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Posted by on June 19, 2007, 2:13 am
All
I recently installed an on-demand hot water heater and use it for both
domestic and space heating. Details are in the document at
www.consol.ca/downloads/Dual_heating_system.pdf
I would appreciate your comments on this article.
Please send your comments via email as I do not subscribe to this
newsgroup.
Thanks!
Roy Jensen
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Posted by Bob on June 19, 2007, 7:12 am
On Mon, 18 Jun 2007 23:13:24 -0700, rjensen wrote:
> All
>
> I recently installed an on-demand hot water heater and use it for both
> domestic and space heating. Details are in the document at
> www.consol.ca/downloads/Dual_heating_system.pdf
>
> I would appreciate your comments on this article. Please send your
> comments via email as I do not subscribe to this newsgroup.
>
I am not an expert in the area but as a reasonably well-educated
lay-person I found your article quite interesting, well written and
offering up an interesting alternative to conventional systems. I saved a
copy.
Bob
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Posted by Dennis on June 19, 2007, 6:49 pm
The advantage for tankless is apparent in lake cottages and other structures
that are not used for part of the year.
However, with the introduction of high efficiency water heaters (some
capable of 95%), capable of venting through PVC, I doubt that a tankless
(based on it's high installation cost) is worth considering any longer.
Considering that it's not just the cost of the tankless heater itself, but
also the additional costs of larger gas lines, possibly a new gas meter &
venting. It can add up.
> All
>
> I recently installed an on-demand hot water heater and use it for both
> domestic and space heating. Details are in the document at
> www.consol.ca/downloads/Dual_heating_system.pdf
>
> I would appreciate your comments on this article.
> Please send your comments via email as I do not subscribe to this
> newsgroup.
>
> Thanks!
> Roy Jensen
>
>
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Posted by on June 22, 2007, 1:07 am
Dennis apparently can't read or is stuck in the mud.
> The advantage for tankless is apparent in lake cottages and other structures
> that are not used for part of the year.
>
> However, with the introduction of high efficiencywaterheaters (some
> capable of 95%), capable of venting through PVC,
HOW MUCH for the high efficiency water heater??
HOW MUCH for the high efficiency furnace??
HOW MUCH energy and $$$ is wasted keeping that water hot?? (~ 37 %)
> I doubt that a tankless
> (based on it's high installation cost) is worth considering any longer.
The cost I quoted is MUCH LESS than a separate high efficiency water
heater and separate high efficiency furnace.
> Considering that it's not just the cost of the tankless heater itself, but
> also the additional costs of larger gas lines, possibly a new gas meter &
> venting. It can add up.
YOU'RE WRONG: same gas meter, same gas lines, and reduced venting
compared with two appliances.
My article is complete, listing all costs. Does Dennis sell high
efficiency appliances?
Roy Jensen
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Posted by Dennis on June 26, 2007, 11:40 am
> HOW MUCH energy and $$$ is wasted keeping that water hot?? (~ 37 %)
Typical losses for a high efficiency tank-type water heater are around 1/2
deg F per hour (actual).
For a gas fired unit, we see Energy Factors ranging from 0.63 to 0.67. For
electric 0.93 to 0.95. Condensing water heaters can reach factors as high as
0.86. (Standard natural gas will be around 0.58).
One of the problems in comparing demand-type units is that manufacturers
like to provide different specifications (intentionally to cloud the issue).
While one may give the you energy input another will state the temperature
rise achievable at the rated flow or another the flow rate at the listed
temperature rise; and so on. In comparing different models, be aware that
you aren't always looking at direct comparisons, especially with temperature
rise and flow rate. For example, while one model might list the flow rate at
a 100°F temperature rise, another might list the flow rate at 70°. Until
there are industry-standard ratings for temperature rise and flow rates, it
will be difficult to compare the performance of products from different
companies. Some companies are beginning to publish energy factor ratings for
these products and this information should make for easier comparisons.
Also, it's difficiult for a consumer to really see the exact amout of
savings the they can expect (other than taking the manufacturers advertising
as gospel - of course we all know that no manufacturer would ever attempt to
mislead the public, right?)
