1, 2, 3, 6, 4, 5, 7.

 

Thanks huesmann. Based on what you suggested, the wall mounted vent hood will have to be removed again to install the slab backsplash, is that right?

1. Buy the vent hood and new gas stove
2. Plumber to install gas line
3. Electrician to put outlet where vent will be
6. Install vent hood (drill screws into Quartz slab?)
4. Duct work in ceiling and through attic
5. Install Quartz slab countertop and Quartz slab backsplash (with outlet cutout?)
7. Drop Gas Cooktop into new Quartz slab countertop

 

Question, what is the anticipated size (cfm) of your new exhaust fan?

Bud

 

Hi Bud, we're thinking of getting the 42" Miele KM3485GSS gas cooktop with a total BTU output of 73,800. We were told 10,000 BTU to 100 CFM, so we're thinking of going with generic vent hood that is around 900 CFM and 48" wide.

 

In all likelihood the gas cooktop will also require a 120V receptacle.

Some electrical codes require a kitchen exhaust fan to be hard wired, rather than use a receptacle to plug it in. Some fans don’t have a plug to allow them to plug into a receptacle. Buying the fan early on is a good idea.

I have some doubts about the plan to support the fan by screwing into the quartz backsplash. Are you confident that the thickness is sufficient to support the load and you’ve scoped out the type of fasteners that would work? If in doubt, I'd open up the wall and add framing to support the fan, getting the quartz fabricator to make holes in the appropriate places so that the mounting screws for the fan could go through the quartz into the wood framing behind.

Is the cooktop installation not on an exterior wall, which is why the duct plan goes up through the ceiling?

Chris

 

Thanks for the detailed response, Chris.

You bring up a good point about potentially needing for it to be hard wired due to code. I'll definitely check with the electrician on that. I'm thinking they'll just pigtail the current outlet used by the electric cooktop to the kitchen exhaust fan.

I have no knowledge or confidence as to whether the quartz backsplash will support the load. I've been screwed over by contractors several times, so I'm trying to learn as much as I can and what to ask before I start hiring for this complex job.

The cooktop installation is on an interior wall. The other side is a formal dining room. It's very complicated because right above is the 2nd floor landing and a closet, so the person doing the duct work will need to be creative to get it done.

 

Not sure what your local code office will say, but all exhaust hoods over 400 cfm may be required to have a make-up air system. Some codes require it, some recommend it, and others look the other way. Opening a window is not a solution.

I've done my job by letting you know the issue exists. I run into it when a house has naturally drafted appliances like a furnace or water heater that can be back drafted by a huge fan, that can be a serious safety issue.

Even at 400 cfm and below the issue of backdrafting needs to be evaluated as other exhaust appliances can add to the problem.

Best.
Bud

 

Is there any practical solution at reasonable cost to this, Bud?

We recently renovated our kitchen, adding an exhaust hood. I knew all about the negative pressure problems that it can create, but I couldn’t come up with a reasonable solution to it. I thought about:

• Adding a fan that would bring outside air into a normally unoccupied space in the house. It would need the same multiple speeds as the cooktop fan and it would require a separate switch which the chef would have to remember to turn on to the correct speed when she switched on the cooktop fan. I contemplated trying to rig up an interconnect to the cooktop fan switch, but with everything on a circuit board that didn’t seem practical.
• Our house has an HRV with two fans, one to bring in fresh outside air and another to push out stale inside air. I investigated if there was a way to modify normal operation to turn the incoming fan to high and shut off the other fan, but that was impractical.

What I hoped was available, but didn’t find, was a cooktop hood fan with built-in make-up air via a second fan. The two fans would be synchronized in speed so that the air being exhausted was matched by that being brought in. There would be a challenge about how/where to dump the incoming fresh air that might not be near room temperature.

In the end, since our house doesn’t have natural gas burning appliances (but does have a radon problem), I gave up and my wife does, usually, open a window when she uses the kitchen fan.

Chris

 

Backing up one step, I’ll ask the question about whether you know about induction cooktops, since you already have 240V to the location and don’t have gas (you would need to check the amperage requirement, though, to understand if the wire is a large enough gauge for a new induction cooktop that might need more power than the old electric). My chef wife was adamant about wanting a gas cooktop when we renovated the kitchen which had an old electric cooktop. Unfortunately there is no natural gas service where we live, so that would have meant propane. We learned about induction cooktops, installed that instead and she says that she now prefers it to gas. There is lots of info online about the advantages of induction cooktops.

I’m not that familiar with the US NEC, but I’m not confident that you’d be able to repurpose the heavy gauge wire used for the 240V electric cooktop as the feed for the gas cooktop and fan 120 receptacles. You might start a new thread in the electrical section to see what advice you get.

Is there already 120V power in the cooktop cabinet for the downdraft fan, or is it remotely located?

When you write that the ducting will be complicated, that doesn’t sound good. Every 90 degree elbow that goes into the duct add the equivalent of 20-35 feet of straight run. It doesn’t take many elbows to create a large pressure loss, resulting in a fan that makes noise but doesn’t move much air. It really would be best to know what the routing could possibly be and check the fan manufacturer information to see if that will work before you buy. That may be why there is a downdraft fan there now.

Chris

 

Eliminate all (if any exist) naturally drafted appliances. Not sure about the gas range never heard it mentioned.
A sealed combustion furnace with direct venting and air supply along with a similar water heater or electric water heater would eliminate the sensitive appliances but unsure if that would satisfy an inspector.

DIYing a replacement air system puts the inspector on the hook for becoming responsible for any future problems. Thus I suspect they would only approve an approved system and those are available just a cost issue.

Bud