rinnai vs rheem tankless

Please refer to the details in my previous post. If you find errors, you won't bruise my ego if you let me know what those mistakes are. There is only one variable, and that is the price of gas, which in my case is $0.915 per therm at the moment. My apologies for stating "at the current price of natural gas"; I should have given the actual cost. However, the price of gas this week or next month is irrelevant for the purposes of

*comparing* tank vs. tankless heaters (the thread subject & my current ambition), as are weather, incoming water temp, etc. I am comparing one type of gas water heater, a storage tank type, to another type of gas water heater, a tankless type.

As to my estimated payback time of 8.1 years, that is based on the current 91.5 cent per therm price. And my estimate is probably off by

10% one way or the other. As the price of natural gas goes up, which it probably will, the payback time will shrink accordingly because the tankless will consume fewer therms over a given time period than a tank-type heater.

Regarding your comment on the downside of endless hot water, you raise a valid point. Another poster previously did as well. So far, that does not appear to be an issue in this household, which consists of two teenage sons and me. In my case, sewer charges are flat-rated i.e. are not tied to water usage. So the only lurking "hidden costs" for this endless hot water -- and the gas to heat it -- would be minimal to unmeasureable, I think.

After this morning's flurry of hot shower-takings, my older son took off to spend new year's eve day with friends. Only two of us remain. The current time is 3:30 PM PST, and no hot water has been used since all those showers. I wonder how many times the old tanker would have cycled on and off during that time? Wait! A lady friend is coming over later this afternoon, perhaps she'll take an "endless" shower. Perhaps I'll even encourage her ;^)

Reply to
maxodyne
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as to heat loss my old tank sprung a leak just after I showered, hearing water running I investigated and found water spraying out of the flue.

so I turned gas and water off and went shopping for a tank. the next day I got a quick shower, the new tank would be in first thing in the AM, i tended to shower after work.

I was happily surprised turned water on, ran and took shower the water was still hot. near 24 hours after its gas shut off for the very last time ever.

tanks reheat very infrequently, and the losses do heat your home. just like other energy uses.

=2E.........................................................................= .............................................. I am very interested in your stated savings and cost comparison. are you basing this totally on the energy guides label?

because water heating cost depends on many factors, temperature of incoming water, temp the tank or tankless is set at, cost of gas varies each year.

do you have a meter on your tankless to find out how many MCFs it uses in a year? and a meter on your old regular tank unit?

way too many variables, please list exactly how you found your dollar savings per year.......

thanks i really want to understand

Reply to
hallerb

I am glad you really want to understand, and I'm happy to oblige. Let's work through this... ......................................................................

No, I'm *not* basing this totally on the energy guide (based on standard U.S. Government tests) label, but I believe that is a good starting point. A therm is a therm (approximately the heat energy of 100,000 BTU

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and the sum quantity of therms consumed in a hot water heating event relates to the total cost of heating that water. A poorly designed heating device will consume more therms to heat (and store, in the case of tank-type heaters) that water than a well designed heating device.

The Bosch 2400 E uses 177 therms per year, according to the energy guide that came with it. You can get more information on this model at:

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After reviewing the Bosch efficiency factor specifications, you may want to compare the estimated therm usage and/or efficiency factors of tank-type heaters so that you can compare "apples to apples". Please note that I am not advocating Bosch over any other brand; Bosch just happens to be the brand that I purchased. There are several tankless choices available in the marketplace, and one should shop wisely & compare efficiencies, performance, features, warranty terms, options availabilty, etc.

No, I do not have a National Bureau of Standards lab here in my home to measure this level of detail. But I do not need one either. The efficiency factor of the Bosch 2400E is .80%, and the efficiency factor of the Whirlpool 50 Gallon Flame Lock? Natural Gas Water Heater is .58%. (you can verify this by comparing heaters on the lowes.com website). An efficiency factor of 1.0% would be a perfect, lossless conversion of all BTU input to hot water output. Anything less than that represents some loss of efficiency. The lower the number, the greater the loss. That having been established, it all comes down to how much money one is willing to spend in order to own a higher-efficiency water heater.

Again, please review my previous post. There is only one variable, the $0.91/therm price of gas. Everything else is a fixed cost. Water inlet temperature, thermostat settings, etc. would be the same if I ran both tankless and tanker in a side-by-side comparison in real time, and one would prove to be more efficient, and more economical to operate than the other in the long run. It's all about the efficiency of the device, and how much one is willing to spend to buy it.

I hope this helps.

Reply to
maxodyne

I don't sell them. I am a general contractor. They are just one of the new popular items since people have become aware of them and how much energy use they can save. I haven't seen any of my customers complain about them. The last one that I installed cost $845, the install was 300 dollars and she got a

200 dollar rebate from the city.

