More on tankless water heaters

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Since there's been some discussion about these critters here lately, I thought I'd add my take on them. I have three customers who actually have them, so I speak from some experience.
First of all, the answer to questions like "should I install one?", "are they more efficient/cheaper/better than a tank heater?" is definitely "it depends". It depends on (in no particular order):
o where the heater is installed (how far it is from the farthest faucet) o how big the heater is o the water usage pattern
The last probably being the most important.
Two of my customers have the same type of older-generation tankless heaters (Aquastar, a French-made unit, now handled by Bosch for spares). Two of them are installed in the attic crawlspaces of a commercial/residential building, probably because the remodeling contractor didn't want to sacrifice any more space in the living units than necessary (and also simplified venting, since they're right under the roof). This makes these two a pain in the ass to service; I've overhauled both of them (replacing water valves and thermostats). Still, they operate pretty well.
One of these had an odd setup, which it took me a while to figure out. Someone had written "OPEN 3/4 TURN" on the inlet valve, and it turned out that sure enough, the heater would simply not function correctly if it was opened any further. Not enough hot water in the shower, though the kitchen sink was OK. The culprit was the shower valve, which was a strange one that was full-on with temperature control; there was simply no way to have anything less than full flow in the shower. This shows that there's a definite limitation to how much flow these heaters will handle.
Another customer has this same heater in their fairly large house. They're very happy with it; they have plenty of hot water and their gas bills are lower.
My other customer just installed a Tagaki heater outside her house. This unit is remarkably small, requires no venting, and supposedly has a much higher capacity (and is more efficient). (Having electronic ignition doesn't hurt, either.) I'm told that this is pretty much the state of the art today. Too early to tell how it'll affect her gas bill.
One thing that ought to be considered is insulating hot water pipes to further avoid heat loss.
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If you're listing issues.......
It depends on (in no particular order): o where the heater is installed (how far it is from the farthest faucet) o how big the heater is o the water usage pattern
better consider as well
o temperature of incoming water o elevation (above sea level) of installation
if the incoming water is really cold (like sub 45) and / or installation is in the higher elevations (like the mountains) forget about a tankless
cheers Bob
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some tankless manufacturers alsao mention installing 2 in series, thats good they sell 2 per install.
careful attention to large enough flue and gas line sizes are necessary.
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You can do 20 per instal, if you are stupid enough....
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On 4/2/2008 11:21 PM BobK207 spake thus:

That's interesting; hadn't thought of that. So what do you think is the maximum practical elevation for a tankless to work properly?
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Its not thought, its fact, but these idiot "Tank" salesman are full of BS. Research Temp Rise at the GPM you need.
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Ransley-
Chill out.....I'm not a tank salesman but you sure seem like a "tankless" cheerleader.
My point is that people considering tankless have to carefully examine their installation so that it works for them.
Cold incoming water & elevation might be factors that could make or break an installation
cheers Bob
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On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:

Why does the elevation make a difference?
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wrote:

It's not a factor, as best I can tell.
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Bob, rather than forget about the tankless, just bear in mind the need to upsize the unit appropriately, of course that may make it less cost effective.

Good question--it definitely makes a difference, boiler manufacturers will have a high altitude kit to change the burner orifices to compensate for the altitude. As to why, my WAG is that since the natural gas is delivered at a particular PSI gauge (relative to atmospheric), the absolute pressure delivered is lower, and so the flow rate in moles/hour is lower. Plus the oxygen pressure is lower, so the burners may need to be reconfigured to provide comparitively more air.
Cheers, Wayne
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Wayne-
I think tankless can be (are) great in certain installations but imo they're not for every installation.
In my reply to Ransley's rant I mention my specific high elevation, high intermittent demand situation.
I've done the calcs even without considering elevation de-rating; the cold incoming water & high instantaneous demand rules out a tankless for me in this situation. I'd probably need two units and a whole bunch of plumbing reworks to get the installation to work. Sounds like $1000's.
If the demand were reasonable & there was no derating, I would go with a tankless.
But as soon as you get several instantaneous demands coupled with cold incoming water........
cheers Bob
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On 4/3/2008 7:59 PM BobK207 spake thus:

