Temp ranges for just started germinated seeds

I start my germinated seeds in rapid rooters in a dwc system in a closet with a small heater to keep temps up. I shoot for temps in the high 70s but I may need a new heater because it is allowing temps to fluctuate from 68 to 86. I'm working to rectify that, but I don't think that either of those temps are dangerous to the new starts, do you?

Doesn't your heater have a thermostat? I'v had successful germinations in cold water (20 Celsius) and some pretty warm water, like in the high 20's. Think it depends on the beans....

The heater does have a thermostat and it used to work, I need a new one. The seeds were germinated in paper towels and then transferred to the system 24 hrs ago. They havent started coming up yet. I usually try to keep temps at this stage in the upper 70s, so I'm hoping the extremes at 68 and 86 didn't hurt anything.