I have one, with two baths, a kitchen, dishwasher and wife and

2 kids. Haven't run out of hot water since I put it in. I got a Rinnai and it has been performing for 5 years now. I cannot compare energy savings head to head, because I went from an electric water heater, to a gas tankless, but my electric bill went down by $45 dollars a month (It averages about 250-300 per month).

You seem to be trying to convince people that they are spawn from hell and I am just trying to present the honest facts. I think you are the one who is biased. It makes no difference to me what the homeowner wants to install, I make money on the whole job, not just one part.

Reply to
Robert Allison

honestly it doesnt matter to me what anyone chooses to buy for their home.

my issue with tankless are the large number of potential downsides to a expensive supposed upgrade, which may disappoint the purchaser to the point of going back to a regular tank.

such things as someone showering, and someone else washes their hands, shower poerson may get nasty chill.

plus energy savings is hard to qualify,,'

since standby losses do help heat your home,

at least if someone going to spend a lot of money they should be aware of not only the positives but the negatives too.

I KNOW MY satisfaction level here went up dramatically here when I went from a 35K 40 gallon tank type heater to a 75K 50 gallon tank. I would of gone 75 gallons but it was too large to fit the space.

often people dont know that high btu tanks are even available:(

Reply to
hallerb

Hi, My family always take tub bath. Some times using big Jacuzzi. When house was built I considered tankless but no one could give me satisfactory guarantee on it. We ended up with two 50 U.S. gallon gas heater. Did not have any hot water issues.

Reply to
Tony Hwang

Robert Allison wrote: > I don't sell them. I am a general contractor. They are just one of the > new popular items since people have become aware of them and how much > energy use they can save. I haven't seen any of my customers complain > about them. The last one that I installed cost $845, the install was > 300 dollars and she got a 200 dollar rebate from the city. >

Greetings, Mr. Robert Allison General Contractor, and welcome to this very interesting discussion about tank-type vs. tankless water heaters!

I'm moving your valuable contribution to an appropriately re-named thread so that we can stay organized -- I hope you will follow it here. The thread started out as rinnai vs. rheem tankless, but soon morphed into a general tank-type vs. tankless water heater discussion. Then I joined in, and renamed the thread as such. I won't ramble on about stuff that I already covered. Hopefully you have picked up enough information from the various posts in this thread.

Now then. You say that you have installed tankless heaters for your clients, and they haven't complained about them. Plus, you own one yourself. This is a good thing IMHO for this discussion group. I recently installed a Bosch 2400E (natural gas) in my home a few weeks ago, and have been mostly satisfied with the unit, as well as my own installation. A dozen or more copper sweat-soldered joints and no leaks. Anyway, I have a question that I hope you or someone else reading this post can answer.

After installing my tankless heater, I discovered one thing the old storage tank hot water heater was very good at: trickling a flow of hot water into a sink. Tankless water heaters have trouble here, because they depend upon a pressure drop to fire the heater. If that drop is less than what the tankless sensor can detect (because so little hot water is being demanded at any given moment), then no hot water. Or as I have observed with my new tankless heater, after running full hot water for a minute or so, and then turning down the hot mix down to below the sensor threshold, the tap flows a combination of hot-then-cold-then-hot-again kind of "checkerboard" hot water into the sink. I know what's going on -- the tankless pressure or flow sensor is reacting to my hot water demand and turning the burner on, off, and back on again as I manipulate the sink hot and cold valves. So, the hot water plumbing is delivering hot, then cold, then hot again water. That all makes sense to me, but I want to improve on that if I can.

I know that tankless water heaters depend upon an inlet-outlet pressure differential to trigger the burner (natural gas, in my case). I recall reading that my Bosch 2400E has a pressure or flow sensor which detects a 0.8 PSI water inlet/outlet differential. I have performance-tested my home plumbing for any hot water "crossovers", and found none.

SO HERE COMES THE $64 QUESTION: Is there a way to adjust this pressure sensor if it is adjustable, or to swap it out for a sensor of a different, lower pressure differential value if it isn't adjustable; or, is there any way to adjust the pressure parameters in the Bosch's on-board computer/processor to lower the burner turn-on threshold so that I can trickle some instantaneous hot water?

I hope all of that makes sense ... if not, someone please hammer on me and I'll re-write my rather long-winded question into a shorter-winded and more concise question if I can.

Reply to
maxodyne

I have but one question. What is the maximum water temperature you can get continously? I see you're in Texas. I suppose the incoming water probably never drops below about 75 degrees eh?

steve

Reply to
S. Barker

Please don't top post.

I have not put a thermometer on it, but I cannot put my hand in the water with just the hot water faucet turned on. You can be scalded by the water coming out of the faucet.

