Range Hood Make-up Air - HVAC - Contractor Talk

Range Hood Make-up Air

 
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Old 02-18-2018, 08:53 AM   #1
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Range Hood Make-up Air


Hi guys,

So it looks like I'm likely getting a job for a range hood installation, & it will be my first. It's a Cavaliere 218 series wall hood. The spec sheet from photos I took of the customer's actual installation manual says it has 4 settings and 900 CFM max. Here's a link to what appears to be the same manual:

http://cavalierehoods.com/photos/wall-install.pdf

Being new to this, unfortunately I'm just now realizing that code requirements for make-up air might apply to this unit because it can move more than 400 CFM. I say "might" apply because I'm still trying to understand the code hierarchy for Marysville, WA, where the range hood will be installed. In other words, which code document takes precedence (IBC, IRC, county code, city code, etc.), and also which year has been adopted.

This may be critical, since past regulations sometimes required the make-up air system to be electrically controlled and wired to the switch which turns on the range hood. Ugh. The 2015 IRC isn't as stringent, however - it seems to allow for passive systems for make-up air.

Anyway, I'm completely new to this and have two basic questions:
1. How would you provide make-up air for a 900 CFM range hood? If it matters, it's a very small kitchen, but it's completely opened into the living/dining area.
2. (For Washintonians) Can anyone state with confidence which codes apply to a job in Marysville, WA?

I have a background in engineering - including some mechanical engineering classes - so I'm familiar with the concepts behind the need for make-up air. Basically it's conservation of mass thing. So if possible I'd like to keep the discussion centered around the two questions above, rather than get into the "why" regarding the need for make-up air. That being said, if the "why" becomes pertinent to answering the questions, feel free, by all means!

Lastly, here's an excellent article that I came across yesterday in researching range hood air.

http://www.greenbuildingadvisor.com/...ir-range-hoods

Thanks for the help!

Steve
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Old 02-18-2018, 10:35 AM   #2
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Re: Range Hood Make-up Air


Hello....
If units are above 400 cfm then codes require make up air installation.

All of my customers are required to provide units less than 400 cfm which avoids this mess.

Simply put, fresh air needs to be replenished for the air removed

There are a few ways to go about this. A hard wired damper that regulates the air can resolve this issue. Also if you are installing a new home, the make up air can be received through the HVAC system via configuration.

You SHOULD consult with the manufacturer.

If the area is tight where the exhaust hood is being installed, installing a wired damper may not be possible.

Easiest solution is to get the same exhaust that is less than 400 cfm if located in a house.

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Old 02-18-2018, 01:22 PM   #3
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Re: Range Hood Make-up Air


Doesn't pertain to me, but an insightful answer in a timely manner by someone in the know, a newer member at that. Nice!


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Old 02-18-2018, 01:37 PM   #4
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Re: Range Hood Make-up Air


Bring in make up air through a return Duct to the furnace. You would need a electronically controlled damper to open when the fan is energized.
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Old 02-18-2018, 05:57 PM   #5
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Re: Range Hood Make-up Air


Hi guys,

I appreciate the responses - thanks. You guys are extremely helpful.

I think maybe I'm in over my head on this one and didn't realize it. I'll likely have to go back to the (potential) customer and let her know that, upon researching it further, I would recommend they have an HVAC specialist do the installation. I don't feel I could do the job justice.

I'm not familiar enough with HVAC systems to do the types of things mentioned in previous posts for providing make-up air. Plus, it may then cross over into permitted HVAC work, and I'm not sure whether that's allowed for me. I do know I can't legally do any plumbing or electrical in WA state, so I don't. But I've never had the occasion to check into our HVAC laws because it hasn't come up yet.

Regarding checking with the mfg - probably not a bad idea, but in the article I referenced in the initial post, they pursued this path to no avail. Maybe that was an isolated situation, not sure. But the article is a really interesting true story. A range hood seems to "slip between the cracks" into an area where people are hesitant to take full responsibility for giving instructions regarding providing make-up air - certainly not the mfgs. Probably because it's highly dependent on the situation, the existing HVAC system, etc. Which brings me back to the conclusion that this is probably a job for an HVAC specialist.

Here's a link to the article again so you won't have to go back to my original post:

http://www.greenbuildingadvisor.com/...ir-range-hoods

Note to self: no more range hood quotes for units >400 CFM. Lesson learned.

Off to lick my wounds...

Steve
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Last edited by svankirk; 02-18-2018 at 05:59 PM.
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Old 02-18-2018, 06:20 PM   #6
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Re: Range Hood Make-up Air


Side note: after skimming the article again, I decided to have a look at a make-up air dampers made by one of the mfg's mentioned (Broan):

http://www.broan.com/products/produc...f-14c942e56875

A quick skim of the installation instructions noted two things:
1. A transformer is included - which implies electrical work. Which I'm not allowed to do.
2. There's a disclaimer about making sure the temperature of the return air on the intake side of furnace system doesn't cause problem with the system.

So bottom line: this only confirms to me this is a job for an HVAC specialist.

If I'm off base here and making this harder than it needs to be, please let me know. But that's the view from my world right now.

