under slab duct

[kaffine]

What type of duct is recommended for under slab? I am working on my kitchen and I want to run a makeup air duct to under the stove. Problem is I don't have a way of getting the vent to under the stove except under the slab. Thanks.

 

[mustangacman]

Years ago we had to vent a Jenn-air cooktop down thru the slab and used 6" pvc pipe. This wood work for freah air

 

[fitter30]

Pvc, aluminum or stainless. Galvanize will rust through. Pvc is preferred if you have the room two 45's instead of a 90* less pressure drop because a long sweep instead of a sharp turn.

 

[Higgins]

There is a light weight type of plastic pipe that they use for installing floor registers in slab homes. It's rather light, and has the typical 90,45s, T's etc.

Check with your local supply houses as they should be able to point you in the right direction.

 

[Jackfre]

There is a light weight type of plastic pipe that they use for installing floor registers in slab homes. It's rather light, and has the typical 90,45s, T's etc.

Check with your local supply houses as they should be able to point you in the right direction.

I think you are referencing Schedule 10 pvc. It is very thin wall. I used it for a footer drain one time and 5 years later, after it collapsed put in schedule 40, which I should have done in the first place. I'd go sch 40 pipe and grade it so you don't have any condensation pooling and creating a mold/mildew issue.

 

[brewchief]

The under slab ductwork that I have done was PCD coated spiral duct.

Sent from my SM-G965U using Tapatalk

 

[kaffine]

Thank you.

 

[mrobins297aaa]

The under slab ductwork that I have done was PCD coated spiral duct.

Sent from my SM-G965U using Tapatalk

This is what we used also they make a special tape for the joints and they also have a spray paint for scratches. I can't remember but they may also make special screws.

 

[yeldogt]

The spiral is one and there is a better plastic available -- the plastic is more expensive. Obviously the spiral will eventually rust. There are codes that cover the type required -- you cannot just can't use any type and have it pass a knowledgeable inspector.

How are you controlling the intake air -- it's going to be hot? Also -- there are situations where having the intake at the stove does not work all that well. Have you done some research ?

My preferred method is to have an 8" intake to the outside w/ dampers. typically I run the air through a dehumidifier as I'm also using the intake for general air change. The 8" intake gets a "Y" --- 8" with a damper controlled by a sail switch on the stove duct and 6" to fresh air intake for the house. In my climate I split it into the HVAC and also into a dead part of the house. Most of my systems use a 10" duct for the stove vent -- so the 8" is not going to get all of it .. but how often is it all the way up and for how long? Even with a spray foam house you get some leaking -- find this works very well. There are sail switches available that will not clog and don't turn on at low settings.

 

[kaffine]

I was going to use powered dampener controlled by the vent hood. I figured I can get away without a fan on the intake it will just make the vent hood work a bit harder. I will be filtering the air just not cooling/heating it. I can't see having a 4 ton AC just to cool the makeup air for the kitchen vent.

I haven't seen much info on how to setup makeup air for residential installs. I was looking at mostly having the air come out the toe kick of the cabinets and possible between the stove and the wall or the wall behind the stove. Not sure if the toe kick will be enough to supply all the air or not.

My thought is the air would flow up just in front of the cabinets and to the vent hood taking the steam and grease with it and without heating the rest of the kitchen too much. Not sure if that will work in reality or just my mind.

There will be a 36" induction stove top with a 36" wide oven below it. So using the space between the floor and oven for vent would work. There will also be a wall oven on another wall.

House is all electric so I don't have to worry about back flow on vents if it ends up pulling the pressure in the house a bit negative. I have been using spray foam any time I open up an outside wall for renovations.

 

[kaffine]

The house uses multiple minisplit units for cooling no central HVAC.

 

[yeldogt]

What's the CFM of the hood? Are you doing this because of local code ?

I would not place that under on the toe kick -- is going to be bringing in hot air right at you.

The point is to balance the depressurization -- not create a pathway. That's why you will see some in the ceiling -- you don't have any ductwork for an easy dump. How high are the ceilings?

 

[kaffine]

I'm looking at around 1000cfm vent hood I don't have it selected yet. My understanding is anything over 400cfm requires makeup air. I doubt the code is enforced around here though.

Ceilings are 8ft. No other ductwork in the house. There will be an in ceiling minisplit in the kitchen.

 

[mrobins297aaa]

just curious why so much air flow?

at 1000 cfm's I think your probably close in your previous post of 4 tons to cover the sensible and latent loads of that makeup air.

whether the codes are enforced or not if you try to run a 1000 cfm's exhaust without makeup air your going to have a problem.

that air is going to try and come back in the building anyway it can, even down any chimneys you may have for water heaters and even plumbing vents.

what size duct were you planning to use on the discharge of the exhaust hood?

 

[kaffine]

I can always run a more powerful vent hood at low speed but you can't turn a weak one up past max. I don't expect to use high power often but when it is needed I want to be able to use it.

I am guessing a 10 inch exhaust I haven't picked the vent hood yet from looking at them most seem to use 10 inch duct for 1000 cfm. Not sure if I will use a remote fan or built into the hood. No good access to the attic above the kitchen so that would leave a roof mounted fan if I want remote.

No gas appliances so no real back-draft concerns.

I guess I could use a swamp cooler setup for tempering the air. In the summer we are normally under 20% humidity. It would help most of the time.

I am getting ready to install a vent hood at my parents house it is rated at 390cfm if I remember right, it was just under the requirement for make up air at the time I got it. It uses an 8 inch duct. I will see how it performs and rethink my requirements as needed.

 

[yeldogt]

The 1200 cfm use 10" round.

Again -- that's full blast. A JennAir downdraft -- think they were 8" -- it's been a while since I had a house with one.

we have a 48" DCS gas in one house with grill and griddle. We will use full blast when grilling meat -- or when searing meat on the power burner. But, it's not for very long ... in an older house .... they leak.

As is said ... even a spray foam house will leak. Unfortunately -- your theory that the hot air will simply flow in and up and out -- does not pan out.

The air becomes defused --- there really have not been enough practical studies done. It's a shame because they need to do them. It seems that the manufacturers want to simply act as if it's not an issue ... as it add costs. Also, the hood manufacturers are often not the same as those who make the stoves. Many of the professional stoves use the same double Broan blower ...

My current project us using the 60" Best (brand) insert .. 1200 cfm

 

[kaffine]

It is better for the air to be diffused in the kitchen though than the living room since I'm not tempering it. Now that you have me thinking of it I might end up trying to do directed vents instead. I can see if the air is coming in horizontally from the toe kick the air isn't going to want to bend upwards and is going to go across the floor. If I can build the vent into the front of the cabinet so it points mostly up it might work better. I'll still get the hot air standing at the stove but it should help keep it from diffusing into the rest of the kitchen.

This is really the trial house. I plan on custom building a house eventually. This house I am using to see what I do and don't like.