in line heater in conjunction with tankless water heater

[Lisa D. Lucas]

When remodeling/adding on to my house I installed a tankless water in the newest side, which happens to be farthest from the water pump/inlet. I kept the original side of the house on the standard 52 gal. electric heater until it failed. At that point, I connected the original plumbing to the tankless heater. Works just fine, except there is an extremely long run for the water before it gets to my kitchen. I am wasting obscene amounts of water just waiting for it to get hot. I envision adding a thermostatically controlled point of use heater at the sink that will turn on and heat the incoming water and then shut off when the water that has been heated by the tankless unit finally gets down the line. Trouble is, I haven't found such a device. Trying to find a cheap, simple solution without involving a recirculating system and tank. Anybody know of such a device? There are numerous point of use heaters, but I'm looking for one that sense the temperature of water coming into the unit and shut itself off.

 

[Reach4]

A small (point of use) conventional electric water heater would do that without the drama of a tankless. Once the water reaching the water heater input is hot enough, the small WH heating element would shut off.

I doubt that any of the water heaters, including tankless, keep their heating elements running once the incoming water is hot enough.

 

[Sponsor]

 

[Jadnashua]

To heat water for a kitchen sink at a typical flow rate of 2gpm would take what amounts to another tankless WH. To have any chance of doing this well, you'd need to do one of two things:
1. Add a small tank-type heater near the point of use large enough so that the incoming cold water wont' overwhelm things before the incoming water gets hot enough...you might still have a cold water sandwich if it was too small, but short uses would work fine. Something in the 5-gallon range might be big enough, it would depend on how far away it is and the diameter of the pipe.
2. If your tankless system allows it, you might add a recirculation system.

To raise 2gpm say 70-degrees (from 50-120, or if you're where it gets really cold 35-120 that you might want for washing dishes), means worst case about 17# of water per minute, or 17*60 = 1020 or over half a TON of water an hour (working in hours, since most are based/hour)...that would be 1020#*70-degrees = 71400BTU/hr, or almost 21Kwhr of energy. To get that at 120vac, you'd need a 175 amps, or half that at 240vac. This is one reason why electric tankless systems are not particularly useful. That would increase in the winter when the incoming cold water got closer to freezing (mine, I've measured at 33-degrees after a cold spell).

A small tank can often run on 120vac, and has a (hopefully) a long time to reheat the water before the next use so the draw can be quite modest. For a longer duration use, it probably wouldn't need to run, since you'd be putting hot into it and it could just pass through without needed to be heated locally in the tank.

For minimizing wasting water, and maximizing comfort, it works best to have the WH closer to the point of use. When that can't be done, recirculation can work, or adding a supplemental heat source closer.

 

[Nakopf]

I might look into a Grundfos recirculation system with a comfort valve - they can be a unintrusive means to add a recirculation loop of sorts.

What model tankless?

 

[e swords]

When remodeling/adding on to my house I installed a tankless water in the newest side, which happens to be farthest from the water pump/inlet. I kept the original side of the house on the standard 52 gal. electric heater until it failed. At that point, I connected the original plumbing to the tankless heater. Works just fine, except there is an extremely long run for the water before it gets to my kitchen. I am wasting obscene amounts of water just waiting for it to get hot. I envision adding a thermostatically controlled point of use heater at the sink that will turn on and heat the incoming water and then shut off when the water that has been heated by the tankless unit finally gets down the line. Trouble is, I haven't found such a device. Trying to find a cheap, simple solution without involving a recirculating system and tank. Anybody know of such a device? There are numerous point of use heaters, but I'm looking for one that sense the temperature of water coming into the unit and shut itself off.

Hello. I realize this thread is very old but your question was perfectly put as per my needs as well. Did you ever find a good solution? Thank you. E