You can typically find on Amazon small heaters for nano tanks, like five gallon heater 3 gallon etc, I’ve had a couple different ones and they worked well, only complaint is no temperature control, but that’s about it. Can’t remember the brands but I would just google it and you should find plenty
How cold is the room? Shrimp tanks don’t normally need a heater since they don’t really like warmer temps. Anything over like 72 isn’t really needed unless you want to encourage breeding. Higher temps also shorten their lifespan.
anonshade64 
You can typically find on Amazon small heaters for nano tanks, like five gallon heater 3 gallon etc, I’ve had a couple different ones and they worked well, only complaint is no temperature control, but that’s about it. Can’t remember the brands but I would just google it and you should find plenty
Buce plants sells a [micro heater](https://buceplant.com/products/micro-aquarium-heater) that you can probably find elsewhere on the internet.
(non affiliate link, just what I use for my 4g shrimp tank)
How cold is the room? Shrimp tanks don’t normally need a heater since they don’t really like warmer temps. Anything over like 72 isn’t really needed unless you want to encourage breeding. Higher temps also shorten their lifespan.