(206) 949-5683, Top Rated Plumber, Seattle

1. <---Nerd.

Mark, this is where our approaches would differ....
BTU = energy to heat 1 lb water one degree, assume incoming water is 40
1 gallon of water is 8.33 lbs X 90 (to 130 hot) = 749.7 BTU
Surface area of a 75 gal cylinder = 27.9936 (28 sq feet)
Code requires WH to have a min of no greater than 15btu heat loss per hour
per sq foot of surface area so -

-28 X 15= 420 BTU per hour on a 75 gal tank @ stand-by = 10,080 BTU/day

-KS faucet = 1.5 gpm (hot alone) Used lets say 1/2 hour/day for dishes etc
= approximately 45 gal/day

-Shower 2.5 gpm (1.25 for hot) with a family of 4 @ 15 min apiece
= 75 gal/day
-Tub, ok, lets toss in a 60 gal bath each day for the mrs
-Laundry, say one load/day uses 30 gal hot
-Lav/misc. Lav's flow @ 1.25 gpm lets say it's used 8 times/day @ a minute
each .63 gpm X 8 = 5 gal/day

thats 45 gal + 75 + 60 + 30 + 5 = 215 gal/day
215 gallons take 161,185.5 btu to heat to 130 from 40,
tank heater is 60% efficient so it takes an actual 268,642.5 btu house/day
add 10,080 BTU for stand-by with the 60% effiiciency offset for
16,800 btu/day.
Thats 285,442.5 BTU per day used for a tank type
Tankless is 85% efficient which means it uses 189,630 BTU /day for 215 gal.
In other words:
a tank uses 8,563,275 btu or 85.63275 therms/month (30 day)
tankless ~~5,688,900 btu or 56.88900 therms/month

My area a therm is approximately \$1.50 ...
tank = \$128.45/month
tankless = \$ 85.34 A family of four saves \$ 43.11/month
\$ 517.32 /year
\$ 5,173.20 /10 years (warranty)

Tankless installed = \$3000.00 - \$5173.20 = -\$2173.20 (saved money)
50 gal Tank installed = \$ 850.00 (draft) + 5,173.20 = +\$6023.20 (10 year)
50 gal powervented = \$1250.00 (still 60%) = +\$6423.00 (10 year)

2. ## Tankless...

FWIW,demand heaters are very popular here.Many people live off grid.
Most are using rainwater catchment systems so there is not a hard water problem.Propane gas is what is used for the most part.People tell me they like the fact that it only uses gas when they use hot water.I do hear the complaint about temp problems if they are using water at a couple of fixtures.
I know of one new house that had 3 demand heaters installed.One in each bathroom and one to take care of the kitchen and laundry.The owner said his gas bill for propane was less than half what it was on his previous house.
Electric is very expensive here so people have gravitated toward these heaters.I"m changing over to a gas stove and heater in the very near future myself...

3. ## did you do your own experiment?

Grumpy wrote
My area a therm is approximately \$1.50 ...
tank = \$128.45/month
tankless = \$ 85.34 A family of four saves \$ 43.11/month
\$ 517.32 /year
\$ 5,173.20 /10 years (warranty)

Tankless installed = \$3000.00 - \$5173.20 = -\$2173.20 (saved money)
50 gal Tank installed = \$ 850.00 (draft) + 5,173.20 = +\$6023.20 (10 year)
50 gal powervented = \$1250.00 (still 60%) = +\$6423.00 (10 year)

Grumpy....
If you had it all figured out, why didnt you tell me this before I went and bought the gas meter???

your figures sound like "fuzzy math " to me....
but of course that is why I am fooling with
the whole thing in the first place.....

I got to prove it to myself.... what a 75 gal
gas water heater costs per month to run

I will test the temp of my hot water tonight,
and the incomming water temp for kicks too...

if the tankless save 45 bucks a month ok, great

I suppose that means I got another 45 bucks to pour into my gas tank...

