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1. 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.

2. 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.

3. ## 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

4. 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.

5. ## Parrellel Universes and sub-atomic particles....

Damn, you know I just hate it when those

sub atomic paiticles and isoteopes clog up the

gas orfice on my outside grill.....

it gives the braukwurst kind of a metallic taste...........

6. 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...

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

7. 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/_productsFu...?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.

8. Originally Posted by Kiril

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???

9. 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.

10. 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.

11. Originally Posted by Furd
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.

12. Originally Posted by Bob NH
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.

13. Originally Posted by master plumber mark
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?

14. ## 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...ater_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

http://www.****************.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...,

15. ## 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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