Your take-away from reading this forum deserves some refinement.

Baffles both collect grease better and pass air with less restriction when dirty than mesh filters do when dirty. Clean, with appropriately matched blowers, mesh filters can be comparable.

In order for either type of filter to work, or for that matter for ventilation to occur at all, three things are necessary:

(a) The hood must capture the rising effluent under its filters
(b) The hood must contain the effluent by pulling it through the filters and expelling it to the outdoors
(c) The air flow moved through the hood to achieve containment must be replaced in the kitchen by some method of make-up air

(a) requires that the filter aperture sufficiently overlap the rising and expanding effluent, or the hood aperture leading to the filter sufficiently overlap the rising and expanding effluent
(b) requires sufficient velocity of air flow at each point on the filter
(c) may only require house leakage for low flow rates: and open windows, passive opening ducts, or active controlled replacement air systems, depending on flow rate needed, house tightness, and other factors, for higher flow rates.

The difficulty with aesthetically optimized designs such as the AEG at the link is that capture is poor because the effluent can slide to the side if the velocity is not high at the filters, and the filter area, around 16 by 23 inches, is too small for direct impingement capture from a 30 inch or larger cooking surface. Either the filter area should be large enough to overlap the cooking surface, or the glass structure needs sides large enough to overlap.

Performance optimized designs, such as restaurants use because the cost of ventilation power and make-up air power is a dominant cost of business, illustrate the performance design leg of the performance-aesthetics-cost triad. The so-called pro designs sold by consumer sources such as Wolf and Modern-Aire try to achieve all three of these factors, but the cost is high and the aesthetics are limited to modest improvements on commercial units. In some cases, liners can be used within cabinets to improve aesthetics.

The ventilation aphorism to remember is: aesthetics, affordability, performance -- pick two [at best].

kas

Kas,

Thank you for your detailed reply. I have read other forum posts by you and you clearly know ventilation. I was afraid that AEG was too small to be effective. They don't have a deeper wider one. We may need to give up the glass wish and I am prepared to do that if we are sure there is not a suitable one that combines function and form. We will pay up for one if necessary as with an island hood it will be centre stage visually. We will have a whole house HRV as in Canada opening a window much of the year is not too energy wise. Hopefully with an HRV that will take care of the make-up air. Please let me know if I have misunderstood.

Can you explain further what you meant when you said: "Either the filter area should be large enough to overlap the cooking surface, or the glass structure needs sides large enough to overlap". You sentence implied to me that the glass counts for the recommended overlap area. We are assuming with a 30 inch cooktop we need to find a hood that is 36 inches wide and 24 inch deep. Does the glass count within that 36 inches of width??

I have checked Modern-Aire and did not see anything that grabbed me. I will check out Wolf. Are there any other manufacturers that might have glass and baffle even for top dollar?

Carol

Oh my, I found a gorgeous hood. I am frightened about the price though. Before I rule it out due to price, I wanted to make sure it was seen as a good quality hood and not just a pretty face. We will have regular chrome faucets in the kitchen, but I do like the mirror stainless, the brushed stainless steel or a a powdered coated colour for the hood. These surfaces are so much jazzier than plain ducting coloured hoods. Why do we always like the most beautiful.

Linked below is the RangeCraft gem. Does it work well?

Here is a link that might be useful: Rangecraft island hood

If the filter area overlapped the cooking area, then effluent impinging on the filter would (with enough flow) be entrained in the flow and pulled through the filter. If the area overlapping the cooking area is glass, rising effluent will "reflect" off of the glass everywhere there isn't a filter. Unless the glass has the general shape of a Tiffany lamp,* the reflection will be away from the filter. (For conservation of momentum, the angle of reflection equals the angle of incidence relative to the normal to the surface at the point of reflection.)

If you look up into a Wolf hood, for example, you will see that where there aren't baffles, there are sloped sides that are steep enough to keep the reflection in the hood and direct it to the baffles.

Even with these ideal hood shapes, insufficient air flow can lead to effluent curling out of the hood as some Schlieren photos accessible on-line show.

The real problem with flat glass is that one generally cannot (wouldn't want to due to the noise, if not the massive make-up air required) flow enough air such that it can entrain effluent all the way to the edges of the glass. Hence the reflected effluent is not pulled into the filter except very near the filter edges (within a few inches at best).

So, glass only counts if it has sides and slopes sufficient to capture the effluent and direct it to the filter aperture.

kas

*A giant Tiffany lamp styled hood would be quite a visual attraction.

