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# Re: \$\$ to run heater

```From: Miles Morrissey <mmorriss at sophia_smith.edu>
>
> I was wondering if anyone had a general rule of thumb about how many
> hours per day a heater is on.  In order to calculate how much \$\$ I'm
> spending to run various instruments in my aquarium I need to know how
> long they're running.  This calculation is easy with lights and pumps
> but I can only guess as to how long the heater runs.  Specifically,
> in my 50G tank which I keep at 75 degrees in a 70 degree room, I'm
> guessing that the heater is on 4 hours / day.  Does this sound
> conservative or liberal?  Given the number of variables to consider I
> imagine this would be a tough one to nail down but what are people's
> opinions?

If you knew the evaporation rate of your tank (how often and how much
you "top off" your tank), you could make a sketchy calculation by
assuming that all the heat lost from your tank is lost through
evaporation and that the "top off" water is being added back at room
temperature.  I'm sure a chemist can do better, but knowing that it
will take 1 calorie to raise 1 mL of top-off water 1 degree Celcius
the tank lost due to evaporation of tank water equivalent to the
volume of top-off water (someone help me...X kcal/mL...it's in a CRC
or chem. book), you can get calories/rate of top-off at steady-state,
which you convert to Joules/second == Watts.

Div. by 1000, mult. by hrs/month and you've got kW.hours to compare
with your monthy energy bill.  Tons of assumptions were made, so throw
in an engineering factor of 2 or 3 to give you a conservative value.

Someone correct me if I'm off my rocker.

Carlos Munoz

```