Jandy heat pump freezing up indoor install

[Mrsith]

I recently installed a new jandy JE2400T heat pump in my shed bc I have no where else to install this monster. I first hooked it up and cut a hole in the wall leaving the door open in hopes that air would circulate enough...wrong. it froze up on the rads 100% and shut down. I then built a diversion off the top to push the cold air from the top out of the building...it only freezes up half way now and is heating the pool...but it can't be running very efficiently. So my question is this...it the manual there is a brief mention of a duct on top to divert the air up n out for an indoor instalation only. Is a 6' long 24" duct going to be enough or will the static air just keep me having issues? I don't want to cut a massive hole in my roof if it won't work. Anyone else have a heat pump in a shed?