My Tankless Experiment

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Furd

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Okay, I lied. :D I use a bit over 12 therms a month for water heating. At a cost of a touch over $1.24 a therm that makes the cost of water heating for me about $15.30 a month not counting the various taxes and fees that are added.

Now if I could save 25% of the gas cost by going to a tankless heater that would translate to about $3.83 a month or just under $46. a year.

Assuming that a tank-type heater will last 10 years and a tankless will last 20 years I will save $920. in gas costs (assuming a constant price for the gas) during that 20 year span.

But let us look at a bit differently.

Say a new tank-type heater is $1,000 installed and it uses 12 therms per month at a constant cost of $1.25 per therm. In ten years it will have used 1,440 therms at a cost of $1,800.00 Add in the original cost of the installed heater and you get $2,800.00 to supply your hot water needs for ten years.

If a new tankless heater costs $3,000 to install and uses 8 therms per month (25% less than the tank-type) then over its life of 20 years it would have a total cost of $5,400.00.

Now if we break this back to a cost-per-year basis it comes out as $280.00 per year for the tank-type and $270.00 for the tankless.

None of this takes into account that a tankless heater is more likely to have some kind of failure or will likely need a bit more maintenance than a tank-type. Also, the 20-year lifespan I used for the tankless may be a bit optimistic.

I really wish that the manufacturers would improve the total efficiency of the tank-type heaters but even as things stand today I won't be going tankless just to save a measly ten bucks a year.
 

Master Plumber Mark

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FURD...very good ....you win a cookie....

FURD....very well stated.....thank you

that is exactly what I have been talking about
and have posted on my web site..tankless page...

the brad white test I got posted claims that the
tankless would save about 600 bucks in 12 years

not including breakdowns or maintaince....


I will see with my own unit...my meter, and my
sloppy innefiecient 75 gallon vented heater..............

according to the felllow I bought the meter from
each number is considered .....one cubic foot.

I will need to search the internet to find out how to
do the conversion from one cu ft of gas to btu's or therms,

should not be too hard to do...
 
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GrumpyPlumber

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Furd, You forgot standby loss.
Roughly 15 BTU p/hour p/sq foot of surface area for a 50 gal.
318 BTU/hour, 229,029 /month - 2.3 therms @ $1.24 about /2.90 month.
Tankless isn't for small households, this was based on Marks family of four, we'd multiply the 12 by 4.

48 @ $1.24 = $59.52 with the differential from 60% to 85% would be $42.00/month rounded off to $17 less per month, plus a 50 gal standby loss @2.90 a month, lets say $20 a month.


Furd said:
I really wish that the manufacturers would improve the total efficiency of the tank-type heaters but even as things stand today I won't be going tankless just to save a measly ten bucks a year.
To heck with that...Tankless should drop their prices.
 

GrumpyPlumber

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master plumber mark said:
I will need to search the internet to find out how to
do the conversion from one cu ft of gas to btu's or therms,

should not be too hard to do...


Mark, I can guess it's been awhile since you peaked in your books.
A cubic foot of gas is 1000 BTU, a therm is 100,000 BTU.
Again, for reference one btu is the energy it takes to heat 1 pound of water one degree, a gallon is 8.33 pounds, 62.3554 pounds in a cubic foot, or 7.5 gallons per cubic foot.
Every CF reading on your meter is 1,000 BTU's.
 
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Furd

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Grumpy, I didn't "forget" standby losses, they are factored in to the already metered 12 therms per month operating costs of the tank-type heater. In other words, if I used NO hot water I would STILL have used gas for the pilot AND for keeping the tank hot.


Also, your factor of 1,000 BTUs per cubic foot is NOT exact. Natural gas piped to a home is a mixture of gases and while 1,000 BTUs per cubic foot is an easy number to remember for approximate usage, the gas company multiplies the cubic feet consumption by a "BTU correction factor" to arrive at the number of therms you are billed. This correction factor is listed on the gas bill and changes on a regular basis.

Now depending upon the individual gas supplier a cubic foot of natural gas might be a little less than 1,000 BTUs, a little more than 1,000 BTUs or exactly 1,000 BTUs during any particular billing period.

Tankless isn't for small households,
That isn't what the tankless proponents would have a person believe. In fact, it seems to me that a "small" (i.e. single person) household should be more suited for tankless because it is more likely that hot water would only be used at very specific and infrequent times and using tankless in this situation could definitely reduce the losses from tank standby operation.



It is obvious that you have "bought in" to the arguments given by the tankless manufacturers hook, line and sinker. Now if only "they" would enforce truth in advertising we all would be in a better position to judge the relative merits of each type of hot water supply.
 

