DIYbanter - View Single Post

David Nebenzahl

On 11/10/2010 5:53 AM spake thus:

On Nov 9, 7:06 pm, David Nebenzahl wrote:

The thing is, the tankless heater can save you money on gas, but it
depends on a couple factors:

o The distance from the heater to the farthest hot water outlet
o The usage patterns of the household

The latter one is the most important. I'm not an expert in this
field, but it seems obvioous to me, at least, that if a household
uses a lot of hot water throughout the day--say, doing a lot of
laundry plus hot showers--then a tankless heater could actually end
up costing more. Why? Because in order to heat the same amount of
water as in a water heater tank, the tankless heater is going to
use a lot more gas.

What is your basis for the above? It would seem to me that both a
tank heater as well as tankless are going to get about the same
amount of heat out of a given amount of gas that goes in. The
tankless just uses a lot of gas or electric over a short period of
time, while the tank type uses less over a longer time. If anything,
I would suspect that a tankless is more efficient compared to a std
efficiency tank water heater. The main energy savings AFAIK, comes
from the elimination of the standby losses from a tank type heater.
Whether that savings is enough to pay for the cost difference,
including install, is questionable.

And I fail to see what relevancy the usage patterns have, at least
with a typical whole house unit. If I use X gallons of hot water,
what difference does it make when I use it, unless the point here is
that with electric units there could be a time of day difference in
rates for some? With a typical whole house unit installed
somewhere, you're going to have piping losses with either type. And
if you put in mutiple tankless to cut down the delay time for hot
water, I would think the increased cost would take so long to recover
you may never come out ahead.

Well, like I said, it was a guess on my part, hopefully an educated one.
Your take is just as plausible; my point is that we really don't know,
do we?

Here's one argument in favor of my thesis:

Consider the most ridiculous case possible, someone who only uses hot
water once a day, say to wash their hands. In such a case, a tankless
heater will fire up exactly once, while a tank heater will fire up
several times during the day to maintain the tank's temperature. So it
seems likely that a tankless heater could save fuel in such a case.

Now consider the opposite case: someone who runs hot water all day long
for some strange reason. In such a case, both a tankless heater and a
tank heater will be burning fuel all the time. The main difference here
between them is the size of the burner: the tankless burner is a lot
larger (think your oven's burner as compared to the tank heaters's
stovetop burner). So again it seems likely that in such a case a
tankless heater could use more gas for the equivalent usage. (Of course,
the other difference is that the tank heater will eventually stop
putting out hot water, unlike the tankless.)

So it seems likely that one could construct some kind of crude curve of
comparative fuel costs vs. water usage.

But I don't know for sure. It's sure be nice to have some better
information on the subject.

--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)