In buildings and modern transport, comfort is always considered a top priority. In most public and mass transit vehicles, HVAC units are installed throughout to provide heating or air conditioning for all passengers. Naturally, heating, ventilation and air conditioning units for large vehicles are linked for ease of use and consistency of temperature and air flow. As a result, they can be somewhat noisy, and temperature is more difficult to keep under control.

As specialists in the field of rubber and plastics, with expertise in the rail and mass transit sector, the CB Frost team are well placed to advise on the most suitable materials for HVAC seals. We take great pride in our extensive technical knowledge and high quality of customer service, combine with our second to none product range.

Key Properties Of HVAC Seals

In order for HVAC units on trains, buses and coaches to function effectively, proper insulation is vital. HVAC insulation seals must fit certain characteristics, including:

Excellent sound insulation – HVAC seals must provide a good level of sound insulation to ensure that noise generated by the units are kept at a comfortable level for passengers.

Excellent temperature resistance – Materials used for HVAC seals must continue to function effectively in both low and high temperatures. As well as external temperatures, seals must also be able to withstand the high or low air temperatures generated by the HVAC units to allow them to provide the appropriate, consistent temperatures.

Fire safety – Any insulation material used in trains, buses and other forms of public transit must comply with government regulations for fire safety. Rail industry standards include BS6853, the British standard for fire testing and fire safety, as well as EN45545, the European standard for fire safety, which is now mandatory across Europe. Insulation materials must be resistant to fire and help to prevent fire and smoke from spreading.

Durability – Durability and longevity of sealing materials is essential. HVAC units must be designed for long term and regular use, so seals and gaskets must be suitable for these specifications to ensure the smooth running of heating and air conditioning units.

Whilst over 100 years’ experience in the rubber and plastics industry is impressive, we don’t stop there. Continual improvement in training, material development, equipment and processes, together with the dedication of our staff, ensures we remain leaders in our market. We strive to deliver the very best levels of service and product quality at all times. Wherever you are in the world and whatever your industry you can trust us to deliver.

Commercial Buildings

HVAC systems are milestones of building mechanical systems that provide thermal comfort for occupants accompanied with indoor air quality. 

HVAC systems can be classified into central and local systems according to multiple zones, location, and distribution. Primary HVAC equipment includes heating equipment, ventilation equipment, and cooling or air-conditioning equipment. Central HVAC systems locate away from buildings in a central equipment room and deliver the conditioned air by a delivery ductwork system. Central HVAC systems contain all-air, air-water, all-water systems.

Two systems should be considered as central such as heating and cooling panels and water-source heat pumps. Local HVAC systems can be located inside a conditioned zone or adjacent to it and no requirement for ductwork. Local systems include local heating, local air-conditioning, local ventilation, and split systems.

Commercial Building HVAC image

HVAC On Buses

Buses are an easy and convenient way to get around whether traveling long distances or just commuting around the city.


Air conditioners on buses operate similar to those on trains, but there are additional conditions. HVAC units on buses are commonly housed on the top or rear of the bus with the compressor being run by the engine as in cars. In recent years, roof mounted units have grown in popularity due to their improved energy efficiency. Constant exposure to the elements and rough road conditions can take their toll on the compressor of a bus HVAC system, so protecting the compressor is crucial to the longevity of the HVAC system.

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HVAC On The Train

While train and subway HVAC systems are less standardized, they operate under similar basic principles and surely get the job done.

HVAC systems in trains are often composed of multi unit inverter condenser and evaporator sections mounted on top of the train or beneath the floor in the undercarriage, although they can also be mounted on the side of the train as well. The systems can also be split so that cooling is distributed from the ceiling within the cabin and heat is distributed from the floor. HVAC systems must be particularly efficient at ventilation on subway cars not only to provide quality air to passengers but also for safety reasons in case of a fire or other emergencies.


As specialists in the field of rubber and plastics, with particular expertise in the rail and mass transit sector, the CB Frost team are well placed to advise on the most suitable materials for HVAC seals. We take great pride in our extensive technical knowledge and high quality of customer service, combine with our second to none product range.

HVAC In The Sea

Let’s also take a journey under the sea to have a look at how cooling is managed in submarines.

There is only a small amount of space for occupancy in a submarine, but within the inner hull, heat is constantly being produced by elements such as engines, storage batteries, stoves, electric lights and even people. With this heat, moisture is also continuously being produced. Only a few cubic feet of space is available for housing air conditioning equipment, but air conditioning is crucial not only for the comfort of the occupants but to control this level of moisture. The temperature at which the air becomes saturated with moisture is called the ‘dew point’ and this dew point must be managed to limit the amount of moisture on board the submarine. To achieve this, air from inside the submarine is drawn by fans into an evaporator that removes moisture from the air and that water is drained away and stored in a tank away from the internal environment of the submarine. The drier, cooler air is returned to the interior of the submarine for a drier and cooler environment.


Key Materials

As specialists in the field of rubber and plastics, with expertise in the rail and mass transit sector, the CB Frost team are well placed to advise on the most suitable materials for HVAC seals.

HT800 Silicone Sponge

HT800 silicone sponge provides an ideal solution for any HVAC sealing requirement. It exhibits fantastic resistance to extreme temperatures and flames, UV light and ozone to provide consistently excellent performance in all environments. HT800’s compact cell structure and unique formulation allows for a much-enhanced sealing performance, resisting the penetration of fine particles and wind-driven rain.

MF775 Silicone Rubber

MF775 is a solid silicone rubber with a range of properties that are well suited for use in HVAC sealing applications. It boasts a high level of resistance to UV, ozone and extreme temperatures and will not absorb moisture. These characteristics, combined with fire safety compliance, mean that MF775 is well suited for sealing gaps of various sizes in HVAC systems.


NH Armaflex is a halogen-free, flexible insulation material with certification for use in marine and offshore environments.

It meets the demand for insulation materials with minimal smoke and toxic emissions in the event of a fire and being a closed cell material, NH Armaflex provides good water vapour resistance


BF1000 and BF2000

Both BF1000 and BF2000 are highly compressible silicone foams with excellent compression set and are as a result highly suitable for use in sealing applications. Due to the softness of the material, they exhibit low closure force, so less force is needed to seal HVAC units, whilst still providing excellent protection and insulation. As is essential for all HVAC sealing materials, BF1000 and BF2000 silicone foam withstand extreme temperatures and resist UV light, ozone and flame in all environments.

Class O

Class O is a lightweight, closed cell flexible insulation foam for reliable and continuous condensation control. It has a unique micro-cell structure (Armacell grade) that makes the foam easy to install with no additional vapour barrier requirements. A combination of low thermal conductivity and high resistance to water vapour prevents long term energy loss, moisture ingress and reduces the risk of corrosion under insulation. The built in Microban protection and excellent fire performance make Class O suitable for use in public buildings and process industries. The Armacell grade of Class O is dust, fibre and formaldehyde free.

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