Water temperature at the lake where our water comes from is at

60 degrees right now. I don't know the actual water temperature when it comes into the house. But it is probably about 60-70 degrees most of the time.

Reply to
Robert Allison

I have no idea. That would be a question for the Bosch company or a company that repairs Bosch equipment. I know that there are different thresholds on different units, but I have never attempted to adjust the threshold (nor have I had a need to do so).

I am sure that it is possible, but I can't answer your questions.

Reply to
Robert Allison

with input water at 70 degrees you have it easy. our incoming water in late winter has been 39 degrees.......

its like taking water out of the fridge.

as to adjusting a tankless for low flow.

its probably impossible for a trickle.

combo of detection ability and the possiblity of overheating water and possible tankless damage.....

imagine a trickle flow going out of tankless, the tankless burner might turn that trickle flow into steam. imagine steam boiling splashing out of a faucet while your washing your hands.

Reply to
hallerb

top posting makes the most sense.

120 degree water will burn your hand. But it won't wash dishes. Thanks for the reply. I'll stick with the tank.

steve

Reply to
S. Barker

Post where you want then.

Using a thermometer, the output at my kitchen sink is 142 degrees. At the hall bath, it is 141. At the master bath it is 141. That is as soon as the hot water reaches the fixture. I did not leave it on to let everything get warmed up.

Reply to
Robert Allison

=EF=BF=BDThanks for

i never have our tank set to more than 120 or so..........

to minimize the chance of a severe burn. i prefer to let the dishwasher heat the water.

i am rewarded my longer water heater life, since the hotter they are the shorter their life.

Reply to
hallerb

Good ideas, snipped-for-privacy@aol.com. Another good reason to *not* maintain high water temps on tankers is that the hotter one stores that water, the more energy will be expended on maintaining that temperature i.e. the greater will be the standby loss expense in $$. I suspect that the increase in expense $$ would rise somewhat with the square of the temperature in degrees, but that is just a guess on my part. Before I converted from tanker to tankless, I generally kept the tanker at about

120F also. The net effect is that whilst taking a hot shower, I am using mostly hot water with a minimum of cold water to temper it. The only rational reason I can think of to keep tanker water much hotter than 120F would be to have more "concentrated" hot water available to "cut" with cold water, so that the available stored hot water could be made to last longer before it runs out. But I am free from such tanker rationale now with my tankless. Free at last!!
Reply to
maxodyne

snipped-for-privacy@aol.com wrote:

Yikes! No doubt! 39 is some cold water. Perhaps you could store this 39 degree water in large insulated tanks & use it for cooling during the summer months LOL!

BTW, tankless mfrs. such as Bosch and Takagi (and I'm sure many others but I don't know it for a fact) make higher-output tankless models to deal with extra-cold inlet water. Check their website documentation on this feature for more information.

this can be done, but...

Right you are: at the point of trickling use -- at the kitchen sink, mainly -- the sink outlet temperature tends to be either hot or cold; very tricky to maintain "warm" at low tankless flow rates. I believe this to be the Achilles' Heel of tankless design. It has proven especially frustrating to maintain a low flow of warm water because just when I think I have the mixture right, the heater shuts down (without my knowledge, as it makes virtually *no* sound when it is running & heating water), but I don't realize that it has shut down until its charge of cold water eventually makes it to the sink. The natural instinct at that moment is for me to compensate by increasing the sink's hot water tap sufficient to exceed the threshold of the heater's pressure drop sensor (causing the burner to commence heating), but as the water in the tankless' heat exchanger is at that point thoroughly cold, there will be a delay until the hot water appears -- despite my compensating, the water grows colder until the heated charge makes its way through the plumbing. Then it becomes too hot, and so I back off on the hot water, causing the pressure drop sensor to signal the burner to shut off, and the cycle repeats in a slow motion too hot/too cold loop. I have found a "magic spot" position for the sink tap (I have a Moen Extensa type single-stalk valve) to entice the warm water to come out, but that spot is very flow dependent.

I am pondering the idea of installing the tiniest possible electric tank-type heater, say a 5-gallon unit or less (if less than that is made), directly under the sink to help compensate both for the temperature time lag caused by the tankless heater, as well as perhaps buffering the too hot/too cold temperature loop. I realize I would be compromising the energy savings brought about by the tankless heater, but it may be a possible solution.

I don't think this is a possibility. I know that the heater has an outlet temperature sensor, and that a modulating valve can adjust the heat exchanger BTU input. At any rate, the heater has a 12-year warranty.

I don't think any well-known manufacturer would allow their tankless heater to turn into a steam cleaner...

As another poster pointed out, most recently manufactured "whole house" tankless heaters are made with modulated heat output, so that the thermostat's setting takes priority if at all possible.

