Thermal Insulation and Duct Liner

[montoy]

I think that thermal insulation is used primarily to maintain the supply air temperature and condensation second. Duct Lining is for sound attenutation. I often heard co-workers saying that if the duct is lined, it doesn't need to be insulated because the liner takes care of the condensation. I thought that it should be both insulated and lined. For example the first 20 feet of duct from the Air Handler, it should be lined for sound attenuation and insulated for thermal reasons. What's the real reasons of insulating and lining?

 

[AbbyNormal]

The liner is for sound. It is also a great place to get wet and let organic matter collect.

Indoor duct work with a liner and external insulation is a waaste of money in my opinion

You can run exposed spiral duct, its double wall meaning it has internal insulation and then an internal perf lining. This application is not uncommon.



The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[IRstuff]

But, doesn't the insulation help you from wasting effort cooling or heating the attic?

TTFN

FAQ731-376

 

[KiwiMace]

The liner has the same effect as the insulation, you should not need to insulate as well.

IAQ concerns are starting to steer away from internal lining these days. The growing preference is to use real acoustic silencers with perf steel liner and sometimes mylar, rather than have the liner deteriorate over time and dust the space with fiber.

 

[walz]

Lining is running out of practice these days due to poor IAQ Performace... it is and was used to attenuate the noise created by the air moving in the ductwork only. Whereas the major source of noise most of the times is fan.

Have a sound attenuator at the discharge of fan, insulate the ductwork and design it at an appropriate velocity to minimize the noise due to air in the ductwork.

 

[VEEKRISH]

I agree. Internal lining is no longer the order of the day considering IAQ ssues. Remember, in most cases only the initial length from the Unit outlet is lined to attenuate he Fan Sound in Duct. This is better addressed using Attenuators. External Insulation is provided to limit rise in temperature of SA towards the tail end of the duct. Idea is to limit the rise in temp from firts outlet to the last to about 2 deg F. More so if the aspect ratio is skewed (> 4). In such cases it may be advisable to insulate the tail end portion of the duct.

 

[walz]

Lining is dealing with the internal surface of the ductwork. means it attenuates the air noise balooning the duct. Noise can be transferred to the duct via external surface as well.