Yesterday evening I had the chance to see a cheap (relatively speaking) Chinese 24,000 BTU model (Air Tempo) in operation and I was surprised at how little heating it seemed to be doing. Outside temperature was 32F. The indoor unit was installed in what to me seemed a surprising place: an 8' x 10' low ceiling basement room with the unit blowing across the 8' foot dimension and set to 72F. The rest of the basement was made up of two other small bedrooms and a washroom. (Basement was only under part of the house.) The unit ran constantly blowing rather strongly the entire 3 hours we were there which surprised me as I thought in such a small room it would warm it up quickly and cycle off. The air it was blowing out seemed to be about room temperature and the room was probably at 72. At one point I upped the temperature setting to 76 and came back 15 minutes later to see if I could feel some warm feeling air coming out of it but it continued to blow room temperature air at the same speed. I'm not experienced with heat pumps and I know the heat they produce is lower than the heat from an oil furnace at 180 degrees but I thought the air would at least feel a bit warm with an outdoor temperature of just 32. Air Tempo claims a lower limit of -5F and we were a long way from that. Perhaps it was just set incorrectly. The people we were visiting didn't have a manual and didn't know much about it. They had put a small vent into the ceiling above the room to let warm air rise into the very large open room on the first floor but surprisingly, they had put a sofa over the air vent in upper room. I put my hand over the vent but couldn't feel much air rising. It wasn't cold in the house and they also had a small wood stove burning on the first floor.
I'm hoping the Mitsubishi 18,000 BTU unit I'm looking into getting will put out more heat than that or am I missing something and is that all they do when the outdoor temperature is 32F?
Seems like you answered your own question. Bottom line, not all units are created equal. There are good ones out there.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013