Any general contractors? Ducted vent hood question

FanOfFanboys

My stove wall backs to the garage. I know the consensus is always duct outside but it’s not a feasible option for me. From what I’ve read it seems the biggest reasons to not vent to the garage are 1) the smell is now in the garage and not outside 2) the fumes with starting a car in an enclosed area is potentially dangerous 3) grease can/will be on whatever is in front of the duct opening

Am I missing any major concerns?

I have a fairly large 2.5 car garage but we don’t park our vehicles there. Boat, workbench, weight bench, and then open area. Nothing would ever be started indoors. Even lawnmower and such are in the yard. My garage is also open a lot of the time, probably half. So I’m not too worried about those valid concerns. I was also thinking about a filter at the opening to catch the grease/oil as that’s my biggest concern. And I know that would require regular change by me or I would make things worse. But I’m curious if a filter is a good idea and how much actual grease/oil comes out of duct?

Anything else I need to consider that I’m missing?

nolaegghead

Most kitchen hooks have a grease trap (filter).  

My concern would be ducting outside your living area into a closed room, that room will need to displace that amount of air and you need to account for that. The make-up air in your house needs to come from somewhere - the garage will be pressurized from the vent so I would put a powered vent to vent your garage outside when it’s on to keep the garage from being positive pressurized relative to the living areas/kitchen.  

I would think you don’t want garage air coming back into your house (exhaust, solvents, fertilizers, etc would contribute to poor air quality in your house).

anyway, I don’t see a problem is you manage all that.  Although that configuration probably wouldn’t pass code, those vents need to be double walled, assume a kitchen fire would roll through the vent… and into your garage.

lkapigian

FanOfFanboys said:

My stove wall backs to the garage. I know the consensus is always duct outside but it’s not a feasible option for me. From what I’ve read it seems the biggest reasons to not vent to the garage are 1) the smell is now in the garage and not outside 2) the fumes with starting a car in an enclosed area is potentially dangerous 3) grease can/will be on whatever is in front of the duct opening

Am I missing any major concerns?

I have a fairly large 2.5 car garage but we don’t park our vehicles there. Boat, workbench, weight bench, and then open area. Nothing would ever be started indoors. Even lawnmower and such are in the yard. My garage is also open a lot of the time, probably half. So I’m not too worried about those valid concerns. I was also thinking about a filter at the opening to catch the grease/oil as that’s my biggest concern. And I know that would require regular change by me or I would make things worse. But I’m curious if a filter is a good idea and how much actual grease/oil comes out of duct?

Anything else I need to consider that I’m missing?

More grease than you think will come out of that duct,even if you don't " fry foods" . A concern would be, it sounds like you will be, going horizontal and grease collecting in that run. Adding and elbow to an exhaust can be done but you need to figure the Total Equivalent Length of that 90 added to the other duct lengths.... can you provide any fan info and duct layout information....is there any reason you cant 45 into the garage and 45 back up out the garage roof? would still total 90 degrees , get the exhaust out of the roof 

Just my thoughts 

FanOfFanboys

We're doing a bunch of home renovation and doing pretty much all at once. So I take full blame but didn't research impact and full picture of every decision. I wanted vent hood, ducted is best, so I ran to that. I also ordered to vent hood, removed microwave, and ripped out those cabinets. Then I started thinking about ducting. And everyone is right, the garage is a terrible idea. 

My house, which I love, is fighting for 1st place of worst house possible for a ducted vent hood. Stove backs to garage, breaker panel on the other side, room above the garage, brick exterior, etc. 

So, here is where I ended up. Going straight from the vent hood to garage with ducting. Can't go down between the walls due to the breaker panel. Instead, ducting will run down garage interior wall under the house. Downstream isn't perfect but I feel good it'll work. From there it'll run under the house via crawlspace to the outside. 

Other than ugly exposed pipework in the garage, which I can address, this should address any issue. And have me at what, 90%? Still better than recirculation. 

