Search the internet for unit ventilators, and the top results will take you to discussions about hospital ventilators. Spend a few more minutes searching ventilation and schools, and it still struggles to appear within a top-10 mention.

While this technology is one of the oldest systems to be used when conditioning school classrooms, it remains a relevant option for replacement and renovation projects across the U.S. In fact, various manufacturers report 30%-50% growth year-over-year in just the education market. A large portion of that growth lies in the single-packaged unit ventilator (SPUV) category. So, why is the technology not rising to the top of a Google search? This article is designed to answer that question.

What is spurring this growth?

  • Aging school infrastructure: The 2021 Infrastructure Report Card states the average school is more than 40 years old. While some schools have undergone improvements to update controls and add air conditioning, the mechanical equipment providing comfort in schools built in the last 30 years are facing the end of the design lives.
  • Deferred investment in HVAC improvements: According to the 2020 GAO study on K-12 schools, 40% of all schools report the need for HVAC upgrades or replacements due to aging or insufficient systems. Mechanical system upgrades are often competed along with Wi-Fi and safety improvements. All these improvements are necessary to support strong learning environments.
  • The ESSER Fund I & II: The Elementary and Secondary School Emergency Relief Funds (ESSER) allocate $85 billion to state agencies to address the impact of COVID on schools. To date, approximately $23 billion of the $85 billion budgeted has been spent. Funding allocations must be committed by the end of fiscal year 2023 for Fund I and the end of fiscal year 2024 for Fund II.
  • Product modernization: SPUVs are not your parents’ unit ventilators. Manufacturers are offering affordable, modern options that enable schools to meet the changes in codes and standards for learning environments.

The urgency around improving IAQ and ventilation since COVID, combined with the significant and time limited ESSER funding, has prompted school districts across the U.S. to replace older SPUVs with more contemporary systems. A review of the Dodge Construction Database shows a significant number of projects in the construction pipeline. Manufacturers report that entire districts are taking the opportunity to change out old products nearing the end of their design lives. This is the case with Cato-Meridian School District, located about 25 miles northwest of Syracuse, New York. According to their federal stimulus plan (2021-2025), New York will receive a total of $9 billion through the ESSER funds. Of that funding, 90% will go through state agencies to school districts. Cato-Meridian’s allocation of $3.6 million will be used, in part, to fund replacing old central air-handling units that are 23 years old with new vertical unit ventilators in the classrooms.

Other school districts are expanding their use of SPUVs during square-footage additions to maintain buildings’ systems and product continuity while meeting the IAQ goals of the schools. In 2021, our firm, Applied Marketing Knowledge (AMK), conducted a voice of customer exercise, interviewing school facility managers across the U.S. We found that more than 80% of interviewees will choose HVAC system continuity whenever possible.

Are funding and system consistency the only drivers of strength in this product category? The answer is no. Let’s explore some of the core and updated product attributes that are available on today’s modern SPUVs and how they align with a school’s HVAC needs.

A survey of numerous manufacturers’ product offerings shows new technology and components, such as energy recovery ventilators (ERV), direct expansion cooling (DX), variable refrigerant flow (VRF) compatible coils, humidity controls, and many other accessories, are now real options that can be added to SPUVs. Air Conditioning, heating & Refrigeration Institute (AHRI) has added a new product category called Single Package Vertical Air-Conditioners and Heat Pumps (often referred to as single packaged vertical units or SPVUs) to provide independent test data on these new modern single packaged vertical unit ventilators. This addition by AHRI provides independent data to decision-makers to demonstrate the energy efficiency performance of modern unit ventilators.

We will review these market needs in detail, showcase some of the options in the modern SPVU category, and highlight some modern technologies that are being integrated into the product design.

Unit Ventilator Basics

Let’s start with a brief technology review. Per the ASHRAE Systems and Equipment Handbook, a unit ventilator (UV) is an encased assembly whose principal functions are to heat, ventilate, and cool a space by introducing outdoor air in quantities up to 100% of rated capacity. A UV differs from a fan coil by virtue of the UV’s ability to introduce up to 100% outside air for economizer cooling.

UVs are available in either horizontal or vertical mount packaged configurations. Inside a relatively small package, manufacturers assemble the UV fan, motor, coils, drain pan, dampers, filter, piping, valves, and controls. Water coils, direct expansion cooling coils, and electric heat coils are commonly used in these units to provide space heating and cooling. These are essentially the same components that go into a built-up air-handling unit. In a unit ventilator, they fit in the space of 8 square feet for a 500-cfm system and up to 15 square feet for a 2,000-cfm system.

The most popular UV configuration is a vertical model packaged for floor mounting. In the traditional arrangement, conditioned air discharges vertically from the cabinet top and return air enters at the front near the floor while outside air enters from the back of the unit. (See Figure 1). These are sometimes referred to as under-window units due to their typical installation location under the classroom windows along the outside wall

FIGURE 1. A section through a typical vertical unit ventilator showing its internal components. Image courtesy of Carrier Corp.

An SPUV is available as an exterior mounted unit or interior installed unit. Exterior wall mounted units have a reduced first cost for the installation while interior units bring all the system components inside the building and use valuable classroom space for the system. Tradeoffs between the exterior and interior include the ability to reliably winterize, maintenance access, security and vandalism considerations, sightline appearance impacts, and classroom acoustics.

Figure 2 contains a cross sectional diagram of an indoor installed SPUV. A SPUV performs well on first cost as either an external or internal unit. Our article focuses on the interior unit as it is the most significant market choice for permanent classroom applications.

