Range Hood Blower Sizing

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Cyclesafe
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Range Hood Blower Sizing

Post by Cyclesafe » Wed Jan 17, 2018 4:43 pm

I have a 36" range top and am installing a 42" wall hood with an external blower mounted on the outside wall of my kitchen. The various rules of thumb indicate that that with my volume of kitchen and my range's BTU maximum output I should get a 900 cfm blower.

My question is - since I am mounting the blower outside is there any reason to not just go ahead and get a 1100 or even 1500 cfm blower? Prices for all three are similar and all require a 15 amp dedicated circuit and 10" ducting. Also, there is no code requirement for make-up air provisions as I live in San Diego where houses are rather porous. And, I can always crack open a window.

Any downsides for oversizing a blower motor?

barnaclebob
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Re: Range Hood Blower Sizing

Post by barnaclebob » Wed Jan 17, 2018 4:46 pm

As long as you can afford it and turn it down if it's too high then go for more power.

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unclescrooge
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Re: Range Hood Blower Sizing

Post by unclescrooge » Wed Jan 17, 2018 5:04 pm

Beyond a certain limit you might start creating negative pressure in your house!

But I don't know what that limit is.

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Cyclesafe
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Re: Range Hood Blower Sizing

Post by Cyclesafe » Wed Jan 17, 2018 5:12 pm

unclescrooge wrote:
Wed Jan 17, 2018 5:04 pm
Beyond a certain limit you might start creating negative pressure in your house!

But I don't know what that limit is.
Well, it would depend on how wide one is cracking open the window. There's also an issue of wind noise coming through the window as well as through the hood.

I was surprised to learn how weak a blower can be to create negative pressure.

https://www.youtube.com/watch?v=JTS7Xxdtm9E

LawEgr1
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Re: Range Hood Blower Sizing

Post by LawEgr1 » Wed Jan 17, 2018 5:27 pm

Cool question.

Theoretically, no leaks, you'll always create that negative delta P equivalent to the positive pressure on the other side. It'll be few pascals at most and will be insignificant. No different than your bathroom exhaust. Given there are (surprisingly) no building code requirements on make-up air, then here is all I have for you -

In terms of volumetric flow: if you trust your rules of thumb with 900CFM I would recommend that's you're absolute minimum size. I'd go a size up to be conservative.

Downsides: Assuming a single speed blower, a larger volumetric requirement will generally mean a change in speed or impeller (blower) diameter or perhaps blade pitch. This directly results in a larger power draw (See Affinity Laws). That said, it won't be significant in this application IMO, but you wanted a downside. This also assumes equivalent drive train design. One could draw 6A and the other could draw 7A; look at the specifications for each it should give output. But again, as you stated, it's rather irrelevant in terms of the circuit design.

If you have a variable speed blower, which would be the ideal case, then you are able to control the operating cost.


In this case, don't overthink it and grab the slightly larger version. :sharebeer

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unclescrooge
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Re: Range Hood Blower Sizing

Post by unclescrooge » Wed Jan 17, 2018 5:34 pm

Rather than spend money on higher cfm ratings, you should opt for lower noise ratings.

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Re: Range Hood Blower Sizing

Post by ThriftyPhD » Wed Jan 17, 2018 5:35 pm

Do they have a rating how loud they are? Do the higher cfm have high/low or variable settings so you can back it off if you don't need 1500 all the time?

We swapped an over the range microwave for a dedicated hood and notice a big difference in performance and how it created negative pressure. We opened a nearby window or door when using it on high. It works better and is quieter if it's not fighting as much negative pressure.

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Re: Range Hood Blower Sizing

Post by Cyclesafe » Wed Jan 17, 2018 5:41 pm

unclescrooge wrote:
Wed Jan 17, 2018 5:34 pm
Rather than spend money on higher cfm ratings, you should opt for lower noise ratings.
Interestingly enough, range hood manufacturers, unlike bathroom fan manufacturers, do not publish noise ratings. I called Wolf tech support and wheedled what I could out of them and it turned out that they simply wouldn't tell me anything other than what was essentially "a bigger motor will be louder". Well, it's mounted outside, so noise may be no issue at all - well maybe an issue for the neighbor.

