Through-the-Wall Versus PTAC Air Conditioners: A Guide for New Yorkers

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Sticking outside in all their boxy metallic ugliness, dripping onto passers-by, and blocking light and views indoors, window mounted air conditioners are as ubiquitous a feature of NYC apartment life as fire escapes and water towers.  (For more info, check out BrickUnderground's guide to all things window a/c).
But given a choice--and assuming central a/c is not an option--nearly every apartment dweller would opt for a more discreet relative of the window a/ that, identifiable only by its flush-with-façade metal venting grille, announces itself more subtly to the street and leaves windows alone to do the things intended by God and architects.
Enter the through-the-wall air conditioner and the PTAC unit.  Here's a primer.
1. What's the difference between a through-the-wall a/c and a PTAC unit?
A through-the-wall air conditioner is exactly what it sounds like.  It is mounted inside a sleeve that has been installed in a space cut into an exterior wall, generally underneath a window.
Another way to keep your windows unencumbered is the Packaged Terminal Air Conditioner (PTAC) like the one pictured in the photo above.  Most combine heating and cooling in one unit. They look similar to an enclosed radiator attached to the wall with a vent on top.
PTACs are usually installed when a building is constructed and hooked up to a building’s hot-water system.  Hot water produced by the boiler flows into the PTAC, and circulates the resulting heat into the apartment.  The PTAC has a separate chamber containing coolant that produces cool air.  They are vented to the outside through a cutout below the window typically covered with a metal grill, similar to a through-wall a/c, says Gary Cottam of Cottam Heating & Air Conditioning
PTAC machines are generally a little more expensive to buy than a through-wall air conditioner, but the cost to run them is about the same. 
2. Choosing the right through-wall unit
Friedrich, LG, GE, Amana, and Frigidaire are the most popular brands.  There are standard calculations  to determine the number of BTUs you need--room size, ceiling height, amount of sunlight, number of occupants, and proximity to the kitchen.
The most of important issue is the size and type of the sleeve, a plastic or metal box installed in a hole in the wall that supports the weight of the air conditioner.  Generally, your air conditioner sleeves were installed when your building was constructed and were meant to accommodate whichever brand of air conditioner was installed at the time.
You’ll need to start your shopping with the dimensions of the sleeve (height, width, and depth) along with the brand, model, and size of the a/c currently in it, and the type of rear (outside) venting grille in the sleeve.   

And don’t forget to jot down the voltage and amperage of the electrical plug, along with the capacity of the outlet the a/c will use.  If you’re buying a unit that requires more electrical power than your existing outlet can handle, you’re going to need an electrician to upgrade your wiring.  And that will require lots of permits along with permission from your landlord, or co-op or condo board.

Timers, remote controls, and programmable thermostats are so 20th century. Now you can control your a/c a with your Smartphone.  Some companies, such as Friedrich, make models that can be controlled over WiFi. Con Edison makes a device that acts as an interface between the a/c plug and the a/c, and can be controlled via the web, and other similar contraptions can be purchased at Home Depot, Amazon, and Best Buy.  
Of course they’re not foolproof and successful control depends on the way your a/c starts, recycles, shuts down, and restarts, so lots of research is in order before you plunk down a C note to buy the gizmo.
3. Installing a through-wall a/c where none has gone before
Although cutting an opening through the masonry of an exterior wall is physically a relatively simple undertaking that costs around $2,000, like most things connected with New York City real estate you’ll have to get the requisite building and construction permits, permission from your landlord, co-op, or condo board, and maybe even an architect,  says Ranjit Singh, president of Cool Air Inc.

Arline Kob, a principal at Key Real Estate Associates, which manages co-ops in New York, says that she’s “never known a co-op board to allow the installation of a through-the-wall unit where none exists.”  The board would be concerned about façade uniformity and breaking the seal of the building’s exterior. 

If your board is through-wall-friendly, you will be expected to install an exterior grille that matches existing ones and lines up to them, says property manager Michael Wolfe of Midboro Management.  The grilles will also need to be flush with the building's facade and the building's architect or engineer will need to review the proposed installation.

In addition, says Kob, "the resident and future buyers, not the co-op, would be responsible for maintaining the newly installed sleeve and the wall into which it was cut.  That includes damage to surrounding apartments that may result.”

If you live in a landmarked building or district you’ll have to get the go ahead from the Landmarks Preservation Commission too.  Good luck with that, especially if the altered wall will be visible from the street.  “Landmarks would never allow it,” says Kob.

Even if you're doing a simple replacement of an existing unit, this is not the place to start skimping on services, says Singh. Wall air conditioners are very heavy and need to be installed correctly with special attention to its degree of tilt within the sleeve, distance between the unit and the sides of the sleeve, distance from the exterior venting grille, and position of the plug that controls how much condensation accumulates.  You’ll be in for some serious headaches and expenses if it’s not installed properly, unless of course you enjoy water leaking into your wall, or that of your neighbor.  
4. The pluses and minuses of the PTAC
PTACs  can have an upside for a landlord or a co-op because they allow greater control of heating costs--room by room rather than building wide.  
Because a PTAC is hooked up to the building’s water, the units need to be rigorously maintained to get rid of clogs that can cause leaks. These can go unnoticed for long periods of time, causing floors and walls to buckle and often damaging apartments below the one in which it’s housed. Damage from PTAC units is, in fact, among the most common apartment insurance claims in New York City, says Jeff Schneider of Gotham Brokerage, with an average claim size of $5,000.
In addition, PTAC units are prone to the musty, mildew-y odor known as 'dirty sock syndrome', which is generally thought to be caused by bacteria and mold accumulating on heat pumps.  The PTAC’s dual heating and cooling functions make them susceptible to it. Frequent professional cleaning can help sometimes, but the problem has no good solution; the very nature of the PTAC unit makes it susceptible.  
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