A blower door test will tell you exactly what the CFM of the hood is, you may have that done anyway as part of construction. More practically (and cheaper) you can test the performance by generating smoke under the hood and seeing whether the hood clears it. Smoke candles or pellets that produce a set volume of smoke in a given time (eg 200 cf in 30 sec) will let you see just what your hood can actually clear. A commercial testing company can measure the air flow at various points around your cooking surface to also let you know about performance.

I prefer the wok test-- if I can char a wok full of chiles in oil without sending the rest of the inhabitants running from the room, it works.

Actual performance of the hood is a function of many factors in addition to CFM, CFM is probably not as overall important as the shape and position of the hood relative to the source --tall, deep, wide hoods work better than flat narrow ones for any given CFM for example. Obstructions like shelves and baffles van make a big difference.

Here is a link that might be useful: example smoke pellets

Thanks for the great info. I have a wolf 36" cooktop with charbroiler in the middle and a wolf 42" 1100 cfm hood. I have cooked veggies and chicken only on it and it seems to smell up the whole house when I cook. The hood is around 35" above the counter. I went into my attic today while it was running and I could feel and here a few small air leaks in the pipe. Could these small leaks cause a problem? I also could not feel any suction when I put my hands up to vent but it would suck a piece of paper up to it, but not hold it there. I like the idea of the pellets. Where are they purchased? I do believe this hood has baffles. The metal things under the hood? Should I be getting this much smell or do you think my hood isn't setup correctly?

Thanks

DO you have make up air? A straw into a sealed bottle can't suck anything out. Air going out has to have air coming in to replace it.

How large it the duct for your hood, and how many bends (45's, 90's)? It should probably be 10" for that fan rating.

If you open a kitchen window, does the hood suck better? My house is so leaky that makeup air isn't required for flow, but yours may be better sealed.

A typical way of measuring the flow would be to measure differential pressure drop along a straight length of duct of a known diameter and calculate the flow rate.

Also check that all damper doors in the ducts can freely open and are not blocked by errant duct-connection sheet metal screws.

kas

I don't have make up air and my house should be really sealed because I have spray insulation. I did try running it with a window opened and couldn't really tell a difference. Wouldn't this kind of be the same thing as make up air? The ducts are 10" before and after the in line blower. I believe there is 1 90 degree turn before blower and 1 after blower. I could take a picture of the setup if that would help. Kaseki how do I go about checking the damper doors and where exactly are the damper doors located? Sorry I really don't know a lot about this stuff.

Yes, opening the window is a good source of make-up air, assuming it is positioned away from the hood vent. In our pretty well sealed house it makes a huge difference. I'm thankful that we're allowed to use such a sensible solution for the 20 minutes a week the hood is cranked up rather than having to install an elaborate and expensive mechanical solution.

Do you have access to the vent on the outside? 1100 cfm makes a big wind if the hood is working correctly. Normal cooking odors should be thoroughly exhausted. Check that the dampers swing open and the path is unobstructed -- if the air is blowing out of the building vigorously that's a pretty good sign. (Once saw an installation where everything was installed with a pipe on one side, grate on the other, but no hole cut in the wall in between. Go figure.) The pipe should be reasonably air-tight, leaks could be blowing some of the odor back into your conditioned space. Seams can be caulked or sealed with "real" duct tape (the kind in the plumbing section that costs $15-20/roll and carries an ASTM rating)

Is there any fresh air intake into your house close to the hood exhaust (eg for an ERV)? You may just be recycling the odors.

There was a link to a seller of smoke candles in my last post.

Typically, hoods have dampers at their duct interface, or the HVAC installer may put one in that location. The roof cap may have a damper. My system has a damper both above the hood and at the roof cap, which includes the blower. I have read where only one damper is recommended, but I think that concept is defective in areas where the duct transits cold spaces.

Looking up into the hood with the baffles removed may show the damper, if present, and its states with blower off and blower on should appear different. Often one can hear the two sides of the damper open at different points in the blower spin up time, and close sequentially when the blower is turned off.

If the only damper is at the roof, then its state when the blower is running should be obvious for some designs so long as there is a position to safely view it.

What is most telling is that there seems to be no difference for your sealed house when the window is open or closed. Something has to be blocking the exit path. The air flow through an open window should be quite strong at full hood blower power.

kas

I will try to check for the dampers when I get home. There could be one where it exits the roof and one above the baffles right? I have to figure out how to remove the baffles also haha. I inspected it a little closer last night and there are 2 90 degree turns before the blower and 1 after. I also noticed that where the duct meets the blower there is a metal plate and the weight of the duct seems to be pulling the metal plate away from the blower. I think I could possibly be losing a lot of the suction in this gap. I could hear the air being pulled through the gap and if I pulled up on the ducting it closed most of the gap and you couldn't hear the air being pulled through. There are not any fresh air intakes around the roof cap. I cooked a couple pieces of sausage in a frying pan last night and it did ok when the pan was covered but when I tried it uncovered some of the smoke went over the front of the hood.