The blower I'm looking at has contiuous variable speed so it can be dialed back as needed.

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Re: Range Hood Blower Sizing

Post by 123 » Wed Jan 17, 2018 5:56 pm

As an previous poster indicated noise is a far bigger factor long-term than having a higher volume of air. If you kitchen is near living areas, like a dining room or TV room some of the exhaust fan noise can be very irritating. From what I've heard it's much more difficult/expensive to make a lower speed fan that is quiet than one that pumps out a large volume. Sure you need a high volume speed for a small fraction of total usage but overall you'll find a quiet low-speed will get far more use. Unless you only do a stir-fry inferno you'll find the fan mostly used to whisk away steam from boiling pots, you'll enjoy it much more if it's done quietly.
The closest helping hand is at the end of your own arm.

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Re: Range Hood Blower Sizing

Post by 8hygro » Wed Jan 17, 2018 6:35 pm

In my neck of the woods the municipal codes required make-up air for anything over I believe 600cfm. Of course, that would only apply to a permitted build/remodel. Duct work size and layout is another factor in helping determine a cfm calc. Elbows and transitions drop the efficiency regardless of blower cfm. Fiberglass duct is known to carry less resonance from the blower compared to metal. You may have a very simple and direct through-wall routing though.

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Re: Range Hood Blower Sizing

Post by WaffleCone » Wed Jan 17, 2018 7:01 pm

All that air getting pushed out needs to come in from somewhere and likewise will need to be conditioned, cooled and dehumidified in your case.

1500 cfm is a lot of air movement! Some whole house fans are that size and they are designed to run with windows fully open. I'm not an expert but even on my 1950's house the architect recommended switched MUA if over 600cfm and even detailed where it would need to be to get the best benefit of the fan (i.e. across the kitchen instead of on a side wall or under the kickplate).

I'd size appropriately and get MUA if the calculation says you need it even if the code doesn't. And I'm surprised San Diego doesn't have some form of the IRC adopted. You may discover that there is some code when the inspector comes by.

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Re: Range Hood Blower Sizing

Post by namekevaste » Wed Jan 17, 2018 7:08 pm

Depends on your location(winter temperatures) and how tight the house is. Newer homes have tight construction and exhaust fans will cause the indoor pressure to fall. Houses constructed using ICF or SIP have exceptionally low air infiltration. One practical consequence of this is that if you do not have a balanced air handling system, unconditioned cold air may be pulled into the house whenever the range hood is on. Open air fireplaces or stoves may backdraft in the winter causing carbon monoxide accumulation or smoke in the house.

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Re: Range Hood Blower Sizing

Post by FraggleRock » Wed Jan 17, 2018 10:20 pm

We have 36-inch Wolf hob. Center burner is 20000 BTU.
With a 36-inch, 600cfm Zephyr hood.
Works great. Even when doing “Chinese” stir fry.
6-inch duct. One 90 bend. Total distance is 10 feet.
Heath Ceramics Dwell pattern for the backsplash.
Image
Last edited by FraggleRock on Mon Jan 22, 2018 10:09 pm, edited 2 times in total.

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Re: Range Hood Blower Sizing

Post by lazydavid » Thu Jan 18, 2018 9:14 am

Even if it's not required, don't skip the makeup air. 900+cfm is a LOT of air. To put that in perspective, for a 3000 sqft house with 8' ceilings, that's removing the entire volume of air from the house every 27 minutes. Unless you live somewhere where the outside temperature is 70F year-round and there are no allergens--or you have a window directly above the cooktop--opening a door or window is not a good substitute.

