Elbows OK in Kitchen hood exhaust?

[CompleteNewb]

We have a house with very steeply sloping roof (2nd floor rooms have that slanting ceiling on both sides, if that tells you anything). The kitchen is on the 1st floor, so please keep reading.

I fry and sear a lot in the kitchen when cooking, so every kitchen surface gets coated with that nasty, greasy residue. So, my plan is to install a hood over the stove. The problem (or so people have told me) is that the hood exhaust needs to stay straight all the way to the outside of the house; no elbows.

Unfortunately, the stove is on the wrong side of the kitchen; the stove is against the wall that's leading to the inside of the house, not against the wall that's the outside of the house. SO, if my hood exhaust goes straight up with no elbows, it will need to got through the 1st floor ceiling, then the "cubby space" (behind the little straight wall ofupstairs, where you can see rafters) of the 2nd floor, and up through the roof of the house about haflway down the roof as seen from outside.

My hope was, rather than getting up in all that cubby nonsense, maybe I could elbow the exhaust as soon as it breaks into the ceiling of the kitchen, go about 5' laterally (horizontally, along the ceiling, the width of the kitchen), elbow again to go up, and come out through the roof on the other side of the kitchen (avoiding cutting through floor of upstairs cubby AND roof of upstairs cubby), which would have the exhaust coming out near the rain gutter on the outside of the roof.

Several people have told me that kitchen hoods should NOT have ANY elbows, should be a straight shot from stove up to outside. My plan has 2 (count 'em, two) elbows.

Are the people that have advised me right (they are not necessarily contractors, they are just general handymen)? Will a hood not work well w/

2 elbows in the exhaust? If I used 2 elbows, would I need additional fans at every elbow to help exhaust? Or would the fans not even help? OR, would having the 2 additional fans be more complicated than just running straight up through the ceiling/floor? Or am I thinking incorrectly that my plan saves some work, and it would actually be EASIER to go through everything going straight up?

Any advice appreciated. I realize a good solution would be to stop frying all the time, but I'm one of those "die happy" types.

Thanks for reading, and in advance for any opinions, advice, etc.

A Complete Newb (and first-time homeowner)

[Grandpa]

From my personal experience - do NOT impede the exhaust flow in any manner. That includes elbows, extra dampers, extra fans, or even screws that stick into the air flow. Any hiccup in the air flow is just asking for a puddle of that greasy grimy residue that you are trying to get out. Then the grimy residue will catch dust, which will further impede the flow depositing more residue which will collect more dust, et cetera. Eventually and especially if you cook the way you describe, your vent will be so restricted that it will become a candidate for a flue fire of enormous proportion. Advice: Move the stove if you can't get a straight shot out. Flue fires are just scary.

[Bill Stock]

We had the same problem as you, kitchen entirely on inside walls, except for the solarium.

The original 4" vent (not connected) went down the wall, through the basement and out a 2" vent through the side wall. There must have been about

3 elbows and 30' of pipe.

We ended up installing 4 large radius elbows and about 20' of pipe. But because we used 3x10 duct instead of the 4" duct that was there before the results were very good. Not ideal, as you indicated, but there were not any other simple options.

[Phisherman]

The longer the run and the more turns, the greater the turbulence and less air flow. Plus, you may lose cabinet space. Ideally, moving the stove to an outside wall is the solution. But that may not be practical nor cost effective. You can...

Install a hood fan that will move more air; ie, has a higher cfm. The tradeoff here is that a more powerful fan produces more noise, so get a fan that has several speeds. Panasonic makes powerful exhaust fans that are less noisy, but they cost a little (30%) more.

Use larger diameter piping. The larger cross-sectional area will allow more air flow. The downside is that you need more space to install it. The piping must be sealed properly, else you may lose air flow, perhaps equivalent to adding another elbow.

Avoid putting a pipe though the roof, if at all possible.

[Pat]

My house is pretty old. The previous owners remodeled sometime in the

60s, I would guess. Stove is on an inside wall. Vent goes up to ceiling, turns, crosses kitchen and goes out. Works fine. Never a problem.

[dpb]

CompleteNewb wrote: ...

...

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Straight shot desirable, not mandatory. The spec's for the exhaust fan will prescribe the amount of outlet pipe length, etc., they can accommodate.

Not being able to see the actual building, which is actually "harder" is impossible to determine and differing folks might have different opinions on the degree of difficulty, anyway. I would say if you were to chose the "jog" over that using two 45's to make the transition would be much better than two 90s.

As for the roof exit, there are undoubtedly a multitude of roof penetrations already, anyway. Properly done and flashed, they're not a problem. One more won't make any difference although you might consider where it is from an aesthetics viewpoint. That, in fact, might end up being the deciding factor on which route to choose.

As for the function, if your cooking produces as much grease as you imply, you probably want more than just a simple exhaust fan but something more like a commercial exhaust that includes a grease trap. Otherwise, the buildup problem could actually be a concern over time.

[bill allemann]

One problem with a straight vertical vent, if you have cold winters, is that you'll get bodacious cold downdrafts coming through it. The backdraft dampers are pretty basic and leak a bunch.

The horizontal runs that are in a lot of kitchens reduce the effect considerably.

[Joe]

FWIW, I installed a Broan midline range hood recently and it works just fine vented outside through 7" pipe with one elbow and about an

11 foot horizontal run. IIRC, Broan recommends venting through a wall, so you may want to call their customer service or review some literature for best practices. In our case the pipe neatly exits through a boxed-in area above the kitchen cabinets. HTH

Joe

[mm]

We all have hoods that just circulate through a filter (carbon?) that costs 15 or more dollars to replace!

Except for 1 of the 100 townhouses which was owned by the electrician who wired the other houses. He had lots of extra lights, along his sidewalk etc, plus one could see the vent above the sliding glass door in front, He had obviously vented the hood to above the kitchen ceiling, then 12 feet forward to the front wall, and vented over the SLDoor. He was** an immigrant, so I don't know if he allowed for the greasy dirt factor or not. Not all stove fumes have grease in them, do they? **Still alive but moved to a bigger house.

[hallerb]

this came up some years ago at a local public school, about their kitchen. they had fire marshalls, firemen, architects, insurance reps, it became a circus.

final conclusion, elbows are fine. they had 8, kitchen was a interior one.

leave some access areas, and blank covers so you can occasionally inspect the inside of the line and clean if necessary.

I like the multi speed fan, low for steam or minor odors, high for frying.

have you considered down and out thru the basement?

[mm]

This sounds a little snotty on my part. I didn't mean it that way. I just mean that I know the country he comes from and even fancy houses don't have range hoods there. One usually doesn't think of every little thing the first time he does something.