How do heaters work?

[Dom]

So I have a pair of 300 watt Finnex heaters in 145 gallons of water. They have been doing a nice job, but lately, with all of the heat, I've been running the central air. This has caused my tank temp to fall to 71 degrees F from 76.

My heaters are connected to a controller.

So how do heaters work? Are they designed to go off after a certain period of time to prevent fires? I feel like they should remain on until the target temp is reached.

 

[twentyleagues]

So I have a pair of 300 watt Finnex heaters in 145 gallons of water. They have been doing a nice job, but lately, with all of the heat, I've been running the central air. This has caused my tank temp to fall to 71 degrees F from 76.

My heaters are connected to a controller.

So how do heaters work? Are they designed to go off after a certain period of time to prevent fires? I feel like they should remain on until the target temp is reached.

Typically, they should stay on until the temp is hit. Is the controller showing its heating? Carefully check to see if they are hot. They may not be able to keep up with your ac depending on how cold you have it set. Also do you monitor temp only with the controller or do you have other thermometers? Do they all agree if so? I use an infrared thermometer to "spot" check temps in my tanks along with controllers where applicable and in tank thermometers on all my tanks. Really I only have heaters on the salt tanks I keep the room at 76 so all my fresh tanks are fine, my reefs probably would be fine as well but I dont want to chance it.

 

[twentyleagues]

Also some controllers have a built in auto shut off if the heaters are on too long.

 

[Jmp998]

Have you double checked the temp accuracy? 600 watts should easily keep a 145 gallon warm for any reasonable house temp.

 

[Dom]

Typically, they should stay on until the temp is hit. Is the controller showing its heating? Carefully check to see if they are hot. They may not be able to keep up with your ac depending on how cold you have it set. Also do you monitor temp only with the controller or do you have other thermometers? Do they all agree if so? I use an infrared thermometer to "spot" check temps in my tanks along with controllers where applicable and in tank thermometers on all my tanks. Really I only have heaters on the salt tanks I keep the room at 76 so all my fresh tanks are fine, my reefs probably would be fine as well but I dont want to chance it.

Yes, the controller is showing "on" and the heaters are warm. I think that yes, 600 watts may not be enough to keep up with the AC.

I have an analog thermometer floating in the tank (which is where the controller sensor is located). It is within a degree or two of the controller setting.

One 300 watt heater maintains. temp fine, but that is during the winter with heat on. I added a second heater during the summer to compensate for the AC. I have a 3rd heater (backup) that I can install. But 900 watts of heating in a 145?

Also some controllers have a built in auto shut off if the heaters are on too long.

I'm not certain about this, but it does make sense. I'm not using an InkBird or some other variation. This is a controller that I purchased and wired up myself.

 

[Aquavaj]

Checked temp accuracy of the temperature controller. Also check if both heaters are kicking on and heating.

 

[Dom]

Have you double checked the temp accuracy? 600 watts should easily keep a 145 gallon warm for any reasonable house temp.

I agree. we're in a heat wave here in the North East. I have the house AC set to 78 degrees and it still runs often.

 

[Dom]

Checked temp accuracy of the temperature controller. Also check if both heaters are kicking on and heating.

I have. They are.

 

[BeanAnimal]

Yes, the controller is showing "on" and the heaters are warm. I think that yes, 600 watts may not be enough to keep up with the AC.

Do the heaters have thermostats on them?

1 Watt for 1 Hour produces 3.41 BTUs of heat.
It takes 1 BTU to raise 1 pound of water 1 degree Fahrenheit

You have 145 gallons of water (likely less, but lets go with 150 anyway).

150 gallons of seawater is ~1250 pounds.

The heaters can supply 2046 BTUs of heat per hour.

That means that they can raise the tank temperature 1.6 degrees per hour.

I highly doubt that your room or AC is sucking heat out of the tank that fast but it is possible.

Reality check.Take accurate tank temp. Unplug the heaters and record temp drop, 15 mins, 30 mins, 45 mins, 1 hour.

We can go from there (also first question is important).

 

[Dom]

Do the heaters have thermostats on them?

1 Watt for 1 Hour produces 3.41 BTUs of heat.
It takes 1 BTU to raise 1 pound of water 1 degree Fahrenheit

You have 145 gallons of water (likely less, but lets go with 150 anyway).

150 gallons of seawater is ~1250 pounds.

The heaters can supply 2046 BTUs of heat per hour.

That means that they can raise the tank temperature 1.6 degrees per hour.

I highly doubt that your room or AC is sucking heat out of the tank that fast but it is possible.

Reality check.Take accurate tank temp. Unplug the heaters and record temp drop, 15 mins, 30 mins, 45 mins, 1 hour.

We can go from there (also first question is important).

No, the Finnex heaters do not have thermostats.

145 gallons is total volume. The display is 125.

But the problem is solved; apparently the controller's sensor pulled out of the tank while doing work yesterday. I should be good now.

 

[mh0ward]

I agree. we're in a heat wave here in the North East. I have the house AC set to 78 degrees and it still runs often.

Unless you have a chiller thats gone rogue, I dont understand how your tank water would be 7 degrees cooler than the ambient air.

 

[BeanAnimal]

No, the Finnex heaters do not have thermostats.

145 gallons is total volume. The display is 125.

But the problem is solved; apparently the controller's sensor pulled out of the tank while doing work yesterday. I should be good now.

suggestion:

I would place the sensor in the same compartment as the heaters, just slightly upstream. That way the heaters are truly operating off of the system temperature.

While doing so may not have prevented your problem (a probe can be dislodged no matter where it is I suppose). it does ensure that the heaters will not run away and boil the sump if the return pump is turned off (or fails), etc.

 

[Dom]

suggestion:

I would place the sensor in the same compartment as the heaters, just slightly upstream. That way the heaters are truly operating off of the system temperature.

While doing so may not have prevented your problem (a probe can be dislodged no matter where it is I suppose). it does ensure that the heaters will not run away and boil the sump if the return pump is turned off (or fails), etc.

I'm really liking this suggestion.

I used to keep the probe in the sump between the heaters and return pump. But I thought it made more sense that the temperature in the tank be monitored.

Back in the sump it will go!