We put in a 1200cfm dual-fan 48" hood without MUA, and even with the dial turned down all the way, if we have a fire in the fireplace, running the fan will fill the kitchen and living room with smoke in about 3 minutes. So we open a window or the sliding door to prevent that, and now we have a nice -12F breeze going right through our living space.

genefl
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Re: Range Hood Blower Sizing

Post by genefl » Thu Jan 18, 2018 9:26 am

We cook extensively and had the same question. The appliance company ordered us the largest fan for a Thermidor hood. When it came to installation, it didn't fit the hood! The installer scratched the hood trying to get it in and we had to get a new hood and smaller fan! Bottom line, the hood may dictate the size of your motor. (As an aside, if you're looking for one, I have a new Thermidor fan in the garage.... :)

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Re: Range Hood Blower Sizing

Post by lthenderson » Thu Jan 18, 2018 9:28 am

Electrical motors are designed to run between 50% and 100% of their rated load with peak efficiency somewhere around 75% of the rated load. When you fall below 50% of the rated load, most motor efficiency curves drop off dramatically. Running significant amounts of time off the peak efficiency can effect the life of the motor. So in your case, I would get a properly designed range hood for your application. Getting something larger and then dialing it back will just mean you have to replace the motor more often.

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Re: Range Hood Blower Sizing

Post by Cyclesafe » Thu Jan 18, 2018 9:36 am

Thanks for all of the responses.

Fortunately, as I mentioned in the OP, I live in a part of San Diego where the air temperature is indeed a dryish 70F year round, so I am not at all concerned with letting in outside air. In 17 years we have used our fireplace one time.

Nevertheless, the cautions I am hearing about getting too big a blower are well founded.

The current internal blower is probably 300 cfm - if that - and is terribly noisy. I think now that perhaps the recommended 900 cfm blower might be the way to go after all. It's always a temptation to get the magnum, the 8-cylinder, the 500ml craft beer, but maybe I should cool my jets and get something more reasonable.

Thank you for your help!

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Re: Range Hood Blower Sizing

Post by Cyclesafe » Sun Jan 21, 2018 10:28 am

Update after spending 10's of hours on the internet dusting off my atrophied math skills and trying to tamper down my bigger-is-always-better testosterone-fueled desire for MORE POWER:

First. It's confirmed that an external/in-line blower needs to be at least 20 feet from the kitchen to be quieter than an internal bower - at least in the kitchen. But of course it will be alot noisier in the room now adjacent to the relocated blower. Also, noise in the kitchen, which is mostly the sound of air moving into the hood, is no different.....

Second. The hood I am/was considering can accommodate a 900 or 1200 cfm internal blower, but requires 10" and recommends 12" ducting - especially for the 1200 cfm unit. I could discharge from the back of the hood directly through the kitchen wall to the outside for minimal friction loss.

Third. I have a stucco house. Although repairing and re-weatherproofing the stucco exterior would be the same as if I used a remote blower, I hadn't realized that this is such a big deal. It would be better to try to use the existing 7" ducting, which leads to....

Fourth. Using 7" where 10" is "required" and 12" is recommended would create (positive) backpressure of roughly 0.35 and 0.60 SPWG for 900 and 1200 cfm, respectively, assuming 13.5 foot equivalent duct length. Trust me. This is waaaay beyond acceptable loss in efficiency. And I think that these numbers might be on the low side.....

Fifth. Of course I could replace the 7" ducting with 10" and rely on the vacuum created by Venturi effect to pull through the 8" terminus more air than the "simple" calculation would indicate. But 10" ducting and transitions take up much more space than 7" ones and the new hood at 18" tall is 3X's taller than the old one. We would have to mount the hood 8" lower than what DW intends (DW expresses displeasure).

So, perhaps I should consider a lower profile hood and save the 8" there. (DW OK with this.)

Sixth. Back-drafting will occur at only at a negative 0.03 SPWG which is surprisingly (for me) low. A 1200 or 900 cfm blower - even operated at their optimal levels of 60-80% (per DOE website) - would be many times this and would require opening a window wide every time the fan is operated. (DW expresses displeasure.)

So, perhaps I should reconsider whether I really need such powerful blowers ......

Seventh. Happy days. The lower profile hood can only accommodate a 500 cfm internal blower. A decision made for me. 500 cfm run through 7" at 13.5 equivalent-duct-feet yields 0.11 SPWG (not great, but acceptable), through 8" at 20 equivalent-duct-feet yields .086 SPWG, and through 10" (8" at terminus) at 28 equivalent-duct-feet yields .039 SPWG. And if operating at 60-80% or at 300 to 400 cfm, these back pressure numbers are, of course, even lower, and ALL acceptable.

