Electric Heaters

A little over 7 years ago, I shut down an ancient boiler that used oil to heat a 6 unit apartment building. It was either that or go bust. I ran 240 volt lines into 5 of the apartments. These are small apartments with 2 rooms - @130 square feet per room. I installed Broan 1500 watt heaters in each room. They are hardwired and wall mounted. Some of them are beginning to crater. The fans are noisy, dust collects in them, and there is no practical way of setting the temperature other than turning the knob clockwise or counterclockwise. I know that 1500 watt space heaters all use the same amount of electricity. I also know that electricity based heating is your worst heating value. Always has been and always will be. I get that. But I’m stuck. There is no room to install small vented gas furnaces plus it would cost me a fortune. If any of you electricians have run into the same situation with apartment owners, what type 1500 watt space heaters hard wired or otherwise would you recommend? I'd like to consider ones that have wall mounted thermostats or at the least some sort of digital readout on the front of the heater. Thanks.