Hello to all. I am a new member here, and this is my first post. I wasn't certain of which forum category this should be posted in - if it should be moved and I should repost the question, please advise and I will do so.
My wife and I just purchased a house in the Raleigh North Carolina area. It is a two-story 2700 ft.² Cape Cod style house built in 1986 with reasonably tight control over outside air infiltration, but it is certainly far from airtight. I am posting today to get some advice about how to proceed with installing a new ducted range hood over the island that is the center of the kitchen work area. The kitchen is wide open into the family room with total space in this combined room of roughly 4800 ft.³. At the far end there is a 10 foot wide x 8 foot tall opening into the living room, which has a wood-burning fireplace. We don't expect to use that fireplace very often when we are cooking but that is possible. We don't do heavy frying, but do lots of stove top cooking. I am a serious home cook. We do nearly all of our cooking at home, and don't dine out frequently.
The present configuration has a 30 inch slide in electric range in the center island, with a downdraft assembly, which I'm guessing is ducted out through the crawlspace under the house. I plan to remove this and install a dual fuel 30" or 36" Kucht range with gas cooktop. It is not a commercial range, but is built to a fairly rugged standard, and probably has maximum output of 60,000 BTU, not including the heat from the oven (if and when we are using it.) I've been doing lots of research on the required size of the range hood for this amount of cubic space, as well as the type of cooking that we plan to do.
My intention is to use an island range hood - probably a Z-Line - and run ducting through the ceiling joists to exit out the back of the house above the deck (the joists run perpendicular to the exterior wall - I should have an unimpeded run.) I'm guessing that my optimal duct material can be assembled in interlocking sections, then sealed properly with foil tape, and slid in from the outside to the point where I add and seal the elbow that comes down into the stack coming up from the hood. I have also considered a single run of spiral pipe but installing that myself would be challenging. have found it exceedingly difficult to find comprehensive or accurate information about performance and fire safety for this type of of configuration. I've ruled out any kind of flex duct, and will only use smooth surface rigid ducting. Having once been a commercial coffee roaster, and having previously installed positive pressure high temperature stainless steel ducting for my 12 kg batch size roaster, I believe in the importance of properly sealed ducting that can periodically be cleaned from the outlet end.
Here are my current questions (note - I have already done a fair amount of reading in this forum about residential range hood installs, and did not find the answers to these questions):
- Should I use double wall duct that has an air space between the outer shell in the inner liner? I know that this would mitigate my concern about heat buildup, but with 10 inch joists, it would mandate that I use 8 inch O.D. duct with 6" I.D for the inner liner. If this is the most prudent approach, is it worth the extra money to get the type of duct in which there is mineral wool insulation between the inner liner and outer shell? Do I need to install a thimble where the duct goes through the exterior wall?
- Is the amount of heat that will be passing through the ducting at a high enough level that I even need to use double wall? My coffee roaster ducting was capable of 500° sustained temperature, with a 2000° maximum for short durations. I'm guessing that the air being pulled through the hood will be no more than a few hundred degrees by the time it hits the first elbow to make it straight run toward the outside. By the way, the horizontal distance from the elbow above the range should to the outside of the exterior wall where the duct will end, is about 10 feet.
- I have seriously considered a range hood that has a 900 CFM capacity when the fan is on high. I had initially thought that 600 CFM would be more than adequate, but when I look at the total cubic footage in this large room, I'm inclined toward the larger capacity, even if I never have to put the fan on high.
- Our house is far from airtight; the clothes dryer is in a closet on the second floor, and the electric water heater is in a small enclosure attached to the outside of the house with its own entry and venting. Heating is provided by heat pump with an outdoor condenser system. That being said, I am concerned about the possible need for makeup air. Would it be prudent to add some sort of makeup air blower that is bringing air back into the room? I would have it coupled electrically so that it would automatically open a damper and be activated when the hood fan was running. Also - if I provide make up air, then where should it enter the kitchen?
- Note: I fully anticipate that I will require professional trade help to ensure that my needs are properly calculated, and also anticipate hiring an electrician at a minimum - possibly an HVAC specialist. I'm posting here because I want to fully understand the requirements before I consult with a professional in person.
I've been known to overbuild things in the past, and don't want overkill on this project, but we love to cook and plan to be in this house for 30 years or longer. I want to do it the right way!
I am not asking for nor interested in discussing any specific pricing here, as that is against forum rules (as I understand them,) but I am budgeting roughly $1600 for equipment and materials, will be doing as much of the installation myself as is practical, and will rely on paying the skilled trades person for the balance of work. Any and all input and feedback will be greatly appreciated!