Heater placement

Hi everyone -- gearing up for big celebrations?? Oh boy -- is it bad here
-- biggest dump of snow in 60 years bad, bad, bad!! Can't do anything
except mess with aquariums.

I have a question. Where is the best location for a heater? At the moment I
have the heater in my 48 gallon next to the filter output. The filter
intake is at the other end of the tank. I used to have the heater close to
the filter intake but the water seemed to be cooling down too much at night
-- so I moved it but it doesn't seem much better. Now I'm starting to
belive that the thermometer stuck on the side is in a "cool spot" because a
floating thermometer says the water is over 80F degrees though the stuck-on
thermometer says as low as 72F in the morning. The heater is a 200 watt and
should be plenty. Anyone have any advice as the best positioning of the
heater for even heating? Or does one have to have two heaters in a 4 foot

in deep, deep snow and it's STILL coming down!