Size first — then mount
A unit that is too large short-cycles; too small never catches up. Use the window AC calculator and window AC BTU sizing before you haul a 70 lb chassis up a ladder.
If you want quiet year-round heat and cool, compare mini-split vs window AC before cutting foam side panels.
Safe mounting checklist
Two-person lift for anything over small 5k–8k units. Falling window ACs are a real injury and liability risk.
- Window and sill in good condition — rotten wood cannot hold the unit
- Exterior bracket or sash support rated for the unit weight (many cities require brackets)
- Unit tilts slightly down toward outdoors for drainage
- Side accordion panels sealed; no big air gaps
- Sash locked or security bar so the unit cannot fall inward
- Never support the chassis with only thin plastic side panels
Power and condensation
Portable units avoid the window chassis but bring hose and efficiency tradeoffs — see portable vs window.
- Plug into a proper grounded outlet on a circuit that is not overloaded
- Avoid cheap extension cords — heat and voltage drop kill compressors
- Follow the manual for drip vs drain-plug setups
- Keep furniture and curtains off the front grille
When a window unit is the wrong DIY
Upper-story installs without proper brackets, casement windows without kits, HOA bans, or rooms that need heat in winter are better served by a ductless plan — start at the DIY mini-split roadmap.