Multiple Rooftop “Package” Ventilation Units as Compared to Enclosed or Penthouse Ventilation Systems for Schools

Multiple Rooftop “Package” Ventilation Units as Compared to Enclosed or Penthouse Ventilation Systems for Schools

a report prepared by CASLE for the N.S. Department of Education.
January 20, 1999
edited for our website, February, 2001

Edit: April 2016

This report marked a huge advancement in the quality of ventilation systems for new schools in Nova Scotia. In 1999, in the face of strong opposition from builders, it formed the basis for the Department of Education to hold fast to the newly minted decision to use fully-ducted full-building ventilation systems for all new schools.

These have also been 100% fresh air systems – a practice which caused controversy in engineering circles used to designing systems that recycled some used air. However, by the mid-2000’s we began hearing and reading from engineers and architects specializing in Indoor Air Quality that 100% fresh air is indeed a better way. Energy efficiency is being accomplished through other methods, without compromising the fresh indoor air.

CASLE consulted several individuals including four Building Science professionals, Occupational Health and Safety Officers from the Department of Labour, one architect, and two ventilation experts.

These consultants are among the many professionals who work as volunteers for CASLE by providing professional advice, but who prefer to remain unheralded. All agreed that the rooftop package units have more problems than advantages. They also agreed that the major advantage of rooftop units, in the short term, is the price.

Specific comments from our sources:

(A) Advantages of rooftop units:

  • They’re inexpensive
  • good when square footage is an issue.
  • They are better than nothing, and better than the ones used for homes.
  • If there is a problem in one unit the whole building’s air doesn’t go down. (On the other hand, several units can malfunction without anyone knowing.)
  • More useful in warehouses where precise air conditions aren’t needed.
  • Good for air conditioning and humidity control, but not for fresh air delivery/exchange and specific environmental control.

(B) Disadvantages of rooftop units:

  • With 10 to 20 separate intakes you are virtually guaranteed having at least some of them drawing contaminated air from some source. With the single intake units the best air can be drawn from the single least polluted location.
  • Air intakes close to the rooftop level, making the material choice of the roof crucial, due to possible offgassing being drawn into building.
  • more filters to change, and all over the roof
  • maintenance is an issue
  • workers may put off rooftop maintenance in winter months
  • worker safety issue: using ladders and working on a roof
  • Nova Scotia weather is harsh. Units tend to rust or break down from elements.
  • Due to the fact that Nova Scotia has a climate of salty air, this can lead to deterioration – although these machines can have a protective coating.
  • They leak; it’s not long before they get mouldy.
  • Leaks go into the insulation of the unit and sometimes the insulation of the building
  • building tiny “rooms” around each one? still have compound problems compared to the single “room” penthouse units.
  • extremes in weather count, “even if you put junk in a penthouse it will last longer than a rooftop unit”
  • harder to synchronize them all as compared to a single or double unit.
  • A lot have side by side intake and exhaust
  • Often only one fan bringing in air. No exhaust
  • Many have an “economizer” which is a single hole which is expected to serve as both the intake and the exhaust. “Doesn’t tend to work well, certainly not fine-tuned air delivery!”
  • filter efficiency is less in most cases
  • fan motors not strong enough for added filters or increased standards
  • high performance is the issue
  • Limited expansion capability
  • Maybe acceptable if retrofitting makes other options difficult, but not a good choice if you are starting from new.
  • several units can malfunction without anyone knowing.

(C) Advantages of enclosed and penthouse units:

  • With the single intake units the best air can be drawn from the single least polluted location.
  • Exhaust can be placed downwind
  • Filters can be changed easily, and all year round
  • A closer eye can be kept on the day to day operation
  • Should the system have a problem, it is more readily noticed
  • worker safety using ladders and working on a roof not an issue
  • Equipment that is protected from the elements and easily maintained lasts longer and works better.
  • Full system easy to control
  • enclosed and penthouse systems very, very seldom have leakage problems.
  • best where quality of air and environmental control are important
  • high quality filters (HEPA, charcoal, etc) can be designed to match the needs of the building/occupants
  • fan motors can be strong enough for added filters and increased standards
  • high performance is attainable

(D) Disadvantages of enclosed and penthouse units:

  • They take away budgeted square footage from the building proper.
  • are more expensive initially (but should be cost effective in the long run, especially when health of occupants is factored in.

Additional comments from consultants:

(The names of the following contributors are available upon request)

(1) From an architect:

“I do not favour rooftop heating units. My experience and those of others is that they only last for about 15 years. The unit is, however, cheap but it also requires considerable maintenance. Two weeks ago, I investigated a school in which the principal had to climb up onto a snow covered roof every few days just to push the reset button. The risk to the principal and his time to do this is inappropriate.

