Actually hood ventilation noise consists primarily of two components - blower or blower mechanical noise and airflow noise (ignoring vibration caused from a cheap and poorly constructed hoods).
A low quality blower will introduce mechanical noise hence one should always strive to install the best quality blower you can - each of those blower options below have specific areas of use - an inline blower mounted remotely will reduce immediate mechanical noise versus an internal blower in the hood HOWEVER an inline blower brings its own risks in terms of resonance (air waves from blower oscillations and minute vibrations) in a confined area. An external blower mounted close to the hood is about the same as an internal blower in the hood - one typically uses an external blower if you have a difficult duct run - sucking air from the end of the duct run along a convoluted and long duct run is far more efficient than trying to PUSH air from inside the hood via an internal blower along the same duct run. At the end of the day noise has mainly two components - poor quality blower that introduces excessive mechanical noise (there will always be some but this can be mitigated by using a good quality blower) and most importantly the QUALITY of the duct run - a duct run that is too small or multiple 90 elbows or has been crimped(dented badly at installation) OR using the ribbed aluminum stuff versus smooth HVAC galvanized ducting introduces a lot of air flow noise - of course the type and design of the filtration system also introduces airflow noise in the hood. By far the biggest problem we have found in over 20 years of custom range hood sales and installations is ducts that are far to small for the airflow generated by the internal blower - modern blowers (good quality ones) sense duct restrictions and run faster (more revolutions and therefore more mechanical noise) to compensate and delivery the requested volume of airflow - a simple mathematical calculation will illustrate this - a 6 " duct which everyone believes is adequate provides 28.28 sq inches of airflow capacity whereas an 8" duct supports 50.28 sq inches - nearly double the volume of airflow - so of course an 8" duct is far more efficient and is why we recommend an 8" duct over a 6" for 600cfm and 10" duct over 8" for 900cfm and 1200cfm. An added tip - another benefit of external blowers is that because they are far more efficient at moving air over distances and bad duct runs is an 8" duct is sufficient for say a 900cfm or 1200cfm external blower - qualification of course being a high quality external blower system such as ours - cant comment on the others out in the market - as always you get what you pay for......at Custom Range Hoods we are always willing to help and will assist anyone with technical questions - placing an order with us will of course open the door to a mountain of experience and good advice - feel free to email us at allenl@customrangehoods.ca.
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