I ran a 10 gallon shrimp tank thru all of last winter with no heater what-so-ever. The temps would go up some during the daytime - around 70; at night would hover around 68. I kept my home at 70 when I'm in and around 68 when we're out and during nightime. I saw no problem with the shrimp living, growing and breeding.
I also selected plants which would be fine with cooler temps.
With your home remaining at 74, I think you 'd be fine with no heater.