So, is this 48-inch BS in the staff quarters or where guests will congregate and chat while food is being prepared? If the latter, then you want the quietest possible high flow hood. This entails at a minimum a roof-mounted blower or remote in-line blower and an in-line silencer on 10-inch ducting. My usual recommendation for actual air flow rate capability for a baffled hood with an assumed 8 square feet of aperture is 720 cfm. This calls for a blower rated at least at 1080 cfm at zero static pressure, but given the possibility of some combination of cooktop and oven use where oven spillage is the most difficult effluent to capture, I'd aim higher. For an island setup, I'd aim for a 1500 cfm rated roof blower. With a wall set-up 1200 should do. (For most cooking you would operate at a reduced blower setting and there will be little fan or baffle turbulence noise.) I use a 1500-cfm rated blower with my Wolf (Independent) Pro-Island hood with a 10-square-foot aperture, but don't have a griddle and have another 1000 nominal/600 likely cfm capable vent over the separately located ovens. A suitable source of (possibly conditioned) make-up air is also necessary. kas

Yes! We got it sorred out. So it turned out to be a loose circuit breaker. It was the new sub panel put in for our kitchen reno. We had some electrical work done and hired an electrician tonadd some recessed lighting. He ran it back to the new subpanel and he comes up from the basement nd asks if we were having problems with the stove. I said yes. He said he noticed the breaker wasnt seated properly. It was making a connection but just barely. He popped it out and popped it back in and sure enough I went and ran that oven at 500 for an hour with no issues. The cause imo was the weak current was causing the computer to think there was a fan issue. An anomaly. Want to say we have since moved and it was a relief to be able to have that taken care of. I will buy Thermdor again! They did send us a new range (after repeated service calls). So would so donit again

I take exception to being called a collectivist. 8-) I guess I should inject the possibility of having the duct pass the second floor in a chase, perhaps located in a closet, an extra wide wall partition, or perhaps outside, allowing a roof blower. This should reduce noise a bit in the kitchen, and in the region of the side of the house where the duct exits. Note that a wall cap may approach the size of a wall-mounted blower housing if the cap is to have free flow. With a larger chase, even a silencer is possible. I haven't audited either the Best of VaH examples so I can't comment on their sound levels. An earlier VaH example (ca. 2007) was measured by clinresga vs. a conventional hood/blower and found to be louder. Functionally, my preference is toward whatever design best approximates commercial designs. kas

... coming out of hibernation to put his oar in, says: This forum has a large wealth of technical information on this topic that should be reviewed by anyone new to the subject who is planning to achieve actual kitchen ventilation. Here are some tidbits, boiled down from various attempts here to provide practical rules of thumb. We will start with opaone's suggestion. Hood function depends on successful capture and containment. Capture depends on hood aperture overlaping the rising and expanding cooking plumes. 54 inches by 27 inches would be considered the minimum for adequate capture of a 48-inch high power cooktop. Hood containment depends on flow velocity at the capture aperture. For this size hood (assuming inside aperture is nearly 54 x 27) I would argue for around 1000 CFM of actual flow rate. To get this flow rate with a real blower, you will need a blower that is characterized (at zero pressure loss) as capable of 1500 CFM. Similarly, if one is constrained at 48 inches hood width (please cook greasy things on the middle burners), the values are 800 and 1200 CFM, actual and rated. Either size blower can easily operate through a 10-inch duct. Hoods with single duct interfaces are widely available from Modernaire, Captiveaire, Wolf, and many others. The actual flow rates noted above are based on a 1.5:1 ratio of nominal to actual, and this assumes some generalities about the fan curves of reputable fans and pressure losses of baffles, ducts, and most importantly -- the make-up air system. (Please review relevant threads on MUA in this forum.) No air flows out the duct that didn't get into the house somehow. At the higher actual CFM levels, house leakage is not adequate for providing this air flow rate. To answer the OP's question just above, higher flow rate through an undersized hood has only a slight to modest effect on increasing the effective size of the hood. The reason is that hoods do not suck cooking effluent from the cooktop, but intercept it and keep it in the hood. The rising plume velocity can exceed a meter per second for gas cooking, and this is what gets the plume to the hood. Air flow velocity for the flow rates I suggest is only half of this at the hood aperture, and rapidly drops off more than a few inches away from it. For actual flow effect at the source of the plume, one would have to use fume hood rules of engagement, where high flow at the effluent generator (welding, grinding, whatever) is achieved. You would need ear protection with such a system, and a huge heating capability for the make up air, perhaps augmented by structures intended to restrict the effluent from escaping the flow. kas