Hey Nadia, there is a heater I just ordered at DrsFosterSmith.com that have exact temp control by the degree. It's made by Rena and is on sale for 15.99 for a 50 watt (5 to 15 gallon nana). Item no #TJ-150032. You might have to mess around to find it, I did. Or just ask live help since lenght is important to you. Ask how long it is and make sure he knows your talking about the heater. Hahaha
temp
- Thread starter sadielynn
- Start date
the ones that we have also have the degree control it is about as big around and long as a fat sharpie pen does great on the heating I actually keep ours 1 degree lower than what I need since they heat so well and there is no glass to break , mine is housed in the filter 
so size was an issue with me as well
http://www.premiumaquatics.com/Merchant ... Finnexheat
so size was an issue with me as well http://www.premiumaquatics.com/Merchant ... Finnexheat