In the continuing adventure of our vent hood, now that we’ve started closing up walls, it’s time to install the hood. The ventilation system is one of the most built-in appliances in the kitchen. In a restaurant kitchen, the vent system is incredibly complicated and functionally a large portion of the structure above a kitchen. In our kitchen, the story is only marginally different. I don’t know if I’ve posted this before, but there was no preexisting ventilation system in the kitchen. Directly above the kitchen is a bedroom, so it wasn’t very realistic to run a vent line up to the roof. The solution was to run a line horizontally to an exterior wall. The good news is that with all the construction, it was real easy to build a soffit into the new wall I was putting up so I didn’t need to cut into joists or anything crazy.
The complicated part of this particular project is that the design of our kitchen is a little at odds with itself. The vent hood is suspended above the open bar area, but the vent line runs horizontal to the hood. This is tricky because the hood needs to be supported structurally from above, but the ductwork needs to run out of the back of the system. The world of residential hood systems is roughly divided into island units and wall units. Island units are suspended from the ceiling and the ductwork goes straight up. Wall units are affixed to the wall and the duct work goes out of the back. You can see my predicament. The solution was to find a vent hood whose structural design would allow the right modification. Specifically, I needed to be able to cut a hole in the back of an island vent.
Luckily, the hood we ended up with worked out just right. The motor housing sits on top of the stainless steal fume hood. It attaches to a flexible duct that connects to the metal duct work I installed. It’s supported by a bracket that is shaped like an upside down “L”. The top of the L screws into structural wood while the bottom of the L mounts directly to the motor housing. Normally all of this is enclosed in a stainless steal chimney. For my mod, I cut a hole in the back of this chimney and ran the flexible duct out of the back. I also partially built the chimney into the soffit to conceal the mod. In the end, I think it has a cool built in look, though it’s going to be near impossible to remove/replace without tearing out some walls.
Another add-on project for installing this hood was a make-up air damper. A few years ago, Ohio adopted a code that requires any home ventilation unit that pulls more than 400 cubic feet of air per minute to include a system for replacing lost air. The idea is that in new construction that utilizes air-tight building techniques, if you have a vent that is pulling a large volume of air out of the building, you could potentially depressurize the structure. The result is you get a backdraft through your other vents that could cause CO from your hot water heater or furnace to be pulled into the house. Now, something like that isn’t a real concern for us. Our hundred year old house probably leaks air like a swiss cheese balloon. But code is code. My choice for a make up air system was to install a motorized damper and a vent line running to an outside wall cap. The damper system is really neat. It’s a simple motor attached to a pressure switch I installed in the duct attached to the fume hood. When the hood is turned on, it blows air down the duct and the air pressure triggers the switch. The switch opens the damper door in the new vent line in the basement. That vent line is plugged into the cold air return for the furnace. Outside air can then be pulled into the furnace and duct system for the whole house.
The make-up air return system was a bit tricky to install. We were lucky in that there was a short run, maybe 5″, from the cold air return trunk and an exterior wall. So it wasn’t a lot of new duct work to install. But it did mean cutting into the rim joist, just above the foundation wall. 5′ of very old lumber takes a long time to cut through. Once I had a hole, the second problem to tackle was the wall cap issue. The wall cap I bought only had a 5″ neck. Normally this is fine, but in this case, I couldn’t attach the duct to it from the inside. Instead, I had to assemble the duct and feed it through the outside of the house. There were a lot of trips in and out as I’d push the duct in a few inches then have to run down into the basement to adjust the angle. In the end, it took about half a day to install, but it works and I even learned a few things about low voltage wiring.