GrumpyPlumber

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Furd, you're confusing the term BTU with something else on your gas bill.
A BTU isn't an adjustable measurement on a gas co's bill, it's a measurement of a unit of energy.
Regardless what the adjusted rate on your bill is, a BTU is and always will be 1,000 BTU's per CF nat gas. (thought not exactly, certainly not variable)
The statement you made that a CF of nat gas is variable & can be slightly more or slightly less tells me you might want to pull out your gas bill and reread it more carefully.
The term is a measurement of a CF of NG at atmospheric pressure at sea level is 1000 btu.
 

Furd

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Sorry Grumpy, but you are just plain wrong.

A BTU is a British Thermal Unit and as you explained it is the amount of heat necessary to raise the temperature of a pound of water one degree Fahrenheit.

Natural gas is measured by the cubic foot but is sold by the therm. A therm is equal to 100,000 BTUs as you also stated.

HOWEVER, natural gas is a mixture of many gases, predominantly methane. Because it is a mixture the heating value varies according to the mixture. Because of this there is no guarantee that exactly one cubic foot of gas will yield exactly 1,000 BTUs. Since the gas is sold NOT by cubic feet but by heating value (in therms) it is necessary for the gas supplier to apply a correction factor to the metered (cubic feet) gas flow to adjust for the actual heating value of the metered gas. One cubic foot measured may have a heating value as low as 900 BTUs or as high as 1,100 BTUs. It AVERAGES about 1,000 BTUs but it is NOT an absolute. By applying the correction factor the customer is paying not for the metered VOLUME but the ACTUAL heating value.

I think my 35+ years as a degreed energy systems engineer beats whatever your time as a plumber, machinist and whatever else you have done.
 

Master Plumber Mark

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YES GRUMPY...it has been a long time

Yes Grumpy, I have not opened the books in a long time....

never been necessary, I have got other things to do....

Honestly , I have been considering signing up for a unioin
job just for the educatioinal value...learing new things
and brushing up on things.....and the 65k a year
they pay.... but a plumber has go to run free...




anyway the meter is now sitting at 185 cu ft

for basically almost 48 hours of fairley heavy use...

now I got to get out my gas bill and see what I pay.

then we go from there...



I think that you and Furd can both agree the
the AVERAGE will work out at 1000
 
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GrumpyPlumber

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Furd, Many gasses, not in any substantial amount.
85% Methane, 15% ethane is the norm on NG.
LP is a mixture of propane & smaller amounts of butane, as you know, and yes those mixtures may vary, yes the BTU's vary per gas.
I'm very happy for your academic accomplishments, but the threads topic is Marks tankless experiment and it's probably a good idea to work with a constant.
We could open a seperate thread dedicated to cerebral prowess and who's smartest, maybe another time, but the simple fact is that 1 CF of methane is a constant, I say we roll with it, rather than take on a team of nasa scientists to aid the process.
Lets not get sidetracked on debate over "My brain is bigger than yours" and get back to topic, as Mark just stated above.
The point in stating the CF is 1,000 BTU's isn't exact is true, in the world of physical science almost nothing is, until you get down to subatomic particles.
We're not concerned with nuclear physics as yet on this thread (though humorous remarks could be made about my "calculations').
For the record:
Natural gas(methane) = 1027 Btu/ft3
LP gas (Propane) = 2,500 Btu/ft3
Utilities/technical professions simply round that number off - as Mark states above.
If we really wanted to, we could analyze the potential for rare isotopes that could occasionally crop up from the source of the gas, I say lets not.
 

ultgar01

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Great discussion. I also believe indirect is the way to go if you already have a boiler in place. I'm putting in a small Munchkin unit with a Superstor tank for the indirect...

munchkin-20406-1.jpg


munchkin-21706c.jpg


vision2display.jpg



I'd love to do a tankless for our 2nd floor apartment (heat is via steam so I can't put in an indirect here) but looks like I'll stick with a 40 gallon tank model until things get a bit simpler.

Here's an install I ran into at a clients house last week....3 munchkin boilers and 2 Superstor units for the house....over 20 zones of heating and cooling.

http://www.ultimategarage.com/homegarage/munchkin2.html
 

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I'm in the process of getting together a list of connection supplies for a Rinnai 85i Plus and have a few questions since I don't have the unit on hand and I would rather spec my own connection materials than use their kit.

1) Will there be a need for dielectric unions for connecting plumbing and gas. Not sure what the material is on the heater since I don't have it.

2) Thoughts on using these combo BV and PRV on hot and cold lines and what pressure would be best (I'm thinking 100psi).

http://www.watts.com/pro/_productsFull.asp?pid=564&ref=1

3) Opinions on the venting kit for the Rinnai 85i

4) Opinions on thread vs. sweat on ball valves.

BTW, good thread. I can post some pics of the install as well as performance in extremely hard water (range 100-620 ppm with 313 being the ave) and my efforts to deal with that.
 

