Inside temperature is 68 degrees, thermostat is set on 70 degrees, outside temp is 73 degrees. If door is left open for a few minutes is it wasting energy?
Your inside heating system will keep trying to get the temp up to 70 degrees. That will take less time with door open when it’s over 70 outside. Leaving the thermostat above the outside temperature while the door is open wastes energy, but not as much as leaving the door closed.
All things being equal…thermostat @70, outside @73… you’re not wasting energy.
My girl friends son went ballistic on me the other day because the heater was on and the door was open while I went out to empty the trash. He didn’t believe that the warmer outside air would warm the house up quicker.
The son makes a good point: from now on he takes out the trash.
And when he does, lock the door behind him.
Why would someone be running the heat at all when it’s 73 outside? Is this an egg hatchery?
I would assume its just the setting on the thermostat. Around here lately we’ve had swings of 40 degrees a day from low to high; generally I just let the thermostat work out if heat is needed or not.
Or you could be right and it is an egg hatchery. 
Yes it was a thermostst setting and turned on early in the morning, we just forgot to switch it back off. We usually turn it on for about an hour and then switch it back off. The house only gets down to about 58 or so.