I run a Rena 300 in my 110 and it does a great job. I have a Kora 3 power head on the side of the tank and the heater in the middle, even in the winters here in MN (and my house being set to 62F) it doesn't run that frequently. You might be able to get by with the 250 but that may lead to more power consumption for the same output (longer duty cycle on to archive the same temperature change).