Residential kitchen exhaust hood

[goldstar]

I'm in the process of a residential kitchen remodel and the exhaust hood the HO is using states that it a 700 cfm exhaust. The bldg. dept is telling us that if an exhaust hood is over 400 cfm we will need a make-up air fan. If anyone has had experience with this set-up would you please post what you've done with respect to wiring, branch circuit requirements, etc. I do not have the specs with me. Much appreciated in advance.

 

[infinity]

Is the requirement for a fan or just some sort of outside air damper?

 

[farmantenna]

Like you, I'm electrician and usually the HVAC mechanical contractor devises a scheme to accomplish this requirement. I've seen a few different ways. duct from heating system to outside damper with pressure or sail switch at hood that activates the damper. In super homes I've seen small makeup air unit that provided conditioned air. My input and work was minimal.
The 400 cfm requirement is why some are rated at 390 cfm!

 

[goldstar]

Is the requirement for a fan or just some sort of outside air damper?

I believe it's more than just an air damper. I'll try to find out more but the bldg. inspector is off this week. I'll post info when I can.

 

[brantmacga]

Is this an inline duct fan, or a hood-mounted fan with its own integral power switch?


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[wwhitney]

Is the requirement for a fan or just some sort of outside air damper?

Looks like a damper can comply:

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Cheers, Wayne

 

[acrwc10]

I believe it's more than just an air damper. I'll try to find out more but the bldg. inspector is off this week. I'll post info when I can.

If you have any appliances that are not sealed (like an 80% efficient heater or a standard water heater) or a fireplace that is open to the living space, a damper will not be allowed. The hood will pull makeup air down the exhaust flues. I have seen a few guys buy a receptacle for a table saw that turns on a vacuum cleaner when the saw is turned on. They just use it on the hood.

 

[kec]

Typically new energy efficient homes today require make-up air with Kitchen exhaust fans rated over 400 cfm
What the HVAC contractors here do is install a sail switch on the duct work to bring on the fan unit on the zone serving the kitchen area that's
tied to a fresh air inlet. All require LV wiring. We may be asked to provide a T-Stat wire to the exhaust duct back to the air handler.

 

[LarryFine]

A coaxial duct could be used to bring in fresh air.

 

[wwhitney]

If you have any appliances that are not sealed (like an 80% efficient heater or a standard water heater) or a fireplace that is open to the living space, a damper will not be allowed.

That's not what IRC M1503.6 says (not relevant in CA, which hasn't adopted the MEP sections of the IRC, so I'm not sure what the UMC has to say on the matter). To quote from my earlier link:

IRC M1503.6 "Where one or more gas, liquid or solid fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a dwelling unit's air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate."

So it says that if you have only direct-vent or mechanical draft combustion appliances, you don't need to provide makeup air for a kitchen range hood. If you have other combustion appliances, and the range hood is in excess of 400 CFM, you can "passively provide" makeup air. I.e. use a damper.

Cheers, Wayne

 

[acrwc10]

That's not what IRC M1503.6 says (not relevant in CA, which hasn't adopted the MEP sections of the IRC, so I'm not sure what the UMC has to say on the matter). To quote from my earlier link:

IRC M1503.6 "Where one or more gas, liquid or solid fuel-burning appliance that is neither direct-vent nor uses a mechanical draft venting system is located within a dwelling unit's air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be mechanically or passively provided with makeup air at a rate approximately equal to the exhaust air rate."

So it says that if you have only direct-vent or mechanical draft combustion appliances, you don't need to provide makeup air for a kitchen range hood. If you have other combustion appliances, and the range hood is in excess of 400 CFM, you can "passively provide" makeup air. I.e. use a damper.

Cheers, Wayne

Well, you are sort of correct, California energy code has what they call an “infiltration rate” for hoods, it’s 1500 square foot of house per 100 CFM of hood. So if you have a 10,500 square foot house, you don’t need make up air to the hood. But even if you don’t have an open wood burning fireplace and all appliances are direct vent, with a 700 CFM hood and no make up air the hood won’t operate correctly. No air in means no air out. Plus, enjoy the smoky room if you do have a wood burning fireplace and you turn the hood on. It’s essentially fun when the whole gang is over for the holidays and the fire is blazing away they you turn on the hood and suck 700 CFM of smoke into the room

 

[acrwc10]

The same issue happens with clothes dryers if they don’t have makeup air and the laundry room is tightly sealed, the clothes take forever to dry. If the water heater is in that laundry room it will backdraft down the flue too.

 

[wwhitney]

California energy code

Thanks for the reference, I see that 2022 California Energy Code 150.0(o)1(k) explicitly calls for compliance with ASHRAE 62.2 Section 6.4, which I haven't yet found the full text of online. But this is not relevant to the OP, who is apparently in NJ, which is why I quoted IRC M1503.6.

But even if you don’t have an open wood burning fireplace and all appliances are direct vent, with a 700 CFM hood and no make up air the hood won’t operate correctly.

Well, it won't give 700 CFM, but it will probably move more air than a 350 CFM rated hood, which never requires make up air under the IRC.

And certainly I agree with your description of the backdrafting problem that IRC M1503.6 is meant to avoid.

Cheers, Wayne

 

[infinity]

Passive makeup air sounds like a duct to the outside with a damper not requiring a fan.

 

[Ken_S]

If it's over 400 cfm, does a mechanical contractor need to handle the installation?

 

[infinity]

If it's over 400 cfm, does a mechanical contractor need to handle the installation?

Good question. I would guess no since it's an electric damper.

 

[kwired]

If it's over 400 cfm, does a mechanical contractor need to handle the installation?

Probably up to local AHJ's.

Some might not even look for this 400 CFM thing depending on their experience and education on such things, others might see it right away as something to look harder at what is going on there.

Good question. I would guess no since it's an electric damper.

HVAC might install the damper and any ducting, EC wires it up would be sort of typical. Here it likely doesn't get make up air on a dwelling though, unless maybe the owner knows anything about this sort of thing and requests it.

 

[infinity]

HVAC might install the damper and any ducting, EC wires it up would be sort of typical. Here it likely doesn't get make up air on a dwelling though, unless maybe the owner knows anything about this sort of thing and requests it.

I can't imagine if the electrician goes to install a range hood that they would also need an HVAC guy just to cut in the damper that the electrician is going to have to wire anyway.

 

[kwired]

I can't imagine if the electrician goes to install a range hood that they would also need an HVAC guy just to cut in the damper that the electrician is going to have to wire anyway.

If EC is installing range hood probably not. I do get some HVAC guys that want to install bath exhaust fan ducting, dryer vent ducting and range hood ducting at rough in though, even if they don't do another thing with any of those at finish time.

I can't tell you how many times I was expected to hang the range hood or over the range microwave/hood unit, so anymore I allow a little extra on estimates/bids to cover it. I will not supply a hood or microwave though. And if they realize I installed duct for those or the bath fans, they often will ask me to vent the dryer as well.

 

[readydave8]

If they find out I have 4 3/4" hole saw they will ask me to vent dryer regardless