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