I have a home office in the back of a detached garage. I have a wall-mounted electric resistive heater with a fan that keeps me plenty warm in the winter. When I moved in, I didn’t really need A/C. On the few hot PacNW summer days, I’d open the door, turn on a fan, and deal with it. But as the number of 90+ days increases, a plain fan isn’t cutting it. What are my options?
The office is about 120 sq ft, has an attic with roll insulation, and two 40"x36" windows. Unfortunately, the windows are fixed with no way to open them. The walls are interior drywall, with cedar siding over plywood on the exterior.
My first thought was to replace a window with something that opens and use a little window A/C unit on hot days. But replacing a window isn’t cheap or easy. Maybe it’s easier to cut a vent hole in the wall? Maybe in the attic where I don’t care so much if it looks good and is well-sealed?
I’m open to all suggestions, with a preference for cheaper and something I can do myself with moderate handyman skills.
Spec out a Portable AC for 120 sq’ or 1000cu’. You will then only need a 4" to 6" diameter vent hole to cool the office. It looks like the small units only need a 4" vent, so pretty similar to a dryer vent. Pretty easy to install and no loss of windows.
I’m pretty sure even a 5000 BTU unit is up to the job but I might err up to a 6000 BTU.
For those sunny and hot days, make sure you have both blinds and curtains for the windows. It will help reduce the heat load.
It is usually not recommended to vent to the attic, though that use to be more common. It is best to vent outside when possible.
Alternately you could buy a small window unit (probably cheaper) and cut a hole for it to be through the wall. But I would spend the extra on the portable unit unless you’re really tight on space.
The only real drawback to the portables is that if it gets really hot they lose effectiveness because of that vent tube, which spills a tremendous amount of heat back into the room. So if you use one you want to put it somewhere so that it’s right up against the wall and that vent tube only travels a few inches inside the room on its way out.
Window units don’t have that problem, since they always exhaust the heat out the back which is outside the room. Rather than actually site it in a window, though, I’d do like they used to do in '60s houses and frame a space through the wall to permanently mount it, and put it up as high in the room as you can to avoid that nasty little surprise where you’re sitting down and all seems nice and cool until you stand up and your head boils. Not fun. Another advantage to doing it this way is that you can, if the electrical service to the office supports it, putting in a 240V air conditioner, keeps the bills down quite nicely.
No, they don’t recommend it but for many decades that is exactly what people did. I grew up in a house with a rectangle cut through the wall for the AC. See the post above yours.
I don’t recommend it either, I recommend strongly the portable and a short exhaust.
If you use a window unit in a wall sleeve it essentially will not work at all and burn up. While they have the same form factor and superficially look the same, wall units and window units are different.
Also both wall and window units cool far more effectively for the energy used and unit cost than portable. But for some spaces portable is the only decent option.
I was thinking a ceiling-mounted unit with an outside vent so my vent hole would be through the exterior siding only. But now that I’m actually thinking, it would be really stupid to stick the cooling unit in the attic where the temperature hits well over 100 degrees. So scratch that idea.
Could someone please explain why a window A/C unit would not work in a hole cut through the wall? It seems like the “hole in the wall” is just like a window. What am I missing?
I think there is a miscommunication between the old trick of a hole in the wall with some brackets to hold the AC unit and those metal sleeves that apartments often use.
The vents in a window unit take advantage of how thin a window is, and are on the outside SIDES (or top/bottom) of the unit. A wall is much thicker than a window, if you put a window unit in a wall hole it will basically block these side/top vents completely which can cause the unit to both barely function and overheat.
There are some techniques you can use (they aren’t good) to get around that, but they sell wall units specifically for this problem.
How is the humidity there? If fairly low during the hot months, a swamp cooler set just outside or inside the screen door works wonders, and uses no more power than a fan. I find that if you use them just as the sun is going down and it is cooling off, it is best.
So in conclusion if you are willing to cut a fairly good size hole in your wall, make sure you pick up a through the wall unit and don’t use the old 60s/70s trick.
He mentions Pacific NW in the OP, so I’m guess pretty humid.
Wall units aren’t really some relic of the 60s/70s, they have been the norm (and are still the norm) in houses in climates where they get nearly year-round use. They generally form a tighter seal than a window unit as well, so are a bit better performance wise.
While it is possible random people have rigged mounts for a window unit such that it can partially sit in a hole in the wall without blocking its vents, it is most likely wherever you see a unit mounted into a wall hole, that it was an actual wall AC unit–they look identical to window units other than where the vents are.