How do Tankless / On demand water heaters heat so fast?

I have never understood how they can heat enough water instantly to wash
my hands, much less heat enough water to fill a bathtub instantly.

If I put a pan of water on my gas stove and turn the flame to high, it
takes quite a few minutes to bring that pot of water to a boil. (And
that's just one gallon or water or less)

If I turn on the power to a standard 4500W 240V 30 gal. electric water
heater filled with cold water, it takes a good hour or more to heat that
water to 120deg or so.

A 30 gal gas water heater, heats faster than electric but it still takes
at least a half hour if the water is cold to begin.

I have an electric element called a "bucket heater". It uses 1500W at
120V. It's made to heat a 5 gallon bucket of water, in a barn or where
there is no hot water at the tap. That thing takes over an hour to heat
5 gallons of water to around 100 deg.


With that said, I cant understand how a "tankless" water heater can
possibly heat enough water INSTANTLY to fill a bathtub, or even a half
gallon to wash my hands. Whether they run on gas or electric, how can
they surpass the speed of heating water above any of the methods I
mentioned above? (And do this continually)?

On Thu, 07 Apr 2016 03:52:45 -0400, wrote:

How do Tankless / On demand water heaters heat so fast?

I have never understood how they can heat enough water instantly to wash
my hands, much less heat enough water to fill a bathtub instantly.

If I put a pan of water on my gas stove and turn the flame to high, it
takes quite a few minutes to bring that pot of water to a boil. (And
that's just one gallon or water or less)

If I turn on the power to a standard 4500W 240V 30 gal. electric water
heater filled with cold water, it takes a good hour or more to heat that
water to 120deg or so.

It is all in the surface area contacted. The amount of water in there
is low compared to the heating surface and they put a lot of power
behind it all.

Put a pot of water on the stove and see how long it takes. Then dump
it out and put just 1/4" in the pot and see how fast it heats.

On Thursday, April 7, 2016 at 4:52:57 AM UTC-4, wrote:
How do Tankless / On demand water heaters heat so fast?

I have never understood how they can heat enough water instantly to wash
my hands, much less heat enough water to fill a bathtub instantly.

If I put a pan of water on my gas stove and turn the flame to high, it
takes quite a few minutes to bring that pot of water to a boil. (And
that's just one gallon or water or less)

If I turn on the power to a standard 4500W 240V 30 gal. electric water
heater filled with cold water, it takes a good hour or more to heat that
water to 120deg or so.

A 30 gal gas water heater, heats faster than electric but it still takes
at least a half hour if the water is cold to begin.

I have an electric element called a "bucket heater". It uses 1500W at
120V. It's made to heat a 5 gallon bucket of water, in a barn or where
there is no hot water at the tap. That thing takes over an hour to heat
5 gallons of water to around 100 deg.


With that said, I cant understand how a "tankless" water heater can
possibly heat enough water INSTANTLY to fill a bathtub, or even a half
gallon to wash my hands. Whether they run on gas or electric, how can
they surpass the speed of heating water above any of the methods I
mentioned above? (And do this continually)?

It's called either a BFB or BFHE.

The last B is for burner, the HE is for heating element, you figure out
the rest.

On Thu, 07 Apr 2016 03:52:45 -0400, wrote:

How do Tankless / On demand water heaters heat so fast?

I have never understood how they can heat enough water instantly to wash
my hands, much less heat enough water to fill a bathtub instantly.

If I put a pan of water on my gas stove and turn the flame to high, it
takes quite a few minutes to bring that pot of water to a boil. (And
that's just one gallon or water or less)

If I turn on the power to a standard 4500W 240V 30 gal. electric water
heater filled with cold water, it takes a good hour or more to heat that
water to 120deg or so.

A 30 gal gas water heater, heats faster than electric but it still takes
at least a half hour if the water is cold to begin.

I have an electric element called a "bucket heater". It uses 1500W at
120V. It's made to heat a 5 gallon bucket of water, in a barn or where
there is no hot water at the tap. That thing takes over an hour to heat
5 gallons of water to around 100 deg.


With that said, I cant understand how a "tankless" water heater can
possibly heat enough water INSTANTLY to fill a bathtub, or even a half
gallon to wash my hands. Whether they run on gas or electric, how can
they surpass the speed of heating water above any of the methods I
mentioned above? (And do this continually)?




The actual amount of water heated in GPM is relatively small and they
use a buttload of power. (at least 5 times what your tank heater
uses). My brother in law wanted tankless and he ended up with 3
heaters, propane powered, One for the kitchen and one for each
bathroom. You can take a shower but the flow restrictor makes the tub
fill slower than you could do with a tank heater.
I think 3 heaters was overkill since I am not sure his well can even
pump water that fast tho.,

they.....
use a buttload of power.

+1

On Thu, 07 Apr 2016 03:52:45 -0400, wrote:

How do Tankless / On demand water heaters heat so fast?

I have never understood how they can heat enough water instantly to wash
my hands, much less heat enough water to fill a bathtub instantly.

If I put a pan of water on my gas stove and turn the flame to high, it
takes quite a few minutes to bring that pot of water to a boil. (And
that's just one gallon or water or less)

If I turn on the power to a standard 4500W 240V 30 gal. electric water
heater filled with cold water, it takes a good hour or more to heat that
water to 120deg or so.

A 30 gal gas water heater, heats faster than electric but it still takes
at least a half hour if the water is cold to begin.

I have an electric element called a "bucket heater". It uses 1500W at
120V. It's made to heat a 5 gallon bucket of water, in a barn or where
there is no hot water at the tap. That thing takes over an hour to heat
5 gallons of water to around 100 deg.


With that said, I cant understand how a "tankless" water heater can
possibly heat enough water INSTANTLY to fill a bathtub, or even a half
gallon to wash my hands. Whether they run on gas or electric, how can
they surpass the speed of heating water above any of the methods I
mentioned above? (And do this continually)?



They require huge amoints of amps or cu ft of gas - to the point many
houses cannot use them without a new electrical service or updated gas
supply.