COLD WATER SANDWICH (hold the mayo)

[KULTULZ]

In my ever continuing Need To Know inquiries here, I need enlightenment concerning tankless water heaters.

This uncertainty actually originated in this thread-

http://www.plumbingforums.com/forum/showthread.php?t=8866

Tankless is often referred to as 'Instantaneous Water Heaters.' Can I expect to have instant hot water at all my faucets and showers?

No. It still takes time to get the water to your faucets, just like it always has. Our heaters provide constant flow of hot water at the desired temperature. To get "instant" hot water, you need a recirculation system.

-TAKAGI

Does the term cold water sandwich refer to the cold water having to be circulated out of the house distribution system (by re-circulation system) before hot water arrives @ the fixture(s) with a tank-less (and isn't this the same as with a tank water heater), or is it the inability of the tank-less to produce instantaneous hot water @ initial start?

I find it hard to accept that once a flow sensor on a tank-less determines flow, that it can instantaneously heat the water, especially electric, to 120F.

Wondering In W(By GOD)V (as are most)

 

[cdimarco1984]

Attached is a picture of how it works. A tankless water heater is not an instant hot water heater. They are referred to as an on demand heater which means as there is a need for hot water that's when it begins to heat the water. So when someone uses hot water than you go behind them and use it at first you might have hot water since the water in the line is still warm. Than you'll get a shot of cold water until the unit reheats the water. You can add circulating pumps to tankless heaters which would help eliminate this issue. View attachment ImageUploadedByPlumbing Forum1459690987.373775.jpg

 

[KULTULZ]

THANX!

So it is safe to a$$-u-me that the term cold sandwich can be applied to both tank-lees and tank water heater systems?

 

[cdimarco1984]

No not necessarily. With a tank water heater you have a burner with a constant flame and than electric have heating elements and both have thermostats so once the temperature in the tank begins to cool it's heating the water back up wether it's being used or not. Unlike a tankless that only heats the water when it's needed. (Which when not being used there is a small amount of water that sits in the pipes of the tankless that get cold). So the only time you get cold water with a tank is when you first turn the hot fixture on or you use up all the hot water in the tank and it needs to reheat.

 

[Mr_David]

THANX!

So it is safe to a$$-u-me that the term cold sandwich can be applied to both tank-lees and tank water heater systems?

NO.

It's the OR of your original question
" or is it the inability of the tank-less to produce instantaneous hot water @ initial start?"

The starting phase of the tankless allows some cold water to pass through it before it comes on. The tank heater does not. The hot water in the line from a tank will also cool between usage, but the water that immediately starts to flow from a tank with the next usage, will be HOT. Not like the initial cold flow of the tankless start up.

 

[frodo]

in my opinion, water heater tank type with circ line is the only way to go