Temperature question (Aquarium specific)

[eybic]

I have a theory (it may well be a bonkers one that makes no sense to people in the know)

I've got an aquarium which is normally kept at 24 degrees, in the warm weather of course the temperature increases.

My theory is that if I turn my heater down to say 23 (temperature drops at night), when it heats up during the day (environmental heat rather than the heater) it's less likely to get as high due to starting off at a lower temperature, I mentioned this on a Facebook group to be lambasted for suggesting something so stupid.

Does my theory make any sense or is it massively flawed?

Thank you

[Mr Pointy]

How hot it gets depends, in general, on the hysteresis on the thermostat. If it's got a +/- 1 degree window the stat will cut off at 25 degrees no matter if it started at 10 degrees or 20. In warmer weather it will just take longer for the temperature to fall to 23 degrees to trigger the heater again & it will reach 25 degrees more quickly as heat loss from the water is lower, although I'm not sure it's by a big amount.

It's the same priciple as women tuning up the stat so the room warms up more quickly.

[eybic]

Thanks,

So if a tank starts off at 23 degrees in a (lets say) 12 hour period will it be cooler than a tank that started at 24 degrees?

[Simon_GH]

eybic said:

Thanks,

So if a tank starts off at 23 degrees in a (lets say) 12 hour period will it be cooler than a tank that started at 24 degrees?

By the laws of physics this has got to be correct. Assuming the room temperature is a constant, the cooler tank will need to absorb more energy than the warmer tank to reach the same temperature and therefore will take longer.

[Mr Pointy]

Simon_GH said:

eybic said:

Thanks,

So if a tank starts off at 23 degrees in a (lets say) 12 hour period will it be cooler than a tank that started at 24 degrees?

By the laws of physics this has got to be correct. Assuming the room temperature is a constant, the cooler tank will need to absorb more energy than the warmer tank to reach the same temperature and therefore will take longer.

It depends on how big the tank & heater are. If the heater hasn't managed to get the tank up to 25 degrees (still assuming 1 degree hysteresis) by the end of the 12 hours then the one that started off at 23 will be cooler, but once you have gone through a couple of full cycles there won't be any difference.

[eybic]

Thanks guys, I thought I was going mad but I'm glad my "madness" has been confirmed.

[deadtom]

I think it depends on a few things, but I think what you are suggesting is mostly correct.

If your fish tank is at a minimum of 24 at all times due to internal heating, then when the room temperature rises above 24 on a warm day, the water will follow suit, albeit at a slower rate due to the heat capacity of water vs air. In this scenario it might take, say, an hour for the fish tank to match the temperature of a room at 25 degrees.

If you switch off/reduce the heater at night then your start point becomes 23, and now is 2 degrees cooler than the room ambient, so say it takes 2 hours to match the room temperature. It gets just as hot, but the time spent at the higher temperature is reduced.

The above is a vastly simplified scenario however, so if you want a more scientifically rigourous answer you will need someone better at thermodynamics than I am (which I must admit, is not difficult)