Tankless hot water heater flow???

I'm have a Takagi jr. with a small problem... the water flow being too low, just at the minimum specs. My ground water temp. is about 41'F and I would like to increase it if I could in a unexpensive way if I can. Any ideas or suggestions out there???
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If the Takagi Jr is too small for your needs, the obvious solution would be a larger unit. Not inexpensive. The Takagi Jr should be providing 3.0 GPM at 77 degree temperature rise, this is insufficient?
You could add a solar water heater into your system. If it never freezes in your climate, the simplest would be a solar pre-heater plumbed in front of the Takagi Jr with a tempering valve after the heater. If it does freeze in your climate, then you'd need to add a tank with a drainback solar system and use the Takagi Jr as a backup.
You could also use a large water tank with your Takagi Jr, as discussed in the unit's manual. Basically I believe you take an electric water heater, remove the heating elements, and use the thermostat to run a pump to recirculate water through the Takagi Jr when heat is required. You end up with something less efficient than a tankless water heater, because you have standby losses on the tank, but it should be more efficient than a standard gas water heater, as there is no chimney in the middle of your tank.
Cheers, Wayne
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wrote:

With those specs I can see your right on the edge. 41F +77F rise = 118F which is just beginning to feel too hot for most people. Still not anywhere really hot scalding water and may need to shower with little or no cold water mixing.
At 3GPM and most fixtures using 1/2 of that while running, all you need to do is run two fixtures and your sucking cold water with a third. If your living alone, that capacity is sufficient but prewarming the cold water by 10F would give you hotter water for cleaning and showering. I bet it works fine in the summer when the incoming cold is not so cold.
The tank idea above sounds reasonable but alternatively, you could run the cold pipe through a heat exchanger (old baseboard radiator) and steal heat from the room it is in before sending it to the HW heater.
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If you have your heater in a basement that's relatively warm - 60 deg - you could feed your cold water into an storage tank (electric water heater not connected to power) before it goes to the tankless and let the tank temper itself from the basement temperature. If all you need is 10 or 15 degrees, possibly the Tstat in the electric tank could be set to 60 deg.
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You said flow is to low, meaning gpm that is related to water pressure and the size of the Takagi pipe size, so if I understand to increase flow you need to increase pressure. Now if temp rise is not enough then look at your gas supply size, my 117000 btu Bosch tankless needs 3/4 size pipe over 10 ft, but gas flow needs to be measured with a manometer to be sure. Insuficient gas flow and you will never get 100% out of the unit.
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Thanks for the all the great ideas...Yes I live in the cold north A heat exchanger sounds like a good cheap alternative. I was even thinking of a spool of very flexible 3/4" IPEX tubing ( if it is cheap enough...)before it enters the WH. I wonder if anyone has tried that?
Thanks again
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pipes to air would be less than for metal pipes and the heat transfer would be even greater if the heat exchanger were submerged in warm water. two 3/8" spirals of copper tubing in parrallel might not cost too much.
Where does that warm water come from, perhaps the drain pipe from your washing machine, dishwasher and shower. In other words, your grey water can be used to temper the incoming cold. You would definately not want leaks and would want to have check or antisiphon valves installed to prevent contamination of the cold by the grey water if there were a leak and you turned off the supply.
However, I can see that it might be prohibitively expensive to plumb such a system unless you already seperate the grey and black waste water, you would need to plumb a seperate DVW line for the grey and have it flow to a holding tank near the cold supply inlet. A tall order.
Alternatively, you could build your heat exchanger into a mass of concrete which you build a small greenhouse around (perhaps you already have a sunny location indoors). The solar gain in the concrete would in turn temper the water for hours into the night. Make sure you plumb a bypass for summer or you will have no cold water that time of year.
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