Trained Eye

 
 
 

Venting Kitchen Range Hood

Question:

Good Day. Our house is approximately 20 years old in Winnipeg . We are currently in the midst of renovations of our living room and kitchen. All our windows have been replaced with triple pane glass and we just had our furnace replaced with a high efficiency, vented to the outside, furnace. With our house becoming more airtight and not requiring furnace combustion air to ventilate the house with fresh air, I'm concerned about air quality degradation and humidity build up within the house. Our furnace is actually only one week old, so we don't know what the humidity will eventually level off to. I replaced a bathroom fan with a high flow unit last summer.

My question regards installing a new combination microwave/range hood over the stove in the kitchen. Our old unit re-circulated the air. We have been asking for advice on whether we should stay with a re-circulating unit, using the charcoal filter only, or have the unit vent to the outside. We so far have received conflicting advice with about half the responses saying vent outside and the other half saying simply re-circulate.

Can you please shed some light on this subject?

Thank you for your time.

Answer:

Your question is a good one for anyone who is contemplating or in the midst of kitchen renovations. Many older kitchens had poor quality recirculation range hood fans or none at all. Upgrading will provide a significant improvement in air quality in the kitchen.

The short, direct answer to your question is that you should definitely install a properly vented range hood rather than a re-circulating unit, as long as it is practical. Venting the kitchen range exhaust to the exterior of the home will not only improve moisture management within the home but will also reduce cooking smoke & residue in the kitchen. If you do a lot of frying and similar cooking, you will notice a marked improvement over the old unit. With your home more air tight than previously, indoor air quality issues such as smoke from cooking may become more of a concern than in the past.

The main consideration for venting the new range hood is ease of installation of the ducting and exhaust hood. If you live in a bungalow with easy attic access and a reasonable pitch on the roof, installation may be simple. If you live in a two-storey home or one with a more complex design, installation may be much more difficult. Walls or ceilings may have to be opened up to install the ducting or valences built to hide the metal ducts. To properly vent a range hood, a solid metal duct with a diameter ranging from four to six inches, or equivalent rectangular ducting, will be required. This will have to be installed and insulated up through the kitchen ceiling and attic or horizontally within the home, itself.

The first method of attic installation is the simplest, if attic access is attainable. This may be possible by cutting a hole in the drywall or plaster ceiling above the range hood, & connecting the appropriate size duct to the fitting on the unit. Once installed, the duct must be well insulated and sealed at the ceiling to prevent condensation and frost in the cool attic. This duct can then be connected to a vent hood mounted either on the roof or at a gable end, if one is present. The visible section of this duct may be hidden behind the upper kitchen cabinet, where the hood is mounted, or covered by a valence. If you have a more complex scenario, the venting issue will have to be addressed by the contractor to find an alternative solution.

The new range hood is essential for ventilation due to the reason you stated earlier. Through your recent renovations, you may have significantly reduced air leakage from your home by removing your old natural draft furnace & replacing your old, drafty windows. Because of this, you have inadvertently made your house air more humid by reducing the amount of water vapour that leaks out with the air during normal activity. The affects of this may be felt most in the kitchen and bathrooms, where moisture generation from cooking and bathing is highest. A lot of this kitchen moisture may have escaped through your old windows prior to the retro-fit, so a re-circulation fan may have been adequate in the past. Now that you have reduced that air and moisture loss, you may have to ventilate mechanically to achieve the same relative humidity level. The new range hood should be ideal for this purpose.

The interesting thing about advice you receive on various house issues is that you should always seek additional information to back up any verbal recommendations. That information may be collected from websites, brochures, construction books & periodicals or from individuals conversant with modern building science. Use of common sense when analyzing this data, along with your own knowledge will usually lead in the right direction. The first paragraph of your question leads me to believe that you already had the correct answer in mind and were simply looking for verification of what you already knew to be the proper method. That is exactly the approach I am talking about.