Newsgroups: misc.consumers.house,sci.energy
From: John De Armond
Subject: Re: IN-LINE WATER HEATERS
Message-ID: <w!0n+#n@dixie.com>
Date: Fri, 25 Sep 92 03:56:59 GMT

pngai@adobe.com (Phil Ngai) writes:

>My water heater is 55 inches high with an external circumference of 56
>inches.  Use the external circumference as a worse case assumption, the
>area is 55 * 56 = 3080 square inches or 21.4 square feet. Assume the
>heater wall has an R-8 value insulation and the temperature difference
>is 120F-70F = 50 F.

>So I am paying about fifty cents per month for my water heater's
>standing losses. It would be nice to avoid that, but I don't see it as
>a high priority.

You have, of course, overlooked the major heat loss paths.  They are
heat lost up the flue and heat lost through the piping.  The former
is very significant because it is driven by the very heat that is being
lost.  Notice how your flue remains warm all the time.  Most people
attribute it to pilot heat but it remains even when the pilot is turned
off.  The latter is also significant because there is convection flow
in the pipe.  There are convection breakers available but almost no one
installs them.

Without actually doing any fancy calculations, I know my tankless heater
dropped my summer monthly gas bill has dropped from about $50 a month
to about $25 even though we also installed a gas stove AND even
though I no longer turn off the furnace pilot in the summer because
it is now in the attic.

John