Tankless HW Heater question?


Can I use a Rinnai R53 to supply a standard 50 gal HW Heater? In other words, I would use it to put hot water into an existing tank. It isn't the most efficient setup, but it seems like a logical way to never run out of hot water no matter how many taps are on.
My HW Heater is new and I own the Rinnai R53. I tried the R53, but had problems. I am convinced the gas supply wasn't heavy enough. I will test it out thicker gas lines though and see if it makes a difference. If it does, I would want to use it in concert with the heater I have now. My thought is, instead of sending cold water into the tank, I'd be sending hot water in. It wouldn't need to heat it and the supply would theoretically be endless. Plus, God forbid there was an issue with the tankless, I still have 50 gal of hot water to play with.
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I think you can do it if you use a recirculating loop system controlled by an aquastat

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Sure you could do it, the only question is why on earth would you? The tankless is supposed to supply water on demand to eliminate the need for a conventional water heater, the standby energy loss, etc. Doing this, you have a big upfront expense for the tankless, but lose the energy benefit, still have to pay for a regular tank, etc.
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On Feb 9, 8:15 am, snipped-for-privacy@optonline.net wrote:

I understand why he would want to do it, but I don't think that it is necessary. A possible reason for this decision could be this:
I have hot water at the temp that I want coming from the 50 gal tank. The only thing I don't like about the tank is the time when I run out of hot water while I'm showering. (I guess maybe other times, but this is the only time I don't like it.) If I can "pre-heat" the water, then it will recover faster. Then I can wash my clothes, run the dishwasher, take a long shower and still have hot water to wash my hands a few minutes later.
An easier, more economical solution would something more like this: Get a smaller tank (maybe 30 gal) that takes less time to recover, insulate it (on the outside) to prevent additional heat loss, and insulate the pipes when they leave the tank. Then get a tankless water heater to supply your shower(s) and use a controlled temp for your shower (and sinks) for a never-ending hot shower.
The only problem is this, what would the smaller tank be for? Washing clothes and dishes? Why store hot water for something you do maybe once a day? Or even once a week? Get rid of the tank altogether and stop wasting heat. If you really need to wash your dishes while you take a shower get a smaller tankless for the kitchen to run the sink and the dishwasher.
Bottom line, if you buy a tankless, the tank is then useless. With the only exception being you have four teenage girls and they all have their own bathroom, and all want to take a 20 minute shower at the same time. But in this case, I don't think they make a water heater big enough to handle that. Of course, if you have 4 or 5 bathrooms in a house, you can probably afford more than one tankless heater.
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Then how do motels do it?
Bob
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How about the other way round? Set the tank to 80 F?
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Your better off input tankless regular tank fixtures, because a low flow like washing hands might not trip on the tankless but will be supported fine by a regular tank:)
I would run a new 1 1/4 or larger line directly from the meter for best tankless operation. at this point you might as well install the tankless properly.
The problem isnt pressure but FLOW, a small line cant carry enough gas: (
Just like a 2 lane road cant carry interstate traffic volume, a jam occurs and everything slows down...
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snipped-for-privacy@ece.villanova.edu wrote:

Your better off input tankless regular tank fixtures, because a low flow like washing hands might not trip on the tankless but will be supported fine by a regular tank:)
I would run a new 1 1/4 or larger line directly from the meter for best tankless operation. at this point you might as well install the tankless properly.
The problem isnt pressure but FLOW, a small line cant carry enough gas: (
Just like a 2 lane road cant carry interstate traffic volume, a jam occurs and everything slows down...
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snipped-for-privacy@ece.villanova.edu wrote:

Your better off input tankless regular tank fixtures, because a low flow like washing hands might not trip on the tankless but will be supported fine by a regular tank:)
I would run a new 1 1/4 or larger line directly from the meter for best tankless operation. at this point you might as well install the tankless properly.
The problem isnt pressure but FLOW, a small line cant carry enough gas: (
Just like a 2 lane road cant carry interstate traffic volume, a jam occurs and everything slows down...
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On Feb 9, 8:15 am, snipped-for-privacy@optonline.net wrote:

As stated in the original post, I have a brand new 50 gal HWH and I own a Rinnai R53. The equipment expenses are long gone and energy cost isn't an issue. Also, I just don't trust the tankless on its own and HW isn't something I can live without. I have a couple high flow showerheads and water depletes too fast.
Short story version -- had an older 40 gal HWH. Replaced it with an R53. Hot water turned ice cold after a minute. Used 3/4" gas line, but pressure was probably low and couldn't keep up. I have a high efficiency gas heater, gas cooking, and even a gas grill outside, so my gas demands are high. I also didn't like how long it took to heat the water. I got nervous, ripped it out, and instead of reconnecting my older 40 gal the plumber gave me a 50 gal at cost and hooked it up for free. He wasn't that experienced with tankless, so chances are he did something wrong. or, maybe my gas pressure just can't support all those appliances.
I would try 1" gas lines in a temp config to see if it works. A few flex connectors, vent it outside, and off we go. If that works, then I'll integrate it into the system. I just need to know if I can. I know its an odd request, but i have what i have. If it won't work, I can dump the Rinnai on ebay pretty easily.
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EXCELLENT!! It will work fine and combines the best of both worlds espically since you already own the tankless and the 50 gallon standard tank:)
Stanby losses will be no greater than stanby losses for a regular tank, and besides they go to help heat your home anyway in the winter!
DO get pro sizing on gas supply lines for all appliances, too great a demand overall might be a hazard!
You will have endless hot water since in many cases the watewr entering your tank will be at or near full temp.
You DONT need any recurcliating lines between tankless and standard tank. do watch teenagers dont run up your water gas bill, they may live in shower:(
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Thank you!
The installer didn't size the gas lines properly originally. I am almost sure of it. that said, I like the security of the 50 gal tank.
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