How Hot Will 40L Tank Get With 25W Heater?

[svenrufus]

I've had two Interpet 50W heaters go bonkers on me in the space of 24-30 months, and despite gradually cranking down the temperature setting to the lowest possible level, the temperature in the 40L tank kept on going up and up. It got to the point that the setting was at 22C but the water temperature peaked at 32C before I finally intervened more drastically - I admit I was a bit 'eye-of-the-ball' towards the end there.  This size heater was what came with the tank.
 
I've ditched the first one completely, and have just turned the newest one off now, so that the water is 'cold' at 17/18C. Fortunately there are only guppies in it at the moment and they seem quite content - slower, but content. I'm fed up with this happening and worried about the risk to the fish of it going wrong more dramatically and basicaly cooking them. That happened with my first tank years ago, when I was a kid, and I was very upset about that at the time, so I'm very conscious of that possibility.
 
Even though this current temperature seems to be working, at least for the moment, I'd like to get some heat in there again. I was wondering about getting a smaller heater in there.
1) If I got a smaller heater, say 25W, would that be incapable of cooking the fish even if it went bonkers and was constantly on?
2) Would it be incapable of heating the tank to any sensible degree?
3) Would it be bad for the heater's lifespan if it was on all the time and struggling?
 
 

 

[Ch4rlie]

Heaters for tanks can sometimes be a bit unreliable, especially if buying unknown brands or second hand heaters cheap.
 
To start with, general 'rule of thumb' is 1w per 1 litre of water. This does not really apply if you live in a warm climate country though may still get a bit too cool at night times and during winter seasons.
 
If your home has a nice steady controlled temperature with the aide of central heating and/or air con etc then the tank water should not fluctuate too much at all.
 
So on that basis a 25w heater is not really suitable for a 40 litre tank, having said that, it should still work to get thetank water to your desired temperature but the heater has to work constantly in order to maintain that temperature therefore this may impact on the longivity of the heater.
 
A heater only switches itself on when the tank water drops a few degrees below the desired temperature, so if the water is at the desired level at say 24C or slightly above then heater stays off until temperature has reduced to below 23C or thereabouts. This makes for a energy effiecient appliance as long as the thermostat is working correctly, this is where a lot of the cheap brands or second hand heaters fails as the component parts for the thermostat are cheap and may not have a long life etc
 
I would conclude its always good to get a slightly oversized heater, in your case, a 50w heater is ideal even though you have had bad luck with your previous 2 heaters at this wattage. And would go for a new heater with a half decent recognised brand rather than second hand.
 
Personally I have used Eheim Jager and Fluval heater brands without any issues at all to date (touch wood!)
Though you will always see a mixed reviews on different brands while some will say that Eheim Jager heaters are not worth it and other swear by them, same goes for any brand
 
Really think its a personal choice on what you feel suits you and your budget best, I have always said when it comes to heaters, you get what you pay for and its worth getting a decent type even if it costs a few more pounds/bucks.
 
Edit - Don't forget that this can depends on your climate on where you live, hot countries may not actually require a heater at all as temperatures tend to be the same most days throughout the year. And of course what the usual temp is inside the room where the tank is situated can be a factor is worth bearing in mind.

 

[Jeremy180]

One simple solution to this problem that I've read is to use two heaters ,each rated for half your tank's capacity, at opposite ends of the tank.
That way, BOTH heaters would have to malfunction at the same time to cause any serious problems.

 

[Ch4rlie]

One simple solution to this problem that I've read is to use two heaters ,each rated for half your tank's capacity, at opposite ends of the tank.
That way, BOTH heaters would have to malfunction at the same time to cause any serious problems.

 
This is certainly another good option, I forgot about! Oops
 
This is especially good with long or large tanks as this help maintain an even temperature thoughout the tank water column.
 
