How to size heater for 100 gallon tank

[All-in Salt Tank]

Hello.

I set up my 100 gallon FOWLR tank in late January and the heater that came with it died over the summer (i purchased a complete set-up and moved it all in Jan). I have another 250 Watt Eheim heater but I want to run two...one as a back-up.

Aquarium heaters seem to be all over the place in size and quality. I ended up getting a 300 Watt Eheim thermocontrol heater for my tank, as it seemed like the best quality and price for what it is. When I got it, though, it seems quite large and says its for 159-254 gallon tanks! I ordered an Inkbird wi-fi controller to run this and my current 250 Watt Eheim heater.

My tank is in the lower level of our New England home, and we do not need to heat this space unless it gets frigid cold outside. In general, due to energy costs and the size of our home, we live cold in the winter! That said, the temperature fluctuates a bit in the fall/winter/spring with room temps in the low-mid 60's at night, high 60's at best during the day. In the summer, I actually have to turn the heater off in the tank and remove the glass cover and use wire mesh.

Silly question....if the 300 Watt heater is capable of heating a much larger tank, is there any reason I shouldn't use it in my 100 gallon tank? Won't it just run to what it is set at and what I set the controller to? I'm thinking it will work harder some of the year and not at all at other times.

Thanks for your help and suggestions!

Best,
Darin

 

[FUNGI]

I have always used over sized heaters...in fact I have 2 x 300w in my 125G right now. I will only see them come on for no more then 5 seconds......(my tank temp is 78)...It seems to be less work for them.....

 

[FUNGI]

In case you get bored, heres a nifty calculator to play with (both heater and cooler)

Heater & Chiller Sizing Calculator

Aquarium calculator; Estimate the size (power) of heater and chiller required for an aquarium.

www.hamzasreef.com

 

[Fish Fan]

Hi, Darin!

I'm not an expert here, but I've used several of those Eheim heaters, they are very good and well regarded here at R2R, but they are very looooooong lol! Don't judge the physical size, get the heater you need for your tank.

The traditional advice is about 3-5 watts per gallon, but when you talk about larger tanks, you can go at the much lower end of the scale.

I'll probably get blasted for posting this, but for a very inexpensive heater, I've been having really good luck lately with these cheap Marina heaters from Amazon. I have about 7 of these, including freshwater systems, and they are working well for me:

Amazon product

But - hear me now, and believe me later - whatever you choose, get AT LEAST an inexpensive heater controller, like this:

https://inkbird.com/products/aquarium-temperature-controller-series?currency=USD&variant=43678318526640&utm_source=google&utm_medium=cpc&utm_campaign=Google Shopping&stkn=a32e45f79ba4&gad_source=1&gclid=Cj0KCQjw1Yy5BhD-ARIsAI0RbXb7h_ryC-rLJOdQ90cTF0nasGJ4SF7XrDcSPqmMM4eyyogicj2hWZwaAmWfEALw_wcB

I recently, and sadly, had a 15 gallon marine tank get smoked from a heater that broke in the "on" state, and I know better, I do, and I'm kicking myself. On this tank, I had a relatively expensive Cobalt NeoTherm heater, but ANY heater can break, and they often freeze "on", which is a much, much bigger problem to have than a heater that's broken "off".

Please get a heater controller! You can find those InkBirds for as little as $20 used on the R2R Marketplace.

Good luck with whatever you decide!

 

[Idech]

I like having 2 heaters on an Inkbird controller, for redundancy and added safety.

In general, I don’t like oversized heaters because if they go nuts, you risk cooking your fish.

 

[All-in Salt Tank]

In case you get bored, heres a nifty calculator to play with (both heater and cooler)

Heater & Chiller Sizing Calculator

Aquarium calculator; Estimate the size (power) of heater and chiller required for an aquarium.

www.hamzasreef.com

Thanks for your help! The calculator is a bit over my head, but it is interesting if you understand it all. I'm going to use the 300 Watt, as I'd rather be over than under. Cheers!

 

[All-in Salt Tank]

Hi, Darin!

I'm not an expert here, but I've used several of those Eheim heaters, they are very good and well regarded here at R2R, but they are very looooooong lol! Don't judge the physical size, get the heater you need for your tank.

The traditional advice is about 3-5 watts per gallon, but when you talk about larger tanks, you can go at the much lower end of the scale.

I'll probably get blasted for posting this, but for a very inexpensive heater, I've been having really good luck lately with these cheap Marina heaters from Amazon. I have about 7 of these, including freshwater systems, and they are working well for me:

Amazon product

But - hear me now, and believe me later - whatever you choose, get AT LEAST an inexpensive heater controller, like this:

https://inkbird.com/products/aquarium-temperature-controller-series?currency=USD&variant=43678318526640&utm_source=google&utm_medium=cpc&utm_campaign=Google Shopping&stkn=a32e45f79ba4&gad_source=1&gclid=Cj0KCQjw1Yy5BhD-ARIsAI0RbXb7h_ryC-rLJOdQ90cTF0nasGJ4SF7XrDcSPqmMM4eyyogicj2hWZwaAmWfEALw_wcB

I recently, and sadly, had a 15 gallon marine tank get smoked from a heater that broke in the "on" state, and I know better, I do, and I'm kicking myself. On this tank, I had a relatively expensive Cobalt NeoTherm heater, but ANY heater can break, and they often freeze "on", which is a much, much bigger problem to have than a heater that's broken "off".

Please get a heater controller! You can find those InkBirds for as little as $20 used on the R2R Marketplace.

Good luck with whatever you decide!

Hello. Thanks for your thoughtful reply. I did order the Inkbird ITC 306-A that has 2 temp probes and is wi-fi compatible with an app. I plan to run the two Eheim heaters on the Inkbird controller.

I didn't know about the controllers until I started reading reviews about heaters that malfunctioned...exactly as you warn. It seems like a small investment for added peace of mind!

Cheers!
Darin

 

[Mr. Mojo Rising]

The old 'rule of thumb' is 3-5 watts per gallon, I like going with 5 watts per gallon

 

[Borat]

The heater should be sized so as not to cook your tank. Generally i size it in such a way that if the heater is left to heat the tank for a period of 24 hours - it will not raise the temperature above 29 degrees celsius.

the assumption is that you will eventually notice that the heater is stuck in on position and be able to switch it off.

 

[Borat]

So that gives you about 150w-200w range for a 100 gallon tank.