Here is a link that might be useful: Tiffany lamps

How far along are you in your kitchen reno? Can you consider placing the cooktop against the wall instead? You have several issues which would be solved just by doing that. Not to mention that when a cooktop is in an island it means the rest of the island isn't that usable. As has been discussed many times on the Kitchens Forum, 70% of the time you spend in a kitchen is actually prepping, not cooking. 20% is cleanup, and only 10% is applying fire to food. It's a mistaken idea to think that a cooktop in the island makes everything more "social" and the center of everything (Cooking shows are to blame for that!). Actually, it's prepping on the island that accomplishes that. Wouldn't it be better to have the largest chunk of your food prep time spent at the island? And then you could have the cooktop on the wall, you'd have a much greater selection of hoods that will provide both aesthetics and better function, better exhaust, and the whole thing will cost you less too.

Regardless of hood location, I would never have a glass hood. My personality is such that the visible splatters on the glass if you just make, say, scrambled eggs, would bother me. Other people don't mind. But there's also the issue that a canopy-style hood gives you the best capture of smoke and grease, and glass hoods are not canopies.

If you haven't already seen the thread I am linking, I think it would be good for you to check out Ctycdm's island hood. It's everything an island hood should be in the way of size, baffles, canopy style. S/he posted on another thread that it is 1000 cfms and with an appropriately-sized 8" exhaust duct.

Here is a link that might be useful: Thread Showing Ctycdm's Island Hood

Hi Shannon,

Thanks for commenting. We definitely want an island cooktop and don't want the induction cooktop against the wall as I startle very easily and can't stand having my back to others. Our island is large (11 feet by 51 inches). We have run our layout passed the kitchen forum people and they have giving us the thumbs up.

You make excellent points about the mess on glass. I will point that out to DH who is very keen to get the glass. I think I could be happy with a vent like you showed in the link. Above all I want it to be functional, but not ugly.

Thanks for your help and the link.

Carol

There is a Vent a Hood that has a pretty similar look to that Rangecraft hood.

http://www.ventahood.com/hoodmodels.jsp?id=58

Hi Carol, I see what you are saying about your preference for the cooktop in the island. But I have to ask this question--since 70% of the time spent in a kitchen is actually prepping, not cooking, and only 10% is applying fire to food, where will you be doing prep? If you are prepping on counters that are along a wall, won't you be having your back to people 70% of the time? I am not trying to be troublesome; I am just trying to understand how to ease your situation. Or, will all prep be done on the island as well?

Hi Shannon,

Thanks for your thoughts on my kitchen.

At my 11 foot island will be a prep sink, close to 4 feet of free counter and then the 30" cooktop. So, yes I plan to prep and cook facing out. The clean-up sink is on a peninsula, so when cleaning I will also face out. There is a secondary prep area along a wall and a snack prep area.

I have included my kitchen plan so you can see. It is a pain to have a fan hanging over the middle of the kitchen, but aside from that downside I am super happy with the layout. Below is the layout and under that is the elevation of part of my outside wall. Please let me know if you see any issues. The elevation picture is not up to date as we will have a wider fridge (probably the Liehberr and will not have the freezer drawers). The closet/dumb waiter wall is also not up to date.

Carol

Hi Needinfo,

Thanks for the link to Vent a Hood. I will go to that site now to see what I can find.

Everyone,

We also thought about dropping down the ceiling over the island to accommodate the Best flat fan as per linked below. Our ceilings are only 8 feet anyway, so with a drop down that would bring the fan to 7 feet from floor. If that is not good enough ventilation we could supplement with a downdraft ventilation (I know they are not that good either). I think I will have to accept that form of the ventilation is going to have to be an important consideration as it is such a focal point in this kitchen.

Anyone tried one of these fans. I can see they would have limited value in a tall ceiling kitchen, but in Canada our ceilings are often 8 feet, so maybe workable in this application?

Carol

Here is a link that might be useful: Best Sorpresa Cirrus hood

Most manufacturers with full size island vents (not built into the ceiling) typically recommend the distance between the cooking surface and vent to be 28" - 36". You are talking about installation a vent build into the ceiling that is at least 60" above your cooking surface if I understand correctly. This is way over the traditional installation spec so that alone should be a warning sign.

The in-ceiling style vent is good for "whole kitchen" ventilation to cycle stagnant air and handle light cooking but is going to be quite useless when you start doing any regular cooking. The vent is simply too high up to effectively capture grease and other particulates.

As others have mentioned, this in-ceiling style vent is really for people who don't cook much or want a conversation piece.

In-ceiling venting is normally impractical for non-commercial kitchens. The size of the hood has to equal the cooktop size plus at least the tangent of 22.5 degrees times the distance between hood aperture and cooktop on each of four sides. This makes it very large.

Because the air flow velocity should be in the range of 1.5 ft/s (90 ft/min) at the baffles, the large area (in square feet) times 90 yields the required cfm. This is a large (a few thousand cfm) value requiring larger sized roof upblast exhaust blowers such as Greenheck makes for commercial applications.

The make-up air system would have to be similarly sized, also based on commercial applications, and air conditioned, as full power would rapidly replace the air in the house (unless you are cooking in the Pentagon).

