Which Tankless? Bosh, Rinnai, Takagi or?

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http://www.askthebuilder.com/451_Tankless_Water_Heaters_-_Some_Surprising_Facts.shtml That article is bogus. In doing the cost comparison, the author assumes that the tankless gas water heater always uses gas at its peak rate, which is false. A tankless gas water heater has a modulating gas valve, and it will only use enough gas to provide the required temperature rise. It is incontrovertible that all other things being the same, a tankless heater without any standby losses will use less energy than a tank heater with standby losses.
The author also complains that tankless water heaters provide a constant temperature rise, so that the hot water is hotter in the summer when the incoming cold water is hotter. While I believe some older models do this, most current models will modulate the gas usage to provide a constant output temperature as the input temperature changes.
In other words, the article's two chief complaints are invalid.
Cheers, Wayne
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Right Wayne, The modulating burners go from something like 18,000-190,000 Btu for the Takagi, My little Bosch does something like 30000-117000 Btu.
The Energy Factor is a True rating nobody making a tank wants to discuss, and few consumers are smart enough to ever check, that is your true rating. Plus rated unit Efficiency. The true tank standby loss is excessive and pipe heat loss im sure not included as very few people are smart enough to install thermal couplings on there water heaters.
Now consider tankless 30 year life, no tank to rust out, its all copper pipe.
Now consider tanks scale. Rated efficiency is downhill from year one, I just removed a 20 yr old tank with 12" of hard scale, now that lowers efficiency alot, tankless do not build heavy scale, but should be delimed every few years.
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Wayne Whitney wrote:

The article does note that tankless water heaters don't run full blast whenever they're used. I guess you missed that part.
The author does his calculations based on peak use, which is valid as long as he compares the cost of the conventional water heater on the same basis.
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The author's addendum to the original article notes this, but he doesn't redo his calculations.

The author compares the measured monthly usage on a tank water heater with an estimate of the tankless usage. The tankless usage estimate is incorrectly computed assuming the peak firing rate whenever any hot water tap is open.
Cheers, Wayne
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In summer with 70f incomming I an turn my bosch at its lowest setting apx 30000 btu and the water is still to warm for me to take a hot water only shower. Now the Rinnai - Takagi have lower Btu modulating valves, so Btu to operate can be very low, that is why I have a total 6 dollar Ng bill in summer.
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I have the Bosch 125 natural gas water heater and I am happy with it. I have had it for 4-5 years and have had no problems. The Bosch 250 might be the one for people who want to run 2 things at the same time. A 125 at each end of a large house would probably be better. Ours has a regular 5" flue but you can get the one with the power vent that uses 3"-4" pipe and doesn't have to be pitched toward a chimney.
--
JerryD(upstateNY)

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