Routing Kitchen Hood Vent Question

[JZ Bowmannz]

Hello Everyone,

I am in the process of remodeling the kitchen, and running into a difficulty installing the vent of the hood. Would like to ask for suggestion / help with your expertise.

Here is the kitchen layout. The vent line direction is going towards right where the wall/window is.

[attachimg=1]

The wall that the hood will be installed on is a regular 2x4 stud wall, which does not provide enough space for the vent.

[attachimg=2]

The ceiling joists (floor joist for second floor living space) are running in "in-and-out" direction, which will be painful to feed the vent line through each one (possibly 5 joists total), plus it will weaken the integrity of the structure I believe.

[attachimg=3]

Is there any good idea / decorative design to build up a small section of soffit both left and right of the hood as solution? Or do you guys have better solution? My wife really likes to have a stainless steel hood, so a build up hood might not be a good alternative.

Any suggestion will be appreciated. Thanks. JZ

 

[Dane]

Well, as you've got it drawn- the hood is too high above the range to be effective.  If you lower it a bit you could also run the duct through the back of the top cabinets to get an adequate pipe size to get enough flow to be useful.  So many hoods are useless because of either the height of duct design.  A shame to blow 1000 bucks on something that doesn't function.

 

[JZ Bowmannz]

Well, as you've got it drawn- the hood is too high above the range to be effective.  If you lower it a bit you could also run the duct through the back of the top cabinets to get an adequate pipe size to get enough flow to be useful.  So many hoods are useless because of either the height of duct design.  A shame to blow 1000 bucks on something that doesn't function.

Thanks for the idea, Dane. If I follow your idea, should I build up something above the window as well just to keep the same flow? As everything else will be up to the ceiling.

And does anyone know the space needed for the vent line? is it 6"?

Thanks.

[attachimg=1]

 

[leakyroof]

The CFM rating of the hood system will determine the size of the piping needed. We have a 1200 CFM hood in our kitchen that has 2 fan units in it, exits directly up and then out an exterior wall through 8" diameter ductwork.  We installed the height of the hood per manufs. recommendations, and on its highest setting, will easily handle grilling work on the stove top if we need it.  Don't forget to think about Make-Up air if your fan pulls many CFMs.
  A tight /newer house can run into trouble if you're exhausting many CFMs[ fumes/appliance exhausts get sucked backwards into the house.]

 

[Dane]

Range hood ducts are almost never less than 8" and the more elbows you add and the longer the run is, the larger the pipe diameter needs to be.  The type of cap you put on the outside also has an effect on flow.  The hood should have a duct calculator in the specs, if not the manufacturers website will.

 

[Gregor]

Having been through the process in my kitchen:

I didn't have had the problem (induction stove), but yours looks like gas (at least on the drawing), so you need enough clearance to the hood (also it should be cleaned often enough) so it won't ignite by accident. Best check the manuals of the stove and the hood for more information about this.

For the duct: Do as less turns as possible, while keeping the length as short as possible and use a big duct. I have seen quite some extraction hoods with >1KW motors in them that didn't suck (as they should) because their performance is killed by the piping between them and and the exhaust being excessive.

For the exhaust: I used Naber GT 150 as a passive system (opens/closes by pressure from the hood), works nicely and when the hood is off cold air won't come in through it in winter.

To make it visually nicer I would go for another cabinet where the hood pokes out of at the bottom:
[attachimg=1]

Should you still be in the planning stage: have you thought about putting the stove in the corner?

 

[JZ Bowmannz]

The CFM rating of the hood system will determine the size of the piping needed. We have a 1200 CFM hood in our kitchen that has 2 fan units in it, exits directly up and then out an exterior wall through 8" diameter ductwork.  We installed the height of the hood per manufs. recommendations, and on its highest setting, will easily handle grilling work on the stove top if we need it.  Don't forget to think about Make-Up air if your fan pulls many CFMs.
  A tight /newer house can run into trouble if you're exhausting many CFMs[ fumes/appliance exhausts get sucked backwards into the house.]

