Tankless hot water heaters

[MARINERMAGNUM]

Swamp, that's what I was wondering, too. When you figure the cost of possibly having to increase a gasline if it's low pressure, the venting of the heater, the repiping of the water lines and the cost of having a small electric heater and circ pump, I wonder how long it would take to pay for itself. Might not be too bad on new construction but adding them after the fact is labor can be labor intensive.

Cost of the parts is not much of a factor if you have the ability to do it yourself. The labor would be the killer.

I still don't understand what purpose this re circ pump would serve..? Mine delivers hot water in a matter of seconds anywhere in the house. I've lived in homes where it took a long time for the hot to make the run from the tank to a faucet. I'd say they have a pressure issue. We have our pressure switch set to kick the pump on at 45lb and off at 70lb. Maybe that helps.

[swamptiger]

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Swamp, that's what I was wondering, too. When you figure the cost of possibly having to increase a gasline if it's low pressure, the venting of the heater, the repiping of the water lines and the cost of having a small electric heater and circ pump, I wonder how long it would take to pay for itself. Might not be too bad on new construction but adding them after the fact is labor can be labor intensive.

I think on new construction you would have to start with the cost of a conventional storage water heater using the lowest cost fuel available, and work backwards from there. Seems to me that retrofits on older systems could get a lot more complicated.

The only advantage I can see to a re-circulating pump on a tankless unit is instant hot water. The selling point of tankless heaters to begin with was the idea that you were eliminating losses associated with standby or storage of the hot water. Now, the selling point seems to be an instant unlimited supply, with less emphasis on efficiency.

[krinkle]

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With the built in recirculating pump there is a external connection for quickly adding a loop to the hot water piping if needed. There is also a control for setting when you want the pump to come on. I set mine to come on from 7am to 9am. Very efficient.

Convenient, maybe...probably not so efficient after you add the heat loss from the recirc loop and the cost of operating the pump.

Had to relook at my post also. The tank in the navien is not a tempering tank either but aids in recirculation. With the recirculation running on a tankless keep in mind it does not take a full 199,00 btus to heat this water. The burners modulate up and down depending how much water is needed. For extra efficiency add in the timer on the pump that comes with the heater. On top of that make sure the piping is properly sized and insulated. Compare this to heating 40 gallons of water every hour of the day every day of the year and it is extremely efficient.

[BobT]

MARINERMAGMUM,

As I've posted already, our off-peak electric rate is $.042/KWH.

My 105gal. Marathon is rated at 94% efficient so 94% of the electricity I pay for is used for heating the water and the remaining 6% is due to heat loss through the insulation and water lines.

Off-peak works like this. The power to the heater is only available during the night. I don't recall what the hours are but I believe it might be from 2:00am - 5:00am? Once the tank is heated we use the stored hot water throughout the day.

My concern before installing was the possibility of running out of hot water during the day. Every time we use hot water we are replacing it with cold water. The tank sits right below a window and our basement is not heated by any heating system.

When I remodeled our house I used low volume faucets and shower heads.

Since installing the system we have never experienced a shortage of hot water. Not yet anyway so I have been more than happy with the result.

As far as the cost being consistent. That is true. During the summer it varies only a dollar or two one way or the other. During the winter I can't say because the dual-fuel heating system is metered using the same meter so hot water and home heating is on one bill. The home heating system is controlled separately by the power company but run through the same meter.

Our total home power use for everything else is around 950KWH per month. A rather significant part of our power consumption is our well because of the livestock. Without metering the well I can't say for sure what those animals cost but I'm sure it's a drain.

To keep them supplied during the winter I installed a Ritchie automatic waterer. It only uses a 40w heating system so even it it ran constantly, it would only cost about $2.30/month at $.082 per KWH. Compare that to using 1500w tank heaters and the cost savings paid for the system quite rapidly.

[swamptiger]

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On top of that make sure the piping is properly sized and insulated. Compare this to heating 40 gallons of water every hour of the day every day of the year and it is extremely efficient.

Some of the better storage tanks are very well insulated - heat loss on some of them is down around 5%, so it isn't as big a factor as some of the more poorly insulated ones.

I would guess the heat loss on a long plumbing run could be substantial even if the pipe is insulated.