Makeup air for range hood

CVBReno

I am remodeling my kitchen (DIY) and putting in a 1200 CFM range hood. To avoid backdraft problems in the fireplace from the vent hood suction, I want to add a makeup air vent from the outside into the kitchen ceiling, with a motorized damper wired to open when the vent fan comes on. I have a few questions about this:

What size duct do I really need? The hood vent is 10" round, but I was thinking 6" for the makeup vent.

What's the best type of outdoor fitting to keep out bugs and dust?

Can you suggest a good source for the motorized damper? I could not find them at the Home Depot, only spring loaded dampers.

Are there 120V actuators available, or will I need to use a transformer for 24V?

Thanks!

Jeff Lawrence_25

1200 CFM?

That's a lot of air!

Honeywell used to make fully motorizied dampers, the ones they have now are 24v spring loaded, but you can change them from power close to power open.

Cosmo_3

This SHOULD be a hot topic

How many new construction homes are we in with this situation? A whole lot of them....

If the inspectors don't enforce codes, why would most cutthroat builder's care?

I see many commercial vent hoods now have the make-up air vents right on the vent hood lip. What this does is prevent the air coming in from mixing too much with the room air. This is good because it keeps users from wanting not turning on the make-up air fan because it is unconditioned. We need this type of system for the large residential-commercial units installed in million dollar homes now.


Cosmo

Fred Campbell

Why Is It?

> How many new construction homes are we in with

> this situation? A whole lot of them....

>

> If

> the inspectors don't enforce codes, why would

> most cutthroat builder's care?

>

> I see many

> commercial vent hoods now have the make-up air

> vents right on the vent hood lip. What this does

> is prevent the air coming in from mixing too much

> with the room air. This is good because it keeps

> users from wanting not turning on the make-up air

> fan because it is unconditioned. We need this

> type of system for the large

> residential-commercial units installed in million

> dollar homes now.

>

> Cosmo

Fred Campbell

Make up air

Whenever I seem to be grappling with an issue I know a residential inspector won't give two sh**s about, it pops up on the wall. Here's an interesting link that the GC just sent me after I made him aware of the situation.

http://www.energy.ca.gov/reports/2003-06-13_500-03-034F.PDF#search="exhaust hood calculate make-up air"

In the past I've installed 600-900 cfm RESIDENTIAL hoods w/out much concern for make up air. Cosmo, you're right. This SHOULD be a Hot Tech Topic. On this current design/build I'm going to bring in makeup air from both sides 12" below the burner top. The six burner stove is recessed in a stone arched opening with a 980 cfm, remote exhauster. I'm thinking of a 24V zoning damper and possibly a simple current sensing relay to open the damper whenever the fan is on. Luckily I can install these controls in the attic near the exhauster motor. A hood with an integral motor might require an access panel.

Residential range hood mfgrs. should address these issues. Are we all rocket scientists or Brad Whites that we can think of all this?

Who needs 1000cfm of their heated or cooled air getting sucked out of their kitchen when they're frying some chicken? All heating and HW equipment in this house is direct vent but still....what about the fireplaces?

Good topic for all of us to think about. TG

Mike T., Swampeast MO

Are you truly sure that you need ANYWHERE near 1,200 CFM?

That's the cubic volume of a room 10' x 12' x 10' with air replaced each minute.

Over an hour, that's 72,000 cubic feet or 60' x 120' x 10'. In other words it would change the air in a 7,200 square foot home with 10' ceilings each hour.

If that kitchen isn't HOT from LOTS of cooking (like a true commercial kitchen) you WILL need to reheat the incoming air in cold weather at anywhere near this level of flow in even a large residential kitchen.

tim smith

makeup air

I had a client a couple years ago that we had a 1500 cfm hood in, we put in a forced air makeup air fan with heated makeup off boiler. Pumped air up from basement stairwell that was open all the way up to all areas. Worked great, used a tekmar setpoint control for discharge air of 70.

Fred Campbell

Yes Mike

You are correct. Do they really need this exhaust? Every "high end" home wants a "high end " kitchen. The fact is...they will rarely use it as such. But, as consciensious (sp?) mechanical contactors we have to address these issues. As designers and architects keep speccing this equipment, what are we to do? Tim e to get the manufacturers involved, I say.

