The past few years have seen a surge in the construction of veterinary hospitals. The trend couldn’t have been illustrated in better words than those of Dr. Brian Cassell, DVM who is a partner at the Anne Arundel Veterinary Emergency Clinic, Inc. (AAVEC, Annapolis, MD). He described the phenomenon as the decline of the “mom and pop” style hospitals and the emergence of large, daytime veterinary hospitals, emergency hospitals, and specialty referral hospitals. Veterinarians are furnishing these facilities with increasingly sophisticated equipment. Pet owners are demanding more quality in the services provided.

A challenge is now facing the architectural engineering design team to provide better-designed facilities. From the standpoint of a mechanical engineer, there are three issues to address. The first deals with temperature and humidity control. The hvac engineer must design a facility that is comfortable for the animals as well as the hospital staff. The second issue is ventilation. Proper ventilation will help contain odors and minimize the chances of health risks from harmful airborne pathogens. The third concern is noise control. Noise transmission depends on the building design and construction material used. Mechanical equipment, however, is a source for noise emission. The engineer has an obligation to design within acceptable noise levels.

Review of the literature has revealed that there are no scientific studies dedicated to the indoor environment of “neighborhood” animal hospitals. The most elaborate specifications for the environmental control of animal housing facilities refer to laboratory animal housing [1, 2, and 10]. While tolerances on the environmental conditions in these spaces are far more stringent, we can draw strong conclusions as to the proper handling and housing of animals in veterinary hospitals. From these conclusions, a guideline for the design of mechanical systems is proposed in this article. Finally a comparison with actual systems at AAVEC and other hospitals is presented.

Figure 1. Floor plans for the Anne Arundel Veterinary Emergency Clinic (Annapolis, MD). The centrally located treatment room is open to most adjacent rooms and is a challenge both for pressurization and noise control. (Photo courtesy of Alt Breeding Schwarz Architects.)

Zoning: Putting the Pieces of the Puzzle Together

The first step before delving into the design is to get familiar with a veterinary hospital. A modern facility (Figure 1) will most likely include the following rooms: reception, waiting lounge, records and filing, exam rooms, treatment room(s), preparation areas and scrub room, surgery room(s) laboratory, X-ray and darkroom, pharmacy, isolation ward, hospital bathing, dog runs, staff room, doctors’ offices, laundry room, multipurpose equipment rooms, janitor closet, and storage area for vacuum and oxygen bottles.

Table 1. A modern facility will include a variety of spaces with an accompanying variety of pressurization needs. This approach breaks the facility into four basic regions, but each individual area is treated as needed. (N=negative pressure; NN=more pressure)
Table 1 proposes a zoning scheme for these rooms. Pressurization is based on ASHRAE guidelines [10] and data gathered from hospitals. Some hospitals separate each surgery room as a zone with its own dedicated hvac unit.

In operating rooms, the need to cool animal surgeons amid the heat from lights and equipment must be balanced with an animal's vulnerability to hypothermia during the surgery itself.

Temperature and Humidity Control

Temperature and humidity vary within an environment due to transient and constant factors. Constant factors include solar loads, building materials, and lighting in some rooms. Transient factors vary between one room and another. Among the transient factors for dog runs are animal metabolism and heat release rate, floor washdown, and frequency of bedding changes. In surgery rooms, the heat generated by the equipment and lighting is a significant transient load. In treatment rooms, transient loads include animal heat release rate, plus makeup air to compensate for large exhaust air quantities at timed intervals. The engineer should take these factors into account. Here is an overview of design setpoints for different rooms.

The reception, waiting lounge, exam room(s), and record keeping should be designed at ASHRAE comfort levels of 70˚ to 74 ˚F db, 20% to 30% rh in the winter, and 74˚ to 78˚, 50% to 60% rh in the summer.

The treatment area is one of the busiest in the facility. It has numerous working tables to carry out procedures and it is used as an “intensive care unit” for post-treatment/surgical cases. The treatment room is challenging because its central location means it is open to many other rooms. Treatment rooms should be kept within 74˚ to 76˚ db and 50% to 60% rh.

