A heat pump that slots into the façade and is pack(aged) with benefits

In elec­tri­fying the heating and cooling systems for Harlem River Houses, the two different sites on the complex required two different strate­gies. While the older, historic Harlem River Houses got a central­ized VRF heat pump system, the second part of the site — a stand­alone high-rise built in 1966, known as Harlem River II, or HRII — was fitted with energy-effi­cient pack­aged terminal heat pumps, or PTHP units, in each of the apartments. 

This tech­nology was selected not only for its ability to provide elec­tricity-powered heat, but also because the units aligned well with other effi­ciency-improving construc­tion planned for HRII — namely, over­cladding the building façade with an Exterior Insulation and Finish System (EIFS) to further insu­late it. 

PTHP boxes are self-contained heat pump units that fit through a hole in the building’s façade, pulling heat from the outside air and using it to warm an apart­ment, or vice versa, depending on the season. They operate using the same basic prin­ci­ples of a regular window air condi­tioner: Each box contains a refrig­erant that changes temper­a­ture and pres­sure, so that it can either absorb heat from the space to cool it, or reject heat from outside to heat the space. 

PTHP units are equipped with internal compo­nents that maxi­mize energy output: An inverter inside the units which allows the energy output to be modu­lated contin­u­ously, based on how hot or cold it is within the building. In essence, they require a lot less energy to generate the amount of heat or cold air needed, making them more energy effi­cient than your regular A/​C unit.

The EIFS over­cladding, mean­while, is a type of energy-effi­cient exte­rior that combines synthetic stucco with an addi­tional insu­la­tion layer applied over a building’s orig­inal façade.

“The overall scope of the project lent itself to doing the pack­aged terminal heat pumps,” said Rupal Singh, asso­ciate at Inglese Architecture + Engineering, the firm involved in the HRH complex’s retrofit project. 

Although PTHP units are not the most energy effi­cient heat tech currently avail­able on the market, these units still produce two to three times the amount of heat compared to older systems powered by oil or gas using the same amount of energy input. In other words, PTHP units have a much higher coef­fi­cient of perfor­mance (COP) rate of 3.31 at 47 degrees Fahrenheit and 1.80 at 13 degrees Fahrenheit, which are the maximum outdoor temper­a­ture condi­tions expected in NYC (known in construc­tion as ​“design day”). 

“It’s not going to get you the highest COP that’s avail­able, but it’s prob­ably the middle ground between what’s prac­tical for a retrofit” and high effi­ciency, said Singh. ​“You still greatly improve the [heat system] effi­ciency without having to spend four or five times the amount of money to put in a ground-source or some sort of water-source heat pump system.” This prac­tical middle ground cost a rela­tively-modest $2.1 million for the instal­la­tion of PTHP units in the tower.

Upgrades like the PTHP units have helped the HRII tower reduce its overall energy use and carbon emis­sions and get into compli­ance with Local Law 97 (LL97). And beyond the bene­fits of improved energy effi­ciency, PTHP units provide an advan­tage of conve­nience. Since these units work as contained systems installed into indi­vidual apart­ments, if a unit requires main­te­nance, manage­ment can simply replace the unit with a working one while the broken unit is taken out for repair. 

According to Singh, chal­lenges in the PTHP instal­la­tions were mostly related to the extra plan­ning work needed before­hand, due to the aged infra­struc­ture of the HRII building. 

Electrifying the tower’s heating system required a lot of infra­struc­ture work, and devel­opers had to work with Con Edison to ensure that enough elec­trical capacity was supplied to sustain the tower’s elec­trical upgrades along­side other elec­tri­fi­ca­tion projects happening in the area. These changes in turn affected the reha­bil­i­ta­tion project’s construc­tion timeline. 

There have already been new iter­a­tions of this type of pack­aged units on the market just in the time since the heat pumps were installed at HRII in mid 2025. Singh believes these pack­aged heating units are an emerging tech that we will see more of as cities like New York push toward energy efficiency.

“I think the industry in general, espe­cially New York City, is going to be shifting away from the VRF type of systems in general. And I think the use case for these pack­aged units is going to be a lot more than the VRF type of units,” Singh said.

Correction (Jan. 14, 2026): This article previ­ously misstated how the elec­trical wiring for the PTHP units was installed. We regret the error.