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Viking hood blower kits: In-line vs. External vs. Internal

Posted by nafex_nate (My Page) on
Mon, Jul 21, 08 at 1:24

I recently purchased a 42" x 30" Viking island baffle-style hood (VIH4208). This hood will eventually be over a 36" BlueStar Drop-in Cooktop (total of ~70K BTU), mounted 32" above the countertop. I was aiming for a 1200 cfm blower, but the three blower options for this hood have me baffled (pun intended). Should I use an internal, in-line, or external blower? My goal is to have the quietest system, realizing the exit to the duct will be near my deck.

This is an install on a first floor kitchen in a two story. The exit point would be on a small roof overhanging my deck's sliding doors.

The first picture is of the interior ceiling. the joists are 12 inches, 16 center-to-center", so I have about a 11 1/2" x 14" space to work with, so I am assuming that I can use a 10" round duct, as there are no obstructions from the light to the exterior wall.

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The second picture is of the roof that, if the line is straight, will exit on the roof.

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The third picture is the available area on the soffit.

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Some options I've been debating:
Option 1: 1200 cfm internal blower. Blower has about 8 feet of duct with one 90 degree elbow above the hood.
I am assuming this would be the quietest option for the deck outside, but likely the noisiest in the kitchen? How noisy are the internal blowers for Viking hoods?

Option 2: Install 1200 cfm in-line blower just under the roofline. The in-line won't fit in the joist area, as it's over 12" wide.
If it doesn't fit in the roof area for a straight exit (or with a 45 degree down, exiting the soffit area), I would have to put another 90 degree elbow in the duct and run it under the small roof and exit it out the fascia. This would be adding another 90 degree and 8 feet to the length, which didn't seem like a good idea to me. How noisy are the in-line blowers? The Viking website mentioned that adding a VSIL10 duct silencer could cut the noise up to 50%, but I couldn't find specs for it to see if it would fit in the joist area. I don't know if a silencer would be effective that close to the hood...is it made for attic type installs?
Overall, would option 2 be more quiet than option 1?

Option 3: Use an external blower. I'm assuming that external blowers are really noisy outside and wouldn't be preferred to have it almost right above the deck eating area? Has anyone installed an external blower close to a deck like this? Would this also need a duct silencer?

Any experiences/suggestions would be greatly appreciated!


Follow-Up Postings:

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RE: Viking hood blower kits: In-line vs. External vs. Internal

i have the 600 cfm internal blower, and it's plenty loud when you turn it up to high. i imagine the 1200 cfm internal is going to be deafening..

i guess my first question is whether you really need 1200cfm?

if money is no object, then your obvious choice is the 1200 cfm external fan. Installation gets more complicated because your now running electrical supply and controls in and out of the house to operate the fan. Download the installation manual for the blower from the Viking site, it will tell you about clearances, etc, and what you need. your duct lebgth will not be a problem with either configuration, 90 degree bends are calculated as adding the equivalent resistnce to a straight 10 foot run of vent tubing.


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RE: Viking hood blower kits: In-line vs. External vs. Internal

I really don't like in-line blowers in a kitchen fan. They are fine for bathrooms, but kitchen fans deal with grease, and an in-line fan is very difficult to get at and clean, leading to an unsafe grease build-up over time.

Unless you have a grill, you will not need 1200 CFM. If you plan on stir-frying a lot, you might consider a 8-900 CFM unit, otherwise 600 CFM seems about right. By reducing the CFM requirements, you also dramatically reduce the size of the ducting, which saves space and money. Lowering the hood also reduces CFM and duct-size requirements-32" seems to high-most are set at 30". Mine was originally set at 36", and I had to have it lowered to 30" to prevent the smoke alarm going off.

Internal motor installs are less expensive and easier to get service for than external ones. As to noise, remember that moving air is the main source of noise, not the motor/fan. The fan blades do make some noise, but most of the noise comes from the moving air.

The rule of thumb is that each 90 degree bend equals 10 foot of ducting. Most hood installs are designed to have 10-30 foot of ducting.

Lastly, I don't think I've ever seen an outdoor fan installed upside down. Is it possible to do this?


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RE: Viking hood blower kits: In-line vs. External vs. Internal

