Built-in pass-through water heater, anybody done that?

[Scoutman]

I read in another thread (may have been yours RoadForce) that the flow pressure switch in these units needs to fully register the pressure drop before kicking the burner in. Meaning you can't just trickle a little bit of hot water. Between that and the cold water that's in the lines there could be some wastage of water just getting hot water to the faucet/shower head. That being the case I wonder if it would be worth putting a T and a valve in the output of the hot line to purge off the cold water and that water routed to a return back to the tank. Basically you'd turn the valve kicking the cold water back to the tank dropping the pressure so the unit can kick on and once a few seconds of hot water were flowing then shut that valve back off.

I could see if you were really concerned with water consumption this may be a way to keep usage down.

 

[pappawheely]

I read in another thread (may have been yours RoadForce) that the flow pressure switch in these units needs to fully register the pressure drop before kicking the burner in. Meaning you can't just trickle a little bit of hot water. Between that and the cold water that's in the lines there could be some wastage of water just getting hot water to the faucet/shower head. That being the case I wonder if it would be worth putting a T and a valve in the output of the hot line to purge off the cold water and that water routed to a return back to the tank. Basically you'd turn the valve kicking the cold water back to the tank dropping the pressure so the unit can kick on and once a few seconds of hot water were flowing then shut that valve back off.

I could see if you were really concerned with water consumption this may be a way to keep usage down.

Sounds like a good idea.

 

[RoadForce]

Yes, no trickling water indeed. I read someplace else about using a valve and running the water back into the tank for another reason as well: navy showers! Not that I like them, but the idea was that - when conserving water by switching the flow off completely - you would get scalding hot water when turning the water back on again, because some water had been sitting in the very hot burner/coil for longer than intended, followed by cold water because the burner was not ignited immediately. With the valve, you could simply cycle the water continuously, not having to turn it off at all (but rerouting it to the tank instead of the shower head when no water is needed).

I don't know if this really works though, temperature-control-wise: the water temperature in the tank will rise, making the water heater's output even hotter, thus you will find yourself adjusting the temperature all the time while showering?

Anyway, for me this is all hypothetical as I don't plan on such a system, but for some it might be something to consider.

 

[Scoutman]

Yes, no trickling water indeed. I read someplace else about using a valve and running the water back into the tank for another reason as well: navy showers! Not that I like them, but the idea was that - when conserving water by switching the flow off completely - you would get scalding hot water when turning the water back on again, because some water had been sitting in the very hot burner/coil for longer than intended, followed by cold water because the burner was not ignited immediately. With the valve, you could simply cycle the water continuously, not having to turn it off at all (but rerouting it to the tank instead of the shower head when no water is needed).

I don't know if this really works though, temperature-control-wise: the water temperature in the tank will rise, making the water heater's output even hotter, thus you will find yourself adjusting the temperature all the time while showering?

Anyway, for me this is all hypothetical as I don't plan on such a system, but for some it might be something to consider.

I don't think you'll get that effect with this type of heater because as soon as the flow stops it turns the burner off. Not saying that the water in the coils won't finish absorbing that residual heat and get hotter but it shouldn't scald your naked *** like a Zodi shower will. If you shut a Zodi water pump off it will keep heating the water that's in the system and completely boil it to steam unless you shut the fire off too (making 'navy' showers difficult). We always had to recirculate the water into a cooler to get it the right temp and then shut the burner off.