One very important consideration that an advocate such as yourself (you do
sell tankless water heaters don't you?) failed to mention (and I was
surprised you missed this as it is the single most important consideration
in favor of a tankless type) is that most tankless water heaters (Energy
Factor of 0.80 or higher) qualify you for a $300 federal income tax credit
through 2007. That can offset the additional costs of purchasing and the
additional costs of installation.
> YOU'RE WRONG: same gas meter, same gas lines, and reduced venting
> compared with two appliances.
A typical tank-type water heater will typically have a rated draw of around
40,000 btu/h. A typical tank-less unit will draw around 170,000 btu/h. This
greater demand must be calculated into the sizing of the gas lines, and
amost always will need to be replaced with larger piping. In addition, it's
not uncommon tha the gas meter itself "may" need to be replaced with a
larger capacity unit. (It all depends as to what meter has been installed.
Older installations were based on smaller demands while newer onstallations
usually have a larger meter installed already). Point is, you're completely
wrong about the sizing and by using the existing 1/2' IPS you may be
creating a problem for the system.
Using a 50 ft. column, a 1/2 iron pipe is capable of delivering 73,000 btu/h
(well within the range of all tank-type water heaters. However, to size the
piping properly to accommodate a 0.5 in. w.c. you would need to go up to 1"
IPS iron pipe (3/4" has a maximum capacity of 151,000 btu/h). Assuming the
meter originally had a 3/4" inlet, you would now need a meter with a 1'
inlet.
Venting is always higher with a tankless (due to the increased input
capacity which is over 4x greater.) Adding the cost of a new vent is also
part of the installation cost the manufacturers don't advertise.
"It is imperitive that you examine your current gas line to ensure that it
will meet the requirments of your new Gas-Fired Tankless Water Heater. The
requirements of the Tankless Water Heater may exceed that of your existing
tank-style water heater." http://www.tanklesswaterheaterguide.com/
A really good article to read concerning all water heaters is the May/June
1996 issue of Home Energy Magazine. It's online at:
http://homeenergy.org/archive/hem.dis.anl.gov/eehem/96/960510.html It gives
a fair and balance view of both sides of the story, pro's and con's
concerning tank-type and tankless.
Tankless has its place, like smaller households and lake cottages. But for a
typical family of four, a high efficient tank-type will almost always be the
better choice. If sized large enough (that is large enough to serve the
needs of the family when hot water is most in demand, early morning)
tankless can be very efficient to operate.
But it's not the panacea you think it is. Typical savings (over the minimum
standard) of a high efficient tank-type unit is estimated at $500. Tankless
is estimated at $1800 over its estimated lifetime, but the installation
costs are much higher.
Note that very hard water will shorten the life of a tankless to 1/2 its
designed lifetime whereas a tank-type can be serviced. So how often you
needed to replace a water heater has a significant bearing on total costs.
My standard efficiency gas tank-type is 29 years old. I would never have
been able to achieve this using a tankless. As we live in an area of very
hard water, with high concentrations of minerals and clear-water iron, I
would have probably replaced a tankless two or three times.
One other negative (tankless vs. tank-type) is when little hot water is
being used, a tankless will shutoff; supplying no hot water at all. The
minimums vary between manufacturer, but a specific amount of flow is needed
to trigger the unit on. (It's probably not a big deal as there are few times
when only a trickle of hot water is desired, but it is a factor that must be
addressed).
Lastly, is how warm the water delivered. A tank-type will deliver 120-140
deg water (or wherever it's set at) up to the capacity of the tank (or
thereabouts). A tankless on the other hand, will deliver water at different
temperatures based on the flow rate. For example, a Stiebel Eltron Tempra
12, running on 240 Volt power, will raise the water temperature by 54°F at
1.5 gpm, 36°F at 2.25 gpm, and 27°F at 3.0 gpm, above the ambient incoming
water temperature, up to 125°F. RE:
http://www.tanklesswaterheaterguide.com/ (This site also has a good guide
in how to properly size a tankless water heater - most are sized too small
for average needs).
Regards,
Dennis
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