[to the "top posting" and "bottom posting" advocates, I have deliberately "middle posted" here because it seemed like the logical thing to do, more like a conversation -- maxodyne.]
Reply to
maxodyne

tankless manufacturers recommend 2 tankless in series, for super cold input temperatures. modulating gas valves are a improvement, but may not have and doont appear to have the range of trickle to full on. if at least one of them did no doubt it would be advertised.

so you went tankless but are now thinking of installing a small electric tank under your sink? electric water heating costs way more than gas, still has standby losses, a new something to maintain..........

putting aside the endless hot water, was the tankless worth it?

Reply to
hallerb

I believe that it was in my case. I needed to do something because the tanker was leaking. I realized that there were choices, and I made one. No, I'm not going to install an electric pre-heater, I was only

*pondering*, both for myself and to see what others might say.

The difficult tankless trickling kind of bothers me ... but running out of tanker hot water, or having to plan my shower around others' showers, or the dishwasher, or the washing machine etc. also kinda bothered me. As I learned to live with the tanker's idiosyncracies, so shall I learn to live with those of the tankless. But really, other than high initial cost and very low hot water flow issues, there are no other drawbacks to my tankless conversion IMHO.

As I mentioned in a previous post, my two children are still living at home while going to college -- but not for much longer. In a couple or so years, it will just be me. That tankless heater will be spending a lot more time in the off mode than it currently is. I believe I will begin to *really* save on the gas bill then, especially if the price of gas goes up -- and I have no doubt that it will.

I really do not like wasting things either, and the tankless is more efficient than the tanker, period. It uses less energy and takes up less space.

-- maxodyne.

Reply to
maxodyne

well honestly I might add a tankless here, when we get a new furnace. currently we have a 75K BTU tank type heater, its over 7 years old. now when a new furnace goes in the furnace will get moved, its in the middle of our basement and kinda in the way. all the gas lines will be changed. our furnace was installed in 1965 and wastes lots of gas.........

so i would like to add a tankless as a preheater, upgrade to a 75 gallon 40K BTU tank, this will get me a 12 year warranty tank, and what should be endless hot water. with no trickle or other troubles.

other than initial cost the tankless wouldnt cost anything to operate since either way the water must be heated.... frankly i dont mind the standby losses, in the winter it helps keep my basement warm. its also my shop.

does your tankless need power line voltage to operate? a power failure at the wrong time could leave you with a cold shower:(

Reply to
hallerb

This sounds like an excellent plan -- I had considered similar before the tanker began leaking. I figured as old as it was, it was gonna go someday; had my tankless already been installed upstream, it would have done the preheat (and eliminated that doggone tankless very low flow issue) although standby losses on the tanker would still be an issue (see next paragraph). Then, when the tanker went, I would be left with an already installed tankless.

I on the other hand *do* mind the standby loss. Not so much in the winter, as the tanker was (and the tankless is) in the laundry room which is adjacent to the kitchen, and some heat is added. Note that there remains a true "total standby loss" at all times of heat radiating from the storage tank up through the flue. Not sure how to calculate that, though. Anyway, I live in southern California where it gets hot enough for several months during the summer that I run my central air conditioner -- which is also cooling the tanker's standby losses. Again, not sure how to calculate the cost of that.

I had considered this issue when comparing tankless heaters. Bosch does make a model that generates its own power from the water flow -- probably some kind of impeller wheel generator, although I don't know for certain -- but the model so equipped was not available in the BTU capacity that I wanted. The self-generating model is the Aquastar 1600 if you are interested. I noticed that other mfrs make tankless heaters that use batteries to ignite the burner & maintain their settings. The

2400E that I installed *could* be plugged into a UPS (Uninterruptible Power Supply) that are commonly used to provide short-duration power to computers during a power outage. The standy current for the 2400E is 40 milliamps; however, it also uses a fan to force positive flue ventilation which needs less than or equal to 2.5 amps (these amperage figures are from the installation manual). The UPS would probably provide backup power for a good long while though, so long as hot water was used judiciously.

While I was in the installation manual, I found the heater specs & modulation range in BTU: maximum input 175K, maximum output 143K, minimum output 31K, recovery efficiency 86.5%. Temperature stability is plus or minus 2 degrees Fahrenheit, although you can obviously toss that figure out the window at very low flows.

I have experienced power outages with the old tanker, and it was rather an unexpected joy to take a hot shower with candles and kerosene lamps to light the way. Much more enjoyable than a "cold tankless" shower would be for sure!!

One of the many good resources on the web for energy-conserving appliances is realgoods.com. I noticed that they claim "Bosch sells more than 1.5 million tankless water heaters each year", so there may reasons why people are buying them. That's just the sales of Bosch; there are many other brands...

-- maxodyne.

Reply to
maxodyne

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