HVAC insulation and why we need it

By Ilana Koegelenberg

Thermal insulation of piping and ducting will protect your building against extreme temperatures and noise, providing a comfortable, healthy, safe, and quiet environment (when installed correctly) — but what are we doing wrong?

In fully air conditioned buildings, the HVAC component ranges between 30 and 60% of the building’s overall energy use.

Heat/cooling transferred through the duct or piping network represents a loss of energy, and in turn increased operating costs. Moreover, thermal losses can lead to fluctuations in the desired air-conditioned temperature of the building.

Thermal insulation’s primary role is to reduce the heat gain/loss of the system thus saving energy. “Energy efficiency is a major consideration when insulating ducts,” explains Craig Sprighton, marketing manager of Saint-Gobain Isover. If a duct isn’t insulated for instance, cold air that moves through the duct will gain temperature. This causes condensation and dripping water, and you will need a larger system to fulfil your cooling requirement.

Insulation also helps to reduce the noise level, absorb the vibration generated by the system, and prevent the spread of fire. Other benefits include preventing the icing of water vapour and condensation on cold surfaces.


Also, make sure not to wrap the tape too tightly or you’ll dilute your insulation. The thickness of the insulation needs to remain constant throughout the installation to prevent condensation.


Well-chosen material can protect the piping/ducting from harsh environmental conditions such as UV light, salt, water, dust, chemicals, and oil. Other characteristics may include the ability to inhibit the growth of viruses, bacteria, and fungi.

Insulation of piping

It is important that the piping of your HVAC system be insulated. But which ones should be insulated and why?

Cold lines are insulated to prevent any air leakage into the insulation that can cause condensation of moisture on the pipes.
Suction lines are insulated to prevent the loss of capacity or sweating due to heat gain. Heat gain causes extra load to the condenser, hence reducing the overall capacity of the air-conditioning system.

Liquid lines do not require any insulation as they are at a higher temperature than the surrounding air. Heat loss to the surrounding air is desirable as it improves the system capacity.

Discharge lines do not require insulation because loss of heat removes load from the condenser. This helps to improve the performance of the compressor.
Insulation of ducting

The first significant factor to consider when attempting to reduce energy consumption in duct work, is the building’s thermal insulation. Knowledge of a building’s thermal load and its compliance with regulations is essential. Ultimately, this will pay dividends in achieving minimum thermal insulation and providing maximum thermal performance, according to Isover’s HVAC Ducts Handbook.

The decision of having to insulate internally or externally will depend on the specification from the architect, or the requirement in terms of performance, explains Sprighton.

Internal insulation such as sonic liner provides a higher level of acoustic performance together with thermal performance. Whereas external insulation such as duct wrap provides external protective performance with the additional benefits of acoustic performance naturally gained from using glass wool products, explains Sprighton.

Sonic liner has a glass tissue facing which helps with absorption and therefore is used for the acoustics. Duct wrap is applied externally, and has a foil facing, which makes it more durable and helps to prevent condensation on pipes.

Isover produces all their glass wool locally using recycled glass, sand and limestone – all natural resources. “Legislation dictates that the ducting must be non-combustible, so it’s important to keep this in mind as well when choosing your insulation,” Sprighton explains. “Combustible materials are can be dangerous and does not comply with the legislative requirements in terms of maximum allowable lengths.”

So, what is new on the market? Isover is currently investigating the possibility of introducing a new product in the market. Internationally it manufactures a product called Climaver, which is a self-supporting duct system. Standard sized boards are transported packed flat to site where the system gets rigged according to measurements. No metal or welding is required, and the whole system is already insulated. “It is very light weight, and clean, and quick to install,” Sprighton says.

Hot insulation vs cold insulation

Equipment or pipework with an operation temperature greater than 55°C in the case of metallic surfaces and 65°C in the case of non-metallic surfaces should be insulated so that the surface temperature after insulation (cold surface temperature) does not exceed 55°C, according to industrial insulation specialists, Vedder & Moffat.

The objective is to select a material, which will serve the insulation purpose at the lowest cost. This can be a complicated procedure. Careful consideration should be given to insulation thickness. On pipework, an over-specification of thickness creates a needless increase in the cost of the outer protection.

Cold insulation should be considered where operating temperatures are below ambient and where protection is required against heat gain, condensation, or freezing. In designing an insulation system where formulae and surface coefficients are used, they should be to an appropriate international standard.

Closed-cell insulation is the most commonly specified material used for cold work because it possesses a degree of resistance to water vapour and because the thermal conductivity (k factor) of some of these materials is better than the fibrous alternative products.

Insulation materials range from bulky fibre materials such as fibreglass, rock and slag wool, cellulose, and natural fibres, to rigid foam boards and sleek foils. Bulky materials resist conductive and — to a lesser degree — convective heat flow in a building cavity. Rigid foam boards trap air or another gas to resist conductive heat flow. Highly reflective foils in radiant barriers and reflective insulation systems reflect radiant heat away from living spaces, making them particularly useful in cooling climates.

