20 YR OLD Water Heaters (2) - Replace or Can I Keep Waiting?

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John Gayewski

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My opinion. Get ot wait for a good deal on a Navien (your application calls for a Navien) the when your heater(s) go out you can go ahead and install it. My humble opinion is that equipment that works should be used. My water heater is from 1986 and still working great. Water quality and heater quality is kind of hot or miss, but I'm using mine until it goes out. Partially out of curiosity.
 

Jeff H Young

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My opinion. Get ot wait for a good deal on a Navien (your application calls for a Navien) the when your heater(s) go out you can go ahead and install it. My humble opinion is that equipment that works should be used. My water heater is from 1986 and still working great. Water quality and heater quality is kind of hot or miss, but I'm using mine until it goes out. Partially out of curiosity.
37 year old tank? or tankless
Yes we never had any issues with hot water on the 2 50s.

After speaking with another guy last night I have now better understanding of the tankless system and I am leaning very heavily in that direction. What I learned (which is probably obvious to you all) is that the Navien will limit the flow as necessary for the temp rise. I know they quote the flow rates for different temps and I saw all that but what clicked in my head last night is the following.....if I am filling that tub, the water WILL be hot but the flow may be adjusted a bit. Let's say my giant waterfall spout into the tub is a 7 gpm faucet (I am just making up numbers). For some reason before I was thinking that if the Navien could only deliver 5gpm of hot, then my water could be just warm at all times coming to the tub. But actually what happens is that faucet will just be water falling at a 5gpm rate. So it's not like I can't get the heat of the water I need to fill the tub, it's just that it might take a little longer. Again probably obvious to you guys but for me I was thinking that if the Navien can't deliver the flow then the resulting water is cooler.....like the Navien just has water flowing through it at a given speed and if the water is too cold then it can't get the full temp rise while the water is in the heat exchanger before it leaves. What happens is the Navien slows the flow to a level where it knows it can get the temp to the right amount.


So I see no downside now to the Navien.

Yeah 50 gal Powervents are expensive now! So buying 2 of them seems dumb at this point, especially if my next set doesn't last 20 yrs like my first set did.
Sounds good! , youll need to evaluate your gas supply, tankless use about 5 times the amount of gas in btu as a 50 gal water heater . of cource for a shorter amount of time but require bigger pipes often times . Yea the tankless wont flow water cooler than the set temp your volume slows down if several several fixtures are using hot water but it will be hot . but not sure you concidered that usualy you have some cold flowing as well so your total flow is all the hot avaiable you said 5 gpm plus some cold a couple gpm so a total of more than 5 gpm
one possible drawback to a tankless is that since when its not in use the hot water pipe dosent have any hot water in it hence you have to wait just a little longer for hot water to arrive
 

John Gayewski

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Hogan

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My opinion. Get ot wait for a good deal on a Navien (your application calls for a Navien) the when your heater(s) go out you can go ahead and install it. My humble opinion is that equipment that works should be used. My water heater is from 1986 and still working great. Water quality and heater quality is kind of hot or miss, but I'm using mine until it goes out. Partially out of curiosity.

Wow that is really old

My theory is that my 20 yr old tanks (they were cheap Menards units with a 6yr warranty) are probably all coated with limescale which is protecting them from rusting haha. So I do wonder if they could last another 10 years or something. One of the plumbers said do not flush them at this point as he sees lots of people like this who flush it after doing nothing for 10+ years and then within a few months the tank starts leaking.

Unfortunately I'm kinda jazzed up now on this Navien option and yanking out the old twin 50s....not sure I can sit back and wait another 10 yrs haha

Will see how the quotes come back but there is a rebate right now that would be $600 so that helps. I can also rationalize that if we sell the house in another 10 yrs, I would bet that marketed properly, the nice cool looking Navien tankless could pay for itself vs some home inspector wigging out about 30yr old 2x 50 gal tanks that are a ticking time bomb.....
 

Hogan

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Interesting now I am being told the Navien doesn't really modulate its flow rate to hold temp.

Does anyone know which is the right answer?

Meaning, let's say we open up 4 showers and are drawing 10 gpm of hot water, and because of the water inlet temp, the Navien can only heat 5gpm to 120 degrees. Does the Navien slow the flow to 5gpm itself so you will have 120 degree water but weak pressure at all 4 showers, or does the water just flow at the same rate thru the Navien so you have the same pressure but the water will be lukewarm and not 120 because it doesn't have enough time in the heat exchanger?


