My cabin is in north Texas (aka Hell’s Furnace) and is 16×24. I have R19 walls, R25 ceiling, and R20 floors. The walls are 2×6 and I have 7/16 OSB sheathing and Tyvek wrap between sheathing and siding. There are two high quality fiberglass doors, and 4 high quality windows, 2@ 36×48, 1@24×36, and 1@12×24. There is one bathroom 6×8 ft where the 12×24 window is. The attic is vented with a ridge vent and vents are in place under the overhangs. Interior walls are 1/2 in drywall. Ceilings are 8 feet.
So having said all that, I am probably going to buy a window unit rather than a portable. From what I hear and research, they’re just better all around.
As far as sizing the unit, the boxes say 10k BTU is appropriate, and a calculator I found said 13k, but that’s seems right for normal places, not the sweltering sauna that is the Lone Star State in the summer. I figured I’d go to 14K. Does this make sense?
Also how is the quality of the big-box window units? Especially the GE models?
Best Answer
I would think that 12 kBTU/h would be fine even in north Texas. One interesting feature of window units is that the chilled condensed water from inside is used to cool the bottom coil of the condenser before the condensate is conducted out to the ground. (At least this was the arrangement in the early 1970s when we had a window unit in north Florida.) Central units just dump the 40 deg F condensate to a drain and so waste the cooling capacity of this chilled water.
If there is a separate bedroom, you might consider a mini-split ductless with one condenser unit supplying two air handlers. This would cost a lot more, and require professional installation, but would almost certainly use less power and cool better. They are advertised as employing "inverter technology"; some of these minisplits have a claimed SEER of 20 to 30 and they are available as heat pumps which would heat the cabin in winter. But personally given the price difference I would first try the window unit.
If you put in a window unit, you could cut a hole in a wall rather than use a window and there are even "window type" units (I think called slide-in) which are designed for this type of installation. Some window units can't be installed in a hole in a wall because the wall is so thick that it would cover the intake vents for the exterior part of the unit.