common sense on gas tankless water heater install

Does it really need stainless to the weather cap? I've had the same flue on my tank type for 10 years since I moved in, and I'm pretty sure it has been there much much longer than that. I could see a couple of sections near the heater needing to be SS, & maybe I'm fussing about nothing, the whole thing can't be much more than 10'. If it is so hot on the stack that stainless is required, how close can it come to wood? Will it be necessary to sawzall the ceiling and roof and put in metal?
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If you have the installation instructions, you should not take it upon yourself to re-engineer and re-design the installation just because you don't understand all the design and engineering the factory put into it. Proper design not only ensures satisfactory operation, but a reasonable expectancy of long life and safe operation under normal and many abnormal conditions.
Follow the instructions and feel confident that it is done properly, will work and last a long time, will not cause a fire or other problem, and will not be a problem in a sale or other unexpected situation.
In general, stainless flues are not specified because of intense heat but to prevent corrosion (rust-out). Each type of appliance and flue design has certain specified clearances from wood or other combustibles to prevent fire. If you have never ever seen a malfunctioning appliance over-firing with a red hot flue thru the ceiling you may not fully appreciate the value of a proper installation.
Don Young
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...

You asked about common sense in the situation. To me, common sense says to follow the manufacturer's instructions. Five years from now, it will be a bigger PITA to change the piping than to spend a few dollars now to do it right today.
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Common sense question WHY A TANKLESS????
They arent as good as a tank type having troubles with low flow no heat high flow not hot enough, require larger gas line since their BTU is so great.
Besides during the heating season they energy the lose goes to heat your home, that cuts energy savings by half around here.
finally they cost so much their payback period based on high efficency exceeds the probable life of the tankless:(
so why are you making this expensive downgrade?
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I would never go back from my properly sized Takagi gas unit (a max 235,000 BTU Mobius TM1 ) to a conventional tank type heater - nor would my spouse let me.
The Takagi does exactly what we require.
When the house is empty, it just sits there, burning no gas at all.
If we are entertaining a house full of guests, it fires up on demand and produces water at the temperature we want, in whatever quantity is required - up to sufficient quantity to run a dishwasher , a clothes washer, two showers, and provide water at the taps at the same time - continuously for hours if required.
That's what we paid for.
And that's what we got.
We love it.
We also use tankless units extensively in rehab rental units - in our case the increase in rental square footage resulting from the reduced utility area footprint alters the "typical" payback calculations.
YMMV.
Michael Thomas Paragon Hone Inspection, LLC Chicago, IL snipped-for-privacy@paragoninspects.com 847-475-5668
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Eric in North TX wrote:

Most gas/propane fired tankless unit produce a HOT exhaust, and the WH manufactures generally spec a UL listed cat III system - in the US the choices I'm aware of are FasNSeal, Z-VentIII and Saf-T Vent - and than it be installed "per manufacturer's instructions".
So you need to read *both* manufacturer's instructions, and then follow them.
For example the SS pipe specified for most tankless heaters is 2x wall material, but still requires clearance to combustibles - FasNSeal for instance requires 12" at the top, 8" to the side and 4" below a horizontal run, and even then if it's other than a one or two unit residence they specified a non-combustible enclosure.
http://www.protechinfo.com/pdf/1150.pdf
In addition, these are engineered systems, so to maintain their ratings each manufacturer is going to require that in so fas as possilbe the entire system be composed of exclusively of their components, and installed per their instructions, and ther only exceptons they allow will be BFPs, wall caps, ect. specified by the appliance manufactuer for use with cat III systems.
Other frequent problems I encounter in tankless retrofits:
- Insufficient combustion air: many tankless WHs are rated at 180,000 input BTU or above, which is more that most GFAFs, often no provision is made to insure increased combustion airflow, resulting in a negatively pressurized utility area (sometimes, an entire house) which can result in back drafting of exhaust vents, etc.
- Insufficient gas supply: most take type units are fed by a .50" line for at least part of the run, most tankless units REQUIRE a .75" line all the way to the unit or they may not operate at full output. In addition, depending on the run and other appliances attached, it may be necessary to replumb the entire supply system, upgrade the gas meter, etc.
This is not a just a "theoretical" problem, either. The *majority* of service calls by Takagi for "defective" newly installed units are the result of an undersized gas supplies, and in the last year I've had to upgrade the newly installed gas meter on a building feeding a Takagi tankless WH and a GFAF because the gas company disregarded our specifications and installed a "standard" sized meter undersized for the actual requirement, and on another project the plumbers had to tear out and ungraded the entire length of newly installed gas supply line because they had failed to size it based on the fact that it would be feeding multiple tankless heaters.
- No backflow preventer in freezing climates - many tankless units require a backflow preventer to reduce the risks of freezing the coils. Sone units (for example some Takagis) have a built-in in coil heater, but this is NOT designed or intened to take the place of a BFP.
So you really have to plan such installations correctly, and then check cafrefully to make sure they are in fact installed as planned.
Michael Thomas Paragon Hone Inspection, LLC Chicago, IL snipped-for-privacy@paragoninspects.com 847-475-5668
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nearly all reports from tankless owners are negative, open a kitchen faucet a little no hot water ever.....
it appears some peoples usage patterns fit a tankless.
in so far as rental units, the added costs for gas lines etc must wipe out any energy savings for many years.
beyond which during the winter a standard hot water tanks heat loss helps heat your home........
of course during a power failure the ONLY showers a tankless owner gets is a cold one, unless it has a battery backup......
With the current terrorism issues a tank type heater is a excellent source of emergency drinking water
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snipped-for-privacy@aol.com says...

