Suggestions for a log run kitchen exhaust

[Mike Hartigan]

I'm finishing up my basement bar that includes a range with a grill. These beasts tend to generate some smoke, so a vented exhaust is a must. I've got a nice, beefy blower, but I'm concerned that the 20' duct that will be installed above the suspended ceiling will leak smoke and/or grease, particularly since the blower will be installed at the hood, meaning that there will be positive pressure along the entire length of the duct. How can I minimize this? 4" PVC would be nice, but I suspect that it wouldn't be well suited to this application (and probably not code). What are my options?

[DanG]

Don't let a code authority or an insurance man know what you are doing. That run of duct will need to be welded steel with fire suppression. No joints allowed. It should technically be a grease hood with Halon, but they may reluctantly allow adapting a conventional hood with a remote Ansul valve. As far as I know, you will need to install an exterior grease fan, not a push type.

Ain't code compliance wonderful?

[AZ Nomad]

Those sound the requirements for a restaurant. Aren't the requirements in a household going to be less stringent? Most home owners don't cook for a thousand people every single night.

[JoeSpareBedroom]

Why should the science of fire prevention be any different at home than at a restaurant? Maybe the ducts in a restaurant reach the danger level in a month, and at home, two years, but at that magical moment, there's enough grease in the pipes to make life interesting. The length of time to the MOMENT is the variable.

[Mike]

Surely, the requirements are different for a home. For example, how many combination microwave/exhaust hoods do you see in a restaurant equipment catalog? And, last I checked, none of the $150 GE microwaves at Best Buy included provisions for Halon. My restaurant experience leads me to suspect that a month's worth of buildup in a restaurant's ducts is more like a century's worth of buildup in a residential kitchen. Your point, while certainly valid, is a bit of a stretch.

[JoeSpareBedroom]

I wonder if that "stretch" might be partially negated by the OP's defective plan to run 20' of 4" PVC as an exhaust.

[Mike]

As I read it, the OP wisely dismissed the PVC idea as not suitable for this application. It also sounds like his goal is to stay within code. While I'm not pretending to read his mind, I suspect he's simply asking for realistic options. What sort of ductwork is routinely used in residential kitchens in which the hood is not on an outside wall? An island range, for example.

[JoeSpareBedroom]

10 years ago, a kitchen place told me I had to use something like 6" metal. Then, the guy said "Good luck cleaning it". This helped me talk my wife out of the idea, and we kept the stove on the outside wall, with a fan to the outside.

I think the OP should tell us the purpose of having this stove/grill in the basement bar. Does he envision grilling lots of typical BBQ food down there? If so, he needs to decide which is less convenient: Running outside to the BBQ, or cleaning the ducts every so often.

[AZ Nomad]

I would guess it would be the same as cleaning any duct or chimney. A rotating snake on a reel, rotor-rooter style, and a brush.

There's no need as long as there aren't any 270 degree turns.

[AZ Nomad]

Irrelevent.

[JoeSpareBedroom]

Really? What if Mike's a youngster who's never cleaned the inside of a heavily used BBQ? That's easy. He'd have no clue what it's like to clean gummy grease out of a cooking fan duct. Neither do you, obviously, although you will disagree in your next message.

[Mike Hartigan]

Sorry, guys. I thought it was a simple question. What kind of ductwork is traditional, safe, and not overkill for a residential range hood that is 20' from the most convenient exterior wall? Note that I'm NOT planning to use PVC. And let's assume, just for grins, that I know how to clean it.

[JoeSpareBedroom]

Call your local building inspector and find out. Please report back here with the results of your inquiry.

And, just for grins:

1) What type of stuff will you be cooking most of the time? Cups of tea? Steaks?

2) How will you clean this 20' length of ductwork?

[Mike Hartigan]

Steaks, burgers, boiling wort, and smoke from my coffee roaster. And maybe an occasional cup of tea.

With the same equipment I use to clean 25' of flue. Don't worry, I'm not a moron.

[JoeSpareBedroom]

I don't think you're a moron. I'm wondering if a fireplace chimney contains crud that the same as the vent from a cooking fan. I've never cleaned my own fireplace chimney, so I don't know the answer to this.

[Boden]

I run about 20 ft from a pop-up down draft exhaust. In my experience down drafts need more air flow than up flow exhausts. I used 8 in spiral pipe, with a good sized FanTech axial blower. Size the pipe so that the exhaust velocity is high, but not so high that you get turbulent flow. Watch the Reynolds number. A pitot tube and a Magnehelic gauge will let you get pretty close. Too large a pipe is as bad as too small a pipe. I put a tee at the bottom of the vertical pipe from the down draft to collect grease and provide access and a cast aluminum access port in the side of the horizontal run. Cleaning is messy but not difficult.

It works well.

[Mike Hartigan]

I would probably use a different set of tools if I did it professionally, but for a once a year thing (which is overkill for a typical kitchen exhaust), it's just a question of cleaning the brushes and a bit more elbow grease.