yeah, i recently bought two and so far it keeps my one gallon (with a Nano filter) pretty much around 80F. i also have plastic wrap over the top (with proper air holes). i use it to slow water evaporation and temp fluctuations. the one i have in my 2 1/2 tank maintains it between 78F - 80F, plastic craft-grid for a lid. i think it works great. i would keep in mind that results may vary considering other factors such as additional heat from lighting, room tepms, lids, water circulation, etc.