EDIT - I called Navien and confirmed that it is the first example (the Navien will slow the flow of water to whatever it needs to maintain the set temperature rise), so in my example above with 4 showers open at once, the water coming out would be fully hot, but the pressure would be lower than ideal if we were exceeding the GPM that the Navien was delivering at the time.
 
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GReynolds929

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Interesting now I am being told the Navien doesn't really modulate its flow rate to hold temp.

Does anyone know which is the right answer?

Meaning, let's say we open up 4 showers and are drawing 10 gpm of hot water, and because of the water inlet temp, the Navien can only heat 5gpm to 120 degrees. Does the Navien slow the flow to 5gpm itself so you will have 120 degree water but weak pressure at all 4 showers, or does the water just flow at the same rate thru the Navien so you have the same pressure but the water will be lukewarm and not 120 because it doesn't have enough time in the heat exchanger?


EDIT - I called Navien and confirmed that it is the first example (the Navien will slow the flow of water to whatever it needs to maintain the set temperature rise), so in my example above with 4 showers open at once, the water coming out would be fully hot, but the pressure would be lower than ideal if we were exceeding the GPM that the Navien was delivering at the time.
Whoever told you that doesn't know what they're talking about and you definitely should not have them install anything.
 

WorthFlorida

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Four showers at the same time would be rare. Shower heads max out at 2.5 gallons per minute. That is 10 gallons a minute and doubtful you have that. Five gallons usually would be the minimum, 7.5 gallons max.

I would install an indirect water heater if you're worried about running out if hot water and flow rate. It's essentially a storage tank with a heat exchanger inside the tank. The tankless would have a circulator that would pump hot water at the bottom, cooled down water at the top back to the tankless. The recirculated water would probably not get cold enough to impact flow and temperature. Set the temperature to 140 degrees for the indirect WH and use a mixing valve to bring the temperature down to 120 degrees. At 140 degrees would be about a 100 gallon equivalent. Indirect WH are expensive and takes more equipment so it can get pricey. Gas tankless units take annual maintenance, descaling and the air intake screen needs to be clean. It's not an install and forget system like a standard WH.

Or a 50 or 65 gallon standard gas water heater set to 140 degrees with a mixing valve.
 
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Hogan

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Whoever told you that doesn't know what they're talking about and you definitely should not have them install anything.
Sorry but whoever told me what? (Which one is wrong in your mind?) It is the Navien that will limit flow to around 5gpm right? (Like Navien customer service told me)
 

WorthFlorida

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Sorry but whoever told me what? (Which one is wrong in your mind?) It is the Navien that will limit flow to around 5gpm right? (Like Navien customer service told me)
With four showers or even one, it will not be 100% hot water. For most people 105º is about the maximum temperature adjusted cold water at shower valve body.
 

GReynolds929

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Sorry but whoever told me what? (Which one is wrong in your mind?) It is the Navien that will limit flow to around 5gpm right? (Like Navien customer service told me)
Navien tankless will modulate the incoming flow rate based on the incoming water temperature and the desired deltaT or desired output temperature. Whoever said Navien doesn't modulate flow rate is an idiot.

Not sure where you are located but no tankless manufacturer will get you 10 gpm unless you are deep south with very warm ground water. You would need to cascade multiple units if that is a need.
 

WorthFlorida

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Here is a good site on tankless recommendations based on inlet water temperature. You biggest problem is inlet water temperature, not GPM. Some are electric, other are gas tankless. You'll need probably the biggest one made (BTU's) and if the gas supply is sufficient.


Another consideration is the pipe type and size. If its copper 3/4" you're good. Usually each fixture will be branched off with 1/2 copper. If you have galvanized pipe you'll never get the water flow you want.
 

Hogan

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Navien tankless will modulate the incoming flow rate based on the incoming water temperature and the desired deltaT or desired output temperature. Whoever said Navien doesn't modulate flow rate is an idiot.

Not sure where you are located but no tankless manufacturer will get you 10 gpm unless you are deep south with very warm ground water. You would need to cascade multiple units if that is a need.

Here is a good site on tankless recommendations based on inlet water temperature. You biggest problem is inlet water temperature, not GPM. Some are electric, other are gas tankless. You'll need probably the biggest one made (BTU's) and if the gas supply is sufficient.


