Tankless water heater. Need some data

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Sjsmithjr

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Have you ever drawn 7 gpm and observed what happens on your own home system?

I observe exactly what I should in a properly designed system - nothing of significance. Your point.

...and you still seem to fail to understand the difference in a storage system and a demand system when it comes to sizing.
 

Ladiesman271

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I observe exactly what I should in a properly designed system - nothing of significance. Your point.

...and you still seem to fail to understand the difference in a storage system and a demand system when it comes to sizing.


Sure I do. You are just being a wise guy!

Since the majority of gas tank type water heaters are installed in the 40 gallon size, maybe you should properly figure out the typical home hot water demand instead of overstating it. Heck, one or two short showers back to back and a 40 gallon tank heater is producing tepid water in most homes if your demand figures are accurate for the average size home.

As a comparison, even with 40 degree incoming water temperature I can get over 120 GPH of 120 degree hot water out of my modest tankless unit (125,000 BTU maximum).

Like Mr. Rat said a hundred times, if you have a high hot water demand lifestyle (AKA 4 to 5 bedrooms - 3 full baths - simultaneous showers required), then you need to size your system to meet the required simultaneous demand.


You should also note what it says in the previously linked to Minnesota summary. You, the "plumbing instructor" and his "friends" should revisit the so called and undocumented simultaneous use requirement of "the code".


Summary

• When looking at a new water heater, be sure
to compare the energy efficiency of different
models by checking the Energy Guide label.
Choose an EF of at least .64 for natural gas
and propane, and an EF of at least .93 for
electric.

• Buy the smallest size you can. Don’t try to
buy a water heater so you can shower, and
wash clothes and dishes all at the same time
without running out. Instead, plan your hot
water use. This is especially important if you
have a large family.


• Locate the water heater as close as possible to
where the largest volume of hot water is
used. Since heat is constantly lost through hot
water pipes, the shorter the pipe runs the
lower the heat loss.

• Insulate the water pipes and install heat traps
if your water heater does not have one.

• Take easy, low-cost or no-cost measures to
avoid waste in using hot water.


Copy of original Minnesota summary with typical flow rate chart:

MinnesotaWaterHeaterSizing-1.jpg
 
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Ladiesman271

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So as Master Plumber Mark has said it all depends on the variables, and once you figure it out make it one size bigger to handle the unforeseen variables.




That may in fact be terrible advice. The larger units have a higher minimum flow rate and may turn off in the middle of "low flow" demand situations.

I hope that you guys do not do HVAC installations!
 

Sjsmithjr

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You are just being a wise guy!

I can assure you I am not. The plumbing system in my home is neither undersized nor is it oversized. It is appropriate for it's intended demand I am not limited to as to simultaneous fixture use. My water heater is not oversized. My observations are not qualitative but quanitative.

Tankless manufacturers recommend that units be sized for the coldest parts of the year, meaning that at least part of the time they are oversized.

As you seem to take issue with the opinions most professionals regardless of field as well as qualified instructors, would you mind sharing your particular area of expertise and qualifications?

Just curious.
 
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Sjsmithjr

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The larger units have a higher minimum flow rate and may turn off in the middle of "low flow" demand situations.

Be specific; which residential units have this problem? What are their minimum flow rates in GPM for a given temperature rise? Even a Rinnai R98 works at 0.6 GPM/50F rise. Even if minimum flow were a problem, one could install two smaller units, albeit at a greater initial cost.
 
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Master Plumber Mark

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its all smoke and mirrors....


Ladies man, you are truly an intelligent person
and I stand in awe of all your knowledge....

index.php


Why are beating a dead horse and having a fun time
trying to pull everyone's chain.. I don't understand...


you are trying to make tankless something akin to
space shuttle technology.....


its simply a bathroom,
and everyone of them in the USA is different ......


get it???


ok lets try to factor in all the variables......

lets try to equate the flow rate when grandma takes
a healthy shit and flushes the toilet while you
are showering with the tankless...



