Installing a range hood DUCTWORK

Press, 12 June 1986, Page 14

Installing a range hood DUCTWORK

(By

A. J. HAND)

For the past 15 years, our kitchen has done without benefit of a range hood. During the summer, cooking heat would build up to tropical levels. And without a fan to draw off steam and spattering grease, our walls slowly began to resemble a tar pit.

Finally, I decided to do something about it. I had two choices: a non-vented range hood, or one that vents to the outdoors.

Because they require no ductwork, unvented hoods are easy to install. But even though the best unvented hoods have very efficient filters to trap grease and cooking odours, they cannot exhaust hot air, so they really only solve half the problem.

Vented hoods, on the other hand, are more difficult to install because they require ductwork to lead exhaust air outdoors, but they do get rid of heat and grease. We decided to bite the bullet and install a vented unit, ductwork and all.

Once you have decided on vented vs unvented, you have to choose a specific model. The more you spend, the more air flow you will get, and the more effective the hood will be.

When shopping for the hood, ask to see the installation instructions. If you cannot understand the instructions, look for another brand.

The instructions will tell you what supplies you will need to complete the job — usually ductwork and wall or ceiling caps. The shop that sells the hood probably will not have the ductwork you need. For that, you will have to go to a sheet metal

shop — the kind that specialises in making and installing ducts for heating and cooling systems. But before you buy any ductwork, plan out the path you want the ducts to take. After you have chosen a route, do some exploration to make sure the route will work. Cut or drill observation holes in the walls or ceilings along the route, and check for any possible snags.

When I installed my hood, I neglected to do this. After I bought all my ducts I discovered that my chosen route was blocked by a run of plumbing, so I had to reroute my whole installation, and buy extra ductwork.

The simplest route to take is straight out the back of your hood, and out through the wall to a wall cap. This installation only works if your range sits against an exterior wall.

If your home is a single-floor type, you can also lead the cut up out of the top of the hood and on up through the roof. As shown in the sketch, hoods have knockouts that let you run the duct off from either the top or the back of the hood, whichever is easiest. Some installations can get complicated. In my case, my range was on an interior wall. I had to run the duct out the top, up to the ceiling, turn to run across the ceiling, then turn up and go out through the roof. Ideally, you want to keep the run of the duct as short as possible, with as few turns as possible, but in my case, I had no choice. Most hoods are designed to take a standard rectangular duct (about B.scm by 25cm), but if you like, you can also use a 15cm round duct. You will need a transition fitting to adapt the round duct to the rectangular opening in your hood, but any good sheet metal shop will have these in stock.

Once you have your route mapped out, go to a sheet metal shop and get

the supplies you will need. A rough sketch of the installation will help the sheet metal shop pick out the right parts. These may include straight sections of duct, elbows for making turns, and roof or wall caps which have dampers to prevent backdrafts, plus screens to keep out pests. To install the ductwork, start at the exit end and work backk to the hood. The most difficult part of the job is cutting the hole through the roof or wall.

Locate the four corners of the rectangular opening, drill through the wall or roof at each point to mark the position clearly.

Then use a sabresaw with a long blade to cut the opening. Make it about 6mm oversize all round to make fitting easier. When you install the cap it will cover the gap.

When your run of duct approaches your hood location, install the hood. It should go directly over the range, and anywhere from about 45cm to 60cm above the cooking surface.

The lower it is, the more effective it will be, but if you go too low, the hood may block your view of the range. Most hoods screw to the bottom of an over-the-range cabinet. If you have no such cabinet, do as I did. Build a boxlike soffit from the ceiling down to the desired hood height.

I framed mine with pine, then after the hood was all hooked up, I covered the soffit with drywall and painted it to match the rest of the kitchen.

It is best to use screws for all this work — rather than nails. Screws are stronger, and if you use nails you often find yourself knocking apart the early stages of your work as you drive the nails in later stages.

Wiring: Most hoods are designed to be wired direct, so you will need to run a circuit to your hood. If you do not know how to do this kind of work, it is best to call in an electrician.