FIGURE 2. An indoor SPUV installation cross-section. Image courtesy of Marvair

SPUV Benefits for School Classroom Design Consideration

The SPUV product category is growing rapidly and continues to strongly compete with newer system types for school classroom applications. Today’s SPUV is well equipped to meet the needs of the school classroom HVAC system:

TABLE 1. Classroom market needs and benefits of SPUV. Data courtesy of Applied Marketing Knowledge

Designers rank and prioritize these market needs when making an overall design choice. The energy efficiency of an SPUV may be on the moderate end of the spectrum, but all other market needs rank favorably against other system options, which explains its longevity as an application for K-12 schools.

Maintenance considerations for school classroom HVAC units should be planned into the budget and system selections. Administrators should aim to avoid complex equipment that could be costly to maintain. SPUV interior installed units have a reputation for being uncomplicated to service. A SPUV national sales manager interviewed for this article noted the ease of maintenance along with noise abatement as top market needs. “…[our] units have full access to the economizer (100%). They stand upright and are very easy to access for maintenance and service. Suction through the return is really the only place where any noise could come from. We use a high-quality frame to keep sound low.”

School classrooms that are equipped with older unit ventilators should be evaluated to determine their ongoing usefulness. Older unit ventilators, including older SPUVs, may lack some of the current functionality in today’s modern units. It’s important to evaluate classroom noise levels. Older, under-window units may have high-velocity outlets near students’ ear levels, and uninsulated cabinets may be causing noise issues that can be solved by modern SPUVs. Air leakage problems with older units and limited or no dehumidification abilities may also impair IAQ. Table 2 outlines some of the improvements between older and more modern equipment.

TABLE 2. Product improvements: older under-window unit ventilators versus today’s choices. Data courtesy of Applied Marketing Knowledge

A major SPUV manufacturer’s product manager mentioned, “The modern, self-contained unit ventilator is taking over the old under-the-wall UV and some giant multi-zone packaged units. The main reasons are ECMs [electronically commutated motors] and energy efficiency, MERV-13 filter requirements, and reduction of damper blade leakage design. AHRI testing and certification data has helped to bring attention to energy efficiency in this product category.”

Contemporary applications and Manufacturer Product Highlights

Today’s SPUV manufacturers offer, as standard, heat pump options with various compressor technology. Most manufacturers are working to actively integrate VRF coils into their offerings. Remote monitoring and smart controls are now available and able to be integrated with the building automation system (BAS).

  • ERVs and Ventilation – Airside technology advancements in these units have resulted in numerous improvements to the offerings of yesteryear. Fans use ECM motors and units have options for CO2 control. SPUV units have evolved to add the integration of ERV components (including energy wheels or plate exchangers) and the flexibility to duct outside air from DOAS air handlers directly to the SPUV units.
  • Heat Pump – Heat pump SPUV installations are highly dependent on geographic location and are more prevalent in the milder climates of the southeast and west coast. All manufacturers offer air-to-air heat pump packages. Water-source heat pumps (including geothermal offerings) are becoming a common offering. Water-source heat pumps are still a small percentage of the systems, but the federal government has renewed incentives for these systems. The Section 48 energy investment tax credit (ITC) was extended with a 6% base credit rate and 30% bonus rate for a geothermal heat pump property that begins construction before Jan. 1, 2035, and was put in use after Jan. 1, 2023. A 10% bonus rate for domestic content is also available — the owner must prove that the manufactured product within the completed project was made in the U.S.
  • VRF – VRF integration into unit ventilators is an emerging option and manufacturers are striving to integrate VRF coils into their offerings. VRF units, on their own, are very energy efficient, but they do not provide ventilation. This combination of the SPUV with a VRF coil solves both the energy efficiency and ventilation requirements and can allow for flexibility and continuity on system choice across the many non-classroom portions of any school building. Accommodations for multiple outdoor compressors are minimized, supporting easier service and support of the building during its lifetime.
  • Acoustics – Using accredited sound labs, manufacturers are reducing noise levels and improving acoustics of SPUV products. The 2011 ASHRAE Applications Handbook, Chapter 48, Noise and Vibration Control, cites ANSI/ASA Standard S12.60-2010 for classroom acoustics as a guideline for school mechanical design.Under the standard, the maximum level of overall background noise allowed in a classroom is a strict 35 dB(A). When you consider a 10 dB(A) reduction makes the space half as loud, this is a very important feature to look at for HVAC selection. School-age children hear only about 75% of what teachers say in the classroom. The rest is drowned out by fierce background noise — noise that is in part due to HVAC equipment. The quality of children’s education, the reduction in teacher voice strain, and the improvement in the classroom environment are all important results of proper system selection to reduce noise. SPUV manufacturers offer numerous options to reduce unit noise for those situations which need sound attenuation. The inclusion of compressor blanketing and discharge plenum options are among the chief offerings. The widespread inclusion of ECMs for unit fans also serves to reduce the overall sound output of units, especially when they’re operating at part-load conditions.
  • BAS and Remote Monitoring – Manufacturers are seeing growing interest in remote monitoring functionality. ESSER funds are helping to fund replacements and upgrades to the system and building controls. Remote diagnosis and monitoring provide value to the district facilities team through system alerts. Remote monitoring features provide confidence to school boards that the classroom HVAC systems are delivering a safe learning environment.


The HVAC industry of the 21st century has placed a premium on creating high-performance learning environments. The resources that are available through the ESSER funds and the Inflation Reduction Act (IRA) provide much-needed funding to update old systems. Classroom HVAC solutions, like the SPUV, deliver a budget-friendly and maintenance-friendly solution for school districts and designers. UVs have advanced since the days of children sitting on top of them and breaking off pencils in their fan outlet grilles. Don’t overlook the technology advancements that make the SPUV category a viable application for your next project.