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

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)?

Reply to
Paintedcow
Loading thread data ...

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.

Reply to
Ed Pawlowski

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.

Reply to
trader_4

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.,

Reply to
gfretwell

+1
Reply to
makolber

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.

Reply to
clare

HomeOwnersHub website 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.