In article , Dick
wrote:

On Wed, 9 Mar 2005 20:39:19 -0500, "Bill Stock"
wrote:

I recently purchased a Won Brothers Pro Heat II aquarium digital aquarium
heater for my 75 gallon. The old heater was too small and I plan to go with
an auto water changer in the near future, which will only make matters
worse.

The box makes claims of +/- 1°F accuracy, which if you read carefully,
refers to the digital readout, not the actual heater. The heater has a
range of 68°F to 93°F. I currently have it set at 68°F, but the tank is
reading 72.3°F on my thermometer and 71°F on the heater LED. I thought 4°F
of error was rather crappy given the +/- 1°F claims and the fact that I
wanted to keep the tank around 70°F. I contacted the manufacturer about the
large error, but they did not bother to respond.

[snip]

I have yet to find a heater that is calibrated. The dial markings
seem to be approximate. I have come to assume the plus and minus are
a measure of how accurately the set temperature holds.

Thus I set the dial to 78, the tank temperature settles at 76. I move
the dial to 80 and the tank settles at 78. Leaving the dial alone,
the measure temperature will vary plus or minus, there is always a
lag.

Most of the heaters I've seen cycle on and off at a rate determined by
the "temperature" setting of the control. If ambient temperature
changes by a couple of degrees, the result is a corresponding change
in water temperature since the thermostat is still adding the same
amount of heat.

I would be interested to see if your "Won Brothers Pro Heat II" actually
had a temperature controller rather than a cycling heater in it. The
former would actually measure the water temperature and adjust the
on/off cycling rate to maintain constant temperature. If any one knows
of a system that does this, I could really use one for my 120 gal. lab.
tank - the room temperature is normally pretty constant, but if the
outside temperature changes dramatically overnight, it can vary by as
much as 6 F, and I have to go adjust the thermostat.

Speaking of which, it's time for my daily tank check...