should for sure look into what exactly the cost will be installed
before taking the leap. It may never pay for itself in savings if the
unit runs in to the thousands of dollars, installed.
I do not think they offer any advantage other than energy savings and an
endless supply of hot water.
Delivery of hot water will be relative to the distance the heated water
will have to travel. You are only changing how the water is heated and
when, not how quickly the water will be delivered. That is of course
assuming your old water heater is not restricting the water flow.
Now with having said that, immediately after install you will get hot
water much sooner from a tankless than from a new tank type heater
which will have to heat the entire tank first.
The physical makeup of the two are so different, it's hard to accurately
With the tank heater, there are two relatively small elements or flame
to heat, say, 50 gallons of water. With the tankless, there are probably
only a couple gallons capacity in the heat exchanger, with the "element"
or flame completely surrounding all the water almost by the drop. Think
of a car radiator and the air flowing through it. I would guess the
heat to volume ration is probably 1000:1.
"Playing is not something I do at night, it's my function in life"
OK, we both know what we are talking about, I think. ;~) It was you
mentioning that there's not much water running through the heat exchanger.
I think what you meant to say was that the heat exchanger does not have
much water in it at one time, unlike a tank type water heater.
On Thu, 10 Jul 2014 13:13:53 -0700 (PDT), "Gramps' shop"
I'd first check the tank warranty - with a friendly Rheem dealer ..
... 10 years is a very early failure ! Mine - on propane - is ~ 23
years old and going strong !
In the past - I've discovered secret 10 year warranty on my Ford
Taurus front springs ... and the SS tub on my clothes washer ..
Somebody asked this question a few days ago on the Home Shop Machinist
forum. In summary, they weren't too fond of the tankless systems:
FWIW: I've have planned, and effected, the installation of "whole house"
tankless water heaters in three of the new homes I've built in the past
Your success depends upon a number of factors: the size of the house and
distance of the unit(s) from fixtures; the number and type of hot water
fixtures (flow rates must be determined for each fixture); the type of
plumbing allowed in your jurisdiction for code purposes; type of unit
(gas or electric); the brand; and, most importantly, the design, and
accurate implementation of the design at installation.
Biggest issue with any hot water system is the time from the demand to
the delivery. Distance is obviously a big factor, as well as any
intervening devices in series (point A, through point B, to C, etc.).
Plumbing methods, utilizing a manifold distribution system (PEX makes
this much simpler) can make a big difference in the time of delivery as
it insures the shortest possible linear 'source to demand point' delivery.
It is my experience that, with whole house units, and without a manifold
system in place, and if you have more than one bath, kitchen, and
utility room with long runs of in series piping, your best results and
satisfaction may require intervening auxiliary tanks and pumps, in some
At this stage of the game I would steer away from electric units in the US.
With gas units, which must be vented to the outside, location of the
unit is very important as the vent must be double-walled stainless and
runs about plus $60/ft, installation not included. This can double the
price of the equipment itself, and the labor/material needed to install
Rinnai is a good unit and worth the price. I've also installed one GE
unit, at the homeowner's request, with no trouble thus far.
Use a dedicated tankless dealer for design and installation, not a
plumbing company that does it as a sideline.
One of the exercises that must be performed is to calculate actual flow
requirements of each and every hot water fixture in the house, the
expected delivery temperature, AND, very importantly, _the ambient
temperature of the water fed to the tankless unit_ coming into the house.
With a good gas unit, proper design of the piping system, and a
knowledgeable dealer who provides the design and installation, you can
get satisfactory results with on demand 'whole house' units.
My home owner's love them and have had no issues thus far, but it takes
a good deal of planning, dedicated supervision of all details, and thus
a good deal more expense than a regular hot water heater in order to
install, and maintain, a tankless system.
Not for the faint of heart...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.