I know this is an older thread but I called the manufacturer and they gave me the following noise rating:
Tempest 2: 6 sones (max level) with internal blower and double blower (9 sones).
Tidal 2: 6 sones (max level) and no information on double blower but I’d assume very similar to the Tempest with 9 sones at max level.

OP, did you need up with any of these range hoods and can give feedback on how their noise levels are?

"I called the manufacturer..."

They measure these without duct in a free-flow state and often hung w/ isolation dampers. They want their numbers to be as good as possible.

Reality is likely to be 3x - 4x as loud once mounted and with duct.

@opaone At the Sirius showroom they told me the opposite. I went there to sound test a hood and the sales person said that it will be quieter once ducted/mounted properly as the air isn’t going anywhere and stays within the hood….
But what you say makes sense too. Never thought that buying a hood is as hard as buying a whole house…

Fingers crossed someone will post with an answer! We're installing the Tempest II with dual blowers, based on some other general venting threads that said that dual blowers set on low would be quieter than a single blower turned up higher to reach the same CFM. Would love to know for sure whether this is true before we cut up the wall for ducting.

@mcarroll16 Have you purchased or decided on the Tempest 2 with the dual blower? If so, please provide an update after you had it installed on how you like it. I hope it is as great as advertised. At least Zephyr Customer Service is very responsive. Didnt have much luck when I tried to reach the Sirius Call Center to ask questions.

I did buy the Tempest 2 and dual blower. It won't be installed though until sometime in June or July. I can give you an update then.

My kitchen reno will also be around the same time as yours. May I ask when you placed your order, how long it will take to get the hood and where you are located? I wonder if there are supply chain issues with Zephyre hoods. I’m located in Canada though.

I ordered my hood in August, received it in late January. So yeah, there are supply chain issues with Zephyr. The accessory parts--extra blower, makeup air kit, etc--have all been shipped very quickly. I'm in the Seattle area.

"@opaone At the Sirius showroom they told me the opposite. I went there to sound test a hood and the sales person said that it will be quieter once ducted/mounted properly as the air isn’t going anywhere and stays within the hood…."

Life lesson #1: Don't ever believe someone who's selling something.

If the air stays within the hood then how does it exhaust effluent? It's quieter because it's not working anymore?

If it's quieter when mounted and with ducting then that's how they would have tested it.

Simply mounting the hood makes it louder because the house structure becomes a speaker. Then the ducting creates static pressure that increases fan blade turbulence.

"dual blowers set on low would be quieter than a single blower turned up higher to reach the same CFM."

If they are done correctly they can be minimally quieter. If not then they'll be louder due to harmonics between the two blowers.

The ONLY way to get a relatively quiet exhaust hood (that also works) is with a remote blower. Anytime the blower is within the hood itself it will be fairly loud.

Thanks opaone! Remote blowers aren't an option with this model, and swapping models is not an option at this point either. Maybe I should return the extra blower. I've got an induction cooktop so the 650 CFM single blower should be enough. Noise reduction at 650 CFMs was the only reason I was opting for dual blowers.

Thanks kaseki! The dual blower uses the same internal blower that comes built in to the single blower version, plus an additional add-in blower. I can't tell from Zephyr's support documents how similar the two blowers are. I'll call Zephyr on Monday and see what I can find out.

Given the money value of time, I would just buy the dual blower hood and, if the noise at some flow rate is not lower, disconnect the second blower. But this depends on configuration. Zephyr's spec sheet is not clear about this, and they provide no fan curves for either option. Speed seems to be controlled to be one of several settings, so if there is an interaction as noted by @opaone it might be suppressed by choice of settings by the manufacturer.

If you can get fan curves for both options it will help. They are needed anyway to determine actual flow rates in the context of duct length and MUA error.

Thanks, I'll see if I can do that. My concern about installing a second blower that I might not use is that Zephyr recommends an 8" duct for one blower, and a 10" duct for two. I've gathered from other threads that an oversized duct is problematic. Grease pooling, maybe other issues. (I read all of your and opanone's threads on venting!). It's a short duct run though. About 3' horizontal and then turning for 3' vertical. Would an oversized 10" duct with one blower be ok?

For best trade-off between grease collection via impingement, and grease collection via condensation, the recommendation is having the air flow between 1000 and 2000 ft/min. But these parameters are usually determined for commercial cooking, and their blowers typically run at constant speeds. For residential cooking, we typically are all over the place, speed wise, so we hardly ever are in the position of having an optimal air flow for the conditions. In many residential circumstances, so little grease is actually produced on a daily basis that what is collected hardens up and doesn't drip anywhere. YMMV.