Your favorite restaurant may have to pay for all this and its significant power cost, but you probably don't want to do so at home.

kas

P.S. Four of the Best units shown in the link above might be sufficient on an 8-foot ceiling. Using only one unit would depend on pulling in missed effluent from the sides along the ceiling. At best by the time the odor is removed some grease will have been deposited.

This post was edited by kaseki on Wed, Aug 21, 13 at 19:46

Hi Kas,

Thanks for your information. Actually, over the last few days I read some dismal reviews on GW regarding these ceiling vents.

How do you like a Modern-aire version of the following? I am getting Modern-aire to prepare a quote for me of a painted hood (not sure what colour and stainless trim). Some of our cabs will be cream, some chocolate. Any idea what colour of hood we should get for the powder coat. The hood we are planning will look a bit like the following with different colour base colour and stainless trim.

[Traditional Kitchen[(https://www.houzz.com/photos/traditional-kitchen-ideas-phbr1-bp~t_709~s_2107) by New York Architects & Designers Minion Gutierrez

I am sorry I can't help you with your hood paint color decision - I am hopeless at that kind of design stuff. The Kitchens Forum people could help you I bet. I'm just posting to say that pic is a gorgeous hood. Wow.

I can't comment on specific hoods that I haven't owned. My impression from other comments on this forum is that Modern-Aire is competent to design and fabricate hoods.

Given the choice in a hood of that configuration, I would choose baffles over mesh filters.

The air flow rate requirement follows from the hood aperture size. Aim for 90 ft/min times the aperture size in square feet unless you like a different rule of thumb.

Blower flow rate capability at zero static pressure loss follows from the air flow requirement and the estimated pressure loss through the assembly and whatever house pressure loss is not compensated by the make-up air system, as evaluated on the candidate blower fan-curve plots. If these factors are not known (as usual) multiply the number obtained above by 1.5 as a guess.

House leakage, unless you live in Pago Pago, will not be sufficient to make up the air removed from the kitchen at that flow rate, and either open windows or an MUA system will be essential. In some places it will be required to pass inspection.

kas

Hi Kas,

You certainly know your stuff. It is my understanding all modern-aire hoods have baffles and we will certainly make sure we get them. Sorry for this dumb question, but given we have an HRV directly ducting into the kitchen (as well as all baths) do we also need something for make-up air? Opening a window in Canadian weather is often not practical.

Thanks for all your help!

Carol

My understanding is that HRVs are intended to provide a modest change in interior air while capturing back some of the heat that would otherwise be lost through air exchange. Typically, they are not scaled for 600 - 1600 cfm flow rates, but I don't know what yours is designed to do.

If your house were perfectly sealed, the flow up the kitchen vent would equal the flow in through the HRV. This might be only 200 cfm even though your kitchen vent blower was rated for 1200 cfm. In other words, the HRV may be too restrictive for the flow rate you want. This leads to requiring a larger duct that opens only when there is significant vent flow. (This part is easy.) But still, the house pressure may drop too low.

Problem 1: For safety with any combustion appliances in the house that are not separately supplied with air, or fireplaces that are almost always connected to the kitchen pressure, the house pressure cannot be allowed to become more than slightly negative. This may force the MUA system to be an active system with a blower.

Problem 2: When you need to heat and/or filter the MUA, then there is yet more restriction and it may again be necessary to provide a blower in the MUA duct.

Problem 3: Controlling this blower so that it works correctly for any cooktop vent flow rate, bathroom fan flow rate, window condition, fireplace operation, etc. leads to a complex design.

The least complex design I can imagine for a high flow rate kitchen hood has these characteristics.

a) All combustion appliances have their own MUA (and no chimneys leak).
b) No fireplaces are used when the kitchen vent is on.
c) A large duct (at least equal to the one above the vent hood) with damper is used to bring in MUA, and the damper is controlled by a hood duct flow switch
d) If heating is needed, an electrical resistance grid that causes minimal pressure loss is used in the MUA duct, controlled by a thermostat. (The power requirement may be significant, at least for the period of high ventilation cooking.)
e) If it is hot in the summer you have to lump it.

All other approaches of which I am aware will have additional complexities and costs. MUA induced into the hood will not work well and doesn't in most commercial settings.

Use of water-to-air heat exchangers, or refrigeration-to-air heat exchangers (heating or cooling) in the MUA duct will cause enough restriction that the house pressure will become too low or little MUA will flow, mandating an in-line blower and its control system. Fin type heat exchangers will also require quality air filtering for further pressure loss and bigger compensating blower.

kas

Hi Kas,

Well it looks like I have a lot more homework to do. Thanks for the education. I will speak to the HVAC guy to incorporate what is needed for make-up air. You are very helpful!

Carol