Didn't even think about the make up air, very good point. Where should I pull the air from and through? It's a two story house with basement, built in 1998, and the house was build by a very good builder with good material, is fairly air tight. Thanks.

 

[Gregor]

Didn't even think about the make up air, very good point. Where should I pull the air from and through? It's a two story house with basement, built in 1998, and the house was build by a very good builder with good material, is fairly air tight.

There are air vent flaps that are motorized which are tied into the hood that open fully when it is active and close airtight when done. You could install two of them, one for exhause and another (at a different place so you don't pull in the output from your hood) to let in fresh air.

 

[JZ Bowmannz]

Range hood ducts are almost never less than 8" and the more elbows you add and the longer the run is, the larger the pipe diameter needs to be.  The type of cap you put on the outside also has an effect on flow.  The hood should have a duct calculator in the specs, if not the manufacturers website will.

Having been through the process in my kitchen:

I didn't have had the problem (induction stove), but yours looks like gas (at least on the drawing), so you need enough clearance to the hood (also it should be cleaned often enough) so it won't ignite by accident. Best check the manuals of the stove and the hood for more information about this.

For the duct: Do as less turns as possible, while keeping the length as short as possible and use a big duct. I have seen quite some extraction hoods with >1KW motors in them that didn't suck (as they should) because their performance is killed by the piping between them and and the exhaust being excessive.

For the exhaust: I used Naber GT 150 as a passive system (opens/closes by pressure from the hood), works nicely and when the hood is off cold air won't come in through it in winter.

To make it visually nicer I would go for another cabinet where the hood pokes out of at the bottom:
[attachimg=1]

Should you still be in the planning stage: have you thought about putting the stove in the corner?

Thanks Dane.

Gregor, thanks.

It's a good idea to add another cabinet on the top of the cooktop and hood, the only thing I am not sure about is, I don't know if the "boss of the house" will approve the concept. She seems like the hood by itself... But I can see many benefit from adding the cabinet though.

Sounds like I should consider at least 8" vent in order to have good result, maybe a variable speed hood helps as well. Does 1200CFM hood need a dedicated power supply from the box? I do have a 220V line from my old cook top that is no longer needed.

We did consider the cooktop at the corner, but the dishwasher will then has to be relocated to somewhere into the kitchen island or where the cooktop is right now in the picture, and it will be too far from the sink...

 

[rizzoa13]

Range goods can usually share a circuit with another small draw appliance like a gas stove. It's a 110v line so your 220 from the old stove won't work. That said I've installed some larger range hoods from Viking that needed a dedicated circuit so read your manual.

On the venting issue you could possibly run straight up into the room above and then out the roof depending on what the room above is. If it's a bedroom or a closet a small soffit running up wouldn't really be a big deal and could be much preferable to having to rig something up in your kitchen. If you do it that way you just need to make sure you aren't exceeding the hoods distance to termination (which will also be in the manual). Any more questions feel free to ask!

 

[Dane]

Make up air is a good call.  1200 CFM is a huge draw and can have negative impacts on anyother gas appliances in the home- if you have a natural draft water heater or furnace, it can back-draft those and draw combustion gasses into the living space.  If you are looking for information on this: http://www.jlconline.com/how-to/insulation/the-science-of-kitchen-ventilation_o

 

[RKA]

Range goods can usually share a circuit with another small draw appliance like a gas stove. It's a 110v line so your 220 from the old stove won't work. That said I've installed some larger range hoods from Viking that needed a dedicated circuit so read your manual.

I believe many 220 kitchen appliances have something inside that runs on 110, so the neutral may have been pulled on the circuit as well.  You have to check the line to see what you have to work with.

 

[tjbnwi]

It's in the linked article, any exhaust unit that moves more than 399.9 CFM must have automatic make up air. It is a national code requirement, check with your AHJ to see if they have amended the code. There are a few manufactures that have 399 CFM vents now.

Don't use the neutral from the 220 volt circuit unless you remove the 2 pole breaker and install a single pole breaker tied to only one ungrounded lead from the 220 volt line. Here the additional line would have to be terminated where is could not be used.