So to address this obvious problem, what about using two tankless heaters in series? Basically using the first one as a pre-heater; it seem to me you could use a smaller one for that purpose. It would need to handle the full water flow, of course, but could have a smaller-sized burner, as all it would need to do would be to raise the water to a normal incoming temperature. Would this work and still (possibly) be more cost-effective than a large tank heater?
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On Fri, 04 Apr 2008 10:30:28 -0800, David Nebenzahl

Placing the heaters in series or tandem is not the answer.
Install two in separate Zones (determine the applications). Zones work.
Soon I get too see a 1M dollar house with three zones. Three heaters; each having it's own demands.
Reading all the tankless heater threads, I see I "could" add a booster too the solar pool panel. Not on my list :))
This site: Tankless Water Heater Buying Guide
A three minute run down on various applications. See the video. http://www.tanklesswaterheaterguide.com /
It does not mention zones.......
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I believe bosch recommends this for difficult installs.........
of course it doubles all install costs, and supply issues like gas.
might as well use 2 larger units since their no standby losses size of first unit is meaningless....
but one could have 3 or 4 grand in the 2 tankless in series install.
in what lifetime would the cost be recouped?
a thousand bucks can pay for lots of insulation, better attic ventilation, some storm windows etc.....
fixating on hot water heating standby losses may leave other easier energy savers ignored.
i mean geez a home has so many standby losses, from cable boxes, tvs, etc etc............
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Combustion processes are effected by the oxygen content in the air.
Just like cars need to be tweaked for higher elevation operation or people need oxygen at high altitude.
The tankless reps that I spoke with didn't recommend installs above 8000 ft. I took them at their word.
cheers Bob
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Yea , What BS, my incomming can be 35, and if you only had a brain enough to not post BS, or did simple spec research. you would see the Cheapest Bosch has a 90f rise, If you cant take a shower in 105f you are anemic or sick! I only need 103f thats a 70f+ rise, and figure in pipe loss of 15f and you still get a real hot shower, well over " Comfort level" You just made another Bull Shit, unsubstansiated , wrong post. at 45f incomming 135f output is what you get on "Cheap models" NOBODY can shower at 110f or you BURN. So STFU Bob , your post is total ,,BS,,crap.
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ransley wrote:

Hi, High altitude? Wouldn't it need orifice change? My question is can tankless heater fill a typical two person size Jacuzzi tub?
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Yes!!
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Dear R-
No need to be rude or insulting, I can assure you that I know how to do the calcs.
I was merely mentioning that one needs to also consider incoming water temp & elevation of installation as well as usage patterns.
As a mechanical engineer I do in fact like the tankless concept...depending on the particular installtion & usage patterns.
I actually looked into getting a tankless for my mountain home. This was a few years ago but all the mfrs' sales reps with whom I spoke suggested that I NOT go tankless.
Their comments were, more or less, "with the derating due to altitude (8000+, their spec..the house is actually at 8300 ft) plus the very cold water incoming water in the winter, you'll be disappointed with the performance."
I should have been more precise in my comment

being able to service a high instantaneous demand at over 8000 ft.
I have researched the temp rise at the flow I need & tankless won't work for my particular installation.
When people come back from skiing and there are three showers running (even with low flow heads that's 7.5 gpm) tankless won't do the job but a quick recovery 75 gallon tank that was cranked up before we left in the morning does the job.
I done the calculus problem, a tank pencils Plus based on actual usage it works (empirical data) . A single tank less won't & I'm not about to rework the plumbing to install two units.
It's a demand thing, in my particular case.
Tankless can work but not in every situation.
Sorry if I pissed you off but really was your reply warranted?
cheers Bob
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I gues the most interesting FACT overlooked, on purpose, Is I myself, and the other poster on the last thread have experianced a reduction of more that HALF in heating water costs, based on summer use ;[ when no heat is being used to heat the building}
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