Greenheck is more often used in commercial applications, which make up the vast majority of outdoor exhaust fan orders. This is probably why the supplier is more comfortable with it. It also explains the shorter warranty; warranties for commercial products tend to be much less generous. Abbaka is more of a residential brand. Both are quality products and will last a long time if applied and installed properly.

It comes down to aesthetics. The Abbaka is a much more low profile unit designed to blend in with the roof of a house. The Greenheck is designed to be put on the roof of restaurants and schools where looks won't matter as much, and there will be plenty of other HVAC equipment up there anyway.

The Abbaka is designed, as illustrated in the link, to exhaust down-slope on a slanted roof, typical of most residences. I don't think it would be good on a flat roof. My Wolf uses the same approach, and my roof slope is around 22 degrees.

The upblast style shown at Greenheck's link can be used on a flat roof, and is probably the most efficient as it is standard for restaurants. A flat roof should be difficult to see from the street so the configuration shouldn't be subject to criticism from passing observers.

What is difficult here is the tiny straw you want to move the exhaust through. For any decent air flow, the blower will have to be sized to meet its flow rate working against a significant pressure loss. If your HVAC guy can estimated the pressure loss (including losses in the baffles and hood transitions), Greenheck can probably choose a blower and motor combination to meet your need. Greenheck may even be able to perform the estimate from the duct length. Just don't expect significant flow in a six-inch duct to be silent.

I would plan on insulating the duct to reduce noise.

kas

Abbaka works fine on a flat roof provided you install it on a curb. I am able to see equipment on top of commercial buildings with flat roofs from the ground all the time.

hvtech42 wrote: "Abbaka works fine on a flat roof provided you install it on a curb." This is a good idea for adaptation of that configuration, however it could defeat the configuration's purpose -- low observability. Curbs that are both strong and rust resistant may not be inexpensive.

hvtech42 wrote: "I am able to see equipment on top of commercial buildings with flat roofs from the ground all the time." I won't argue with that, but the OP is in Brooklyn and observers on the street looking at the OP's brownstone while having a line of sight to the roof edge may not have a line of sight to the blower unit if it is back from the edge.

The point is that both approaches need to be considered in context of where they need to fit, how they fit, and what compromises are needed to utilize them. Abbaka's blower is likely sized for up to a few tens of feet of 10-inch duct. Abbaka may not have a motor/blade option for high pressure loss six-inch-duct configurations. This can be answered, of course, by contacting Abbaka and asking.

For reference, the fan curve for the Wolf Model 336 "1500 cfm" external blower (same configuration as the Abbaka) has zero flow rate when the static pressure reaches 2.2 inches of water column. I likely use up 1.2 inches w.c. with baffles, transitions, duct length bends, and a Fantech silencer, all ten-inch duct, which is why I have routinely reported here my estimate of 900 actual cfm given minimal added MUA loss.

With 35 feet of six-inch duct, my blower (and Abbaka's) might find its operating point to be only at 200 cfm at full power. This is why blowers intended for high static pressure operation are configured differently. It may be that even Greenheck is not prepared to deal with the losses of a long six-inch duct. In such a case, an in-line vane-axial fan such as Rotron makes (or possibly Fantech) may be needed. A silencer would be recommended for high speed six-inch fans, as they will likely be loud even when pulling only a few hundred cfm through the duct. Fantech may make silencers as small as 6-inch duct size.

kas

Kas and Hvtech42 - Thank you so much for all the information. I'm feeling so much better having some educated opinions on this!
So, this blower will be installed on the roof behind some really ugly and big central air conditioning equipment.I can't see any of it from the street, so, aesthetics aren't really an issue. The abbaka I'm looking at is for an 8-inch duct - closer to my situation than any of the fantech or broan solutions. The abbaka engineers thought it would be okay putting it on a 6-inch - I would of course lose efficiency and cfm, but it was looking like my best/only option in the residential range.
Given that aesthetics are not important, it may be worth the extra $500 to go with the Greenheck, as the professionals on my project are most comfortable with it. Though I think I should probably speak to the engineers over at the supplier one more time to make sure that they've considered all the complexities which you guys have outlined so well here. I'd hate to pay the premium only to find that it didn't do the job as well as the abbaka would - that's really my fear here.
The advice is much appreciated! Thanks!

This post was edited by jjinbrooklyn on Thu, Jul 17, 14 at 11:47

You will also need to ensure that the kitchen exhaust is not within 10 ft of an A/C air intake, although there might be exceptions depending on how the exhaust is directed. Local code should be consulted before cutting holes in the roof.

kas

My hood is about 13 feet from the intake (on paper, but air would have to travel around a wall making it about 20 feet) but only about 12 feet from a fireplace (which has draw problems so we are putting a fan on top of that too). Hoping this won't cause any problems...

As far as I know, there is no problem with exhausts being near each other, although if they nearly abutted each other various low-probability scenarios could be imagined, such as fireplace sparks interacting with greasy effluent.

kas

What is the length and diameter of the duct? A 10-inch Fantech silencer is 14 inches in diameter, as I recall, and maybe about 4 feet long. (Check their website.) A silencer will remove high frequency blade tip turbulence noise, generally the highest noise source. Next loudest would be baffle hiss, but that should be tolerable for general conversation.

duct is 10" and now has been placed in the space above the kitchen. It now runs all the way down the room, 30 feet away from the hood and vents to the roof. The silencer is huge! I was surprised they could get it in the space, but it worked. I'll let you know how it sounds once its up and running.

Debbie, looking forward to hearing how it works and sounds. If you have time could you download a good sound meter app for your phone like Decibel X (https://itunes.apple.com/us/app/decibel-x-db-dba-noise-meter/id448155923?mt=8) and take some measurements. All should be 'A-weighted'. With the fan on HIGH: from directly in front of your range where you'd be standing to cook and then another from 10' away. And then do this again with it on low.

Thanks,

BTW, for reference.

A quiet house is about 45 dBa.

The Vent-A-Hood in our house (on high) is 69 dBa @ 0' and 61 dBa @ 10'

A commercial hood in an open plan restaurant is 66 dBa @ 0' and 58 dBa @ 10'

Ok, finally. Here is the dBs for Abbaka 1400 remote blower with silencer. Vent pipe is 10”. Vents out to ceiling about 30’ from stove top.
I used the Decibel X app as recommended.

On high:
Under stove top, 64.1
10 feet away, 53.7
30’ away, under silencer in ceiling 51.7

On Low:
Under stovetop 54.2
10’ 41.6
30’ 39.8

We really like it. Probably the most important feature we put in our kitchen! Can’t stand kitchen smells of garlic and onions and dislike a lot of noise.
Thank you all for your input. Sorry it’s taken me so long to get back to you with numbers. I blame the 7 slabs of granite that cracked, broke or were not advertised size.
Thanks again for all of the input.
Debbie

If those are dBa and not dBc readings then they are very good!

Thanks Debbie; I'm sure your results will prove useful to others.