Take your two candidate blower packages' specified CFM values, multiply each by 2/3 to get some realism, and calculate the air velocity in each duct size for each CFM. Then decide where a sweet spot might lie. I personally might just go for the 10-inch duct anyway as I could in the future adapt a larger external blower that I knew was quiet at lower air flow rates.

Thank you, that is very helpful! I hadn't thought of eventually converting to an external blower. But you reminded me that I want to eventually upgrade to a 42" hood. Really regretting not doing that now, but that's water under the bridge.

K H, if you're still following, here are my results from the calculations kaseki recommended.

Velocity for a 10" duct: 1,468 FPM (feet per minute) for dual blower, 734 FPM for single blower.

Velocity for an 8" duct: 3,440 FPM for dual blower, 1,147 for single blower. And here's a link if you want to run calcuations for another model, https://learnmetrics.com/duct-velocity-calculator/

Your dual blower probably would be gagged with the 8-inch duct, so the actual velocity would likely be lower. Clearly, Zephyr's recommendations for duct sizes vs blower quantity are appropriate.

Thanks so much for all of your advice. So helpful. I'm going to go ahead with both blowers and the 10" duct. The entire duct run will be completely exposed and accessible in the garage. So if I disconnect one blower, and grease does pool, It will be relatively easy to deal with.

@mcarroll16 Thanks for the velocity calculation.

I was considering buying only one blower for now to see if 650 CFM would be sufficient for us. I contacted Zephyr last week and got this response:
”You can install later, but if you do choose to do it later, make sure the correct duct is installed prior or else you will have to reinstall the correct size ducting. The 2nd blower can be installed at a later date.”

However, we don’t know how complex it would be to install later as we will have professionals doing the installation duting our full kitchen renovation. not sure if we will find anyone to do that job at a later time…

I’m wondering if the one blower can be turned off if we wanted it to operate with only one blower?

Without any data to go by, I would bet at least a donut that each blower is electrically connected using a standard two-prong plug. However, the entry source and exit path are the same, so turning one blower off will allow some ON blower air to be recirculated backwards through the OFF blower. I would want, in that case, whatever blocking panel the manufacturer installs in the one blower system available and actually replace the second blower with it.

Always protect your cooktop when mechanically ravaging your hood interior.

Thanks kaseki. Something to keep in mind. Most likely we will install the two blowers since we would already have it.

Hello KH, just wanted to follow up and see how you're liking the two blowers. Did it end up being too loud? I'm in a similar predicament at the moment, torn between getting one or two blowers.

@J Y Yes. We installed the two blowers in the Tempest II and have had it for over a year now. It was the best decision ever and the range hood is one of our favorite purchases during the kitchen renovation. It is not loud when you use it on speed 3 which is the speed we use all the time when cooking. We can still have a conversation in the kitchen at that speed without having to yell at each other.
It has 6 speed settings and we only have to use speed 4 when we fry steak occasionally. The two blowers make such a huge difference in sucking up all the cooking smell. Can’t smell someone is cooking as normally the smell would travel up to the rooms upstairs. Very happy with Zephyr’s customer service as well as I called in a couple times prior to making my decision on a range hood and they had been very helpful in answering my questions.
Let me know in case you have other questions.

Thank you for the quick response!

Do you remember if the zephyr actually ended up being not as loud once ducted? I visited a showroom yesterday and the sales person said the same thing to me. Level 3 and maybe even 4 seemed bearable, but 5&6 were definitely too loud for me to have on during an entire cooking session.

Sounds like you basically use the rangehood the same way I have in mind: buy the 1200cfm but probably rarely use the 1200cfm level since it's so dang loud. Seems like 1200cfm is still nice to have to turn on briefly when I accidentally burn something though 😂

Also, do you by any chance do any wok cooking? I am curious to hear how it does with that, since I've noticed there always seems to be more smoke and grease when I use my wok :)

Also, how high above the range did you end up mounting your hood? :)

@J Y, we never got to test the noise level of a Zephyr in a showroom. The one we tested and considered was a Sirius range hood which was scarily loud in the showroom. Our Zephyr one is definitely quieter than the un-ducted Sirius hood. We’ve never had to use level 5-6 yet and would probably only need to use it if we had food burned by accident. We are also doing a lot of wok frying (maybe 3-4 times a week) and only on level 3. Level 3 on 2 blowers is definitely quieter than level 6 on one blower and you’d get the same CFM.
We mounted it 30” above our electric stove top.
Hope this helps in your decision making.

@K H, just thanking you for sharing your experience as we are considering the same hood with a similar set up.