Animals recovering from anesthesia or during surgery are hypothermic and require elevated temperature of the environment, typically 81˚ to 84˚ db. Newborn pups and kittens do not have fully developed body temperature regulation mechanisms, so they should also be housed in environments with higher temperatures, typically between 85˚ to 90˚ db for the first week of life [1]. It is common practice to use heat lamps or spot draft air warmers to avoid hypothermia. Laboratories, X-ray, pharmacy, and surgery scrub rooms should be maintained between 72˚ to 76˚ db and 50% to 60% rh.

Two things should be kept in mind when designing surgery rooms. The first is the surgeon’s comfort while working under the operating lights and amid the heat generated by equipment. The second is avoiding patient hypothermia. Surgeons are typically comfortable in temperatures between 63˚ to 66˚. A humidifier might be needed to avoid static discharges when conditions are very dry. The hospitals examined had two or more surgery rooms, usually each is equipped with different tools for certain procedures. Room temperature can be controlled separately to meet the surgeon’s needs.

Table 2. Recommended temperatures (db) for common laboratory animals (ILAR1996).
Dog boarding rooms also known as “dog runs” must have temperature control. If not properly designed and controlled, changes in the temperature and humidity of the room may cause health problems to the animals [1, 2]. Table 2 (Excerpted from Reference 2) indicates the most common environmental conditions for various pet animals. The temperature of rooms housing dogs and cats should be maintained within 64˚ to 84˚ db and relative humidity between 30% to 70% rh. The temperature of the housing wards cannot exceed 4 hrs below 45˚ or above 85˚ under emergency situations [1]. In fact, it could be life threatening if unadapted animals are exposed to such environmental conditions [2].

Some hospitals provide year-round air conditioning and heating for dog runs. These facilities usually handle ten dogs or less. The economics of larger facilities usually dictate only heating and ventilating. In this case, the exhaust fan is the only means of controlling temperature buildup in the space. At least one additional exhaust fan should be installed to operate when the space temperature exceeds 85˚. The same fan may be used to dry the newly washed floors in dog runs to reduce humidity buildup. Ventilation rates will be discussed later.

Temperature should be controlled automatically for each zone in the hospital. This may be accomplished using high-quality hvac systems and controls. However, many hospitals have been designed with light commercial-grade equipment, and if properly zoned, programmable thermostats accomplish an acceptable level of control. Most of the hospitals researched were designed around packaged unitary rooftop units (RTU). To accomplish zoning, either one RTU served one room or variable-volume and temperature (VVT) terminal boxes were installed for each room.

Ultimately, factors such as energy efficiency, energy savings, budget, expandability of the facility, and the lifecycle of the project will determine how the space is zoned and which equipment best suits the building.

Due to significant ventilation loads, most dog runs receive only ventilation and heating. Whether air conditioned or simply exhausted, the ventilation sysems for these areas should not tie into the distribution system of any other zone in the hospital. This separation prevents transfer of any potential animal pathogens or objectionable odors.


The sense of smell as a visitor walks into a hospital has an impact on the first impression of the facility. Animal hospitals, by their nature, have higher levels of objectionable odors. Ventilating an animal hospital is necessary in order to maintain a pleasant and healthy environment to the animals, the hospital staff, and the visitors. A properly designed ventilation system introduces oxygen-rich filtered air, dilutes airborne pathogens which may be harmful for animals, maintains temperature and humidity levels within the designed limits and, finally, provides pressure differential between spaces.

Ventilation rates in the reception, waiting lounge, filing area, and exam rooms are designed to meet the cooling and heating loads of the space. Some hospitals recommend installing an exhaust fan in each exam room. The fan runs on a manual timer switch.

Treatment rooms are heavy traffic areas and should be designed per ASHRAE guidelines, typically between 6 to 10 air changes per hour (ach) and usually kept neutral. However, it is good practice to install an exhaust fan in the room that can be controlled by a timer switch. The fan is usually sized between 3 to 4 ach. It serves to quickly exhaust odors emitted by animal vomit and other secretions.

Laboratories, pharmacy, X-ray, and isolation wards are typically adjacent to the treatment room and thus share the same ventilation system. Isolation wards are kept negative by exhausting at the rate of 6 to 10 ach to the outside. At AAVEC, a special room was dedicated to internal medicine procedures such as ultrasound and chemotherapy treatment. The room had a 4- by 3-ft stainless steel hood for preparing chemotherapy drugs and was exhausted to the outside.

