Roof top ventilator unit, rusted

Written by admin, 12 January 2023

Rusted roof top ventilator located on top of the roof's hotel has large holes at the bottom of it's drum. We have increased the efficiency of this RTU by repairing the holes. JW Portable Welding, London, Ontario, 2022

Rusted roof top ventilator on the roof with holes all over and holes in other parts of RTU consume your budget. Your roof top unit must work harder and longer to make your clients comfortable. And this cost money. JW Portable Welding repairs the holes usually within one day significantly increasing the efficiency of rusted roof top ventilator, and drastically reducing the operational cost of running roof top units. The utilization of the repair lasts longer than sheet metal patch on the another rusted sheet metal. In the repairing process, we use multilayered mechanical epoxy with rust killing additives. Our repairs not only sustain vibration of operating equipment but also protect the surfaces against the rust.

Replacement of roof top ventilators and more specifically their fans and drums that are part of roof top unit is not an easy task. RTU’s, roof top units, are custom made for hotels, condominiums and office buildings. Replacement mechanical parts are available for newer models but older models, more than 20 years old, face parts scarcity. All units, however, face challenges in regards to sheet metal structure surrounding and protecting mechanical components. The wait list for custom orders for roof top units range from 2 to 5 years now and the purchasing cost will make a significant dent in your annual budget. Why not repair the roof top ventilator in your RTU on the roof and save the money running the roof top units efficiently.

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First step – assessing damages on the rusted roof top ventilator

Our initial visit on the roof has many goals. Most importantly, we have to assess damages of the rusted fan, location of holes and their sizes. We also look for the easiest access to the damaged areas that as you are aware is not an easy task on many RTUs. At the final stage of initial inspection we must take measurements of damaged areas and their squared footage. In some instances we have to take templates of damaged areas, and more specifically we take templates from vibration areas.

Additionally, we look for the easiest way to transport our equipment to the roof. Most of the roof top units are on the roofs of hotels, condominiums and office buildings and some old buildings have a very restricted access to their roofs. Therefore, we have to inspect the roof access area.

We also need to inspect the top of rusted ventilator to assess damages there. Therefore we need to know in advance how high is the top of the ventilator’s drum.

We schedule repairs for Spring, Summer and Fall

At the end of the visit, we discuss with the client how we plan to fix the damages. The mechanical epoxies are rather expensive and we guide the customer in the decision making regarding the surface of the repair areas, number of mechanical epoxy layers, and physical attributes of each layer. We also discuss possibility of stiffeners in areas that require additional structural support.

Finally, at the end of our initial visit we schedule the date to repair you roof top ventilator. Since the mechanical epoxies are very sensitive to the outside temperature during curing, we tend to schedule the repair on the hot and dry day. We do not conduct any repairs in Winter due to the necessary curing temperatures.

We seal the rusted holes in roof top ventilator's drum with mechanical epoxy. Through these holes the hot air is sucked by the ventilator and then pushed to the building. JW Portable Welding, London, Ontario, 2022
The hot air from outside is sucked by the working fan of roof top ventilator through these rusted holes and then pushed to the building. JW Portable Welding, London, Ontario, 2022

Fans on the roof rust first

The roof top ventilator rust first considering the whole RTU but more specifically the drums of these ventilators rust first. In many RTUs the drums are looking terrible but the rest of the RTU looks fairly good. The rusting process of drums begins actually inside of the drum. Therefore, these drums actually rust from inside out and all the damages what you see outside are fractional in comparison to rust damages inside.

As we are trying to repair the holes in the drum of a roof top ventilator, we tend to increase significantly the area of epoxy coverage. In this way we increase significantly the utilization of your roof top ventilator and simultaneously we increase utilization of the whole roof top unit.

The 3 layers of epoxy resins cover the whole bottom of the roof top ventilator's drum. In this way we improve the surfaces that going to rust in the future or surfaces weakened by minimal rust. JW Portable Welding, London, Ontario, 2022
The 3 layers of epoxy resins cover the whole bottom of the roof top ventilator’s drum. In this way we secure surfaces that are going to rust in the future or surfaces exhibiting pitted rust. JW Portable Welding, London, Ontario, 2022

These ventilators in roof top units push already conditioned air to the buildings and because they increase the velocity of the air, the excess moisture of the air tends to condensate and then accumulates at the bottom of their drums. Some drums have drains in these locations but many do not. Also, many drains are plugged by dirt or by rusted particles resulting in excessive accumulation of moisture.

Repair of the top roof ventilator’s drum

Basically the process to repair your top roof ventilator’s drum consist of two stages: preparation stage and epoxy application stage. Each stage involves numerus activities that improve the quality of a final repair.

Preparation stage

Preparation stage is extremally important for the quality of final repair. This stage involves cleaning by hand or mechanically the rusted surface of your damaged fan. In most instances we are not able to completely remove rust but we tend to remove the remaining paint. Fortunately, we have the method to deactivate the remaining rust on the surface of the drum.

During the preparation stage we use variety of chemicals that help us to prepare the surface in the best way possible to accept our mechanical epoxies. Therefore, even though we are working in open air you will be able to smell some chemical odors. These chemicals have industrial purpose and create risk for the public, that is why we tend to ask clients to leave us alone.

Moreover, during the preparation stage we tend to install stiffeners. The stiffeners help us to achieve the desired shape of the final epoxy layer.

Epoxy application stage

The epoxy application stage begins with application of epoxy rust deactivator that also increases adhesion of our mechanical epoxy. Then we apply from 3 to 7 layers of different types of epoxies. Some epoxies are applied due to their vibration resistance, others increase playability of finished layer, and still others go deeper to the metal. Each application of epoxy is precisely timed since some of them can cause burns when they solidify. Therefore, we not only time the epoxy application to avoid spreading the partially solidified product but also to avoid burns to our hands. Please keep in mind that our rubber gloves will not protect us from high solidification temperatures. That is why it is better to leave us alone.

After the epoxy application stage is finished, we usually ask not to turn the roof top ventilator for at least 6 hours but preferably for at least 12 hours. This time period is usually enough to allow all layers of applied epoxy cure properly. Certainly, increasing the number of mechanical epoxy layers will increase curing time pushing it to 12 hour.

The left and right area on the bottom of ventilator's drum is covered in 5 layers of epoxy for about 6" wide on each side. Additionally, each side of epoxy covered surface overlaps damaged area for 2". JW Portable Welding, London, Ontario, 2022
Two sides of the ventilator’s drum are covered with 5 layers of epoxy. The overlap between the epoxy layer and damaged area is 2″. JW Portable Welding, London, Ontario, 2022

If you want to know more about epoxies and their varieties here is the link.

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