Eighth. The manufacturer of the range still recommends 900 cfm and I've talked myself down to 500 cfm. So, back to the internet....

Range Width Method: 3 ft @ 100 cfm/ft = 300 cfm
Room Size Method: 4455 ft3 x 15X/60 min = 1114 cfm; kitchen area only 1170 ft3 x 15X/60min = 293 cfm
BTU Technique: 95200 BTU/100 = 952 cfm
Range Hood Area Technique: 3.5 ft x 1.83 ft x 90 cfm/ft = 576 cfm
Ductwork Technique: 2 elbows @ 12.5 + 1 wall cap at 40 = 65 cfm added to the largest number above.

So, not much help here...

Ninth: Ask DW how often she uses the whole stove and whether she woks or barbeques on the stove. Answer: "Not even once. That's what restaurants are for..."

Tenth: Decision time. Since we don't want to break our house, we have to use a low profile hood that can only accommodate a 500 cfm internal blower which will be mostly adequate for our (her) actual use. If she can be a little flexible as to how high above her head the bottom of hood is placed, I can go with the most efficient 10" ducting unfortunately partially impaired with a 8" terminus.

My plan is to wait for demo, dry fit 10", and see where the bottom of the hood is likely to be. If DW approves, I'm done. If wife doesn't like it (she wants the new hood a full 5" above the level of the old one; she's also raising the counter 1" and the stove an additional 1", so the distance to the burners is still less than the 36" maximum), I can return the 10" fittings and try again with 8". Repeat.

Thanks for reading. Any comments would be appreciated....

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Bengineer
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Re: Range Hood Blower Sizing

Post by Bengineer » Sun Jan 21, 2018 11:16 am

I've done a couple range hoods. Agreed, quiet trumps power. I installed a 600cfm 30" with an 8" pipe up through the roof over a gas range in my last house. We cook daily and I never used max speed. It was loud running wide open and not all that quiet at lower speeds.

Consider that while you may have a saturn-5 cooktop, you're unlikely to have much of it going at once. Sauteeing is midrange and requires attention. If you've got 4 burners going, at least a couple are likely to be simmering.

Variable speed is nice. I'd want several speeds at least.

Argue for as low as your DW will go for to make the hood more efficient at capture. A clear view of the back burners for the tallest cook, was my criteria.

Think about how far the hood projects too. You'll likely do your sauteeing, etc on a front burner. Often, the hood will have lights (seldom used in my case) in the front edge and the grease grates at the back. You might want to space the hood out a couple inches, depending on cabinets, etc.

Look at the grease grates and think about cleaning them and the interior of the hood. Would you need to disassemble the grates? Sharp edges? Nothing like ripping out a chunk of your hand while doing the cleanup.

Is the blower servicable? Can you take it apart to clean the squirrel cage and oil the motor bearings?

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fortfun
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Re: Range Hood Blower Sizing

Post by fortfun » Sun Jan 21, 2018 11:20 am

FraggleRock wrote:
Wed Jan 17, 2018 10:20 pm
We have 36-inch Wolf hob. Center burner is 20000 BTU.
With a 36-inch, 600cfm Zephyr hood.
Works great. Even when doing “Chinese” stir fry.
6-inch duct. One 90 bend. Total distance is 10 feet.
Image
Nice kitchen. Thought I was on Houzz for a second :)
https://www.houzz.com/

stan1
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Re: Range Hood Blower Sizing

Post by stan1 » Sun Jan 21, 2018 12:39 pm

FraggleRock wrote:
Wed Jan 17, 2018 10:20 pm
We have 36-inch Wolf hob. Center burner is 20000 BTU.
With a 36-inch, 600cfm Zephyr hood.
Works great. Even when doing “Chinese” stir fry.
6-inch duct. One 90 bend. Total distance is 10 feet.
Image
A question: do you have a link to the counter stools? Been looking for something like that.
Thanks

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Re: Range Hood Blower Sizing

Post by stan1 » Sun Jan 21, 2018 12:51 pm

No point trying for more than 600 CFM with 7" duct. You won't get the air flow and it will be noisy. Cooking style matters. If you are using a wok, indoor grill, or cook arromatic curries I'd enlarge the ducting. On the other hand if you are usually going to have at most 1 or 2 burners on high boiling water you are fine with the 7" duct.