Surgery rooms should be air conditioned and supplied with filtered air. HEPA filters (highly recommended) or Safeguard-type filters should be used in the supply. Some hospitals supply 100% fresh air to the surgery room. The room should be positively pressurized with respect to adjacent rooms. Sterilization and clean equipment storage rooms should also be positively pressurized relative to adjacent rooms (except surgery). Recovery rooms should be well ventilated, conditioned, and maintained under positive pressure. These rooms should have more flexibility such as means for providing additional heat for hypothermic animals. Exam rooms may have exhaust fans with a manual on-off switch. This will help minimize the migration of gaseous chemicals to adjacent rooms.

As noted, the majority of animal hospitals researched provide only heating and ventilating to dog runs while completely air conditioning and ventilating other spaces. This is understandable because of the cost of air conditioning the large airflow rates for dog runs. Normally, ventilation rates are dependent on the size of the room in which the animals are housed, the quantity of cages, the number and size of the animals, the frequency of cleaning (or bedding changes), and the solar load on the space.

For dog housing rooms, 10 to 15 ach is an effective airflow rate that has become industry standard [1, 2, 3]. This rate should be used with caution. Changes in any of the parameters indicated above may result in over- or under-ventilation. It is therefore best to refer to ASHRAE standards for calculating total heat gain of a space and then properly calculating the minimum ventilation rate to offset the cooling load (see temperature and humidity sections).

Ventilation in large dog runs is designed for 100% exhaust to the exterior. Recirculation of air should be avoided. Whether air conditioned or simply exhausted, the ventilation system should not tie into the distribution system of any other zone in the hospital. Animal pathogens may be transferred by the air distribution system to other rooms and create health risks and objectionable odors.

The space pressure should be kept negative with respect to other areas, such as waiting lounges and surgery rooms. Typically .04-in. wc differential is acceptable. If recirculation is inevitable, high-efficiency filters should be installed and properly maintained in the system. Not only are these filters expensive, they also add at least 1 in. wc of static pressure on the system, resulting in larger motors in the air-handling units. When all is said and done, recirculation systems end up to be more expensive and more of a headache. Installing an auxiliary exhaust fan in dog runs is a recommended practice. The fan is typically sized for 6 to 8 ach. It can be used to relieve heat buildup when temperature is exceeding the limits earlier indicated and also to dry up newly washed floors and thus minimize humidity buildup.

Air Distribution

In general, most areas except surgery and dog runs can be designed with both supply and return in the ceiling. Surgery rooms should have low return/exhaust grilles and high supply diffusers. This article does not tackle the subject of laminar flow.

Dog runs should be supplied high near the ceiling and exhausted low near the floor. Six to 10 in. from either is typical. The supply air should be designed so as to avoid creating drafts on the animals. Exposed ductwork should be avoided to minimize dust collection. Air outlets should be installed with minimum cracks and penetrations in walls or ceilings. Animal hair and dander can collect on these surfaces and can harbor mold, mildew, and other pathogens. One way to reduce dust, animal hair, and dander in the exhaust air stream is to install .5-in. throwaway filters in exhaust grilles. Avoid volume dampers and registers in the exhaust ductwork.

Noise Control

Animal boarding rooms, and in particular dog boarding areas, are a source of noise that can be a nuisance to hospital staff. Noise levels between 80 to 110 dB are typical in dog housing rooms [1]. Construction material should be selected for maximum sound attenuation. Ducts penetrating sound control walls should have sound traps at the penetrations. The trap must be cleanable and must not harbor vermin.

Similarly, pipes penetrating sound control walls should be caulked and sealed [4]. Equipment such as fire alarm systems and paging systems can transmit ultrasonic frequencies. These frequencies can be detected by certain animal species. This equipment should be located to minimize such interference [2].


The shortage of mechanical design guidelines on veterinary hospitals creates a challenge to the engineer. In these facilities, both humans and animals are a dynamic part of the equation! Therefore, the engineer needs to first understand animal comfort levels, diseases, and handling procedures. Then, translate these parameters to quantitative measures such as temperature, humidity, and airflow. Finally, the engineer would design a facility to meet the needs of the veterinary hospital.