The best U-shaped and saddle window air conditioners

The U-shaped window air conditioner is the only meaningful design change this category has seen in years, and it is genuinely good. It also carries one specification that catches people out.

A conventional window unit is a single box that sits in the opening. The sash comes down onto the top of it, and the whole machine — compressor included — is in the plane of the window.

A U-shaped unit is split into two halves joined at the bottom, with a channel between them. The sash closes down into that channel, so the window shuts against the unit rather than on top of it. Three things follow:

• The compressor is outside the closed sash. The glass and the frame sit between you and the noisiest component, which is why these are consistently reported as quieter indoors. Note that this is a design argument, not a measured one — no window air conditioner publishes a certified noise rating.
• The window still opens. You can raise the sash for ventilation without uninstalling anything, which in a small room is a real gain.
• The seal is better. The sash closes into a channel rather than onto a flat top, which is a more forgiving joint to make airtight.

This is the finding that matters most, and it applies to the broader family of units that straddle the sill.

Two-thirds heavier and half again as deep, on average. The two saddle heat pumps in this roundup weigh 129 and 140 lb; the conventional 6,000 BTU efficiency leader weighs 31.6 lb.

Counter-intuitively, the heavier saddle units frequently need no support bracket — the design bears on the sill and frame rather than cantilevering out. The certified data shows bracket requirement is essentially uncorrelated with weight: median 57.3 lb for units that require one against 56.0 lb for units that do not. What it actually tracks.

That does not make 129 lb easy. It still has to be carried, lifted and positioned over an open window, and above ground level that is a job with real consequences.

The U-shape has a narrower set of windows it works in than a conventional unit, and returning one is unpleasant.

1. It needs a vertically opening sash. Single-hung or double-hung. A casement that cranks outward or a slider will not work — and no certified unit is recorded as casement-capable at all.
2. Check the sash height clearance. The units here are 13.5 to 24.0 inches tall and the window must open at least that far. The 24 inch saddle units are the ones that fail this test.
3. Check the depth outside. These project further outward than a conventional unit — 31.3 inches on average — which matters near a walkway, a neighboring wall or a balcony rail.
4. Check the sill. The unit sits astride it, so a sill with an unusual profile, a deep interior stool or an exterior storm window can all interfere.
5. Check your building rules. Some leases and associations restrict what may project from a window.

Comparing like sizes across the certified data:

• 6,000 BTU: best conventional is CEER 16 at 281.3 kWh; best U-shape is CEER 15.1 at 298 kWh. A gap of $3.06 a year.
• 8,000 BTU: best conventional is CEER 16 at 375 kWh; U-shape is CEER 15 at 400 kWh. A gap of $4.58 a year.
• Saddle heat pumps invert this entirely — CEER 17.6 is the highest of any certified room unit, in a saddle format.

So the U-shape costs roughly $4.58 a year at typical sizes, which is a modest price for a window that still opens and a quieter room. It is not a compromise you should agonize over.