I'm still using the original range hood that came with the house. I think it is not sufficient as I get grease smoke escaping out the sides of the hood.

I think it's a Hoffco HC240 - I have no manual and no specs but I suspect it's a low CFM unit. Maybe 250cfm? Max 300cfm? I think the venting is a rectangular 3x10" duct that goes in the wall between studs into the attic; there I think it transitions to a round duct (6"? 7"? not sure) through the roof.

I want to improve the hood performance - get a new hood. But I don't want to do any roof work; I'd like to use the existing attic ducting (again 6" or 7" duct; I doubt it's 8" but would be great if so. I need to go into the attic someday and check).

Assuming that the duct is less than 8" it seems like my max flow is going to be about 400cfm.

Am I going to see much difference between 300 and 400 cfm?

Would ducting at the hood matter? Would it matter if I use the existing in-wall ducting or use new 6" or 7" ducting (matching the existing attic ducting) from the hood to the attic?

I don't want to deal with roof changes or make-up kits.

Need some help so that I can figure out what constraints I have in choosing a new model (Bosch or Hauslane or Sharp are contenders right now; still researching brands).

Thanks!

I have to ask: are you cracking a window open somewhere to allow air to come in?
It's hard for a ducted fan to move air out of the house if none can get in somewhere.

Also, can you determine that the duct is not obstructed anywhere?

No. And prefer not to open a window: AC or heater is usually on; also dust and pollen. Would prefer not to get a make up air kit.

I get what you’re saying but I thought 300-400 would be okay; I think make up air is indicated for 600+ cfm. But I’m not an expert; just what I think I read somewhere. Two reasons to keep 400 cfm or less is avoid make up air and larger duct through roof.

I’m hoping 300-400 cfm will be an improvement over whatever I have now with minimal change to existing ducting.

I did a superficial test of my existing hood with window open and closed: didn’t see any difference.

On our recent project we put in a 1200 cfm ducted vent with stainless steel panels like commercial kitchens instead of filters. It is amazing! On low evacuates most smells and smoke and for heavy duty use like fry or roux high sucks it all out!

Don’t listen to the airflow specialists who will tell you this won’t work. Most homes have plenty of “leakage” and if that’s not enough there’s plenty of air in your house…..

I’m running it 15 minutes not for a week. My objective was to be able to slam doors.

I’d go as high as budget allows.

Without make up air, I heard the fan may suck in outside air through the fireplace, wall/switch sockets, bathroom fans, other house leaks like door gaps.

Maybe this is good enough for 400 cfm. You’re saying 1200 cfm is working without make up air? Wow.

Remember that the fan noise will drive you crazy. You will need to purchase Bose Quiet Comfort 2 headphones to maintain sanity.

Remember that grease fires start in exhaust fan ducts at McDonald, with industrial draw cfm. Do you want grease in the duct in your home?

Remember that the electrical circuit has only so many amperes, based on wire gauge and run length and breaker capacity. Match fan motor to circuit.

Off topic alert.

Is the air in the "gilded cage" so bad that you don't dare open a window? Seems like a strong exhaust fan might exacerbate that situation.

quote:

Originally posted by konata88:
Without make up air, I heard the fan may suck in outside air through the fireplace, wall/switch sockets, bathroom fans, other house leaks like door gaps.

My hood has a pretty large flow from what I recall. I have to be very careful when the fireplace is being used to not put the hood on high, smoke starts pouring into the house. I'll have to check my CFM.

Another thing that can happen is that installers don't mount the hood at the correct height above the cooking surface. Each should have a distance range in their specifications.

Proper make up air won't pull much of anything into your house as it should be near your stove and go right back out the hood.

From your previous posts on remodeling it sounds like you don’t have a modern home (built in the last 10 years or so. If that’s the case make up air won’t be an issue because your home isn’t that tight.

Assuming that you are looking for a 30” range which is the most popular for standard homes this model available at Lowe’s will get you 600 cfm with a 6” pipe. There are other, more expensive options that can push more but this is a start.

Going to an 8” pipe usually isn’t necessary unless you have a gas range 36” or larger.


https://www.lowes.com/pd/Zephy...lse&idExtracted=true

quote:

I'm still using the original range hood that came with the house.

How old is the motor in the range hood? Could the bearings be going bad, slowing down the cfm?

Thanks guys, appreciate the help.

4mul8r: trying to interpret your comments. Are you reminding me that undersized ducts will be noisy and accumulate grease? Or not sure what you're advising me.

Opening windows here means hot or cold air gets in when the AC or heater is running and creating great expense given utility prices (except a couple of months when we don't need either). Also dust and pollen. I do use the windows in the morning (whole house fan) but otherwise try to keep the windows closed which also means during lunch and dinner time).