Master Plumber Mark

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Kiril said:
BTW, good thread. I can post some pics of the install as well as performance in extremely hard water (range 100-620 ppm with 313 being the ave) and my efforts to deal with that.

You will certainly need to get the bypass valve flushing kits for that tankless unit to de-lime it

are you on well water or something???
 

Furd

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It is the engineer in me that insists on being precise. I will agree that for the purpose of Mark's study that 1,000 BTUs per cubic feet of gas will be close enough to assess the differences between tank-type and tankless water heaters on a short term basis.

On a long-term basis, i.e. ten years or more, the differences could have some bearing.
 

Bob NH

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One thing missing in all of these analyses is that the difference between a $3000 instant heater and a $1000 tank type heater, if used to purchase a CD at 5%, would return $100 per year. That is more than the saving expected on most of these systems.

Many homeowners are paying more than 5% on their mortgages and a fair number are paying 15% on credit card balances. They would be better off if they paid off some debt, which would produce a greater saving without any maintenance or depreciation.
 

GrumpyPlumber

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Furd said:
It is the engineer in me that insists on being precise. I will agree that for the purpose of Mark's study that 1,000 BTUs per cubic feet of gas will be close enough to assess the differences between tank-type and tankless water heaters on a short term basis.

On a long-term basis, i.e. ten years or more, the differences could have some bearing.

Of course they would, but the point is that the same gas would be feeding a tank OR a tankless.
Besides, Mark is measuring actual CF, not btu's.
 

GrumpyPlumber

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Bob NH said:
One thing missing in all of these analyses is that the difference between a $3000 instant heater and a $1000 tank type heater, if used to purchase a CD at 5%, would return $100 per year. That is more than the saving expected on most of these systems.

Many homeowners are paying more than 5% on their mortgages and a fair number are paying 15% on credit card balances. They would be better off if they paid off some debt, which would produce a greater saving without any maintenance or depreciation.

Humorous & true.
On that note, I charge all my stock, then pay it off immediately for that very reason.
You bring up a very interesting point, people seem to obsess over fuel costs lately, without looking at what intersts their cards have, mortgage or auto loans and maybe consider refinancing/ switching cards...etc.
So I guess this narrows it down to only large families with no unpaid loans that would benefit from tankless's.
 
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Kiril

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master plumber mark said:
You will certainly need to get the bypass valve flushing kits for that tankless unit to de-lime it

are you on well water or something???

Yes, well water. Got a link or pic of that?
 
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Master Plumber Mark

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Links to de-limeing issues

I think that this lady is on well water....

you should be able to call her she is so pi//ed off
that she left her telephone number for anyone to call
about her ordeal with a Bochse unit

she has fought with it for 5 years and switched back to
a tank type heater...

read # 4 and 5 .......that she posted



http://www.complaints.com/2007/march/1/Bosch_Aquastar_240_FX_tankless_water_heater_18190.htm



almost all tankless brands out there sell the "expensive accessories"
that they dont like to mention too much about

I got two sets of them n my office....I think that they are worth
about 100 bucks each...

http://www.designerplumbing.com/store/ISO1.html




and If I could get my wife to stop chargeing things on the master card
I probably would be debt free...,
 
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Dunbar Plumbing

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Damn......that's some fine looking art of plumbing there

Art indeed. (right clicks-saves as, puts company name on pictures) Yeah I worked all night on that one!!!

RUGGED's two favorite metals >>>> Copper, Brass

That system above is one that'll be there for years, the mice won't bother taking any interest in it cough!cough!pex~! and the way it was built....top notch design with isolation valves everywhere to service it down the road.


I couldn't even read all the factors that were posted on the comparison draw with tank against tankless; It all gets thrown out the window because you are stating CONTROLLED laboratory/mock testing on both products.

The real life scenarios with one week of cold weather.....another week of REAL cold weather.....then a slight increase in temperature. OR.....if you are out west.......it's always warm! How easy is it to bring warm water to hot? Pretty simple I'd say.


And to think that "only tankless owners" will keep their plumbing in good repair? Meaning they will instantly stop a leaking tub faucet or lavatory or kitchen sink faucet? NEVER. That's wishful thinking and that destroys the savings on the equations laid out. They keep making these units cheaper and cheaper so of course that allows the low-end users the ability to afford that application too.

The majority of people have leaking faucets and some leak for years before they are fixed. Not everyone......but there's a good amount of people that ignore that "oh it's just a small leak" situation.

I put in any of these treats......the rules of engagement are as follows: You are allowed a minimum of 1 call per 12 month period to ask me questions why it is not working right....or why it's giving you an error code when mindy your wife is washing daughter natalie in the jacuzzi and just can't get the water warm enough. I didn't make it.....I just installed it. Boo-yah!!!

Keeps me employed.
 
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