Now lets factor in a well, and now lets factor in
pressure balanced shower faucets....



Now factor in grandmas bowel movement not going down
all the way with one flush...and she flushes three times
to get that stubborn nasty hard turd to go down....



then she jumps into the other shower and attempts to
take a bath while you are in the other bathroom



so what's the pressure drop going to be..?????

man I can see that curve drop in my mind right now..

so what's going to happen to the guy showering if the tankless is undersized??? ....






When a simpelton like me sells a water heater

the first thing I ask is how many people are presently living in the home,
and how old everyone is living in the home....


if they have a few children about 9 years old....
I KNOW that the demad will be going up in about two years .
..



and I KNOW that the 40 gallon heater will not suffice.
..


so we usually go one size larger for the variable of

larger increased demand when the children become pre-teens in a few years

so they buy a 50 gallon..





Now all I state....

if you are putting in a tankless, I simply suggest
you oversize the unit for future issues and other variable factors....
like grandma and pressure drops....




but this is just too damn simple for you.....

isn't
it???..
 
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NHmaster

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flow rates and demand aside why not address the real folly of tankless heaters and that is that the average savings is a crappy 4% over conventional tank heaters with the installed price being 2 to 3 times that of a tank type heater. That's a lot of money to save very little floor space. Why not address the common problem of long wait times for the water to get to the faucet or how if you just crack a faucet the unit will not fire or how the temperature and pressure fluctuate enough to keep quite a few pressure balanced valves from operating correctly. better yet ask anyone from Europe that has grown up on these things what they think about tank type water heaters when they come over here for a visit?
 

gregsauls

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Folks, here's what 15 or more pages of debate boil down too. Several (ie, more than 2) DIYers have installed tankless systems in their homes and are happy with them. Plumbers around the country are installing them successfully (ie. no manufacturer recalls). A few "boys" here hate them for highly biased reasons.

Bottom line, don't let NHmaster install one in your home as he can't cope with it. And don't let Rugged in your home or you may be "scammed" out of a water heater that is under warranty.

Now for more FUD (and dumb pictures) from the "boys".
 

Sjsmithjr

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Several (ie, more than 2) DIYers have installed tankless systems in their homes and are happy with them.

In the interest of being fair and unbiased, let's not forget that many of those DIY'ers voided their warranties in the process.

Let's be clear, I don't hate tankless water heaters. My interest in tankless water heaters and the sizing of hot water systems comes from the current (and growing) interest in obtaining LEED certification for new construction projects. I am not so jaded either way as to not consider all of the factors: installation, parts, service, warranty, functionality, fuel consumption, and water consumption. I also have to consider cost.

The green that consumers and organizations seem to be interested in the most are the dollars in the present worth calculations.
 
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Master Plumber Mark

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Un-believer----

flow rates and demand aside why not address the real folly of tankless heaters and that is that the average savings is a crappy 4% over conventional tank heaters with the installed price being 2 to 3 times that of a tank type heater. That's a lot of money to save very little floor space. Why not address the common problem of long wait times for the water to get to the faucet or how if you just crack a faucet the unit will not fire or how the temperature and pressure fluctuate enough to keep quite a few pressure balanced valves from operating correctly. better yet ask anyone from Europe that has grown up on these things what they think about tank type water heaters when they come over here for a visit?

we are all boys and simpeltons,
dont you understand???

we have not seen the light yet......

Getting a tankelss heater is like converting to a new faith or religoin....


it is literally like blind faith,
sort of like some other fanatic religions out there...


you have to take that leap of blind faith,

and then never question your faith.....ever again





 

NHmaster

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No matter what wisdom issues forth from these two cretans the fact is that the average annual energy savings is a wopping 4%. So in a way I suppose I am thankful that there are those out there so pig headed and ignorant that they would gladly spend 2 to 4 times the cost of a conventional water heater. God bless capitolism. :eek:
 

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Redwood

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Yes, God bless capitolism.

and,

"Never Give a Sucker an Even Break." ~Otis Criblecoblis~ 1941
 
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