Glass wool (fibre glass): The most common material used for insulating heating and cooling ducts is fibreglass. Fibreglass duct insulation is available in various thicknesses and R-values, and in either a flexible or rigid form. The flexible type comes in rolls and is relatively easy to install on either round or rectangular ducts. The rigid type is best suited for rectangular ducts. In some cases, the ducts themselves are constructed of this material (called ‘duct board’), reducing or eliminating the need for additional insulation. Any duct insulation material should incorporate a foil or vinyl coating to prevent moisture from being absorbed by the insulation. Any existing insulation that has gotten wet should be replaced.

Sonic liner is a flexible glass wool insulation blanket faced with an acoustically permeable black woven glass cloth on the airstream surface. A 35mm overlapping flange of the facing material is provided on both sides to enable effective sealing. It provides outstanding acoustic and thermal performance with low air friction.

Mineral wool: The term ‘mineral wool’ typically refers to two types of insulation material:

  • Rock wool, an artificial material consisting of natural minerals like basalt or diabase.
  • Slag wool, an artificial material from blast furnace slag (the scum that forms on the surface of molten metal).

Mineral wool contains an average of 75% post-industrial recycled content. It doesn’t require additional chemicals to make it fire resistant, and it is commonly available as blanket (batts and rolls) and loose-fill insulation.

Polystyrene: Polystyrene — a colourless, transparent thermoplastic — is commonly used to make foam board or bead board insulation, concrete block insulation, and a type of loose-fill insulation consisting of small beads of polystyrene.

Moulded expanded polystyrene (MEPS), commonly used for foam board insulation, is also available as small foam beads. These beads can be used as a pouring insulation for concrete blocks or other hollow wall cavities, but they are extremely lightweight, take a static electric charge very easily, and are notoriously difficult to control.

Polyurethane: Polyurethane is a foam insulation material that contains a low-conductivity gas in its cells.

With closed-cell foam, the high-density cells are closed and filled with a gas that helps the foam expand to fill the spaces around it. Open-cell foam cells are not as dense and are filled with air, which gives the insulation a spongy texture and a lower R-value.

Foil and plastic facings on rigid polyurethane foam panels can help stabilise the R-value, slowing down thermal drift. Reflective foil, if installed correctly and facing an open air space, can also act as a radiant barrier. Depending upon the size and orientation of the air space, this can add another R-2 to the overall thermal resistance.

Doing it by the book: standards

“Naturally, the hardware of an HVAC system takes priority when being constructed, but taking the legislation relating to insulation into consideration, will make a big difference in the performance of your system,” Sprighton says. “Legislation should always be adhered to, as it serves as a guide to energy savings, and optimal performance of the system.”

South Africa’s mounting energy crisis means that we all need to think of innovative ways to save electricity. Our buildings typically account for 40% of all the energy consumed in South Africa. Insulation can go a long way in lowering this percentage.

When it comes to HVAC insulation, there are two main guidelines: by the international Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) and the South African National Standards (SANS).

When it comes to ducting, specifically SANS 1238:2005 (‘Air-conditioning ductwork’) and SANS 10173:2003 (‘The installation, testing and balancing of air-conditioning ductwork’) is applicable. These provide comprehensive guidelines on what is allowed and what is not. It is important to make sure you are working according to the standards when it comes to insulation on duct work. If you don’t, you risk the inspector not approving your work after handover — a costly exercise if you have to then redo all the work. Rather do it right the first time.

Also, the National Building Regulations were updated and Part XA (Energy usage in new buildings) was added. Part X which covers environmental sustainability. SANS 10400-XA states that the use of energy by air conditioners and mechanical ventilation must be in accordance with the requirements of SANS 204. Sans 204 states that all chilled water and refrigeration piping, conditioning air duct work and flexible ducts shall be insulated to limit the heat gain / loss to not more that 5% from source to the furthest point of delivery on a system


When it comes to rectangular duct supports, hanger rods must never be set against the duct insulation, to avoid damage.


SANS 10400 –T states that an HVAC system shall be designed as to prevent the distribution of products of combustion in the event of a fire. An HVAC duct including any internal or external insulation and flexible joint shall be constructed of non-combustible material in accordance with SANS 10177-5. Combustible flexible connections may be used where the length does not exceed 1,5m.

Pipe insulation – dos and don’ts

Charel Marais, lecturer at the ACRA training academy and RACA Journal contributor, shares the following tips from his experience out in the field …

Things to look out for:

  • Pressure gauge clashing with insulation — this would make it difficult to remove the gauge;
  • Insulation saturated; and
  • Condensation dripping on cladding.

It is important to note that if closed cell type insulation is used outdoors it must be UV protected. Else it will crack and not last very long. K-Flex must not be used external to buildings or near UV lights for the same reason.

When it comes to pipe supports, it is important to refer to the regulations. The use of wooden blocks is not recommended. To prevent thermal bridging at supports, insulation props of similar material and preformed to suit the pipe, with sufficient density to support the pipe, fluid and coverings, and equal thickness to insulation must be provided — according to the standard.

Insulation on strainers that are not done correctly will cause damage to the insulation and eventually cause rust to piping, end caps, and fasteners. Insulation over the end cap must be removable for maintenance.

