"Derek Benson" wrote in message
...
On Tue, 3 May 2005 17:40:40 +0100, sophiefishstuff
wrote:
In message , Derek Benson
writes
On Sun, 1 May 2005 15:02:38 +0100, sophiefishstuff
wrote:
my new (secondhand) tank came with a heater, which looks to be about
the
right wattage for a cold winter's night, but rather overdone for the
summer... 35 (US) gallon; heater = 200W.
Is this a problem?
What I've usually seen on the spec sheet that comes inside the box
with a new heater is that the manufacturer recommends 3-5 watts per
gallon. This can also be found in various books and probably on the
Net. In my personal experience 5 watts per gallon is too much,
particularly in smaller tanks; and I'm talking about the heater
functioning correctly, I'm not thinking of a situation where the
heater gets stuck. Just for general use, these 5 watts are too
powerful.
I would never use anything stronger than a 100 watt heater in a 35
gallon tank.
Thanks for this, Derek, I appreciate it. I do wonder though if your
ambient temp might be a bit higher than mine? I'm in the UK and I don't
have the heating on at night or during most of the day during the week,
so from October - April I need a temperature hike of a _minimum_ of 8
degrees C and often more, and I wonder if a 100W heater would be
suitable for this? I'll keep a careful eye on things over the next few
weeks as the weather warms up.
If the weather is warmer (and I have to say it is not for many days a
year that the ambient temp. is close what I want the tank to be) won't
the heater just switch itself off? The original heater I had looked
very
dodgy, so I got rid of it and got a (very expensive) Hydor Theo, also
200W... I take it you think this was a mistake ;-) The info on the box
recommends the 200 for the temperature hike I need and suggests the 100
wouldn't be adequate, and the fish-shop man agreed - he's someone I'd
trust, btw.
I have a tank which is 86 liters, how many gallons is this? 25 or a
bit less? The heater which came with the tank was 100 watts. I was a
bit skeptical at the time but the store guy said, yes yes this is
correct for the tank.
After a few months I noticed that the temperature fluctuated a bit up
and down, more than it should IMO and more than I like anyway. What I
discovered was that when the heater turned off, the orange light went
out so it's off, there is still some heat in the heater coil (or
whatever it's called) which must dissipate in the water. This is how
it is with all heaters, when that orange light goes out there is still
warmth in the thing, it needs to cool down. So this heater was pushing
up the temp 2 or 3 or maybe even 4 degrees above the target temp,
because of this extra dissipating heat in such a small volume of
water. I still have this heater today and there's nothing wrong with
it; I'm not using it at this moment but it functions as its supposed
to.
I replaced this heater with I think a 50 watt heater, and this
fluctuating temp problem disappeared.
My personal opinion is that it's impossible for a 100 watt heater to
have any problem raising 35 gallons of water 8 degrees over ambient
temp. But I've never done it, I keep my living room warm enough that I
can use a t-shirt, I don't want to wear a sweater every day when I'm
at home. I've also never owned a 35 gallon tank. The 100 watter would
be on a little bit longer than the 200 watter every time it turns on,
this is all. But if you've never seen this temp swing that I'm talking
about or don't see it, then there's nothing specifically dangerous
with the 200 watt heater in this tank.
-Derek
If I can comment on Derek's observations, a 100W heater causing a 2,3 or
4 degrees over-temperature swing in a 22-1/2g tank would suggest to me
that there was a defect in the heater and/or insufficient water flow past
the heating elements.
For those who are technically inclined, this calculator
http://www.kernsanalysis.com/HeaterCalculator.cgi will tell you exactly
how many watts of heat that your tank will radiant (which is the amount
you need to replenish to keep a uniform temperature). As a calculated
value, it will always be lower than what you actually need, as real life
tends to change temperature more ;~), and certain types of filters can
lose heat while others add heat, so there is a little 'ymmv'.
Someone mentioned that an oversized heater cycles more often (absolutely
true). There is an optimal size which is a balance between wear and
safety margin. If you don't need much safety margin (your ambient is at
a fixed temperature 24/7), then you might reduce the size of the heater
to reduce wear, but you need to be significantly oversized to run into
real trouble, so it might not be worthwhile. The most common problem is
underestimating the requirements. Looking purely at the wear issue, the
most susceptible types are the analog heaters (their contacts arcing) and
the least susceptible are the ones with solid state switches. In either
case, the heating elements fail eventually but that takes many years. I
seem to be getting about 12-15 years out of elements, so I can't complain
;~).
Another factor (which is important to me), is that bigger heaters are
more practical for people with many aquariums (and heater prices are
fairly flat and independent of wattage). I'm always putting tanks into
or out of service, and smaller than 200W is of minimal usefulness. If
all my heaters are 200-250W, I find that I have the most flexibility (ie:
doubling up for larger tanks), and I don't have to deal with the risks of
300W heaters. jmo
)
--
www.NetMax.tk