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Ventilation is very important when cooking as cooking often gives oven odors that can be offensive. When using a gas range or a gas cooktop it is absolutely necessary to use ventilation due to the carbon monoxide that will occur along with other toxic fumes. Ventilation is used to remove heat, humidity and odor. Ventilation units are rated in cubic feet per minute. (CFM) Proper ventilation must remove odor and smoke in about 5 minutes from the time one finishes cooking, after that time odor and smoke has contaminated household surfaces such as carpets, draperies and upholstery. That is why after burning something there is a point where no matter how long you run the fan the odor doesn’t dissipate, this is due to contamination.
Ventilation is available as a hood fan or a downdraft. The hoods work more efficiently due to the physics principle that heat rises. Hood fans come in various widths, heights and depths depending on the use and the look one is trying to achieve. Hoods are rated anywhere from 170-1200 CFM. One can have too much power, but usually consumers buy too low a power unit. A 1200 CFM Fan can empty a kitchen 12’ x 10’ x 20’ in 2 minutes. That translates into a lot of lost heat and therefore more energy consumption as the homes heating or air conditioning system works to restore the normal room temperature.
Hood fans come in a variety of decorator styles and finishes. You can make the hood a feature point in your kitchen. Blower units alone are available to overlay in wood to match your cabinets if desired. Check with local building codes to make sure that what you plan will pass building codes. Vertical clearances are extremely important where combustibles are used in finishes. Hoods are available as under cabinet, wall hood and island hoods.
Under cabinet hoods are usually 12” or less in height. Wall hoods are 12”-30” or higher. Island hoods can vary quite a bit. For a normal electric range a hood 30”-36” wide with a rating of 170-300 CFM. Going to a 36” rather than a 30” the added volume will help remove more odor and smoke as the larger hood has a larger capture area. The capture area is the volume of the hood. A flat surface made up of air filters will actually be less effective than a lower power hood with recessed filters as the flat surface will experience spill-over as smoke and odor curls around the front of the hood and rises to the ceiling. Most hoods have a variable speed and some even have sensors too automatically turn on the fan if the temperature in the hood increases to a point that it deems it beneficial to remove the heat.
Island hoods have higher power blowers 600-1200 CFM. The higher CFM rating is necessary due to the fact that the unit is drawing air from all four sides where as one installed against a wall is drawing from three sides. Island hoods require specialized installation so make sure the installer understands how to install it properly.
Downdrafts pull the air down so they require higher power blowers. The air is then vented through duct that run along the floor joists to the outside. Jenn Aire units have built-in downdraft between the two sets of surface burners. They are rated at 300 CFM. Other down drafts are either on a swivel type pop-up or a rear pop-up intake. Both retract when not in use. Do not use a downdraft behind a professional type range or slide in range as the intake will be so far from the front burners it will be in effective. Most Downdrafts are from 300-1200 CFM.
CFM is a very important specification along with the required duct size for exhaust. A 170-225 CFM unit requires a minimum 4” duct, Up to 450 CFM blowers require a minimum 6” duct, 450-900 CFM blower requires a minimum 9” duct and a 900-1200 CFM blower requires a minimum 12” duct. A unit higher than 170 CFM will require make up air. Make up air is where an intake duct and blower is tied into the vent system to bring in air to replace the air being removed by the ventilation system. This is very important so the home doesn’t have a vacuum and lack of oxygen causing health hazards as well as problems gas furnaces, hot water tanks and fireplaces. The vacuum caused without adequate make up air can draw carbon monoxide back down the furnace and hot water tank exhaust and into the house causing death if not rectified. The vacuum is also sufficient to draw smoke and ashes from a wood burning stove and fireplace back into the home. As you can see make up air is vital to family safety and proper operation.
In cooler climates make up must also integrate a built-in heater to heat the incoming air so it doesn’t cause the home to become uncomfortably cold. Make up air can be low cost as well as run several thousand dollars. Be sure to find out what your contractor will charge you for proper make up air for the unit before you buy it. Get it in writing so you don’t get a surprise bill at the end of the project.
The best unit on the market for both efficiency in removing smoke, odor and steam as well as safety is Vent-a-Hood. It is the only unit that is 100% fireproof. Any unit with filters has the potential to catch fire due to the trapped grease. Once a hood catches on fire it gets into the duct as some grease accumulates in the duct system. Vent-a-Hood has no filters, instead it has a grease trap. The fan turns a h high enough speed to force all grease entering the fan into the grease trap, so there is no grease build up in the ducting. The vacuum created will not allow a fire to enter the ducting. In fact if you were to have a fire on the cooking surface turn on the Vent-a Hood unit to draw the flame to the blower. It will help contain the fire. Do not do this with any other hood.
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