Makeup air requirement for range hoods over 400cfm

[jaylectricity]

We went with the pressure switch. Easy install. The grease problem is addressed by filters on the hood. If there were to be an excess of grease, we'd also need a grease trap.

How do you get 400cfm coming in without a fan on the inlet?

You don't necessarily need to get 400cfm coming from the makeup duct. You just want to alleviate the loss of pressure so you're not drawing air in through the flue of the chimney, or all the plumbing drains creating a situation where sewer gas is coming into the house.

 

[GoldDigger]

We went with the pressure switch. Easy install. The grease problem is addressed by filters on the hood. If there were to be an excess of grease, we'd also need a grease trap.



You don't necessarily need to get 400cfm coming from the makeup duct. You just want to alleviate the loss of pressure so you're not drawing air in through the flue of the chimney, or all the plumbing drains creating a situation where sewer gas is coming into the house.

The IMC/IRC except cited refers to the makeup air coming in at a rate approximately equal to the exhaust rate. But I see this as a requirement for the flow capacity of the makeup air system under a reasonably low interior negative pressure, not a requirement that the makeup air be fan forced.
If you take the other interpretation, that the makeup air has to come in through the duct even if all of the kitchen doors and windows are open, then a multi-speed hood fan would require a matching multi-speed makeup fan.

 

[Gregg Harris]

We went with the pressure switch. Easy install. The grease problem is addressed by filters on the hood. If there were to be an excess of grease, we'd also need a grease trap.



You don't necessarily need to get 400cfm coming from the makeup duct. You just want to alleviate the loss of pressure so you're not drawing air in through the flue of the chimney, or all the plumbing drains creating a situation where sewer gas is coming into the house.

IRC M 1503.4

. Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m³/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

Sewer gas would be the least of your problem. Carbon monoxide can and will be created if fossil fuel equipment is installed in the structure. This very issue has lead to pressure testing to assure the level of make up air is being provided.

 

[GoldDigger]

Sewer gas would be the least of your problem. Carbon monoxide can and will be created if fossil fuel equipment is installed in the structure. This very issue has lead to pressure testing to assure the level of make up air is being provided.

+1
This has become much more of a practical concern as buildings are designed tighter and tighter to prevent air infiltration for energy efficiency.
In some cases a fan forced air-air heat exchanger is needed to provide sufficient ventilation, even without an exhaust fan or fossil fuel equipment.

 

[jaylectricity]

I'll let you know if the final building and occupancy permit goes through.