tankless electric water heaters, any good?

[readydave8]

I can't see you feeding back into the general cold water supply.

I had heard of this and can find on Google but no personal experience

 

[kwired]

Circulation loops I'm familiar with do a feed and return to the hot water tank to reduce the lag for hot water at the sink or shower or whatever. I can't see you feeding back into the general cold water supply.

When there is no other water "loads" the circulation is basically back to the hot water tank. The less fixtures are on the long line the less chance you get hot water when you first turn on a cold tap, but at same time if you want coldest water possible at the far end you need to run water long enough to purge the heat out of the cold water line to that fixture, kind of opposite effect of why you install such circulation system. For the convenience of quicker hot water the inefficiency is continuous heat losses in the line even when no hot water is being used.

 

[winnie]

IMHO I think the approach you suggested, using a tank water heater combined with the double circuit mod and possibly a small external tankless 'booster' would be a good choice.

By using the tank you have no issues of minimum flow or temperature response. You also don't need a huge circuit rating to handle sudden demand load (several people using different fixtures at the same time).

By increasing the wattage of the tank system you maximize the hot water available for several showers in a row.

I wonder if any ordinary resistance water heaters have 'smart' controllers which turn on the elements in response to water flow, even before the tank temperature has dropped?

Another option to consider is running the tank at higher temperature and then using a thermostatic mixing valve to reduce the temperature right at the tank output. This has the effect of increasing the stored BTU in the tank

Yet a third option (out there, cutting edge) is to use a storage type water heater where the tank contains a phase change salt medium which stores heat more densely than hot water. The water flows through a heat exchanger in the tank rather than sitting in the tank hot. Again the goal here is to increase the stored BTU per gallon in the tank.

-Jon

 

[wwhitney]

I can't see you feeding back into the general cold water supply.

There's definitely commercially available products that do this, and it seems to work fine as a retrofit solution when there is no dedicated hot water return pipe. Typically there is a "thermal bypass valve" that cross connects hot and cold at the distant fixture whenever the hot water isn't hot enough, and then closes when the hot water gets to temperature. That can be paired with a a dumb pump that just tries to pump the hot water. E.g.

Hot-Link System

Hot-Link® System is a quick, easy retrofit using the existing plumbing. Mount the by-pass valve under the sink and the pump at the water heater. The valve's unique thermal disk technology sends cooled water back to the water heater so hot water lines remain hot.

www.tacocomfort.com

Cheers, Wayne

 

[kwired]

IMHO I think the approach you suggested, using a tank water heater combined with the double circuit mod and possibly a small external tankless 'booster' would be a good choice.

By using the tank you have no issues of minimum flow or temperature response. You also don't need a huge circuit rating to handle sudden demand load (several people using different fixtures at the same time).

By increasing the wattage of the tank system you maximize the hot water available for several showers in a row.

I wonder if any ordinary resistance water heaters have 'smart' controllers which turn on the elements in response to water flow, even before the tank temperature has dropped?

Another option to consider is running the tank at higher temperature and then using a thermostatic mixing valve to reduce the temperature right at the tank output. This has the effect of increasing the stored BTU in the tank

Yet a third option (out there, cutting edge) is to use a storage type water heater where the tank contains a phase change salt medium which stores heat more densely than hot water. The water flows through a heat exchanger in the tank rather than sitting in the tank hot. Again the goal here is to increase the stored BTU per gallon in the tank.

-Jon

I suppose is possible with PID control methods, need to factor temperature and flow into it, or possibly just temperature differential between upper and lower tank. Something like this may even vary the power delivered to the element(s) or even would send at least some power to both an upper and lower element simultaneously depending on demand conditions

 

[winnie]

I suppose is possible with PID control methods, need to factor temperature and flow into it, or possibly just temperature differential between upper and lower tank. Something like this may even vary the power delivered to the element(s) or even would send at least some power to both an upper and lower element simultaneously depending on demand conditions

Agree, certainly possible. But I wonder if anyone actually sells this as a consumer product. Or maybe we should design it here and license it

-Jon

 

[SSDriver]

There's definitely commercially available products that do this, and it seems to work fine as a retrofit solution when there is no dedicated hot water return pipe. Typically there is a "thermal bypass valve" that cross connects hot and cold at the distant fixture whenever the hot water isn't hot enough, and then closes when the hot water gets to temperature. That can be paired with a a dumb pump that just tries to pump the hot water. E.g.

Hot-Link System

Hot-Link® System is a quick, easy retrofit using the existing plumbing. Mount the by-pass valve under the sink and the pump at the water heater. The valve's unique thermal disk technology sends cooled water back to the water heater so hot water lines remain hot.

www.tacocomfort.com

Cheers, Wayne

I would think they make them for electric tankless as well. My LNG tankless has a built in pump. You then install a 4 way valve under the sink(has some sort of spring bypass in it). It just splices inbetween the faucet water line with two new flexible hoses. No electrical or pump needed under the sink like 10 min to install. Water is warm when first opened and hot in 20 seconds. Cold water is warm for literally 2 seconds and then cold. My house kind of has 2 loops so I installed it at the furthest 2 sinks. Works perfect.