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Posted by Wayne Whitney on June 26, 2007, 12:58 pm
> 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.
This last sentence is not correct, as I understand it. The meter is
rated for a certain maximum flow, so as long as the meter rating
exceeds the rating of any individual appliance, and exceeds 70% of the
total rating of all appliances, the size of the meter piping through
the meter outlet is immaterial. The regulator is typically adjusted
to provide a pressure of 7" w.c. at the meter outlet.
> A tankless on the other hand, will deliver water at different
> temperatures based on the flow rate.
Modern tankless gas water heaters do not do this; they modulate the
burn rate to provide a constant output temperature independent of the
flow rate. Admittedly there is a slight lag when the flow rate
changes, maybe 1 second.
Yours,
Wayne
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Posted by Dennis on June 27, 2007, 12:36 pm
>> 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.
>
> This last sentence is not correct, as I understand it. The meter is
> rated for a certain maximum flow, so as long as the meter rating
> exceeds the rating of any individual appliance, and exceeds 70% of the
> total rating of all appliances, the size of the meter piping through
> the meter outlet is immaterial. The regulator is typically adjusted
> to provide a pressure of 7" w.c. at the meter outlet.
I wasn't aware of the sizing procedure on meters, poor choice of wording on
my part. My information as to the sizing of meters comes from the National
Fuel Gas Code; sec. 5.7.1. It states "Gas meters shall be selected for the
maximum expected pressure and permissible pressure drop". As the
International Codes offer no guidance on meter sizing, is there a code or
standard where this information is specified?
If meters are currently sized at 170% of calculated demand, I admit that it
may be possible that adding a tankless unit may not push the gas lines out
of compliance. Still, replacing a 35,000 btu/h water heater with one with a
rated 4x to 12x the original demand, would certainly seem to me that this
would necessitate a larger meter. (Basing this on IRC Table 2413.2 --
142,800 btu/h for a 2 gal/min unit, 285,000 btu/h for a 4 gal/min unit or
428,400 btu/h for a 6 gal/min. unit).
>> A tankless on the other hand, will deliver water at different
>> temperatures based on the flow rate.
>
> Modern tankless gas water heaters do not do this; they modulate the
> burn rate to provide a constant output temperature independent of the
> flow rate. Admittedly there is a slight lag when the flow rate
> changes, maybe 1 second.
I was thinking about when the demand exceeds to rated flow. Tankless will
continue to deliver hot water but no longer at its design temperature.
Again poorly worded on my part, thanks for keeping me honest ;-)
One thing that worries me now, is dealers may be installing these appliances
and not getting nuilding permits; even though the code would require it in
Section R105.1. A local inspector will immediately put the cahaush on a
simple R&R without requiring a recalculation of the existing gas lines and
vents. (Undersizing gas lines can produce a very hazardous situation).
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Posted by on August 11, 2007, 2:42 pm
Back from holidays...
> One very important consideration that an advocate such as yourself (you do
> sell tanklesswaterheaters 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 tanklesswaterheaters (Energy
> Factor of 0.80 or higher) qualify you for a $300 federal income tax credit
> through 2007.
I am totally surprised that, after such a thorough read-through, you
ignored the last section. So, to answer your question: NO, I don't
sell the units. I have no intention of selling the unit. I AM A
CHEMIST! I do drugs and explosives for a living. (Pass this on to your
idiotic Department of Homeland Security like a good Nazi.) If I wanted
to make money on these things, I would have patented it.
And the tax credit -- is that in the USA or Canada?
> > YOU'RE WRONG: same gas meter, same gas lines, and reduced venting
> > compared with two appliances.
>
> A typical tank-typewaterheater 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.
Okay, so I am wrong. Typical energy use in Edmonton requires larger
gas lines. I will have to add info on gas lines.
> 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.
My pricing included new venting.
I disagree with everything you stated on installation costs and
lifetimes.
Roy Jensen
P.S. If your HWT has actually lasted 29 years in a hard-water region,
great. Probably went through a lot of anodes.
Don't expect the next one you buy to last more than 10 years:
engineers have gotten better at building to the rated life expectancy.
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Posted by Dennis on October 10, 2007, 5:59 pm
> And the tax credit -- is that in the USA or Canada?
Sorry, missed your question.
Both countries.
For Canada see: http://www.oee.nrcan.gc.ca/corporate/incentives.cfm
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Posted by jeremy on June 23, 2007, 2:21 pm
Dennis wrote:
> 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.
The high cost of purchase and installation is easily offset by the reduction
in gas usage and AC bills. My first tankless only took three years to amortize
the costs.
When I put in the main unit for the showers and baths, it gave two major
advantages; unlimited hot water and more space in the utility room. With the
precise temperature control the water usage was reduced significantly.
Low maintenance and long service life are just added bonuses.
JJ
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