So please, let me know where I'm wrong so I can address and fix it lol 

nolaegghead

That sounds fine, but you definitely need double walled ducting, also sized correctly.  Every bend and foot of length adds static pressure and decreases your flow rate.  There are tables for static pressure and duct size all over the web.  If you have tough inspections and codes, you may want to run this by that dept, they may make you remove it all if it doesn’t fly.

lkapigian

At the very least you have 270 degrees of offsets, which is more than allowed for ventilation, fortunately it’s not “ flue gasses” . It will probably be fine … can you share the fan specs 

Thermadoor is the only downflow stove\range vent system I know of 

FanOfFanboys

lkapigian said:

At the very least you have 270 degrees of offsets, which is more than allowed for ventilation, fortunately it’s not “ flue gasses” . It will probably be fine … can you share the fan specs 

Thermadoor is the only downflow stove\range vent system I know of 

This is a massive learning curve for me so I appreciate everyone's comments. Reading as much as I can online but it is not a simple direct process due to variables, it seems

The hood is a Zline 400 CFM. Reading through their manual it says 40 feet of ductwork max and no more than 2-3 elbows or 90-degree turns. 

I have read that for each elbow or turn you should subtract 5 feet from your max, though in other places I have read subtract 10 feet. So my max would be anywhere from 10 to 25 feet, depending on which formula I follow. To get it from the vent hood to my crawl space is about 12 feet. So far I think I am ok. Please let me know if I am wrong up to this point.

The next, and I think final, step is what to do once it is under the house. I know I will have a backdraft damper. My crawlspace is pretty large, I can stand straight up at 5'7. So I think I am fine to just let it vent there from a practical standpoint. But that would not pass inspection. (I will probably stay in this house until I die, but even if I moved and needed an inspection prior I could make a change.) But if I vent it outside of the house then I would pass inspection, assuming my distance is within an acceptable range. Again, please let me know if I am wrong up to this point as well. 

So I am going to measure from the point in the crawlspace to the closest direct exit. If it is under 10 feet, because at this point I cannot add another elbow or turn, then I am golden. If I am not then I either decide to leave it venting in the crawl space or I have to add another fan to push it out. I have not looked into that option yet. 

I will use a steel duct that is rigid with a smooth interior, butyl aluminum tape, and the vent hood will be on an individual branch circuit.

I have learned a lot the last couple of days on this, hopefully I am getting close to a good working solution 

FanOfFanboys

This is the elbow from the garage to the crawl space. That will be 1 of 3 total. 

lkapigian

FanOfFanboys said:

This is the elbow from the garage to the crawl space. That will be 1 of 3 total. 

Thanks for the info, being that it is a "Forward Curved" fan ( blower vs Prop Fan) it will be OK with the added static , you will be about at its limits but should be OK, I would want to make sure you have access to the remote blower for service as you will get built up in the vanes of the blower and will need cleaning , even with a grease filter ....Nice Hood ( vs the hood I live in LoL)

FanOfFanboys

lkapigian said:

FanOfFanboys said:

This is the elbow from the garage to the crawl space. That will be 1 of 3 total. 

Thanks for the info, being that it is a "Forward Curved" fan ( blower vs Prop Fan) it will be OK with the added static , you will be about at its limits but should be OK, I would want to make sure you have access to the remote blower for service as you will get built up in the vanes of the blower and will need cleaning , even with a grease filter ....Nice Hood ( vs the hood I live in LoL)

Thanks! Just picked up all the duct. No double insulation but I should be good. Is there a tool that can test the air pressure at the exit to see if it's working the right way? Maybe something I can rent

And thanks, it's one that looks like copper (real copper was 5x the cost) so we're excited. Itll be a statement piece in the kitchen for sure. Tiling behind it instead of painting

lkapigian

FanOfFanboys said:

lkapigian said:

FanOfFanboys said:

This is the elbow from the garage to the crawl space. That will be 1 of 3 total. 

Thanks for the info, being that it is a "Forward Curved" fan ( blower vs Prop Fan) it will be OK with the added static , you will be about at its limits but should be OK, I would want to make sure you have access to the remote blower for service as you will get built up in the vanes of the blower and will need cleaning , even with a grease filter ....Nice Hood ( vs the hood I live in LoL)

Thanks! Just picked up all the duct. No double insulation but I should be good. Is there a tool that can test the air pressure at the exit to see if it's working the right way? Maybe something I can rent

And thanks, it's one that looks like copper (real copper was 5x the cost) so we're excited. Itll be a statement piece in the kitchen for sure. Tiling behind it instead of painting

You can get a inexpensive vane anemometer off of Amazon, either stand alone or one that will work with your cell phone , for a once in a while use they are ok , it will read out in feet per minute , multiply by the square foot of the duct will get you cubic feet per minute, CFM