Just using a heater isn’t enough - you need to make sure the air in your grow room is being warmed evenly. Otherwise, you’ll get cold and hot patches.
To make matters worse, when this happens, you can get inaccurate temperature readings (depending on where your probe is placed).
The solution is simple - you just need to keep the air in your greenhouse well mixed. That’s where air circulators come into their own.
The KlimaHeat has an ‘air circulation’ function that mixes air. Or you can dot around some air circulator fans. They don’t cost much to buy, but help you keep your climate spot on.