Range hood ductwork questions
I’m a homeowner installing a ModernAire island range hood liner with an inline 8” Fantech blower and silencer in the attic. I’m using 8” rigid ductwork and I have a few questions about how to do it properly. I’ve tried asking someone at my local HVAC supply store but they weren’t much help :/
1) My attic is not climate controlled. Should I wrap the ductwork with fiberglass insulation? Or, since the blower is not wrapped, is it moot? I assume it will help reduce noise if nothing else.
2) The roof cap I bought has a built-in backdraft damper. Is it still recommended to install a damper at the ceiling level to keep cold air from coming down from the attic? Might that increase noise or reduce airflow when the blower is running?
3) Should I seal the ductwork with mastic, foil tape, or both? Any mastic recommendations?
4) Should I screw duct joints together or just rely on tape to hold them in place? I’ve heard screws can reduce airflow but i don’t know if it’s major concern.
5) Is there a recommended vibration reduction strategy when mounting the blower to the trusses? I have some Fantech mounting clamps but they aren’t meant to be used with a blower this size or larger. So I have to use the side brackets. I found some rubber and spring isolators on Amazon. I’ve also seen people use rubber tie downs but that feels a little sketchy to me.
Any help is appreciated!
Comments (7)
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Comments (4)Circular cross section is smoother (and therefore more effective and quieter) than rectangular. Plus your 7" circular cross sectional area is bigger (rectangular cross section area is 3.5x10=35" whereas your 7" diameter circular cross section area is 3.5x3.5x3.14=38"). Go for the circular 7" one if you can....See MoreAssembling Ductwork For Range Hood
Comments (3)Thanks. I offset the seams by three inches and inserted one of the three screws securing each section between the offset seams. I used Polyken 339 to seal the sections and seams. I used CCWI-181 on the 90 degree elbow seams. http://polyken.com.mx/Archivos%20Polyken/PDF/Industriales%20Trad/Fichas%20Tecnicas/FICHA%20TECNICA%20339.pdf http://www.ductoutlet.com/CCWI_181_Duct_Sealant_1Gal_p/ccwi-181.htm...See Moreductwork for range hood
Comments (4)Well, I'm one of those people who spouted off the top of his head about rigid ducting. I'm a health economist by training and self-taught in HVAC, electrical, plumbing, etc. So you need to take everything I say with a grain or two of salt :) There are different types of flexible duct. Heating often uses wireflex, which is insulated and the inner coating is plastic. This is good for forced air heat, but not for venting a stove. There is metal flexible duct-- like the kind you probably have behind your dryer. Then there is rigid metal duct. I did the venting for my hood and used rigid duct because my GC who was doing the framing, said that is what I needed. Perhaps it would have been fine to use flexible metal, I don't know. I have no data on which is sufficient for code. Flexible and rigid metal differ with regard ease of installation. Rigid is a pain to work with, so your contractors are likely to want to use flexible. I would take the statements that your hood is too big with a grain of salt. When I worked with Prestige to identify our blower volume, they recommended a min of 1000 cfm based on my needs. Unless your contractor knows your needs well, it is hard to make blanket statements about what is too little or too much. Sorry if I couldn't be of more help with regard to code specifics....See MoreWhich range hoods fit this ductwork?
Comments (5)"Are there alot of varying duct sizes that will restrict which range hoods I can choose? " You might be thinking about this backwards. It looks like you have a 7"-8" duct. You could then use anything that uses this size or smaller. And 3.5x10 can be converted like this one to a round duct of a similar area size. "How can I tell what size duct that is? Do I need to take a tape measure and wrap it around the outside to get the outside diameter or measure the size of the opening edge to edge?" Pretty much. I'd measure the duct size directly. I would also go check out where this duct goes outside the house and what shape the cap on it is in. I think replacing this is a fairly simple job, say 4 hours. You'll need a jig saw to recut the hole and some additional vent pipe, and some metal duct tape. Electrically, vent hoods are designed to be hardwired. However, the outlet for the microwave is nearby and can be reused....See More
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