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More on tankless water heaters David Nebenzahl 04-03-2008
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Posted by BobK207 on April 3, 2008, 11:59 pm
>
> > On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>
> > > 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
>
> 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.
>
> > Why does the elevation make a difference?
>
> 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

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


Posted by David Nebenzahl on April 4, 2008, 2:30 pm
On 4/3/2008 7:59 PM BobK207 spake thus:

>>
>> > On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>>
>> > > 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
>>
>> 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.
>>
>> > Why does the elevation make a difference?
>>
>> 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.
>
> 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........

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?


--
The best argument against democracy is a five-minute
conversation with the average voter.

- Attributed to Winston Churchill

Posted by Oren on April 4, 2008, 5:50 pm
On Fri, 04 Apr 2008 10:30:28 -0800, David Nebenzahl

>On 4/3/2008 7:59 PM BobK207 spake thus:
>
>>>
>>> > On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>>>
>>> > > 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
>>>
>>> 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.
>>>
>>> > Why does the elevation make a difference?
>>>
>>> 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.
>>
>> 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........
>
>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?

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.......

Posted by hallerb@aol.com on April 4, 2008, 5:51 pm
> On 4/3/2008 7:59 PM BobK207 spake thus:
>
>
>
>
>
>
> >> > On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
>
> >> > > 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
>
> >> 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.
>
> >> > Why does the elevation make a difference?
>
> >> 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. =EF=BF=BDAs to why, my WAG is that since t=
he
> >> 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. =EF=BF=BDPlus the oxygen pressure is =
lower,
> >> so the burners may need to be reconfigured to provide comparitively
> >> more air.
>
> > 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. =EF=BF=BD =EF=
=BF=BDSounds
> > 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........
>
> 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?
>
> --
> The best argument against democracy is a five-minute
> conversation with the average voter.
>
> - Attributed to Winston Churchill- Hide quoted text -
>
> - Show quoted text -

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............


Posted by BobK207 on April 3, 2008, 11:36 pm
> On Thu, 03 Apr 2008 00:21:56 -0700, BobK207 wrote:
> > 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
>
> Why does the elevation make a difference?


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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