Standard vs. Legacy PTAC Sizes: What Philadelphia Property Owners Need to Know

Published October 15, 2026 by Philly PTAC, powered by Air Distributors Company, Inc.

Most PTAC units sold today fit a wall sleeve 42 inches wide and 16 inches high. Many Philadelphia buildings were built before that size took over, or bought from manufacturers that used their own dimensions. Knowing which one you have decides what you order, what it costs to install, and how long the room is out of service.

What the 42 x 16 standard means

The wall sleeve is the metal box built into the exterior wall. The PTAC chassis slides into it, and an outdoor grille covers the back. The sleeve stays in the wall for decades. The chassis gets replaced.

Over time, most manufacturers settled on a sleeve 42 inches wide by about 16 inches high. GE has used that size for Zoneline since 1961. Amana, Friedrich, LG, and others built to it as well. Because the size is shared, a building with 42 x 16 sleeves has choices. A current GE Zoneline slides into most of them, sometimes with a gasket kit or a different rear grille.

Depth varies more than width and height. Sleeves in thick masonry walls run deeper than those in frame construction. Most standard chassis tolerate a range of depths, and sleeve extensions cover the rest.

What a legacy size is

A legacy sleeve is anything that is not 42 x 16. These sleeves come from three sources:

Older production from major brands. Some brands built other sizes before standardizing, or offered special sizes for particular markets.
Manufacturers that left the business. McQuay ended its PTAC line in 2014. Its units, and those sold under the Singer and Remington names, used several sizes that no current mainstream unit fits. Smaller brands such as AAF, Islandaire, Slant Fin, Climate Master, and Zoneaire also built to their own dimensions.
Special designs. Some buildings used three-piece through-the-wall units, units with hydronic coils on the building boiler, or units built for narrow window bays.

Common legacy widths include 32, 36, and 44 inches. Some sleeves are 42 inches wide but have a sloped top or a different height, so the width alone does not make a sleeve standard.

Why legacy sleeves are common in Philadelphia

Philadelphia built a lot of apartment towers, garden apartments, hotels, and senior housing between the 1950s and the 1980s. Many of those buildings are still in service with their original wall openings. Center City and University City towers, Northeast Philadelphia garden apartments, Upper Darby apartment blocks, and older suburban complexes all carry sleeves from that era.

Older Philadelphia buildings also tend to have central boilers. Many through-the-wall units in those buildings carry a hot water coil for heat instead of an electric heater. That adds a second compatibility question on top of the sleeve size.

How to tell which one you have

Measure the sleeve, not the unit. Pull the chassis or remove the front cover far enough to see the sleeve opening, then measure:

Inside width, left to right
Inside height, floor to top
Depth from the room-side face to the outdoor grille
Top shape, flat or sloped

If the opening is 42 inches by about 16 inches, you have a standard sleeve. If not, you have a legacy sleeve. Record the numbers to the nearest quarter inch and photograph the tape measure in place.

The model number helps too. A brand and series that was never built on 42 x 16 tells you the answer before you measure. See how to identify your existing PTAC model number.

Replacing a standard sleeve unit

With a 42 x 16 sleeve, the job is simple. Choose a current unit by heat type and voltage:

Electric heat or heat pump, 208/230V or 265V, from GE Zoneline
Hydronic heat on 42 x 16, from Applied Comfort's NA, NF, or NY series, which cover slope-top, flat-top, top-coil, and bottom-coil designs

Check the outdoor grille. Some grilles from other brands restrict airflow on a new chassis. Check the sleeve condition, especially the floor, where water collects. A sound sleeve stays. A rusted one is easier to replace before the new unit goes in.

Replacing a legacy sleeve unit

You have two paths.

Replace the chassis only. Applied Comfort builds PTAC chassis to many legacy sleeve sizes. The new chassis slides into the existing sleeve and uses the existing grille. No masonry work. No facade change. The room is back in service the same day. For discontinued McQuay units, see McQuay PTAC replacement.

Replace the sleeve and convert to 42 x 16. The wall opening is cut or rebuilt, a new standard sleeve goes in, and a new grille covers it. This opens up more unit choices later, but it costs more up front. It also takes the room out of service longer, makes noise and dust in an occupied building, and changes the exterior. In historic districts, a facade change sometimes requires review before work starts.

For most occupied buildings, the chassis-only path wins on cost, time, and disruption. Converting makes the most sense during a full gut renovation, when the walls are open anyway.

Lead times differ

Standard 42 x 16 units are usually in stock at the distributor or the manufacturer. Many legacy chassis are built to order. If your building runs on legacy units, keep one or two spares on site so a failure in January does not leave a room without heat while a replacement is built.

Electrical and heat type still apply

The sleeve decides whether a unit fits. The circuit and heat source decide whether it works. Before you order, confirm:

Voltage: 208/230V or 265V
Amperage: the circuit size, which limits electric heat output
Connection: plug-in or hardwired
Heat type: electric, heat pump, or hydronic

The replacement guide walks through each check.

Next step

Measure one sleeve, read one nameplate, and send both. Standard or legacy, there is almost always a replacement path that keeps the wall intact. Request a quote or call 800-866-1210.