You can check to see if you have one by dropping the inside cover. If you see a small u shape tube with fins on it to one side that is the heat strip. I close the vents on the opposite side because this air does not blow over the heat strip. It does take awhile, maybe 5 min.s to start warming. With 2 units in my 34' I can keep it 70 inside with the outside temp in the low 40s. When it dropped to the teens this weekend the furnace that was set around 67 would kick on now and again. The noise that AC fan makes drowns out the furnace coming on, with will wake me up. I would not buy them if I did not all ready have them, ( about $100 or more) but since I do I will use them.
"Humans get a lot done,not because we're smart, but because we have thumbs so we can make coffee." Flash Rosenburg
"Decaffinated coffee is the devil's blend."