I am 5'7" and insisted on a hood that was mounted over my head. Tired of hitting my head on our old hood (which also had sharp corners). Also insisted on rounded edges.

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Cyclesafe
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Re: Range Hood Blower Sizing

Post by Cyclesafe » Sun Jan 21, 2018 2:06 pm

My wife is 6'0" so, as I mentioned, we are also raising the countertops and raising the range as it aligns with the countertop. If I can only get her to go barefoot in the kitchen.......

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Re: Range Hood Blower Sizing

Post by itstoomuch » Sun Jan 21, 2018 4:48 pm

the amount of air drawn from the volume of the source of fumes is proportional to the distance :wink:
that proportion may be the cube of the distance {I forgot the math}.
I may be blowing hot air. :oops:
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Re: Range Hood Blower Sizing

Post by perl » Sun Jan 21, 2018 7:03 pm

Can I add some questions to this thread? We're planning to add a range hood to our kitchen. I'd like resources for figuring out how powerful it should be - where are the formulae in this thread from?

Also, what retailers of hoods have you used? The ones we have looked at haven't been appealing.

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Re: Range Hood Blower Sizing

Post by itstoomuch » Sun Jan 21, 2018 7:05 pm

We have PacAir Range Hood.
Rev012718; 4 Incm stream buckets: SS+pension; dfr'd GLWB VA & FI anntys, by time & $$ laddered; Discretionary; Rentals. LTCi. Own, not asset. Tax TBT%. Early SS. FundRatio (FR) >1.1 67/70yo

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Re: stools

Post by FraggleRock » Sun Jan 21, 2018 7:48 pm

stan1 wrote:
Sun Jan 21, 2018 12:39 pm
A question: do you have a link to the counter stools? Been looking for something like that.
Room & Board.
I do not see them on the website.

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Cyclesafe
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Re: Range Hood Blower Sizing

Post by Cyclesafe » Sun Jan 21, 2018 9:17 pm

perl wrote:
Sun Jan 21, 2018 7:03 pm
Can I add some questions to this thread? We're planning to add a range hood to our kitchen. I'd like resources for figuring out how powerful it should be - where are the formulae in this thread from?

Also, what retailers of hoods have you used? The ones we have looked at haven't been appealing.
It I were to study this again I would:

1) Decide whether due to cost, the limiting step to a range hood retrofit is the diameter of the existing ducting. Unfortunately, most homes do not come with ducting big enough to efficiently run anything larger than about 600 cfm (8"). Also determine whether local building codes require make-up air. If they do (>=400 cfm), think about these additional costs in addition to the costs of upgrading your existing ducting.

2) Think hard about whether or not you can settle for a blower that is optimized by your existing ducting and is small enough not to require make-up air. That (likely <400 cfm) blower will be a lot smaller than what you think you want, but remember your intent is to gently wisk away smoke, smells, and steam, not suck up anything not bolted down in your home. Separate NEED from WANT. Learn to love a smaller blower: cheaper, quieter, more efficient going through narrower ducting etc.

3) If you still want more power, you'll need to replace your ducting and depending on the code, cut another hole in your house, wire the damper, and figure out how to condition the air if you live in an inclement weather zone. Think again whether you really need the power.

4) There are many heuristics for sizing a range hood. None of them work. If you barbeque, grill, or use a wok - on multiple similtaneously used burners, you will need to make the above described investment. If you use two or three burners at a time, boiling water, simmering, and at worst one burner frying, you're OK without upgrading as long as your house isn't REALLY old and you have 4" ducting. If this is the case, you might as well upgrade to 10-12" ducting and have at it. 4" really won't cut it for much of a blower - 100-200 cfm tops.

So. With 6", 7", or 8" ducting, pick the hood you like that is appropriately optimized - without running afoul of the possible code requirement for make-up air. The decision should then be easy(ier).

