CAA-Quebec - Residential tips -

There’s nothing quite like the anticipation of tasting a dish that you’ve been slowly cooking to perfection. Cooking has its downside, though: odours, smoke and steam. Those mouthwatering aromas come with all sorts of toxic fumes and plenty of moisture, likely to affect the air quality in your home. It’s hard to escape them—unless you have an effective range hood.

Ducted or recirculating?
Whether the hood is of the classic, built-in or chimney type, its suction and exhaust capacity are the keys to its performance. A hood connected to a duct that draws foul air outside the house is more effective than a ductless (also known as recirculating) model. The latter filters the air and returns it into the kitchen, which means steam and some odours will remain.

The fan: A guarantee of performance
Everything starts with a quality fan. The first thing to remember is that blower fans (the ones that look like hamster wheels) outperform impeller fans (the ones with blades). They’re also quieter.

How much exhaust capacity do I need?
Exhaust capacity is usually expressed in cubic feet per minute (CFM), or sometimes in litres per second (L/s). The National Building Code of Canada states that the minimum exhaust capacity for a kitchen is 100 CFM (50 L/s).

Specialists say you should choose a model even more powerful than that, recommending a capacity of 100 CFM per linear foot of cooking surface. So, for a standard stove with a width of 30 in. (76 cm), a 250 CFM capacity hood is more appropriate. Why? Among other reasons, to counteract the reduction in performance caused by factors like the diameter, length and type of ductwork, and the number of bends in it.

Other determining factors
The distance from the cooking surface to the hood inlet is also a factor in performance. If that distance is greater than 30 in.—which is often the case if the stove or range is built into a central island—you will need to allow for an increased capacity of 100 CFM for every 3 ft of extra height. If you enjoy preparing grilled meats and other dishes that tend to produce a lot of smoke or steam, that’s another reason to choose a hood with a greater exhaust capacity.

If you own a gas range, the rule of thumb is 1 CFM per 100 BTU of cooktop output.

You don’t want to get carried away, though. In a particularly airtight house, or one containing combustion equipment, such as a wood stove or oil-burning furnace, a fan with a capacity in excess of 600 CFM can draw more air outside than comes in, leading to other problems, like negative pressure or chimney backdrafting.

Components: Quality above all
Settings, noise level, filters. . . The features of a range hood are more than just conveniences; they contribute to its overall performance. Here is a checklist of the main aspects you should be aware of.

Settings: The more the better
Controls with multiple settings mean you can adjust the fan power to your cooking needs—and also control the amount of noise generated by the hood.

Quiet, please!
Fan operating noise is measured in sones. When running at low power, around 100 CFM, the quietest range hood fans produce about 0.5 sones. That’s a clear advantage when you’re slow-cooking a meal over several hours. The quietest hoods are those with the fan located far from your ears—inside the duct, for example, or even outside the house.

Filters: For minimum maintenance and maximum performance
The characteristics of a hood’s filters are an important in ensuring maximum performance:

  • Filters that cover the full hood opening are more effective than smaller ones (grease tends to build up faster on smaller ones as well).
  • So-called micromesh filters do a better job of capturing grease particles, even on low power settings.
  • Keeping your filter clean is an excellent way to optimize hood performance. Stainless-steel and aluminum filters are dishwasher-safe, and should be cleaned every two months. Carbon filters, however, usually need replacing, every six months.

Tips for optimum installation
A good-quality hood offers superior performance—provided, of course, that it is properly installed. Here are some guidelines:

  • The exhaust duct should be made of smooth metal to maximize airflow and prevent grease from adhering.
  • The duct dimensions must be equal to or greater than those of the hood’s outlet, typically 3¼ in. x 10 in., or at least 6 in. in diameter.
  • The ductwork must be as straight and short as possible. Refer to the manufacturer’s installation guide for the maximum length of duct runs and equivalents for connectors.
  • Avoid 90-degree turns; it is better to smooth things out using two 45-degree connectors.
  • A very short duct connected to a hood installed against an outside wall should run upward a bit before turning to the outside, to prevent frost from forming in the hood.
  • The ductwork should be covered in an insulating sleeve over at least 5 ft of its length.

A seal of quality
Look for the Home Ventilating Institute (HVI) seal, which guarantees that the manufacturer’s exhaust capacity (CFM) and noise level claims have been subjected to rigorous testing by an independent laboratory.

Our thanks to Michel Robitaille, President of Les Échangeurs d’air Expair Inc., a member of
CAA-Quebec’s network of Approved Residential Suppliers, for his contribution to this instalment of Tips & Tricks.