600 CFM should be fine.

Thank you!

You're lucky. Code in my town is MUA at or above 400cfms. I thought that was becoming standard.

My town is so small, no one even knows what MUA is!:)

600 CFM is enough to remove all the air in a typical 10x15 kitchen every 2 minutes. You will be fine.

I wonder whether the code authority realizes that a 600 cfm blower is rated that at zero static pressure, and that in a real installation with duct and hood transitions, baffles or wire mesh, duct length and turns, the actual flow rate will be less. Depending on the blower design, it might be a lot less, e.g., 2/3 the rating. But you probably don't want to get into an analysis contest with the AHJ.

The other point I want to make is that even at 400 cfm, one can easily drop the house pressure to a level that could cause back-drafting of furnaces and hot water heaters, particularly the very efficient types that run cool on the exhaust. Unless you are fully electric, or such units are separately supplied with MUA, a partly open window or door is recommended at the higher end of the blower operating range.

kas

I have a 36 inch Miele induction cooktop paired with a Vent a Hood PRH-242 that has a 600 CFM rating--actual, not the "Ventahood magic equivilant". :-) It works beautifully. I have had it installed since August 2010, have fried, grilled on a grill pan, done fish, all kinds of smokey, smelly and greasy stuff. No grease on my cabinets and no smells outside the immediate cooking area. However, when I'm cooking and my husband comes home from work, he says it smells like a restaurant outside! So, yes--at least in my home, 600 CFM is enough. And my small town has no requirements for MUA, either.

Cj

Thank you so much everyone!

Breezygirl, I was relieved to find out our limit was 600 cfm. The GC at the Home and Garden Show who told me this said several cities/suburbs in the area have 400 as their limit.

Pricepal, most of my friends who have already updated their kitchens didn't know what I was talking about! I think their DHs must have taken care of that or maybe their GC automatically took care if it if they had to have MUA (they didn't know if they had it or not).

Jakvis, the working part (i.e., not including the eating area) of my kitchen is about 10 x 13.

Kaseki, great information and I'll ask the GCs I interview about this. I don't think I'll lose much power on the vent because the cooktop is on an east exterior wall and should be able to be vented directly out that wall. I'm really not concerned about the pressure dropping in our house as neither of our 2 gas fireplaces (one in FR and other in master bedroom upstairs) have a damper on them so cold air pores in if the doors aren't closed. I was told the dampers were taken off to comply with the code in our area back when our house was built in 1990, but I appreciate the information and warning.

Cj, it's great to hear that you're happy with the 600 cfm when used with your Miele! I'll be so happy when I finally have a vented hood!

Thanks again!

Ohhh! I hadn't thought about that being an advantage to going with induction! I'm hoping to find an appliance store that has a functioning induction cooktop that I can try out to make sure my 2 big pots can be used at the same time (spaghetti sauce in one simmering and water for noodles in the other). It would be great to be able to chop onions and hot peppers under the hood!

Perhaps I was unclear, flwrs. When operating, the fireplace normally sends the gas combustion products up the chimney. It depends on temperature differences to get the gas to rise. This is equivalent to having the room pressure very slightly positive with respect to the outside. If you lower the house pressure sufficiently, the combustion products will be back drafted into the room. This won't be as immediately obnoxious as with a wood fire, but is still undesirable, as imperfect combustion means carbon monoxide generation.

kas

Does makeup air apply to a recirculating hood?

No worries for you.. MUA is for air being moved out of the house. MUA supplies the air to replace what is being evacuated. Think about a straw in a soft drink cup. Suck on the straw to pull liquid out of the cup and you draw air into the cup to replace the fluid going up the straw. A recirculating hood just moves the air around within the house. Like a straw just sitting the glass.

Like a straw just sitting the glass.

and equally effective I'm sure :-) Thanks.

36 inch induction should have one independent burner and then the other 2 sets boost off each other but check for sure.
Like breezy- we had to be under 400 or MUA issue - but no requirement to have a hood - duh?
I do not like my Broan evolution and hoping to swap it out - but store the original in case of selling the house to keep within code.

One important concept to keep in mind is that there is always MUA that exactly matches the air flow expelled by the hood. If the house is "sealed," then the hood moves very little, no matter what the fan rating is, and the MUA leaks in through the walls, down the fireplace, or backwards through the furnace.

kas