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How critical is ductwork?

Newly developed fans are quieter and more efficient, mainly due to the larger ductwork they employ. The increase in duct size is a critical factor in reducing sound. Increasing the duct size means that at a given flow rate (CFM), air can move more slowly. A six-inch diameter duct is more than twice as large as a four-inch duct and will pass the same volume of air at less than half the velocity, resulting in quieter operation.

Another consideration: long duct runs with multiple turns build up static pressure, robbing air flow and increasing noise. That is a concern of the mechanical contractor, but it is a factor architects should be aware of because the location of the outside discharge relative to the fan will have a bearing on its performance. If duct runs must be lengthy, the duct size should be increased. Rigid ductwork is recommended over flexible ducts, and it is important that high quality wall and roof caps be used.

Ventilating the kitchen

The primary purpose for kitchen ventilation, as it is in the bathroom, is moisture control. The kitchen is complicated, however, by elements not present in the bathroom.

Cooking grease is vaporized, becomes mobile and can remain in the air for several days.

Smoke is another potential by-product. Both grease and smoke are easily distributed throughout the home if not immediately and completely removed from the environment.

A common problem in the kitchen is that the cook top fan is not ducted to the outside. Range hoods and over-the-range (OTR) microwaves that are installed non-ducted are not ventilation devices. Their fans recirculate smoke, heat, grease and moisture from the cooking surface into the kitchen and throughout the home. Kitchen ventilation must be ducted to the outdoors.

Another common problem is that many range hoods are only used as light sources for cooking, nightlights and ambient lighting, largely due to undesirable noise levels.

It is for this reason that leaders in kitchen ventilation continue to reduce sound levels with the introduction of revolutionary new range hood technology —some earning HVI’s certified sound rating of one SONE. It can also be achieved by over-sizing the blower and then operating the range hood at a lower performance level.

In addition, external and in-line blower systems provide alternate means to remove sound from the kitchen while providing appropriate performance levels —up to 1500 CFM.