Range Hood and Ventilation

Getting Cooking Air Out of a House That Stays Shut

In most of the country a smoky kitchen gets fixed by opening a window. In Scottsdale, from roughly May to October, that is not an option anybody takes. The house is sealed, the air conditioner is carrying the load, and the heat, grease vapor and moisture from the cooktop stay inside. The range hood is the only thing in the house designed to deal with that, and in a surprising number of kitchens it is not doing the job.

We see three common situations. The first is the recirculating hood or over the range microwave that vents back into the room through a charcoal filter. It traps some grease and does nothing about heat or humidity. The second is a hood that is ducted, but badly: flexible foil duct, too many turns, a run that ends in the attic instead of outside, or a wall cap with a damper that has rusted open. The third is the opposite problem, usually in newer custom homes in DC Ranch or Desert Mountain: a large professional style hood installed in a tight house with no way for replacement air to get back in.

Capture Comes Before Fan Power

People shop hoods by fan rating, and the fan rating is the least useful number on the box by itself. A hood works by catching the rising plume of hot air and smoke, and that depends on three things before the fan even matters.

• Width. The hood should be at least as wide as the cooking surface, and better a few inches wider on each side. The plume spreads as it rises.
• Depth. A shallow hood misses the front burners, which are the ones most people use.
• Mounting height. Every hood maker specifies a range. Mount it too high for the look of it, and a strong fan captures less than a modest one set at the right height.

A wall mounted hood against a backsplash captures better than an island hood with the same fan, because the wall blocks cross drafts. Island hoods over big ranges in Pinnacle Peak and Gainey Ranch kitchens usually need to be larger and stronger to perform the same way.

The Duct Is Where Most Hoods Fail

A hood is only as good as the path the air takes out. We run smooth rigid metal duct at the size the hood maker calls for, with as few elbows as the framing allows, sealed at the joints and terminated at a proper roof jack or wall cap. On single story ranch homes in south Scottsdale and McCormick Ranch, a roof route is often straightforward. On two story homes and in condos near Old Town, the route may be long, awkward or not permitted by the building, and we will tell you when a ducted hood is not realistic rather than sell you a fan that cannot perform.

The exterior cap deserves attention here. A wall cap with a weak or stuck flap is an open hole during a monsoon dust storm. We use caps with a damper that closes positively and sits where the prevailing wind will not force it open. In HOA communities a new cap on a visible elevation may need design review, so we plan the location with that in mind.

Make Up Air

Every cubic foot of air a hood pushes out of a sealed house has to come back in from somewhere. With a small hood the house finds that air through ordinary leaks. With a large hood it cannot, and the hood either loses much of its rated flow or pulls air backward through places you do not want, such as a fireplace flue or the gaps around an exterior door, bringing dust with it.

Codes set a threshold above which a hood needs a dedicated make up air system, and the exact figure depends on the code edition the city has adopted. We confirm it during planning. A typical solution is a dampered supply duct wired to open whenever the hood runs, sometimes paired with a filter so the incoming desert air is not simply delivering dust to the kitchen.

What a Ventilation Job Includes

• A look at how you cook, what the range or cooktop puts out and where the current hood vents
• Hood sizing, mounting height and a duct route drawn before anything is ordered
• Rigid duct, sealed joints and a damper cap on the roof or wall
• Make up air when the hood size calls for it
• The electrical circuit and switching the hood needs
• Permit and inspection where the work requires it

If the rest of your kitchen is in good shape, a proper hood and duct run can be a job of a few days, and it changes how the whole house feels in July more than new cabinets would.