Tankless Water Heater - Seeking Suggestions

[earlyre]

Originally Posted By: ueberooo
Solar hot water would make so much sense. I at one point thought about that too. The big difficulty is avoiding the risk region of temperature where Legionella can breed. I think that temp range is somewhere from like 85f to 110f, peaking somewhere near body temperature. As long as the major volume of water to be preheated isn't sitting in that range for long then all is ok, esp if you later feed it into a 50C / 122f tank of hot water.

Solar in combo with heat pump would be excellent in efficiency.



Which is why most properly designed solar systems don't send the potable water up to the roof/heater. what they employ is a heat exchanger tank. the heated water runs into a set of coils inside the tank filled w/ potable water, giving up their heat to the water. or dual sets of coils, one with the potable water, one with the stuff from the roof(usually some sort of antifreeze/coolant solution)

 

[Shannow]

Nearly every one I've seen in Oz passes the potable water through it, then has an electric booster in the tank for the not so sunny days.

 

[Virtuoso]

Originally Posted By: JHZR2
+1, the tankless is 30% more efficient than the best tanked gas heater.

Electric is 100% efficient though on heating, and has a tiny, low standby loss because there is no stack.


Our Rinnai R75LSi is rated at 84% efficiency. There were tank heaters on the market when we installed it with higher thermal efficiencies than that.

Unfortunately (at least for my statistical purposes), we only had our old, popcorny tank heater in the house for 9 months before we upgraded to the tankless, so I don't have a lot of summer-gas usage data to back it up. But I don't think our gas bill dropped much. Maybe ten bucks?

I do believe our hot water usage increased with the tankless, though. There's just more of it available now!

 

[PandaBear]

Since gas is not an option, based on my experience back in Hong Kong (220-240V) I'd have to say you should get a tank one that you can turn on manually before shower to preheat, and turn it off afterward. It is inconvenient but it is the most practical thing as even at 220/240V in apartment will not be powerful enough to heat a small tank for shower without tank.

 

[Garak]

Originally Posted By: JHZR2
+1, the tankless is 30% more efficient than the best tanked gas heater.

Electric is 100% efficient though on heating, and has a tiny, low standby loss because there is no stack.


In my business, the original install of the original Rinnais was an utter disaster. There were eight home speced installed. They didn't have the capacity, so some genius put a water storage tank that would store hot water at whatever setting was chosen. So, the Rinnais ended up being part of an overly complex tanked system. They were also powering the floor heat at the time.

Needless to say, they petered out in short order. I put in eight industrial Rinnais and pitched the storage tank. Then, a boiler was installed for the floor heat.

The July of 2010 gas bill was $2500. The July of 2011 gas bill was $250. Bear in mind that no floor heat was running in either July, so you can imagine how bad things got in January. The winter gas bills now are cheaper than the previous summer gas bills.