heater sizing recommendations are way off

[BeanAnimal]

Clearly I don't know how a heater cycles Please tell me

Aquarium Heaters: What you need to know! | BeanAnimal's Reef

Aquarium heaters are the most overlooked, yet critical piece of equipment in the home aquarium. Learn how to protect your aquarium with a fail-safe setup.

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[BeanAnimal]

I do know how Bi metal works I looked up the answer on new tech and I got the answer I expected A Thermistor. However I don't understand why this is not a wear part

Not a “thermistor”. Mechanical thermostats in aquarium heaters have a bimetal strip with a contact welded to one end and a spring pressing against it. The spring sets the temperature at wich the strip can separate. So with each cycle, the strip bends and makes or breaks contact. This causes both metal fatigue and a spark. Over time the contacts erode and/or the metal gives way and breaks, leaving the contacts touching. Contacts also can weld together as the erosion and carbon tracking create larger and larger arcs.

 

[Freenow54]

Most “modern digital” thermostats in context to hobby aquarium heaters are SCR based and minimally designed circuits with no failsafe, the failure mode of an SCR is “on”.

I would never rely on an aquarium heaters on board controller to switch power and maintain temperature.

Good to know I put one in my new Build. Luckily nothing alive in it. So in your opinion I should close my eyes and Throw it out ?

 

[Freenow54]

So no for sure failsafe ? I lost 8 tank born fish over a weekend to a fail closed heater ie on

 

[Freenow54]

Also almost ended up on the wrong side of the dirt because of my own stupidity drained water out with out shutting one off and then started dumping water in luckily the sound of the glass breaking and my then cat like reflexes saved me but not before I got a good jolt

 

[js-3Design]

I use 300watt titanium for 75 gallon of water (60+15 sump)
My controller is set to turn on at 24.7 and off at 25.00 to make the temp swings little.
I will never use a heater with a build in thermometer.

I have the heating in my house on very little. This way i can have a room temp of 17 degrees C and still keep my aquarium warm. Below 17C 300 watt is not enough anymore.

Works well.

 

[BeanAnimal]

Good to know I put one in my new Build. Luckily nothing alive in it. So in your opinion I should close my eyes and Throw it out ?

I suggest using a commercial quality temperature controller like a Ranco. They are far more reliable than the onboard controller.