For chilled water piping insulation, it is important to glue K-Flex and armoflex insulation joints to ensure a continuous vapour barrier, else condensation will make insulation tape come undone.

On that note — make sure you use the correct glue on closed cell insulation, for example polystyrene. Bitumen helps to seal/hold it properly. If you do not use the right glue you will damage the polystyrene.

Also, make sure not to wrap the tape too tightly on armoflex insulation or you will dilute your insulation. The thickness of the insulation needs to remain constant throughout the installation to prevent condensation.

It is a good idea to use K-Flex on flanges and bends as it is more practical and easy to apply. The use of polystyrene is difficult and time consuming, especially when trying to cut it neatly to fill gaps behind bolts.

It is also important to ensure that the cladding is properly sealed. You do not want to get water inside the cladding. That is why you should also keep an eye on the weather, especially during the rainy season if you are working outside. Rainstorms can be disastrous to your insulation installation!

Flexible connections covered with plaster insulation is not correct. This will crack and not last very long.

If fittings are installed on top of piping it must be properly insulated. Closed cell insulation with a bitumen coating is recommended. After the cladding is applied, use some silicon to seal the opening around the fittings.

Duct insulation – dos and don’ts

There are many requirements in the regulations that aren’t always being adhered to.

It’s a good idea to have the HVAC&R contractor submit duct samples for approval before manufacturing or to deliver equipment to site, Marais recommends.

Sections of ducting complete with insulation on:

  1. Bends
  2. Spigots
  3. Spiral ducting
  4. Shoe connection
  5. High density foam on duct supports
  6. Sample of a duct section with sonic liner
  7. Double skin, also known as cladded ducting sample.

It is up to the individual to ensure that the manufactures and the installers understand to what standard the work must be done and what quality of workmanship is expected. Requesting samples will minimise defects and will avoid a lot of equipment from being rejected.

Things to check when insulating a duct:

  • Was the surface to be insulated clean?
  • Did you use the right paint on the support?
  • Did you remember to apply the adhesive?
  • Are all the pins placed correctly?
  • Is the ducting being damaged by the supports?
  • Is the insulated ducting lying in moist dirt?
  • Were the fasteners and clamps correctly installed?
  • Was the cable installed correctly so it doesn’t hurt the insulation?
  • Were the S & Drive joints correctly sealed?

It is important to work neatly when it comes to sealant on duct section joints.

Another area where some contractors often make mistakes, is when it comes to supports for spiral ducts. The SANS standard is very specific about what is allowed and what not. Doing this incorrectly can easily damage the insulation.

Another oversight in the installation or the handling of the product, is that the insulation can get damaged during transport or if it’s left outside on site and get wet. This can all affect the insulation. ”Insulation materials should be kept dry, clean and undamaged to maintain optimal performance,” Sprighton advises.

When it comes to rectangular duct supports, hanger rods must never be set against the duct insulation, to avoid damage.

Sheet metal channel must not be used instead of angle iron or unistrut. The HVAC contractor must avoid creating their own defects. For example, if they decide to use mild steel angle iron it must be painted and inspected. By using galvanised unistrut, those concerns or defects disappears. Different sizes (height) of unistrut can be used.

Bricks should never be used as a duct support. It’s a safety hazard and can damage the insulation.

Pins are required on the sides and the bottom of the ducting. Then there is the issue of fixing the pins and which pins are the most practical and correct to use. Regardless of effort, pins seem to break off when trying to bend them over. Extreme care must be taken during the bending of pins.

It is not mentioned in the standards that pins must be bent over, but failure to do so poses a safety hazard. For that reason, pins must be bent over and covered with aluminium tape to provide a continuous vapour barrier.

If pins are put in too deep, it will squash the insulation and washer edges, causing damage to the vapour barrier. However, if they are too loose, everything can come undone.

An option is available to cover the pin with an aluminium cap. The depth of the cap will prevent the spring washer from squashing the insulation more than the specified 15%. The vapour barrier can still be placed over the cap.

The positive outcome is that pins do not need to be bent over for safety reasons, and there won’t be loose pins.

Duct insulation shall be fastened to ducting in accordance with Table 1.

 Duct size  Fasteners
 <300mm  Adhesive (100% coverage of area)
 300mm ≤ duct <600mm  Adhesive and straps at 300mm centres
 ≥ 600mm Adhesive and pins at 300mm centres

Table 1

Strapping must not be pulled so tightly that it cuts into the insulation. PVC corner protection is available to avoid damage, but it was tried and rejected as it causes more damage to the insulation.

Also, make sure that workers do not stand on the insulation or put it on the dirty floor. It is recommended that the contractor builds a suitably sized table that can be used on all projects. This allows insulation work to be done neatly and prevents workers from getting as tired as when they are working on the floor. This allows more work to be done quicker and causes less defects.

Get training
For more in-depth training and info on what to do (and not to do) with regard to HVAC insulation, you can contact Charel Marais at charel@acra.co.za.

Sources

  • US Department of Energy
  • airconditioning-systems.com
  • veddermoffat.co.za

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