On-demand hot water heater for domestic and space heating...

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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On Mon, 18 Jun 2007 23:13:24 -0700, rjensen wrote:

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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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.

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Dennis apparently can't read or is stuck in the mud.

HOW MUCH for the high efficiency furnace?? HOW MUCH energy and $$$ is wasted keeping that water hot?? (~ 37 %)

The cost I quoted is MUCH LESS than a separate high efficiency water heater and separate high efficiency furnace.

compared with two appliances.
My article is complete, listing all costs. Does Dennis sell high efficiency appliances?
Roy Jensen
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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 100F 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.

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 54F at 1.5 gpm, 36F at 2.25 gpm, and 27F at 3.0 gpm, above the ambient incoming water temperature, up to 125F. 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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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.

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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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).

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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Back from holidays...

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?

Okay, so I am wrong. Typical energy use in Edmonton requires larger gas lines. I will have to add info on gas lines.

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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Sorry, missed your question. Both countries. For Canada see: http://www.oee.nrcan.gc.ca/corporate/incentives.cfm
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Dennis wrote:

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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snipped-for-privacy@consol.ca wrote:

......And I'm too Nifong lazy to check back here."
Fixed it for ya.
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I like the on-demand concept simply because it saves a lot of water that is typically wasted by waiting for the water to heat up.
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