Best heat exchanger construction in tankless?


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Old 09-25-13, 09:08 AM
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Best heat exchanger construction in tankless?

I'm researching condensing tankless hot water heaters and all brands seem to be pretty similar and possibly all come from maybe 3 factories (all Asian). One noted difference is in heat exchanger material. I'm using unsoftened well water so will there be a lifespan difference between units made of aluminum, stainless or copper? I would think it matters but all have 12-15 yr warranties. I haven't found this discussed anywhere on the 'net.
 
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Old 09-25-13, 10:48 AM
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Whats the PH of your water and sediment level?

I think in most instructions for the tank-less the water must meet certain criteria or warranty gets voided.....
 
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Old 09-25-13, 11:48 AM
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Going DIY so I doubt there will be any warranty anyways.
How much will the water pH matter? From what I've read the condensate is especially acidic and that seems to be the bigger concern on these.

This is for my cottage so idle concerns prevail over use concerns, if that matters.
 
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Old 09-26-13, 09:36 AM
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I found units with the same specs and warranty with heat exchangers made from aluminum, copper or stainless. Aluminum just seems like a bad idea for durability. My thinking is that even though SS doesn't have good heat transfer, it is durable and may last longer with well water. Make sense?
Rheem claims a SS heat ex. but in a photo of the innards it looks like copper to me. Navien is one brand with SS primary and 2ndary heat exchangers. The brand gets low marks from amateurs (Amazon, DIY forums) but mostly good posts from the pros on heating & plumbing forums. Navien is the only brand I found that doesn't void the warranty when used on well water.
 
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Old 09-26-13, 10:20 AM
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Yes I would do SS or copper absolutley........

I personally install Noritz tankless when I do install them. I install none smaller then 199K btu. I only use the units that install with PVC venting. If you ever priced the other you will know why....

Let me know if you need more info regarding this brand... Its only my opinion but I have had good success with them and customer service is very good.... I have been using these for 10 yrs now, but the last one I did was 2008.....


On-demand Hot Water Heater | On demand Gas Water Heaters


Just a note: I have ripped out many Bosch tankless, and cannot speak for the other brands I highly recommend a whole house pre filter and a buffer tank be installed.....
 
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Old 09-26-13, 12:18 PM
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About that buffer tank--The Navien offers each condensing model in 2 versions: one with 1/2gal internal buffer + a small recirc pump that can be used to keep the buffer water hot for quicker demand, or external recirc to keep all the water in the pipe hot (instant hot but costs energy). I was going to go the simple route. Do you feel a buffer offers much extra comfort? I assume it's normally there to smooth out the delivered temperature. Is 1/2gal big enough?

At the beginning of this research I was surprised to learn these tankless units do contain a little water so they are not freeze-proof. A buffer tank would add another step in my annual winterization. If I still go forward with the plan at least they are way simpler & faster to empty than a 40gal tank.
 
 

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