I found the opposite when I was looking at going tankless, almost everyone who had a properly-sized heater raved about it. The complaints I've seen are mostly people whose heaters are so small they shouldn't expect better than lukewarm water anyway.
I've certainly enjoyed the switch -- plenty of hot water, fast. Enough that I can run the dishwasher and the laundry while I'm taking a shower and not worry about exceeding the capacity of the heater. I don't think I'd ever go back to a tank, unless I had enough spare room for a *huge* heater.
--
snipped-for-privacy@phred.org is Joshua Putnam
<http://www.phred.org/~josh/
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Joshua Putnam wrote:

happy it worked for you.......
in cold climates a tankless may have trouble heating the water enough when incoming water temp is low....
honestly it doesnt matter what heater anyone buys, doesnt effect me in the least.
just feel bad for folks trying to do something good, then finding out it was poor investment...... provided worse service than original heater.
or their teenagers now freed of running out of hot water remain in shower forever:(
i should look for a old discussion of this, and all the problems people had
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http://groups.google.com/group/alt.home.repair/browse_frm/thread/347cc3fcd9defb59?q=tankless+hot+water+heater&hl=en &
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http://groups.google.com/group/alt.home.repair/browse_frm/thread/347cc3fcd9defb59?q=tankless+hot+water+heater&hl=en &
The upshot of the whole issue (the thread is filled with quite a bit of scientific nonsense[+]) is that _if_ a properly sized tank-type water heater will do the job satisfactorily in _your_ home, the break-even cost point for a tankless (if it even exists with your situation) is so far out in the future, it can be more-or-less ignored.
But there are situations where tankless truly are superior. Those are where the hot water line length from where you have to put a tank to the fixtures is excessively long, and you lose a lot of heat (and have unacceptable to _you_ wait times) waiting for the hot water to arrive. That's where point-of-use and/or tankless stand out.
Another situation is where the current HWT is undersized, and you don't have room for a larger one and/or the appropriately sized tankless could usefully supplement it at a reasonable install cost.
Most houses these days are set up so that the HWT tank is placed more or less a minimum distance from the fixtures. Eg: bathrooms and kitchens clustered around where the HWT is. Eg: stacked bathrooms in multi-floor homes etc. Costs less in terms of plumbing, particularly DWV, etc.
[I have a large two story. The plumbing is arranged such that all hot water requirements is along a 20' horizontal line. All of the plumbing is contained in about 10% of the house's overall footprint. One corner, and about halfway down one side. That's it. Except for the cold feed from the well, which is at the opposite corner. No hot water flow path is more than about 20' long.]
But if you have a strange house - eg: sprawling single story homes with bathrooms/kitchen[s] strewn randomly around, sometimes one (or even more) tankless units really help.
A friend of mine had one such strange house. The hot water line to one of the bathrooms was well over 100' long. Seemed to take forever for the hot water to arrive. That would have been perfect for a tankless. Instead, he happened to have a small 3 gallon tank-type 120V water heater sitting idle. So we installed it in the bathroom, fed from the hot water side of the main HWT. Instant hot water, and if you were taking a shower and were going to exhaust the teensy 3 gal tank, by the time it started to matter, the line from the main HWT to the bathroom HWT had warmed up and you were getting hot water heated by the main.
Efficiency wise, it wasn't too great, because you ended up losing a _lot_ of heat in the 100' line. But the 3gal HWT was free. And at the time tankless wasn't really available. These days I'd install a tankless instead.
Or another example: a kitchen doesn't really use a lot of hot water compared to a bathroom or clothes washer. If the kitchen is a long way away from the rest of the plumbing, a small tankless really works.
As someone previously opined, there is NO UNIVERSAL solution for ideal water heating. It depends on your circumstances and requirements.
[+] For example, the comment about "efficiency loss of 28% while tank is idle". That's 28% of almost nothing (because modern tanks are so well insulated). In operation, the efficiency is the same. You're going to spend hundreds (if not a thousand or more) for something that at most saves about the same amount of power as turning off a 60W lightbulb? Even environmentally, that makes no sense. If it's the only reason you're doing it, it's wrong.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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snipped-for-privacy@aol.com wrote:

In houses without basements, like 99.999% of all homes here in Southeast Texas, the water heater goes OUTSIDE the conditioned space. This is a CODE requirement. It is NO help in heating the house in the winter.
There is NO universal solution for domestic hot water.
1. Available energy sources 2. Hot water demand in the house 3. Code requirements for gas powered appliances, electric too 4. Cost of equipment and installation 5. Temperature of incoming water 6. Quality of incoming water
All these factors and more affect the decision on which system to purchase.
In some cases, an electric tankless will make the most sense for households that can drain an 80 gallon normal tank.
In some cases, a natural gas or propane tankless will make the most sense, again for households that use ALOT of hot water.
In other cases, a conventional electric, natural gas or propane tank will solve the problem
In other cases, solar panels will supplement the existing tank
In other cases, geothermal heat pump will supplement or replace the conventional tank (still retain conventional tank as a backup, but turn it off)
Bottom Line, there is NO UNIVERSAL solution for domestic hot water.
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An excellent debate, and now I'm if anything, more undecided. My original thought was this: We are on propane, our only cold weather is normally November through March, and there are many 70 degree + days even then. To fill my tank at the end of summer last was over $300 it had been topped off in April. That means that the clothes dryer and hot water tank used all that, there is a gas range, but that was used minimally as we ate a lot of wraps and things like that through the summer. The tank (30 gal) is less than 4 years old and the house was re-plumbed for propane at the same time (3/4 black iron pipe). I feel I can do the install for < $1200 for a 240 sized unit even with the stainless exhaust. the closet is very centrally located, new insulated runs are planned (for later) to the bathroom and kitchen/ laundry room. I feel if it would save $10 a month it wouldn't take long to recover the original investment especially with a $300 tax credit. That would take 7.5 years. Optimally it would pay back faster. Normally there are just 2 people in the house, we are retired, so we are there all day, I realize every hand washing is going to fire the tank, that in itself may be the deal killer.
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check tankless warranty, typically not 10 years and payback often takes that long... make certain your existing propane tank lines and regulator can supply the tankless big consumption....
you will save the regular tanks standby losses, what about adding a water heater blanket to reduce standby losses even more?
It sounds like your current tank is inside your heated space? in the winter the stanby is no loss.......
so you figure payback at 7.5 years?
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Somehow I doubt that, The installer made a big deal out of making the closet air tight and installing an air intake into the attic, claiming it would never pass inspection the way it was; (louvered door, only the exhaust pipe going into the attic). Actually, my first choice would be to install solar with a small tankless backup, but I may need to win the lotto first. Shame to waste 30 100 degree + days a year and still be paying for water heating.
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you can do nearly anything, trouble is cost vs benefits.
heck cover a few acres with solar panels, spend a couple million and go off grid.
payback? never panels will be worn out long before you get 2 million of electricity from the install.......
now super insulating your home, solar hot water, some things have a payback within a reasonable time......
hows your home insulated? might be a better way to spend the bucks?
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>hows your home insulated? might be a better way to spend the bucks?
R16 in the walls, tinted double glazed windows with an inch between the panes, attic is the weak spot, but I'm holding off till I get the wiring all the way I want it. It has blown cellulose level with the rafters with some r-13 on top, I want attic blanket to replace the r-13, but will just tear it up running wires if I do it now. It is miles from where I found it, but in the 50's insulation wasn't a big deal in Texas. Our inclimate weather is summer heat, any benefit on the heating side is a minor thing, but something that cuts the AC use is a huge benefit.
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i would spend the tankless money on the wiring and insulation upgrade
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