Hope this helps.

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Re: Range Hood Blower Sizing

Post by perl » Sun Jan 21, 2018 9:45 pm

Very helpful, thanks.

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Re: Range Hood Blower Sizing

Post by Nebster » Mon Jan 22, 2018 7:41 am

Although OP has reached his conclusion(s), I'll still chime in.

I chose a 900cfm remote 4-speed blower with a 12" duct, because duct diameter is where you get your flow and quiet. The blower is ~20 feet from the kitchen, in our garage. Total run has two 90deg turns.

We placed the hood about 2.5 or 3 inches lower than standard, because we are short and because a slight change in distance also makes a huge capture difference:

Image

We installed a switched MUA that eliminates the negative pressure, since we do have a gas furnace. It also makes the hood more efficient.

Net-net, the thing is nearly silent on speeds 1 and 2 and unobjectionable on the higher speeds. And it captures all the grease, as long as you stick to stir-frying on the big element in the center of the cooktop. (If you need to make a mess on the side elements of your cooktop, you should size your hood 6 inches wider -- or more, if you're going to put it up high.)

It's hard to imagine needing more than a 900cfm in a residential install with sufficient duct sizing.

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Re: Range Hood Blower Sizing

Post by Cyclesafe » Mon Jan 22, 2018 9:28 am

Nebster,

You did it right. (And your kitchen looks awesome!)

If you were remodeling, what did you replace and roughly how much did it cost you for the re-ducting and the MUA system?

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Re: Range Hood Blower Sizing

Post by Nebster » Mon Jan 22, 2018 9:38 am

Cyclesafe wrote:
Mon Jan 22, 2018 9:28 am
You did it right. (And your kitchen looks awesome!)

If you were remodeling, what did you replace and roughly how much did it cost you for the re-ducting and the MUA system?
Thanks, I found the whole hood thing way more complicated than I expected. There were also zero demonstrations available, even in the high end stores, that were anything except unacceptably noisy and/or unrepresentative (or just, fake). At some point I just had to over-spec everything a little and hope for the best.

Hood, blower and MUA were about $2300. That rear wall in the picture there is my garage wall, so we could freely open any duct we wanted, and I didn't care about how unfinished it might look in the garage. The prior kitchen had a recirculating fan on the microwave above the range, so no ductwork.

The MUA ductwork was also a pretty straight shot because of the shape of our home and the location of the furnace in the basement. We probably got lucky there.

Both ducts plus the intake and exhaust penetrations on the garage walls, plus labor, was about $1200.

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Cyclesafe
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Re: Range Hood Blower Sizing

Post by Cyclesafe » Mon Jan 22, 2018 10:37 am

Nebster,

You piqued my interest.

Your 20' run of 12" with two 90's, say 25 equivalent feet, gives 0.043 SPWG back pressure with 900 cfm at zero SPWG. That's pretty darn efficient. If you run the blower at 60% capacity you get 0.016 SPWG, much better. No wonder, with the blower being remote and the oversized ducting, your hood runs so very quietly.

For our house, a remote blower placed far enough away from the kitchen to do any good would involve way too much expense unless we were to use ducting on the exterior of the house - not going to happen. My best case would be an internal blower hood with a rear outlet to vent straight out the kitchen wall. If I were to do this, I'd go 12" too. Why not? And get a straight wall cap. That would be a total run of 2' with no turns. And we could get the hood that DW originally wanted. I think, though, I'd still back off on the power - maybe to 600 cfm because I won't be putting in MUA (no code requirement for it in San Diego). 600 cfm with 2 equivalent feet of 12" duct would yield an SPWG of .002; throttled down 60% to 360 cfm an SPWG of .001.

https://www.engineeringtoolbox.com/duct ... d_444.html

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Re: Range Hood Blower Sizing

Post by mkc » Mon Jan 22, 2018 3:16 pm

We're going through this analysis (and designing MUA) as well.

