Tankless Hot Water Heater Questions

 Hello:

Have been looking at homes lately, and find that many are using
tankless water heaters for supplying the hot water faucets in the home.

Know nothing about how these works, or their pros and cons.

I can figure out how the electric models work, I think, but how
do the gas and oil ones operate ?

I had a very old house once that had a tankless water heater on the regular
home furnace.  I'm not sure if the heat from the furnace, or some of the
water
used for the forced hot water heating system was on the primary side of this
heat exchanger.
Just out of curiosity which was most likely ?

a.  Any explanations on how my old one probably functioned, and how the new
ones do now would be most appreciated.

b.  are they generally considered to be cheaper to operate than the stand
alone tank types (I live in the Northeast) ?

c.  are they very popular these days ?

d.  pros and cons ?

Much thanks,
Bob

  Robert11 wrote:


Fuel cost is less. Convenience may vary with use.
 

Depends on what you define as popular.


Tankless units generally cost more than tank units.
Fuel cost is generally lower than tank units.
Depending on capacity, a tankless may or may not "run out of hot water".
If one planned to use a solar hot water heater, or other conservation
measures, it would be reasonable to spend more money for a tankless.
If one was not concerned with conservation, the bottom line would recommend
a standard tank water heater.

Note: if you plan to attach a solar hot water heater, make sure there is an
anti-scald feature, that detects inlet water temperature. Such models will
mix cold water with the scalding water to prevent injury.

 jetgraphics wrote:


  It would seem like you wouldn't "run out" in the same way you do with a tank.
 If, for example, you had two showers and a dishwasher going, there might not
be enough capacity to keep everything at desired temperature -- it's a function
of load rather than size.  Perhaps someone can give an example of how many
different hot-water usages (say, two not-too restricted shower heads?) are
typically possible with different size tankless heaters?


  Not sure I follow this logic -- how is a desire for conservation different
from a desire for a lower electric bill?

  The main reason I have been hesitating to buy one of these is exactly that it
*doesn't* run out of water -- sometimes the bottom of the tank is the only
thing that will get teenagers out of the shower.  

JGM

 jgmclean0@aol.com says...


We have the Takagi TK-2.  It will easily handle running two showers, the
dishwasher, and the washing machine at the same time.  Of course, your
mileage may vary depending on your intake water temp, energy density of
your fuel gas, and the specifics of your plumbing.

Our Takagi replaced a large tank water heater in the kitchen -- we wanted
the extra room in the kitchen, and the TK-2 cost less than any reasonable
alternative for installing a tank heater since we didn't have any
convenient alternative location for the tank.  

In new construction, I've seen it pencilled out that tankless costs less
overall if you mount the heater on an outside wall to minimize venting
costs, *if* you include the cost of the building space consumed by a
large tank.  6-10 square feet isn't unusual for a tank, and not every
house can conveniently have the tank in the garage or other low-cost
square footage.

--
josh@phred.org is Joshua Putnam
<http://www.phred.org/~josh/>
Books for Bicycle Mechanics and Tinkerers:
<http://www.phred.org/~josh/bike/bikebooks.html>

 JGM wrote:
(snip)

There is always an inlet valve on the tank. In my house kids get the
warning knock on the door after they are in the shower for 20+ minutes
then I'm heading downstairs for the valve ;)  I wish someone could
invent a coin operated hot water valve :) then kids can spent as much
time as they like in the shower and spent less $$$ elsewhere.

FC