Tom_35

Manufacturers don't understand

We have been working on a custom home for nearly 3 years and this is one of the issues that we contended with. The homeowners purchased a roof-mounted exhaust fan that was variable speed and had 1600 cfm. The range is a Wolfe gas range. When I explained to the architect what the results could be, things got interesting.

When I called the factory to inquire what they recommended, they had no clue as to a recommendation. In fact, they said that I was the first person to ever question them on the matter. I tried to explain to them about the home going negative, backdrafting, etc---they still didn't have a clue.

This home has 5 fireplaces that could backdraft if the exhaust fan were to be run for any significant timeframe. The variable speed of the motor compounded the problem when the makeup fan came into the subject. If the exhaust fan was set to a minimum, and the make-up fan was set at "x" setting, we can easily have a positive pressure in the kitchen---which would not be recommended.

We ended up installing Field Controls metering air systems on all 8 of the HVAC systems, which will at least give us some makeup air that is filtered and somewhat measureable.
We have a makeup air fan that will supply 500 cfm directly to the hood and have installed a filter section in this duct so that the air being introduced to the hood is somewhat clean.

Our client is supposed to move into the home next month. We totally assume that we are going to have to make adjustments to fine tune the exhaust.

By the way, an exhaust fan like this is absolute overkill for a home.

Tom Atchley
Ft. Smith, AR

Techman

Kitchen Exhaust

Morning!Commercial exhaust hoods SHOULD be incorporating the use of a makeup air fan,which dumps the makeup air directly into the stove area ,not into the common air inside the building where it has to be cooled or heated , the ammount of makeup air is supposed to be about 80% of the exhaust air. Doing this requires the use of a "double walled "stove hood" so now its up to the mfrgs to make them for residential use.Enjoy your day!

Unknown

Try your local

restaurant supply company. They design dual exhaust and make up air units that will meet the BTU requirment of your equipment. Many of the commercial type equipment going into homes today requires this. I put one in my sons home for his six burner double oven gas range with a built in wall oven in addition. It was sized by a local company who specializes in this and the unit is matched to make up the air needed for combustion on this unit with it running a full tilt it is set up for three speeds and is made by Vulcan I believe. Maximum CFM on this unit is 750 CFM. Many of your Jenn-Aire units run at 800 CFM so this would more than handle your application. Anything above 750 is over kill.

Brad White_9

Do any kitchen designers

really consider the issues? I mean, the type of cooking, the "line" of appliances beneath the hood, the "capture" distance (lessen that and the amount of air drops by the square of the distance)... all the factors that go to good design.

Incredibly wasteful otherwise, just plunking in a hood sized to cover the area above the cooking appliances then meeting the presumed airflow.

Gaylord, Halton and other companies have good resources on kitchen design. Also NFPA-96 has been revised (not that it necessarily applies to residences nor that it is code on a given area) to allow lesser airflows so long as proper capture is made.

My $0.02

Brad

Dan_15

What sort of residential appliance on this great earth could possibly need 1200 CFM of venting? Our new kitchen has a Miele cooktop that makes 60,000 BTU max assuming all burners on high simultaneously; with a matched Miele hood that pulls 625 CFM maximum. I cannot imagine a cooktop needing to vent 1200 CFM unless it had something like six 20,000 BTU burners. That is a lot of heat for cooking.

Unknown

Keep in mind that most of the time

when an oven or ovens are also a part of the package that BTU's can be as follows

Top Burners 10,000 to 12,000 each

Ovens 22,000 to 30,000

Double oven 20,000 to 22,000

The load in that kitchen could end up being 62,000 up to 112,000 BTU's

Dan_15

Fair enough. Seems that Wolf makes hoods in 600, 900 and 1200 blower options. I just cant conceive of needing to move 1200 CFM for long periods of time. When do you have both ovens and all six 20,000 BTU burners going simultaneously on high heat for hours at a time? Seems like overkill. Maybe ventilation should be sized using "cooking days" like boilers use degree days. I'll bet that 1200 CFM blower is noisier than an idling truck, too; which will probably cause it to be used at lower speeds most of the time anyway.