Gardenweb (now Houzz) has a lot of good (and bad) discussion on vent hood capture sizing and blower sizing.

https://www.houzz.com/discussions/appliances

Look for member kaseki for good info on the subject https://www.houzz.com/activities/user/kaseki/comments

Michelle

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Re: Range Hood Blower Sizing

Post by itstoomuch » Mon Jan 22, 2018 3:37 pm

how about a spritzer system using
https://www.poopourri.com/?utm_source=A ... aign=Spray :wink:
and to reduce MUA heat loss/gain :?: in a big pipe :confused
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Re: Range Hood Blower Sizing

Post by Nebster » Mon Jan 22, 2018 5:21 pm

Cyclesafe wrote:
Mon Jan 22, 2018 10:37 am
For our house, a remote blower placed far enough away from the kitchen to do any good would involve way too much expense unless we were to use ducting on the exterior of the house - not going to happen.
Yeah, retrofitting a sizable duct into existing wall can be almost impossible a lot of the time. If you can go straight out the wall, that would be ideal.
I think, though, I'd still back off on the power - maybe to 600 cfm because I won't be putting in MUA (no code requirement for it in San Diego). 600 cfm with 2 equivalent feet of 12" duct would yield an SPWG of .002; throttled down 60% to 360 cfm an SPWG of .001.
MUA is really just for a safety issue with gas appliances. Depending on how tight your house is, I think you'll see any typical blower fan cfm curve fall off pretty quickly once pressure builds... but, really, for those rare times you want maximum ventage, you can just open a window or a door. You're in SD! :)

Nebster
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Re: Range Hood Blower Sizing

Post by Nebster » Mon Jan 22, 2018 5:23 pm

itstoomuch wrote:
Mon Jan 22, 2018 3:37 pm
and to reduce MUA heat loss/gain :?: in a big pipe :confused
This is a good point. With our system, in Colorado, just a few minutes on high in the winter dumps a considerable portion of our conditioned air outside. It is almost like having a whole-house fan, so some culinary planning becomes important, at times.

itstoomuch
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Re: Range Hood Blower Sizing

Post by itstoomuch » Mon Jan 22, 2018 5:53 pm

we got two fans in our PacAir unit (standard) . It does throw out a lot of air out. New units are at 960 cfm at 30,36,42,48 widths. https://www.pacairusa.com/mainThisRHPro ... D=KU-30SSB

My son has a Zepher hanging range hood, glass. It seems to accumulate a lot of oil on top of the glass. It's placed to high above range and is ineffective.
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Cycle
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Re: Range Hood Blower Sizing

Post by Cycle » Mon Jan 22, 2018 5:59 pm

Without makeup air, the pilot lights can go out, which is what the code in most municipalities is for.

Even if u get a super strong fan, the board can usually be modified to remove the higher settings. I did this on a couple I installed under permit in a remodel.

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Cyclesafe
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Final Outcome

Post by Cyclesafe » Fri Mar 02, 2018 5:35 pm

Couldn't efficiently connect to existing 7" ducting so rerouted new 10" ducting with two immediate 90 degree turns to exterior vent. Paid someone $400 to repair the damage to the exterior stucco.

Had a choice of 600, 900, and 1200 cfm internal blowers for the 42" Wolf Pro Hood (422418). Went for the 1200 because the amp draw was closest to that of the insert blower being replaced. Surprisingly, the smaller 900 (actually two 450's) drew 50% more amps. Go figure. And 600 cfm was a bit small for my 36" Wolf range top (SRT366). No code for make up air in San Diego. Installer never heard of it.

After installation, the installers, DW, and myself gathered around the hood for it to be switched on. No drama whatsoever. Turned down to its lowest level it was pretty quiet - much better than the ~300 cfm blower it replaced. Also, no wind coming in from the spacing around the windows; no effect on the pilot light in the water heater in the garage. Just a quiet blower that at its low setting draws up an unfolded Kleenex from about half way between the cooking surface and the hood. When turned to its highest setting it is a bit loud, but I can't imagine actually using it at that level for more than a few seconds.

All and all a success. Thanks to those on this board who helped me out.,

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Re: Range Hood Blower Sizing

Post by Nebster » Fri Mar 02, 2018 5:37 pm

Well done!

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