I will run out and buy one tomorrow

4. Originally Posted by master plumber mark
Grumpy....
If you had it all figured out, why didnt you tell me this before I went and bought the gas meter???
What? And ruin all the fun?!?!?
Originally Posted by master plumber mark
your figures sound like "fuzzy math " to me....
but of course that is why I am fooling with
[/SIZE][/B]
Absolutely fuzzy!
I might be a nerd, but I never said I was a smart one.
one example, I knowingly over-estimated the cost of a therm for my area @ 1.50...it's slightly less and I'm pretty sure my area is more expensive relative to the norm.
If one figure in my whole scenario is off, it's multiplied by 3,653...however the rough savings should be right on in terms of percentages.
The actual figures I typed are just for an example of what you'd save @ 215 gallons of hot per day, most likely even your family uses less.
Duly note though, even half that amount would break the cost of a tankless vs tank type within the warranty period.
Also, I didn't factor in the fed tax credit of \$300 (which means \$75-\$100 in real money for most tax brackets) and local gas companies offer a \$300 cash rebate for installing them here in New England.
Bottom line is YOUR method will be the most accurate.

5. Your summer gas bill should be almost all water heating. The amount used for cooking should be negligable.

So you could compare your demand (Therms) with Grumpy's 85 Therms per month.

I think the hot water demands are excessive. The kitchen faucet (45), laundry (30), and Mrs bath (60) in addition to shower are probably 2 times what the those uses would be in a real family.

6. Bob,

Grumpy is simply thorough. He over engineers most things. He also likes the ladies clean!

Tom

7. As a reference, I used 15 therms last month of gas with an indirect, gas dryer, stove, barbeque. The previous year, I used 18 therms for the same month. The heat was from a Trianco Heatmaker that is a hybrid tankless (87% efficient boiler). I've used my new barbeque more than the older one, letting it run for at least an hour baking potatoes, that I didn't do last year.

8. I use about ten therms a month for water heating. I live alone, like long showers, occasionally use a 6-foot long whirlpool tub, and have a 50 gallon Kenmore Power Miser 6 water heater with a continuous pilot.

I did remove the restrictor from my shower head but I also use the volume adjustment of my Moen shower valve.

9. [quote=Bob NH]Your summer gas bill should be almost all water heating. The amount used for cooking should be negligable.

So you could compare your demand (Therms) with Grumpy's 85 Therms per month.

you are not accounting for the GAS DRYER in the home like I got....

my wife runs the gas dryer sometimes for 5 ++ hours per day.... lots of laundry to do

that is why I got the meter...to monitor the heater only

now all I got to do is wait for the fellow I bought it from to answer my questions...

as far as factoring in a 300 dolllar credit, you also got to factor in
yearly maintaince on a tankless heater.....

what is that worth???

10. Originally Posted by Bob NH
yearly maintaince on a tankless heater.....
what is that worth???
How much is a bottle of vinegar, a small pump & a double ender going for these days?
About as difficult and time consuming as flushing a tank type.

Originally Posted by Bob NH
I think the hot water demands are excessive. The kitchen faucet (45), laundry (30), and Mrs bath (60) in addition to shower are probably 2 times what the those uses would be in a real family.
Fine, then let's modify my original "equation" by going to the opposite extreme and cutting it all in half...
Originally Posted by GrumpyPlumber
a tank uses 8,563,275 btu or 85.63275 therms/month (30 day)
tankless ~~5,688,900 btu or 56.88900 therms/month
My area a therm is approximately \$1.50 ...
tank = \$128.45/month
tankless = \$ 85.34 A family of four saves \$ 43.11/month
\$ 517.32 /year
\$ 5,173.20 /10 years (warranty)
[/B]
Ok, now lets say the family saves \$20 a month - 240/yr - 2400 for ten years.
The tankless cost 3K to install, you're in for \$600 after saving over ten.
Tank (75 gal draft NOT PV) costs at least 1000 with ten year warranty PLUS the extra 2400 not saved. You're in for \$3400 over ten, make it \$3200 for a 50.
As for maintanence, here's a foolproof way to guage.
I've seen one inquiry here regarding a tankless misfiring, with probes that were gummed in over 3 months.
Would this forum be an excellent way to guage that?

11. Okay, I lied. 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.

12. ## 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...

13. 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.

Originally Posted by Furd
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.

14. Originally Posted by master plumber mark
[SIZE=3]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.

15. 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.

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