Since these are both exhaust flues and ducts, no clearances are required. Clearances are only required when an air intake vent, door or window opening is located near a flue exhaust, vent hood or dryer duct terminal. You do need to consult your building code office, however, because there has been a change in some mechanical codes this year that require the installation of 'make-up air' ducting when using an exhaust hood rated over 400cfm. If you do not already have a make-up air intake duct, your code may now require one, and if it doesn't, you should still consider adding make-up air anyway.

I am also getting this code along with "lint filter" signal light.We have new house,have had the dryer for 3 months.It has been doing it since day one- but more so lately.We had the plumber come in and check if the exhaust vent was clogged(as is gas dryer). It was not- he pulled off the vent exhaust and tested the dryer unvented-it was still giving that same code. So that proves the ventilation is not the issue,but they did check the exhaust to the outside just to be sure & it was not clogged. I had an independent repairman here to check it-first, he points to the ventilation.Say its too long. Mine goes out of dryer 45 degrees down into floor then one 90 degree and straight out (24Ft.) to outside.I believe what runs thru the floor is rigid.Louvers of outside vent seem to blow open unobtructed.So he said he'd try and order me a new sensor. Then Bosch repairman was here.He also commented the ventilation setup is too long (Although the book allows up to 48 feet).He said its not sensor because that isn't used on timed cycle.He said try & wash filter because of the dryer sheet residue.If that don't work will try a new "controll". So I washed the filter with soap and hot water and tried it and its still doing samething.So I called and told them to order the controll.Wait & see. Sorry so lengthy!

A good suggestion by weedmeister. The answer to resulting air flow rate will depend on the blower chosen as well as the restrictiveness of the ducting. For example, the Wolf 801640 Broan-NuTone exterior blower flow drops to 300 cfm at about 0.7 inches w.c. (some of which includes fan housing loss). The Broan 331H exterior blower is similar in performance. But the Broan RM325H interior blower drops to 300 cfm at 2 inches w.c. http://www.broan.com/common/productDigitalAssethandler.ashx?id=c6cb8514-86ed-49f2-bb1e-9c5443ad495c The former two blowers are intended for 10 inch duct, while the latter is intended for 8-inch duct. Fan curves for in-line blowers may be found as tables on Fantech's web site. At 300 cfm, I would expect the hood baffles to cost around 0.3 inch w.c., although this is a stab in the dark as this information is almost never available except for commercial hoods where HVAC analysis is expected and required, and in any case the commercial filters will have been optimized for pressure loss and. grease collection efficiency, while residential filters will have appearance and fabrication cost dominating the design. (A higher-end baffle filter link) http://www.filtersales.com/pdf/flame_gard_grease_filters.pdf If you consider your ducting with its bends and higher loss due to being rectangular to be equivalent to 40 ft of 7-inch round duct, then at 300 cfm the loss might be around 0.4 inches, w.c. (This can be calculated using on-line calculation tools; I am just WAGing it here.) The MUA is another source of pressure loss. Even a window screen can be significant, and a 3M furnace filter in line with an intake air duct will be higher yet for the same area. Usually, one needs blown MUA if the house pressure relative to the outside is to be kept close to zero. This is not needed for safety in this case. So, whatever blower is selected for this application, it should be of the higher pressure class and overcome an inch or more static pressure loss at 300 cfm for a high probability of success at achieving 300 cfm. Even if possible, enormous duct sizes are not optimal; choose ducting size to set the air velocity at the CFM achieved to at least 1000 ft/min (higher can be used in warm ducts). kas

Who cares what the builder thinks. This is a TERRIBLE Install and a very poor choice of venting location. It would violate code here. Any roof vent of hot emissions (furnace, dryer, etc.) that is through a roof must be at least four feet above the roof line AND four feet away from any portion of the roof that is the same height or higher. A proper vent cap should be used such as this: Or this: What is on there now looks like a standard roof vent. That is designed for passive venting of the attic space, not a forced air exhaust like a dryer. The problem now is that they cut the vent pipe very short so a proper vent cap may not fit. A dryer vent should have no screen (they catch lint). It should have a self closing flap or hinged door that opens when the dryer blower comes on. When the dryer shuts off it should fully close to keep critters, insects and the elements (rain, etc) out of the vent pipe. You will also also need to crawl up on the roof at least once or twice per year and check for clogged lint. You will also need to look in the attic several times per year to make sure the vent pipe has not come loose. If they wont fix it I would find a Building inspector and ask if that is code. I highly doubt it. Where is the dryer located? If it is in a closet or a small room then it may not have enough makeup air for what it is tying to push out the vent. If it is in a closet, leave the door open. If it is in a small room leave the door open or open a window in the room if it has one. If this prices the drying time then you need to supply more makeup air to the location where the dryer is installed. You would do better with a condenser or heat pump dryer that is ventless than that setup. Here is a Charleston home inspector who discusses this very topic: http://www.summerville-home-inspector.com/content/charleston-home-inspector-discusses-dryer-vents