Thanks,

Steve
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Last edited by svankirk; 02-18-2018 at 06:31 PM.
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Old 02-18-2018, 10:34 PM   #7
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Re: Range Hood Make-up Air


Good Answer: you were a few hours away from creating a CO2 and or CO posioning accident when the hot water and or the furnace flues backed up under the partial vacumn you created with an unbalanced air loss.

You need to pump an equal amount of tempered(heated with the exhaust air) via an ERV device of the correct size and software, with the discharge as near the burners as possible, behind the range under the Hood.....

900 CFM is more air than 4 natural gas fired clothes dryers exhaust....And a single dryer can create chimney flow problems in a tight modern home....
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Last edited by Fouthgeneration; 02-18-2018 at 10:48 PM.
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Old 02-19-2018, 09:47 AM   #8
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Re: Range Hood Make-up Air


Hey - thanks for the input.

FWIW, I called the customer yesterday afternoon & let her know this installation was really a job for an HVAC specialist - that I wasn't the right man for the job. She (understandably) took me to task a bit, stating that it was "just a residential hood", and that if it was a big commercial thing she could understand. I explained that her unit was 900 CFM & moved more than twice the air stipulated by the code in its requirement to provide make-up air (400 CFM). She wasn't happy, but I'll spare you the details.

So again one of the lessons here for me is this: a range hood installation for units >400 CFM really can't be done "in a vacuum" (pun intended). In other words, you can't just treat it as an isolated appliance and install it without regard to the rest of the home. It really becomes part of the entire home's HVAC system & needs to be considered as such.

Translation: get an HVAC specialist.

Again, thanks to all who gave input on this. I really appreciate it!

The wounds are beginning to heal...

Steve
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Old 02-19-2018, 10:16 AM   #9
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Re: Range Hood Make-up Air


Some very well written posts Steve. I believe you are making the right decision.

What I would like to know is how did the homeowner arrive at the decision to install a 900 CFM hood in a small residential kitchen. That is massively oversized for a house.

FourthGeneration was spot on in his post about the consequences of using such a large exhaust. In order for the house to be able to use the hood the make-up air would have to be located IN THE HOOD via ducting from the exterior.

I know as I have had to design systems like this for Sheet Metal and A/C shops that I worked for.


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Old 02-19-2018, 10:51 AM   #10
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Re: Range Hood Make-up Air


Hey thanks, Andy. I appreciate it. It's nice to have confirmation that this is the right decision. Thanks to others who have confirmed this as well. Priceless info.

FWIW, I think the customer ended up with the fan innocently enough. She has a small house that is single-level and fairly open. Her existing hood is ductless, and she was tired of having clothes in their bedroom closet smell like bacon. So she did what any rational human being would do: she went on Amazon & found a good deal on a big fan. (Who knew?)

Question regarding previous posts: wouldn't providing make-up air right at the back of the range create the "short-circuit" condition for air flow that was described in the article (see excerpt below)? In other words, it's probably ideal for air movement, but not so much for actually containing the smells? My guess would have been that it's better to provide the makeup air elsewhere in the kitchen, but near the range. And maybe in a couple spots, ideally - and preferably between the kitchen and where it transitions to other rooms, to "catch" the smells before they leave. But I'm just guessing.

Excerpt from the article:

Lacking any guidance from GE, neither Cheryl Morris nor her HVAC contractor were sure how to proceed. The contractor’s $1,000 solution was to install two 12"x12" exterior air makeup air grilles on the wall between the stovetop and the range hood. Unfortunately, this source of makeup air is so close to the hood that an airflow short-circuit was created, allowing cooking smoke to drift into the kitchen.

Have a good one!

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Old 02-19-2018, 11:55 AM   #11
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Re: Range Hood Make-up Air


If the question is, would opening up a window, while turning on the fan would be sufficient, the answer is yes. For the majority of homes, one of those super hoods is overkill. But, the code is the code.

The return duct thing, typically is the best way to bring in the fresh air without cutting extra holes in floors or walls.
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Old 02-20-2018, 02:55 PM   #12
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Re: Range Hood Make-up Air


I am curious to see what actually works. I've done restaurants and everything needs to be sized to work together and here in Southern California it required a swamp cooler to cool the make up air and not put the load on the HVAC unit. The HVAC unit doesn't pull in outside air anyway. I have looked into the make up air units that are fan operated to actually push air into the room but they make no provision to heat or cool the outside air and they need to be a fair distance from the hood to work. It seems to me that you could do it on a gut remodel but trying to get it all switched together requires money and disruption. Looking forward to see if anyone actually knows what the solution is for the requirements
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Old 02-20-2018, 04:32 PM   #13
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Re: Range Hood Make-up Air


Talk to HVAC guy and see how you can provide makeup air for that house. Makeup air must be properly installed to maintain safe and comfortable condition and at the same time provide efficiency.

You can spend a lot of money trying to provide makeup air but if it was done improperly, makeup air systems can create drafts, stressed out HVAC unit, could also cause mold and house depressurization.

Also, keep in mind that most design guides recommend makeup air supply temperature to be within 10 degrees of the room temperature. So if in the winter you keep the house at 69 degrees makeup air supply temperature should be not less than 59 degrees. It's all about calculations.

Here are a few examples using the mechanical system and using the engineered system.
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Range hood make-up air-capture1.jpg   Range hood make-up air-capture2.jpg  

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