The increased sophistication of rooftop products has benefits for installation accuracy and troubleshooting. Contractors who install them need to be familiar with the higher-end technology, found on products like the Bryant DuraPac Plus. The units also have the advantage of “plop and drop” installation on some existing rooftop configurations.

What’s the hottest growing HVAC market these days? Some manufacturers are saying it’s the rooftop market, particularly in the 3- to 25-ton range. Removing the old packaged system and hooking up a new one is easier than it used to be; poking and patching new holes in roofs is not always required. Product innovations are making rooftop packaged system replacements a much simpler affair for the installing contractor.

The market has great potential for light commercial HVAC contractors. “We have a great in-stalled base of 3- to 25-ton units, literally hundreds of thousands of installed units,” said Hank Gellert, Bryant commercial marketing manager.

“With the strong markets in the commercial sector, many residential and light commercial contractors are finding light commercial is offering an excellent opportunity in their business model,” Gellert said. “Many of today’s rooftop systems will fit on existing roof curbs, making this business even more attractive,” he continued. “They can take existing connections without having to punch new holes in the roof.”


“Because of the high number of membrane-type roofs, people want to stay away from what we call patch pockets,” Gellert said. “The emphasis today is to run utilities through the curb into the bottom of the rooftop.” In some cases, however, the utilities may already be on the roof and the position of the new unit is not exactly where the old unit was. “You have to just deal with it.”

Often a contractor is fortunate. “Locations of the electrical connections, for many of our new products, are in the exact same locations as the old rooftop connections,” Gellert said. Gas connections may need to come to a different part of the opening if they are coming up through the curb.

There is another alternative: adapter curbs. According to Gellert, the adapter allows the airflow connection to go from the old unit to the new one. Aligning the duct connections is a major aspect of replacing an old packaged system with a new one. “The industry has accepted the use of adapters,” Gellert said.

These curbs, however, can add up to 30 inches of height to the rooftop application. The unit sticks up higher into the line of sight from ground level, which can be a problem for some customers. It also increases wind resistance and the weight of the unit on the roof.

In addition, “The indoor fan system of the rooftop unit has to be able to adapt to the airside pressure drop of this adapter curb,” Gellert said. There is an increase in fan horsepower, which can add to the cost in terms of using a bigger motor, plus the added operating expense.


In terms of the contractor’s manpower, “probably the number of people doesn’t change to set a replacement unit, but you don’t need to get additional trades involved because you’re not changing the existing roof,” Gellert said. The cleaner replacement may also prevent the need to bring in a structural engineer.

“Nobody wants to repenetrate the roof,” he said. “Putting new holes in the roof is your last resort.”

When making a rooftop replacement with much of today’s equipment, “you don’t have to tie up the roof to pull off the old curb and put in the new one,” Gellert said. This can be a plus for the timing of a project, especially as it relates to the comfort and convenience of building occupants. “There is usually somebody in the occupied space,” he said. “In many cases, you will be impacting them for less than 24 hours.” In addition, the increased sophistication of products over the years has benefits for installation accuracy and troubleshooting.


Many contractors will look to find a rooftop unit that replaces the old unit without an adapter curb. “‘Plop and drop’ is a very lucrative business, but it requires knowledge of the existing unit, and knowledge of which units can be replaced without reconfiguring utilities,” Gellert said.

“Many people are looking at replacing like with like.” However, the replacement unit should be brought into compliance with the latest local codes. Often, the older unit may not have an airside economizer, while new energy and ventilation codes mandate the use of this item.

A contractor also should be aware of the advantages of using an airside economizer, which Gellert says can supply significant hours of ‘free cooling’ in many climates. “For example, if the outside air temperature is below 58°, typically compression is not needed as outside air can be brought straight into the economizer.”

Additionally, a routine evaluation should include the building load, wire sizing, and airflow requirements. “Many owners may have assumed that the old unit was satisfying their HVAC needs. If you talk to the occupants, however, that may not be the case.” The business also could have changed a few times since the original rooftop units were installed. “Maybe it started as a grocery store and now it’s a pizza shop, with the load of the ovens to be accommodated,” he said.

The commercial rooftop market is very competitive, Gellert said. “Where the equipment has a niche advantage, that could be the contractor’s decision maker.”

Sidebar: Rooftop Unit Location

The location of a new rooftop unit on an existing roof can be very important. Hank Gellert, Bryant commercial marketing manager, said contractors need to be aware of:

• Clearances around the unit from an operational standpoint - Is there enough space for service and maintenance?

• Parapets to hide the units - Do they restrict airflow? If so, they could starve the outdoor coil, and prevent sufficient fresh air for ventilation purposes.

• Is the outdoor intake air free of contaminants? IAQ sensors and outdoor air quality sensors can keep a contractor or building owner-operator alerted to changing conditions.

“Don’t blindly bring in outdoor air to satisfy your ventilation requirements,” Gellert said.

Publication Date:06/18/2007