range hood installation question

I want to install a range hood on the same horizontal vent hole as a bathroom fan. there's no hole for either right now and I don't feel like making two holes.
the bath fan duct is 4" in diameter. what happens if I connect a range hood to a 4" pipe?
also, I bought the flexible duct of aluminum/poly for the hood and a vynil one for the fan (easier to work with than the solid aluminum one). the aluminum/poly one says "fire resistant" can it be used with the hood?
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Codes vary by location, but not by much so the manufacturer of the equipment will have a good idea. If you hook it up wrong and there's a fire and an investigator finds ashes of the wrong type of material, your claim will be denied. Merry Xmas. -B

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I'm more interested in the diameter of the pipe not the type of pipe.
also the fire will not be started by the tube, it will start somewhere else and by the time it reaches the tube inside the wall, everything else is burnt already
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I hope you are not planning to use the same vent for both the bath and range hood. Big bad idea.
I hope you are not removing a bath fan to use the vent for a range hood, bath vents are code in many areas and can reduce moisture damage to a home.
I strongly suggest not considering anything other than a solid metal vent material for a range hood. They are subject to the occasional fire. Ask you local fire department about this. Also ask you insurance company who may not want to pay off if you have put non-code materials into your home. In this case your insurance company has your best interest in mind.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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we're renovating.
there's currently no bathroom fan and no range hood vent. it's an old house.
since I'm doing most of the work (due to lack of money) I didn't feel like doing two holes in the wall (the wall is a 4" thich piece of wood followed by 2" of brick) so I was thinking of connecting both hood and bathroom fan to the same hole.
I was wondering if a range hood is OK if it goes through a 4" pipe instead of 6" (even if I choose the aluminum flexible pipe, which is solid aluminum, the bath vent hole is still 4")
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Sure if you're a hack.
If it was "ok" for a 6" pipe to be reduced to 4" AND combine it with a bathroom exhaust pipe, don't you think everyone would do it?
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well I'd like to know WHY, and so far nobody's given any reasons.
"becasue nobody else does it" is not a valid reason.
what is wrong with connecting two pipes via a T connector and putting flow regulators on the pipes to make sure air from the kitchen doesn't go into the bathroom and vice versa?
other than the fact that 4" might be too small for a 200CFM fan, what's wrong with connecting two pipes?
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Ok..one, its illegal. You say you are renovating...so do it right the first time.

You are right...however, no one else does it for several reasons.

Its hackish, illegal, wont work for long, etc...

ok...you want a list?
1- Against code. You say you are renovating. You now have to go with current code. 2- Your vinyl bathroom duct is against code. Anything now must be in metal duct, flex is ok under 14 feet. 3-Your kitchen hood fan duct must be, in any case, to code. 4 inch flex isnt. 4-I can bet even the instructions with the fan tell you not to reduce the diameter of the run of duct. 5-Your idea of a T is illegal, and has been for years. 6-Flex duct, of any diameter on a hood range violates building code in every juristiction. 7-Your T, even if it WAS legal, would allow for nothing more than the movement of the grease laden air to the bathroom after a few weeks when the dampers you THINK are airtight stick due to the grease buildup. 8- Your fart fan will also just move air to the kitchen for the same reason. 9-100CFM is required for a kitchen vent...and you wont get it with a fan on one hood in a 4 inch duct..period. 10-Independent system required Section 501 of the Mechanical code, section 501.2 to be exact. 11-Section 505 of the Mech Code Domestic Kitchen exhaust equipment: Where domestic range hoods and domestic appliances are equipped with exhaust located within dwelling units (read: inside the home) such hoods and appliances shal discharge to the outdoors through ducts constructed of galvanized steel, stainless steel, aluminuim or copper. Such ducts shall have smooth inner walls and shall be air tight. 12-11 good reasons above. 13-It takes less time to do it correctly, and smartly, and not hackish, than it does to throw a mess together, to do over later. 14-Try to sell the home and let an inspector find it...here, you are automatically responsible for fixing it.
Now...there is nothing wrong with connecting two pipes...just not the two pipes you are wanting to.

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I don't think it is a good idea to combine the two. First they are not like sources. The are situations where two bath vents may be combined, but not post fan. I can't think of any situation I would recommend combining a bath and kitchen vent.

The question of size has to be answered by the manufacturer of the range. Check the documentation for the vent. I would have to guess at best it would reduce the effectiveness and increase noise, at worse it may overheat the motor and cause a fire. (not likely in my opinion buy possible.
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Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Hi,

Combining different vents/exhausts is never a good idea.

Range hoods usually use 3&1/4" X 10" duct or 6" round.

Solid metal is best, check the range hood manufacture instuctions for what thye recommend, hate to see you void any warranty by using the wrong ducting!
jeff. Appliance Repair Aid http://www.applianceaid.com /
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Other than not code in any area now, and thats ANY, its really a waste of your time.

It wont pull...for starters.

Foolish. Every bit of greast will stick to it, and make one hell of a mess...and a fire hazzard. There is a reason that range hoods must be ducted in hard duct, of the proper diameter....the same that the start collar is on it.

Also now illegal. The ONLY duct that is legal by IBC and IMC is: Metal duct for bathroom fan runs, metal flex can ONLY be used on 14 foot or under runs. Over 14 feet, the run must be made in hard metal. Period. No exceptions.

No. And honestly, I dont know why you would even want to try. Make the second hole. It takes only a few moments, even with a brick facshia, and then, its done right the FIRST time.

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