Rooftop units do not use a chimney. Thus, the fumes are exhausted from the top of the unit through a square hole. Hot air will draw the fumes out of this hole, but in the winter, the fumes are cooled very quickly and drop down around the rooftop units. Unfortunately the air intake is on the same unit, and I have found many instances where the fumes, including carbon monoxide, are drawn back into the school.

At the _______school, we extended the “chimney” up about two metres with an insulated chimney. Even then, the fumes can migrate down due to wind conditions on the roof. Servicing or maintaining the rooftop units is possible only by being on the roof. Since most roofs are not made to withstand foot traffic, it shortens the life of the waterproofing membranes. Even changing the air filter is done on the roof. In the winter or inclement weather, this is not a high priority. If this is a new school, they should not use rooftop units for the reasons mentioned above.”

(2) From a ventilation expert from Ohio:

Rooftop units have a number of disadvantages, including:

1. units are inefficient in that everything (fan, coils, filters) is compacted into a small area and the equipment capacity is reduced;

2. rooftop units are located in an area that is difficult to access for maintenance;

3. fan “system effect” is always a problem and the designers are usually ignorant of this performance reduction factor;

4. roof leakage is a frequent problem.

Rooftop units are cheaper to install but my experience is that the savings in operating costs and maintenance costs over 20 years more than justifies installing the equipment inside the building.

(3) From a Nova Scotian ventilation expert:

– there is lack of maintenance for these units during the winter season and during inclement weather.

– Due to the weather factor, these machines are difficult to adjust and set up properly and because of the weather elements, they tend to malfunction.

– It is impossible to put HEPA filters on these free-standing machines because the fans are not strong enough to push sufficient air through the system.

(4) From a company specializing in air system cleaning and maintenance:

Our company services rooftop units all over the city. The biggest problem is winter maintenance. It is very difficult to change the filters. The units rust, and parts need replacing. The representative said they definitely prefer the enclosed units because they are easier to keep an eye on and to maintain.

(5) A healthy buildings consultant

Enclosed or penthouse units must be roomy and have stairs or other easy access from indoors. Some existing enclosed or penthouse units are so crowded that maintenance is impossible. Some penthouse units even have hatches that require ladder access from classrooms. These units also need to be built roomy enough to allow for future expansion as the ASHRAE standards keep changing. Penthouse and enclosed units must be well designed and not shortchanged.

Additional comments from CASLE:

It bears asking, who will be liable if the wrong choice is made?– If a single unit system breaks down it is noticed. In a local high school, a school which was having significant IAQ problems, only 3 units out of 20 were found to be working, and had likely been this way for years.

– We understand that carbon filters can not be used with these units, as our sources said additional filters can not be added because of fan motor limitations. CASLE recommends carbon and high efficiency filters such as HEPA filters for schools because all schools have children with asthma and other relevant health challenges, and it is important that children do not detoxify the air with their lungs.

– CASLE’s final comments must be about cost effectiveness versus health effects:

It is important to remember that children are not mini-adults. The health risk from air pollution can be as much as six times greater for children than for adults, so it is important to install the safest and most effective type of ventilation units. The cost of not doing this increases the chances for long-term and short-term health problems for staff and students. It may also impact on the student learning environment, comfort, and attendance. It is much more cost effective to prevent harm than it is to try to regain health once it is lost.

It bears asking, who will be liable if the wrong choice is made?


We understand that there are improvements in some newer model’s design, but most of the inherent problems remain unchanged. CASLE concludes that according to the information from all of our sources, even if rooftop units are less expensive in the short run, the design flaws and opportunities for mistakes in installation and maintenance, as well as the reported tendency to not stand up well in Nova Scotian weather conditions make the rooftop package units questionable for reliable Indoor Air Quality over the short or long term.

We ask the decision makers to consider the following quotes in your deliberations:

“What is the cost of doing this? What is the cost of not doing this? – Dr. Gerald Ross, Past President, American Academy of Environmental Medicine

“Anyone who says it is going to cost more to do it right, is wrong. Healthy schools save in the long run.” – Mary Oetzel, President of Environmental Education and Health Services, Inc.

“Whenever any intervention is done at a school, an explicit and automatic question should be asked, ‘What effect will this have on the children?'” – Dr. Jeff Scott, Provincial Medical Officer of Health, Province of Nova Scotia

Thank you for the opportunity to provide input on this important issue of fresh air delivery in schools.

We hope this input helps clarify the choice between package and enclosed units, and we await the Department’s decision.

Citizens for A Safe Learning Environment