What does the range instruction sheet say. IMO 48” ranges are never needed in a home so they have requirements that need to be met , steel studs with cement board is athought but you need to follow the instructions. A picture of the space where the range is going would also help.Also your MUA and hood are going to have to be decided.

We are considering a couple models, all state the same thing, minimum 6" from COMBUSTIBLE wall if no backguard is installed. The walls are ripped apart, what is the proper procedure/materials to build a "non combustible" wall. I have the opportunity to do this now but can't find exact details on what a non combustible wall is.

There are a few discussions on it that always revolve around the same thing, tile/cement board does not = non combustible due to the wood studs behind. But no real explanation of what actually need to be done to meet these requirements.

So if I replace the wood studs with steel studs is that sufficient?

Or do I need to go further and replace the drywall on the other side of the wall as well with type x gypsum.

There was also mention of a 1" air gap between combustible materials to meet code. So would that be Cement board -> steel stud -> 1" AIR GAP -> steel stud

One of those "recent" discussions had a reference to a source with various tables defining material combinations and distances. I didn't note the reference, but perhaps you can find it. It may provide information on what kind of a test is used for the purpose of approval.

Another path would be to consult with the authority having jurisdiction (AHJ) also known as your code enforcement officer. If he can't answer the question, he may point you to someone in the Fire Department that has to deal with such questions.

These tables talk about reduction methods for combustible walls. So for example if you build a reduction wall of 24gauge galvanized steel with 1" spacers between the combustible wall, studs for example, you can reduce the clearance to 2".

I am not looking for that, I am talking about rebuilding that portion of my wall to be a fully non combustible wall.

I can probably piecemeal those requirements together, for example build the reduction wall mentioned above as well as put in steel studs then the distance to the nearest combustible material (the drywall on the other side) would be 4".

Adding in the sheet metal beneath cement board is not a big deal or big cost, I just want to get it right since I am in a position to rip out the studs if needed.

It's pretty simple. You need 2x6 steel stud wall, covered with cement board. A 2x4 wall won't give the 6" horizontal clearance to the surface cladding on the opposite side side of the studs.

Or pull the range 6" away from the rear wall. Then do the same with the hood above. Making sure to use only noncombustible products fill any spaces. Like OldBat2B did. And then adding more CFM for the hood, and more required Make Up Air system that you should already have engineered.

Just buy the back guard. It functions better, looks like you really cool, and is FAR cheaper than rebuilding your kitchen's walls or doing a bump out.

I just went through this with my own kitchen remodel. Great question!!! I used 2x4 steel studs around the range with cement board. On the other side I finished with cement board as well, it’s just a garage in the back. One foot past the range sides, one foot below range surface, and I went to just under the height of my hood. Remember the steel studs do not have weight bearing capacity, so frame the area like you would a window. If you like I’d be more than happy to share photos of the process.

Hey Catinthehat, thanks for the info. Unfortunately the rear wall is a hallway, I could replace with type x gypsum maybe. I will keep investigating options.

On another note, where did you end up putting your mua vent? I saw another thread you started but didn't seem like you got and actual answer. Are these supposed to be unobstructed? Did you add a filter in line? How did you handle the outside air temperature, winter being cold, summer being hot etc... For the incoming air?

Thanks!

Hi drewski,

So long as the drywall (or any material you use) is rated as noncombustible in accordance with astm e136 then you are fine. Last I checked there are some brands offering type x drywall with an astm e136 designation.

I ended up placing my MUA vent location on either side of my range under the cabinets. I have two 8” vents that come up through the floor in my crawl space. I have hole cutouts just above the cabinet toekicks where they cannot be seen. The two vents connect under the house to a common header which draws air from the side of the house with a filter unit.

The nice thing about this setup is it eliminates the need for conditioning the air before it enters the house and it actually improves the efficiency of the hood. When the hood is turned on and the MUA dampers are activated, outside air is drawn from immediately below the hood (through the vents on cabinets to the sides) and ejected outside before it has time to mix with the rest of the kitchen. It also helps direct effluent grease and smoke upwards and toward the hood rather than rising up in a “V” to the sides.

I have confirmed these observations through about 4 months of use now in temperatures ranging from 35 degrees to 101 Fahrenheit. I live in socal so we don’t usually get weather outside these extremes anyway. I was given many reasons on this forum why this method would not work and yet it does =). Fred S was an invaluable resource in explaining why I couldn’t put the mua vent holes directly beneath the range.

Hope this helps you.

A stainless back guard with warming shelf can look pretty great.

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Hey Catinthehat,

Do you know how your damper was wired? I am assuming you went with Broan since they seem to be the go to MUA Damper. If you have a parts list that would be appreciated?

Thanks!

On January 21 Drewski 22785 asked a question that wasn't answered, at least in this thread. Ideally, in an MUA system there will be a filter to keep critters and/or dust out of the house, one or two dampers to keep wind out, a heater (depending on environment), and in in some locales, air conditioning. Because the filter can cause significant pressure loss, the ideal system would also include a blower that was controlled based on house differential pressure relative to outdoors pressure.

Such an ideal system would have significant financial costs. Pressure balancing, for example, requires control sensors and electronic blower motor drivers, or counterpart pneumatic controls. When would pressure balancing be needed? It would be needed if the house pressure at full hood power drops below a level that can back-draft any combustion appliances present that take their intake air from the household air rather than having their own MUA path to the outside. Obviously, if there are no such combustion appliances the safety issue is moot and MUA is needed only to allow the hood to reach its desired flow rate, and to keep the hood system from pulling exterior air through the walls.

Hence, the necessary system complexity is very household dependent and without more information a complete answer cannot be given.

Hi drewski,

always happy to help. Yes I did all the wiring myself. I used one Broan 10” damper which is under the house in the crawl space. The wiring diagram that comes with the damper is incredibly easy to follow. You essentially are running a low voltage line with a pressure switch from the hood to under the house where the damper is. The only thing I’ll add to the instructions is make sure you put your pressure switch tap in a long section of the attic vent to prevent turbulence from disturbing the switch. In the future, in the event you need a separate blower for the MUA, you can tap into the low voltage signal from the damper, incredibly easy to do once you see the wiring diagram.