In order to maintain a healthy environment in your home, you need to remove stale air and replace it with fresh air. Because modern homes are well insulated and sealed to optimize efficient use of energy, natural ventilation is not up to the task and additional ventilation is needed.
The most effective strategy for providing supplemental ventilation in a home is a combination of local, intermittent ventilators for dealing with short lasting problems like bathroom moisture and cooking smoke, plus a continual low speed, whole house ventilator fan.
One area that can benefit from intermittent ventilation is the kitchen. According to the Home Ventilation Institute, a residential kitchen’s ventilation rate should be fifteen air changes per hour. For commercial kitchens, one complete change of air every two minutes is the norm. The only way to achieve such rates is with exhaust hoods, also known as range hoods. There are two main kinds of range hoods; downdraft and updraft.
A downdraft hood pulls air downwards away from the stovetop. While they have the benefit of taking up less space than updraft types, downdraft hoods necessitate using a larger fan motor and cannot effectively capture steam or smoke from tall pots or front burners. Updraft range hoods are located over the stovetop and are preferable, since hot air’s tendency to rise works in their favor.
Range Hood Installation
Updraft and downdraft exhaust hoods can both be hooked up to a duct for venting exhaust to the outside. They can both also be installed in non-ducted recirculating configurations. With the recirculating type, air is drawn through a filter, typically activated charcoal, and then expelled back into the kitchen. For natural gas stoves, a ducted rangehood is mandatory, since filters are unable to remove the combustion products that gas stoves produce.
Recirculating cooktop rangehoods should only be used if it is not possible to install a ducted hood or if the house is constructed such that a ducted exhaust could cause backdrafting. A backdraft condition is caused not enough indoor air, which creates a partial vacuum relative to the outside air.
During a backdraft, the flow of air is reversed and combustion products are forced back into the house. If your gas range is having backdraft problems, a ventilation contractor can inspect the situation and supplement the incoming air supply with draft assist fans or vents.
Popular updraft rangehoods are attached to the wall or the underside of cabinetry directly above a stove. It is important to locate the hood correctly, observing the proper height above the stove. The bottom of the hood should be from twenty four to thirty inches above the cooking surface of the stove.
Size of the hood is also important; for stoves adjacent to walls, the hood should be at least three inches wider on each side than the cooktop as well extend forward enough to cover the front of the stovetop. For kitchen island installed stoves, the hood should project two to three and a half inches past the front and rear edges of the stove as well as three inches beyond each side.
The fans used in range hoods can be either the squirrel-cage centrifugal type or axial propeller type of fan. Centrifugal fans move air with high force and are used in hoods that have long ducts with multiple bends. For rangehoods connected to ducts with short runs with fewer bends, axial fans are more suited, since they move large volumes of air but at lower speeds. Ducts used are of galvanized or stainless steel material and can be either round or rectangular.
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