Tom

 

[JZ Bowmannz]

Make up air is a good call.  1200 CFM is a huge draw and can have negative impacts on anyother gas appliances in the home- if you have a natural draft water heater or furnace, it can back-draft those and draw combustion gasses into the living space.  If you are looking for information on this: http://www.jlconline.com/how-to/insulation/the-science-of-kitchen-ventilation_o

Thanks for the link, Dane.

Reading the article now.

 

[JZ Bowmannz]

Range goods can usually share a circuit with another small draw appliance like a gas stove. It's a 110v line so your 220 from the old stove won't work. That said I've installed some larger range hoods from Viking that needed a dedicated circuit so read your manual.

I believe many 220 kitchen appliances have something inside that runs on 110, so the neutral may have been pulled on the circuit as well.  You have to check the line to see what you have to work with.

Thank you both for the tips.

 

[JZ Bowmannz]

It's in the linked article, any exhaust unit that moves more than 399.9 CFM must have automatic make up air. There are a few manufactures that have 399 CFM vents now.

Don't use the neutral from the 220 volt circuit unless you remove the 2 pole breaker and install a single pole breaker tied to only one ungrounded lead from the 220 volt line. Here the additional line would have to be terminated where is could not be used.

Tom

Tom,

I did read about the code for 400 CFM. And the level of NOx and CO are concerns as well, my kids' bedrooms are directly above the kitchen. Make me thing about going back to electric cooktop now.

I am using a licensed builder for construction and to implement the changes, hopefully, he is as knowledge as all of you guys.

Appreciated all your input, this is a great place! The project starts in two to three weeks, so please let me know if there is anything that I should watch for.

 

[JZ Bowmannz]

Range goods can usually share a circuit with another small draw appliance like a gas stove. It's a 110v line so your 220 from the old stove won't work. That said I've installed some larger range hoods from Viking that needed a dedicated circuit so read your manual.

On the venting issue you could possibly run straight up into the room above and then out the roof depending on what the room above is. If it's a bedroom or a closet a small soffit running up wouldn't really be a big deal and could be much preferable to having to rig something up in your kitchen. If you do it that way you just need to make sure you aren't exceeding the hoods distance to termination (which will also be in the manual). Any more questions feel free to ask!

I have to go check if I can do this in the closet, I think the wall is under the upstairs bathroom. But it's well worth to check, and it would be ideal. Thanks.

 

[Cheese]

For placement of the hood, the bottom of the hood usually needs to be 24"-32" above the cooking surface. Check with the manufacturer of your hood and cooktop. The hood mfg will probably dictate the dimensions & placement of the hood, while the cooktop mfg will dictate suggested CFM's for the blower, it's all about the BTU output of your burners. I'm guessing that a 5 burner gas cook top will be in the 500-700 CFM range.

I'd also definitely use 8" ducting and don't forget the backdraft damper, locate it as close as possible to where the vent exists the house.

I had a similar problem as yours because a bathroom is directly above the range hood. I attached a single 90 degree elbow and vented it out the side wall. I've included pictures below.

 

[JZ Bowmannz]

For placement of the hood, the bottom of the hood usually needs to be 24"-32" above the cooking surface. Check with the manufacturer of your hood and cooktop. The hood mfg will probably dictate the dimensions & placement of the hood, while the cooktop mfg will dictate suggested CFM's for the blower, it's all about the BTU output of your burners. I'm guessing that a 5 burner gas cook top will be in the 500-700 CFM range.

I'd also definitely use 8" ducting and don't forget the backdraft damper, locate it as close as possible to where the vent exists the house.

I had a similar problem as yours because a bathroom is directly above the range hood. I attached a single 90 degree elbow and vented it out the side wall. I've included pictures below.

Thanks Cheese.

How do you like the Wolf hood? I've looked them up and they didn't have the noise level spelled out. Are they quiet?

 

[Cheese]

No JZ they're horrible. It's an in-line 500 cfm blower, I wanted the external blower version but there was no room for it. I've called them up and they are very aware of the issues, (as in lots of complaints), but Wolf pretty much says "it is what it is" when you're in the over 400 cfm range. That's the reason they push the external blower option.