Tankless Water Heater Scaling etc. [RE-wrenches]

[Bill Loesch, Saint Louis Solar]

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Fellow Wrenches:

Scaling is a function of water "hardness" and water temperature. 

Heat hard water and you precipitate the suspended minerals. Heat hard water
a lot and you precipitate a lot of minerals. Scaling happens in tanks just
the same as in tankless. The gas hot water tank control continues to
function (albeit with less sensitivity) long past the time the tankless
control _requires_ service. 

I am unaware of any good reason to heat the tankless hot water above what
you would utilize at the tap. 

Both the tank and the tankless manufacturers _recommend_ maintenance. The
tankless unit (in a hard water area) will require maintenance.

Water conditioning is the solution to hard water and scaling. This can take
the form of a water softener or a "scale inhibitor". Water softeners
benefit all downstream plumbing and offer user benefits. Scale inhibitors,
installed upstream of the water heater, in the form of a cartridge filter
or similar, also benefit only downstream plumbing. Obviously, there is
ongoing maintenance (and cost) with either the softener or the inhibitor.
Hopefully less than descaling. Cuno manufactures more than one style of
scale inhibitor under the Aqua-Pure label (and perhaps others).

Rinnai in their latest installation instructions recommends adding hose
bibs inboard of the full port ball valves during the heater installation.
This is solely to facilitate subsequent descaling of the heater.This also
provides an opportunity for Rannai to sell a matching cover for the
additional plumbing.

Regarding the minimum flow, no tankless will provide a trickle of hot
water. If you must have a trickle you must have a tank. In the case of the
frugal hot water user below, she must be instructed to open the tap to at
least the minimum flow rate (0.5 gallon per minute or higher with larger
models) to activate the heater. A legitimate frugal dishwasher would not be
using running water to wash the dishes anyway, she should be using a
dishpan. It is a matter of education or lifestyle change and should be
discussed _before_ the installation as well as a number of other issues.

The one hundred watt idle draw was probably one of the electric freeze
protection heaters actuating inappropriately. Some of the tankless
manufacturers are recommending mounting these tankless units, often in a
ganged configuration, on commercial rooftops in freezing climates. The
internal electric heaters only protect the heater itself, not the
connecting piping. Obviously, if the power fails during a freezing
condition there is no protection whatsoever. IMHO, another not so good
idea.

Bill Loesch
bill_loesch at compuserve.com
tel / fax 314 631 1094
Solar 1 - Saint Louis Solar
www.solar1online.com
9905 Vasel Drive
St Louis MO 63123-4321



Ray Walters said:
> Hi Scott;

>We've seen this scaling problem here with Aquastars. I quit selling them 
for the most part,
>because of the scaling problem and the fact that they  don't fire at low
flow rates. Nothing like
>selling a good customer a Staber  washer and an Aquastar and then the
Staber doesn't use enough
>water to get  the Aquastar to fire! Or the frugal old lady on a rain catch
cistern that  washes
>dishes with a quart/ minute and it won't fire either. I recently had a
customer with a "Rannai"
>hotwater heater. It had an almost  100 watt draw while in standby!  It
must have had a glowbar or
>something in  there. It also was not mod sine friendly. It was replaced
with an Aquastar,  since
>there wasn't space for a regular hotwater heater.

>Ray 

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