Hi - this thread is a little old now so this might be too late, but I have some related Qs even after reading all this helpful advice. I'm starting gut reno of a 120+ year old townhouse in NYC and plan to install 36" bluestar with 2, 22K BTU burners (in addition to other smaller burners of course) which we'll use primarily for stir fry. We HATE grease smell in the house and cook all the time, so want to get what we need for the stove we have. So I'm fine getting major CFM, if that's what it takes, but my concern is the ducting. It seems we have 2 options - up an existing chimney (which we're having relined and is not used for fireplaces; fireplaces were all sealed up decades ago) - but that would be 3 stories or about 50 feet needed to get to the roof and I wonder if that's too far for it to function properly...2nd option would be to bring it down into a soffit on the floor below (a rental apartment that already has a dropped ceiling) and vent out of the exterior wall, but this would require making a new hole in our masonry, and would mean the venting would be just outside our kitchen, under a french door that we're likely to want to open often while we're cooking - so the smoke could in theory end up back in the kitchen, no? I am by no means an expert so forgive me if I'm totally off base here, but any thoughts/advice would be much appreciated. Thanks!

In principle, any hood with an internal blower could be gutted of the blower and operated with an in-line or roof mounted blower. (GreenDesigns may have meant that using it while leaving the blower inside would be a poor plan.) I can imagine construction details that might cause non-optimal internal hood flow patterns, but I have no detailed knowledge of the internal construction of myriad hoods to know whether such are prevalent. There may be nanny jurisdictions that would claim that code approval of the hood was violated when it had its blower removed. Any hood available for order without a blower likely is fully compatible with an external blower. This, of course, can be confirmed with the manufacturer. The most important adaptation requirement is that the blower be continuously controllable, and that the hood control be a continuous motor control. A hood with just a few motor speed positions on a switch might require a compatibly-wired motor. While a multi-position hood control could in principle be replaced by a continuous control, par. 2 may apply. When I was doing my kitchen reno, I chose a compatible hood/roof blower combination (supplied by Wolf) because the entire scope of the project (gutting and reconstructing part of a house) made playing with the details of the blower circuit a side project of tertiary importance that I couldn't afford the time to deal with. As it happens, inside my Wolf (Independent) hood is a diac/triac motor control circuit, about the simplest design available that goes back to the '70s. The compatible Wolf (Broan) roof blower uses a typical induction motor that is easily controlled by this type of circuit. The cost versus time value trade-off needs to be considered when dealing with issues like this. kas

I agree with having a separate HVAC contractor. Get a few quotes separate from what the GC has done. Have the HVAC contractor do all the work related to these systems, including the required duct and heating/cooling calcs. As you've found, there are many popular ventilator companies that don't manufacture heating/cooling systems, so it's probably safe to assume a capable HVAC man can integrate whatever is chosen In suggesting the the HVAC contractor sub-out the duct design and installation, maybe fsq4's thoughts come from practices in his own country and area and that he's not familiar with what's done in the US. Here, established HVAC contractors, especially those who do new construction, often have the terms "sheet metal" in their business names because very many (most) do metal work themselves.

The reason I asked is that there are two approaches to MUA (not the number of architectures possible). One is to just be compliant inspection-wise, while not risking safety, and the other is to be compliant functionally, accounting for every present and future household configuration contingency. The former may do for your case. The idea is to solve the safety issue for your present configuration by putting a damper controlled small diameter MUA duct into the laundry room from outside, terminating close to the dryer. In concert with keeping the laundry room door closed when running the hood ventilation at any significant flow rate, this will avoid back-drafting of the dryer. Then a larger MUA externally connected duct (nominally the same size as the hood duct) bringing MUA to the kitchen can be installed via any of several paths as allowed by your house architecture and aesthetic considerations. This MUA system can now be passive (no MUA blower), and tolerate a damper and dust/bug/critter/condor filter as desired. This hood MUA path's restrictions at high hood blower power, given no blower of its own, and given some furnace like dust filter, could cause a pressure drop in the house that would exceed the safety level (0.03 inches w.c.) for the dryer if the dryer didn't have its own MUA. However, now both MUA paths are simple and relatively low cost, safety is achieved without overkill, and the configuration is likely to meet the expectations of the Code Enforcement Officer who is unlikely to run pressure tests to compare to some robotic rules that don't account for the actual safety situation. At some future time fireplace MUA may have to be considered. The attic heater will need its own MUA also (or a ventilated attic) if it is to be run. kas