Another consideration is the pipe type and size. If its copper 3/4" you're good. Usually each fixture will be branched off with 1/2 copper. If you have galvanized pipe you'll never get the water flow you want.

Thanks I will check out those links. Yes this is Chicago area so will be cooler inlet water especially in winter. We have a 20 yr old house and the main outlet from the current hot water tank is larger copper.

If I go tankless was hoping to just do one rather than spend the money on 2 hooked together. Like said, I don't think we ever have more than 2 showers at once and probably not that often that both are exactly together.

In any case if I go tankless my mind is already made up on which one. Navien 240A2 which is a 199K BTU. Comes highly recommended from many I've spoken with. They show their flow rates at different temps so I have a sense for what they would be. Prob still around 5gpm even in winter here.
 
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Hogan

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Navien tankless will modulate the incoming flow rate based on the incoming water temperature and the desired deltaT or desired output temperature. Whoever said Navien doesn't modulate flow rate is an idiot.

Not sure where you are located but no tankless manufacturer will get you 10 gpm unless you are deep south with very warm ground water. You would need to cascade multiple units if that is a need.

I don't think I need 10gpm. I know that is how all these guys advertise but yeah I get it, probably best case my Chicago inlet water might be 65 in the summer? Or maybe 70? I'm just guessing. But in the winter much colder.

As I think about how these work, why wouldn't you set your Navien to heat to 110 or something instead of 120+? That might increase the flow rate a little. I don't think we are worried about sterilizing the water in a tankless system in the same way they suggest you keep a tank at least 120 to make sure you aren't growing stuff. Seems like slowing the flow rate to get the water up to 120 just to then mix it with cold water at the tap isn't as efficient as it could be? What am I missing
 

Reach4

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I probably best case my Chicago inlet water might be 65 in the summer? Or maybe 70? I'm just guessing. But in the winter much colder.
I am thinking your incoming pipe is about 40 inches down. I am expecting the temperatures will be lower than you are thinking. You could use a temperature probe at the incoming pipe, wrapped by cloth or insulation, and measure while you are using water. You could also point to the incoming pipe with an IR thermometer.

If the water then goes a considerable distance in the basement before hitting the WH, it could warm up some on the way.
 
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Hogan

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I am thinking your incoming pipe is about 40 inches down. I am expecting the temperatures will be lower than you are thinking. You could use a temperature probe at the incoming pipe, wrapped by cloth or insulation, and measure while you are using water.

If the water then goes a considerable distance in the basement before hitting the

Ok yes you're right at least according to the websites. Various websites say it is around 50 degrees. Maybe it is a little more in the summer when the lake water starts warmer but let's use the more conservative number.

I just ran the math on various temps for the hot, mixing with (55 degree) cold water to a target 100 degree shower. Reality is that the cold water within the house probably gets warmer than 55 by the time it gets through all the pipes. But in any case whether you set the tankless to 110, 115 or 120 it gets to a similar total output of a blended 8gpm. At 110 it is a little more 8.125. (You use more 110 water in the mix than you would 120 water, but you use less energy to bring it to 110 vs 120? Or maybe not (does the Navien modulate it's burner so maybe it is pulling 199k BTUs at 120 but less at 110? Or is it just going full fire because it is trying to max out flow?)
 

John Gayewski

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The lower the set temp the more effeciant the heater will run.

Optimal temps for legionella bacteria is around 90 to 120 degrees. These temps prompt legionella to reproduce at high rates. Your water might start to smell and the vapor can make you sick. Efficiency takes a back seat to this. It doesn't really matter what temp you run as the heating can only happen at a set rate. You'd be better off running higher temp and using less hot water as it's safer for your health. Your talking about saving pennies a year.
 

Hogan

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The lower the set temp the more effeciant the heater will run.

Optimal temps for legionella bacteria is around 90 to 120 degrees. These temps prompt legionella to reproduce at high rates. Your water might start to smell and the vapor can make you sick. Efficiency takes a back seat to this. It doesn't really matter what temp you run as the heating can only happen at a set rate. You'd be better off running higher temp and using less hot water as it's safer for your health. Your talking about saving pennies a year.
Totally understand this for a Tank system. I didn't know whether Tankless was different because the water isn't sitting in a 50 gallon tank at that temp all the time.
 
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