Paul Pollets

MUA

we often install custom range hoods and 1200CFM fans. We must use a MUA intake for fresh air. I've seen fireplace flames roll-out of the enclosure as the house draws a large negative pressure. It can also draw the flame out from under an atmospheric boiler or furnace, trip the rolout switch and possibly cause a fire. Heated MUA intake is required for cold climates.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

CVBReno:

If you search Google regarding this situation you'll find that it's both a serious concern and that residential codes are exceptionally vague regarding just how the problem should be addressed. Most all "solutions" are custom as I've yet to find a residential system that addresses everything. Of course you could use a true commercial venting system...

If you haven't already purchased cooking appliance(s) with such bodaceous ventilation requirements you might want to re-evaluate the need.

I do quite a bit of cooking of all sorts including fairly frequent large-scale cooking in a commercial kitchen. If this is true commercial equipment be aware that the low-end range of most burners is unsuitable for some fairly common residential jobs like maintaining a bare simmer (even in a quite large pot--not to mention a small pan of sauce).

The only problems I've ever had with a typical residential cooktop (they usually have one higher-output burner) involves boiling lots of water. It's rather slow if you're doing a lot of water bath canning, but pressure canning is usually preferred for most things anyway and even a normal output burner is quite sufficient for a 7-jar pressure canner--and you want nice fine adjustment of the flame to boot. It takes a very long time to boil one of my 6-gallon stockpots for LOTS of shellfish, corn, etc., but it works. One high-output burner in the "commercial" range should be sufficient unless you're typically cooking VAST amounts of food and MUST do so very quickly.

In any regard, I'd suggest you do some researching to find out just how much ventilation you truly need. This has MUCH to do with the design of the hood--how high above the cooktop, amount of overhang, location of air inlet(s), etc.

In my own home I'm using a cooktop that "looks" commercial, but has residential-type outputs with the exception of one burner. It's 60" long and my ventilation solution is two residential (but fairly high CFM) hoods ganged together. That way for typical cooking I can use just one hood and still have good performance without concern for make-up air. If everything is cranking, the kitchen WILL be hot and I'll open a nearby window--not so much because I have to, but because I'll naturally want to.

Unknown

How about Thanksgiving

and Christmas???? These are times when by the way a tendency for CO poisioning is greater.

Those units are actually very quiet at high CFM about the same as a large window fan.

Couderay

make up air

Has any of these homes have windows in the kitchen or surrounding areas. If they have that kind of money surely a window can be open.

Douglas Hicks

One of the services my company offers is installation of exhaust hoods for commercial kitchens. One of the things I have learned is to go to the professionals. As such I am posting some links from my favorites list. http://www.upyourstack.com/
http://www.captiveaire.com/
http://www.ventilationdirect.com/
http://www.greenheck.com/
I don't know residential, but commercial needs are normally about 2400 CFM. But there are residential kitchen that I have seen using commercial appliances. There are variable speed commercial fans available, during heavy cooking loads, the fan speeds increase, during light cooking loads, the fan speeds decrease. Commercial exhaust fan and the intake fan are to be wired so the intake fan operates when the exhaust fan is used. The use of heated/cooled make-up air is a good idea. Call Captive Aire, I have found them to be very helpful when I have had problems.
fireguy

Fred Campbell

Thanks

Thanks for the links fg.

Unknown

It is not a good

idea to open windows in order to supply make-up air. In many cases it can cause a reverse effect and pull air out of the space causing even more problems.

All make up air and combustion air should be controlled mechanically and not rely on atmosphere to provide air.

By the way while we are discussing this make up air and air for combustion are two different things. Make up air is air required to equalize pressure in an area or home caused by mechanical exhausting and other air removal issues.

Air for combustion is the air required for the appliances to operate safely. The traditional two openings one 12" from the ceiling and one 12" from the floor are not the best way to go. Ideally a mechanical air provision is the best solution with its built in interlock system to prevent operation if the mechanical device fails.