Sounds like make up is not immune given it has a built in heater....? But may be the effects are limited.... Still, would like to avoid if possible.

When I turn on the whole house fan (on high), if I don't have enough windows open, I can hear air being pulled through the bathroom ceiling fans. I don't have a modern home I guess - I think there are lots of leaks in the house (which also means it's not very efficient for cooling / heating; temp inside changes pretty quickly to outside ambient w/o ac/heating).

I have a 36" range but BTU on the lower side (cheap GE builder special). But I usually only use 1 or maybe 2 burners; I haven't used the low btu burners - still basically new. The problem is that the hood only extend out to partially cover the front burners (the ones I use). So, if I get a new hood, I'll get one with more depth and also raise the height from 24" to 30" so that I don't hit the hood with my head.

The motor seems to be going strong but it's original. I think it's just a weak unit to begin with. The unit does suck out smoke but not very strongly and not all of it; smoke escapes out the side of the hood. The air filter in the room detects it and tries to clean it up.

I think I'll go to the store and see what my options are per their recommendations:

1) options for keeping rear vent 3.25x10" vent
2) options for 6" duct
3) options for 7" duct
4) i'm ruling out 8" duct for now unless by chance the builder used 8" duct in the attic (will go up one day and check). Would like to avoid roofing work for now). If I move to it, would prefer to open window rather than install make-up air kit. If code forces a make-up kit, that will likely rule out anything that requires it.

I replaced my original 30" range hood a few years ago. I wasn't interested in a big fancy gourmet kitchen type thing I just wanted one that was more effective yet not too loud. After much studying I chose a Broan that has 3 speeds; low moves 150 CFM @ 0.6 sones, high 450 CFM @ 5.5 sones. In addition to moving much more air (I believe the old one was only 250 CFM) it is 20" deep vs the old one at 17.5", the extra 2.5" really helps when using the front elements. It works so well I almost never use high generally low or medium. My 3" x 10" duct runs straight back through an outside wall.

I would get up in your attic and check the duct and flapper. Hopefully it's fine but it wouldn't surprise me if someone ran round flex that could be partially crushed or even chewed through by a rodent.

My range hood has a washable filter. If yours does, is it clean?

quote:

Originally posted by ridewv:
I replaced my original 30" range hood a few years ago. I wasn't interested in a big fancy gourmet kitchen type thing I just wanted one that was more effective yet not too loud. After much studying I chose a Broan that has 3 speeds; low moves 150 CFM @ 0.6 sones, high 450 CFM @ 5.5 sones. In addition to moving much more air (I believe the old one was only 250 CFM) it is 20" deep vs the old one at 17.5", the extra 2.5" really helps when using the front elements. It works so well I almost never use high generally low or medium. My 3" x 10" duct runs straight back through an outside wall.

I would get up in your attic and check the duct and flapper. Hopefully it's fine but it wouldn't surprise me if someone ran round flex that could be partially crushed or even chewed through by a rodent.

This is hopeful - I'm hoping to get a deeper hood that will extend out to the edge of the burners; I hope this will make it more effective with less cfm. Especially with the existing 3x10" rear ducting (although mine elbows up in the wall and then up through the attic).

quote:

Originally posted by Pipe Smoker:
My range hood has a washable filter. If yours does, is it clean?

Don't all hoods have washable filters? I assumed so. It's clean; just builder special.

High cfm could pull grease into duct. Accumulated grease is a fire risk. Size fan for duct.

quote:

Originally posted by 4MUL8R:
High cfm could pull grease into duct. Accumulated grease is a fire risk. Size fan for duct.

How is this done? I believe I have a 3.25x10" duct in the wall that transitions to a 6" or 7" round duct in the attic. How do I size the fan for the duct? It sounds like the max recommended is 400 cfm for 6" and 600cfm for 7" - is this what you mean?

So choose a fan based on the existing duct size (tbd) unless willing to install new ducting and roof vent as required?

I visited a couple of stores - didn't help with fan choice (brand, air flow, type, etc). They suggested that I decide on a style first (under cabinet, wall mount, desired canopy height, etc). Then decide on air flow (cfm), vent type, etc. Backwards from the way I was doing it - I wanted to understand my constraints first (what relief is needed to improve on desired behavior, if any).

They are more aesthetics first then decide on specs. I actually don't really care about aesthetics - I'm more about most function with least of amount of cost beyond straight replacement.

Anyway, sounds like up to the attic is next step to find out what the existing ducting is. And then figure out how the current hood is mounted and vented. I sure which I had the specs for it.

quote:

Originally posted by konata88:

Anyway, sounds like up to the attic is next step to find out what the existing ducting is. And then figure out how the current hood is mounted and vented. I sure which I had the specs for it.

Isn't the model number inside behind the grease screens?