A good point

 

[Akasha72]

don't suppose the heaters that went 'bonkers' were the Interpet Delta-therm? If so there seems to be a general fault with this heater. I was looking for a heater for my Dad as his tank heater was going bonkers too and I came across some really bad feedback for the Interpet Delta-therm heater. He was going to buy one but I told him not to touch it with a ten foot barge pole and then read him some of the feedback. It would appear to be a fault with it's thermostat and I hope Interpet are seeing the feedback and doing something about it. I'd hate to see a company with such a long established reputation go down over something so easily fixed.
 
There was better reviews for the Tetra heaters and Hydor too. I currently have a Clearseal 150 watt heater in my little 30 litre tank (it's my quarantine tank and I've got some new baby fish in there at the moment) which is set to 24 and according to two thermometers it is 24 degrees in the tank. This clearseal is the most accurate heater I've had apart from maybe the Juwel heaters 
Whilst the general rule would be normally 1 degree per litre (as others have said) You can add heaters of a larger wattage as I have done with my liitle Q tank. The heater is coming on for less time as it's working less hard to heat the water than a 50 watt would be. It could end up saving you money if you buy a heater slightly larger than you need. It also gives you options should you decide to upgrade your tank at a later date

 

[PepperjacksMama]

Well even with two heaters, one can still stick and cook.
Sadly heaters fail. It happens.
I have used Fluval heaters for years without complaint.
As for size, I generally go larger than needed. Heater doesn't work as hard, and maybe it's just where I have been purchasing them. But I have found 250 watt heaters cheaper than 50s.

 

[StevenF]

 
 
Well even with two heaters, one can still stick and cook.

 
Yes if your heat is oversized.  However if you sized the heater so that it could only get the water to 5C over the setpoint your fish would probably be fine.  If you then replace the one heater with 2 half power heater the water would never get too hot.  If one heater sticks on the other would turn off and the tank would probably cool down slightly.  if both fail your water will only be 5C over setpoint and your fish might be OK.  The difficulty is determining the exactly how many watts are needed to just maintain setpoint.  
 

 
 
but the heater has to work constantly in order to maintain that temperature therefore this may impact on the longivity of the heater.

A heater that is on constantly on will like have a longer life than one that cycles constantly.  The reason for this is that at the heart of a thermostat is a switch.  And most switches have a finite cycle life.  Switches typically have a cycle rating.  on - off is one cycle.  So a heater constantly cycling on and off will have a lot more switch cycles and a greater likelihood of failing than one that is on most of the time.
 
another way to reduce the likelyhood of fish loss from a heater failure is to get one of these:
http/www.amazon.com/gp/product/B007480AP6?psc=1&redirect=true&ref_=oh_aui_detailpage_o08_s00
 
This external thermostat will turn off the heater if it gets stuck on.  Also if the external thermostat gets stuck on the thermostat in the heater will turn off the heater before the water gets too  warm.   in order for the heater to get stuck on both thermostats would have to fail at the same time.  I have the thermostat in the link and it has been working fine for 2 years.  

 

[NickAu]

 

One simple solution to this problem that I've read is to use two heaters ,each rated for half your tank's capacity, at opposite ends of the tank.
That way, BOTH heaters would have to malfunction at the same time to cause any serious problems.

I have 2 Aquael 75 w Easy heaters at opposite end of the tank.
 
I now refuse to use anything but aquael heaters, These things are worth the few extra dollars.
http/www.thetechden.com.au/Aquael_Easyheater_Professional_100_Watt_p/106106.htm

 

[svenrufus]

Thanks everyone for some great and really interesting responses. I'm still kind of torn between getting the smaller heater/s or one larger one of better quality.
 
In reponse to the quesion "Was it the Interpet Delta-Therm?" - yes it was. Both times. Both bought new - the first was in the tank as part of the kit on purchase. The second was purchased because I thought that was a trusted brand! Ho hum.
 
I like the idea that the smaller heater being on more could even extend it's life as the switching process is the limiting factor on the thermostat. I'm tempted at the moment to use one smaller heater and see what that does on it's own, but then supplement a second to add backup if needed. I want to run the tank towards the lower end of the temperature range anyway, so that fits in with that idea.
 
Lots to think about, but thanks again for the input.