heartsurgeon and cpovey,
Thanks for the info. In March, after reading hours (days?) of hood information on GardenWeb, I had decided to get a VAH 42", 600 cfm (VAH doesn't make anything higher than 600 cfm for a 42" hood and 48" was too big). I had made a cardboard hood of that size and mounted above the cooktop (no cooking allowed!) to get an idea of sightlines. 32" was best for viewing across the greatroom for me, but the cook in the house was fine with 30". The VAH rep insisted to never go above 30", so we were set to go with VAH at 30".
But, since there was a delay in the BlueStar cooktop we wanted, we waited. The housing market got worse and a large appliance place folded and liquidated their inventory, and I got a deal on a Viking that I couldn't pass up.
The hood didn't come with a blower, so that's why I have been asking the blower questions. Since higher CFM blowers were available on the Viking, I thought I could push the hood up to 32" with higher CFM and be OK.
I figured the internal motor probably has twice the noise...the air noise through the baffles and then the air noise through the squirrel cage blower. So heartsurgeon, it wouldn't surprise me that it's noisy when on high at 600 cfm. Do you even hear the motor...or is it all air?
The external probably does look like the best option, as I agree with cpovey that an in-line motor would be a hassle to maintain. Looking at the specs, I think the external would fit on the roof.
Cpovey,
I don't know if I could install the external upside down either...is there a damper that would be upside down? I had been only considering venting out of the bottom if I used the in-line. If I use external, it would go on the roof.
Now today when I picked up my hood, I scrounged around the warehouse and found that they had a 600 cfm internal blower left for that hood, which I able to pick up for a good deal as well...so I couldn't pass that up either. So I"ll start with a 600 cfm internal, mounting the hood at 30". If it end's up too noisy, it's not that much of a loss and it would allow us to find out if we need more than 600 cfm. If we don't, but want to use an external for noise reasons, we will still come out ahead cost-wise.
I think I'll still use 10" duct work in case I do want to go up in CFM if we go to an external...it's not that long of a run, so it shouldn't cost that much more. Also, I would think that a 10" elbow above the hood would make less noise than a 7" elbow.
I plugged the 600 cfm fan in (not inside the hood) to an outlet to see how noisy it was. It does make some noise, but it seemed less noisy when I added some wind resistance, so I won't be able to tell much until it's fully installed. It sure could blow some air when unrestricted though! This got me a little concerned that if the vent exits on the top of the roof...it will be only about 8 feet away from the deck table, pointing right at it. Will this cause an unappealing breeze to the outside dinner guests? Maybe the baffles cause enough resistance that it really doesn't blow out that fast in the real application?

I am still interested to hear if someone has put an external fan this close to an outdoor sitting area and what the noise level is like. I'm guessing that it may just be a white noise-type situation outside?


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RE: Viking hood blower kits: In-line vs. External vs. Internal

Looks like Viking's lowest CFM for an external is 900.


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RE: Viking hood blower kits: In-line vs. External vs. Internal

This is very timely as I have an opportunity to purchase a 48" Viking hood from Craigslist at a great price, but it needs the blower. I will be putting it over a 48" range, no grill and don't really stir fry. It will be on an outside wall. While I hear conflicting opinions, I do think 600 CFM would probably be enough for me. Looks like the in line blower is the least desireable. So is the internal or external blower the better option? Thanks!


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RE: Viking hood blower kits: In-line vs. External vs. Internal

malhgold,
If you are on an outside wall you probaly have a very short run to your exterior vent. 600 CFM should be plenty. I have the 600CFM Viking but I have a good 15' run straight up. I have the internal blower that sets right inside the hood behind the baffles. Mine is over 8 years old and no issues at all.
The motor does make some noise but it is primarilly air. If you have never had this type of hood system before it will seem loud at first.
nafex, I would suggest speaking to a professional installer before going ahead with 10" duct work on a 600 CFM internal blower. 10" pipe could alter the performance of a 600 CFM unit.


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RE: Viking hood blower kits: In-line vs. External vs. Internal

I think I'm going to stay with an internal blower, even though it may be a little louder (I'm going to check that out tomorrow at a store that has both to see how different they are).
I talked with some retailers today to see what other people are installing. All three said the internal blowers were the most common, primarily because they are cheaper and easier to install. One said that they rarely sell externals in our area (Minnesota) and that he doesnt recommend them because they can freeze up in winter. That does make some sense, though I haven't heard of this complaint on-line yet.
As far as using a 10" duct on a smaller blower, I think the rules are fairly simple for vents, which is to make the exit the least resistant to air flow as possible, improving the vacuum at the hood. I haven't gone through the math on this one, so maybe a 10" doesn't buy very much improvement over a 7", but it won't hurt...as long as I can find an adapter to take the 7" hole in the mounting plate up to 10". Larger ducts effectively reduce the calculated length of the run, just like elbows lengthen it. If there was an issue with this, then there would be warnings about having ducts too short, which I have never seen. The comment above about venting a wall 600 cfm right out the wall is an example of a system that would have much less resistance than my 7' long 10" run.
Someone else posted(http://ths.gardenweb.com/forums/load/appl/msg0311080322597.html) that they saw a requirement that you should have a 2 foot straight duct right after the internal blower, which is almost impossible to do on an 8' ceilings in a two story.
This was a 1200 CFM Viking. If this is true, I would guess that this might be due to the turbulence of pushing air out of the blower right into the elbow. I would think oversizing the duct would help this. (Though oversizing for a 1200 cfm is really difficult, unless you run two ducts, as someone suggested).


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RE: Viking hood blower kits: In-line vs. External vs. Internal

Now looking at the previous 1200 cfm post, It may have been an external 1200 cfm blower that Viking said needed 2 feet of straight duct before the hood. Maybe clax66 will clarify that.


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RE: Viking hood blower kits: In-line vs. External vs. Internal

I checked out a Wolf hood with a 1200 external blower unit at a store (baffle unit, very similar to my Viking hood) and it sounded fairly quiet to me. I doubt that my 600 cfm internal will be that quiet. If the 600 cfm internal is too loud I think I would switch to the external and risk the possibility of it freezing up, since I have reasonable access to that small rooftop above my door.


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