FIELD NOTE · SUPPLEMENTAL SET
70 percent of the minimum: California's hood-exhaust cap
ISSUEDJULY 11, 2026DRAWN BY THE NIGHTLY SWEEP
A wall-mounted canopy hood over a gas under-fired broiler has to move at least 400 cubic feet per minute for every linear foot of its length. That is the floor in the 2022 California Mechanical Code. The 2022 California Energy Code caps the same hood at 280. One appliance, one hood, two state codes, and the ceiling in the second sits below the floor in the first. The cap is exactly 0.70 of the minimum, and I wanted to know whether that ratio held anywhere else.
Take the four wall-mounted canopy cells. Light duty: a 200 cfm minimum against a 140 cap. Medium duty: 300 against 210. Heavy duty: 400 against 280. Extra-heavy, which is solid fuel only, charcoal or mesquite: 550 against 385. Four floors, four ceilings, and every ceiling is seven-tenths of its floor. The one cell that breaks the pattern is backshelf or pass-over light duty, where the minimum is 250 and the cap 210, a ratio of 0.84. No source I read explains why that one cell is different, so I am not going to guess.
The 2022 CMC minimums bind unlisted hoods. Section 508.5.1.1 exempts a listed exhaust hood installed per the manufacturer's instructions, and 508.2 requires listed assemblies to be tested to UL 710. A hood that carries a listing and runs at its labeled rate is out from under the table floor entirely.
The 2022 Energy Code cap fires only where the combined Type I and Type II kitchen exhaust for the facility exceeds 5,000 cfm. Below that threshold, Table 140.9-C does not reach the hood.
Section 140.9(b) is a prescriptive requirement. The CEC's 2022 Commercial Kitchens Fact Sheet states the commercial kitchen requirements may be traded off on the performance method of compliance, so a project modeling to the performance path is not bound by the cap at all.
The condition that matters most on a remodel is the last one: the cap does not reach an existing hood retained through the work. The route it travels is worth naming, because the exception only makes sense once you see the rule it modifies. The Note to Section 140.0 says Sections 140.1 through 140.10 apply to newly constructed buildings. Section 141.1 is what pulls the applicable subsections of 140.9 into an addition or alteration in the first place. And Exception 2 to that prescriptive requirement switches the cap off for an existing hood not replaced as part of the work. So the correct reading is an exception to a rule that applies, not a rule that never applied.
AB 671, effective January 1, 2026, added a restaurant tenant improvement clock inside that health review: 20 business days to approve or deny a complete plan, or it is deemed approved for permitting purposes. A resubmittal after a denial gets 10 business days, limited to the deficiencies already identified, with no deemed-approval language attached to it. The statute says working days in one subdivision and business days in the other, and the two are not interchangeable. And a new hood counts as a change of scope, which LA County Public Health reviews on the full 20 business days, not the 10-day resubmittal track.
That layering is why the hood is rarely the whole job. The 2022 CMC alone drags in duct clearances, a grease duct velocity band of 500 to 2,500 feet per minute, rooftop termination geometry, and an automatic fire-extinguishing system: Section 513.2.2 puts the UL 300 wet-chemical requirement inside the mechanical code, not only the fire code, and Section 513.4 turns its discharge into an electrical scope, shutting off fuel and power on activation. Whether a grease interceptor comes with it is a separate call, since 2022 California Plumbing Code Section 1014.1 conditions the interceptor on the authority having jurisdiction deciding pretreatment is required, sized per Section 1014.2.1 or Section 1014.3.6. A hood line item is worth catching the day it posts, because the rest of the restaurant files behind it: we read new permits across the 50-plus SoCal portals we track and score them by trade, so a Type I hood filing surfaces as the leading edge of a build carrying mechanical, suppression, and electrical scope, and that coverage runs across 18 trades on pricing posted month to month.
So the two numbers are both real, and both binding, just not at the same time on the same job. The floor governs an unlisted hood on the prescriptive path above 5,000 cfm. The cap governs that same hood's energy budget under the same conditions. Everywhere else, a listed hood, a performance model, or an existing hood kept through the work, one of the two lets go.
Sixteen of seventeen cells land on exactly 0.70
It holds almost everywhere. I put the two tables side by side, cell by cell, for every hood type and duty rating both codes carry a number for. Seventeen cells. In sixteen of them the Energy Code maximum is exactly 0.70 times the Mechanical Code minimum. In all seventeen the cap is below the floor. The ratio appears in neither document; it is arithmetic on the two tables, and you can run it yourself. Every number here is a 2022 edition value. The 2025 California Mechanical Code, on the 2024 UMC base, has governed permit applications since January 1, 2026, so a hood drawn on a 2026 tenant improvement should be checked against the 2025 minimums; Table 140.9-C, at least, carries into the 2025 Energy Code unchanged.Take the four wall-mounted canopy cells. Light duty: a 200 cfm minimum against a 140 cap. Medium duty: 300 against 210. Heavy duty: 400 against 280. Extra-heavy, which is solid fuel only, charcoal or mesquite: 550 against 385. Four floors, four ceilings, and every ceiling is seven-tenths of its floor. The one cell that breaks the pattern is backshelf or pass-over light duty, where the minimum is 250 and the cap 210, a ratio of 0.84. No source I read explains why that one cell is different, so I am not going to guess.
Four conditions keep it from being a contradiction
Two codes describing the same airflow with opposite words looks like a fight. On a real tenant improvement it usually is not, and four conditions are why.The 2022 CMC minimums bind unlisted hoods. Section 508.5.1.1 exempts a listed exhaust hood installed per the manufacturer's instructions, and 508.2 requires listed assemblies to be tested to UL 710. A hood that carries a listing and runs at its labeled rate is out from under the table floor entirely.
The 2022 Energy Code cap fires only where the combined Type I and Type II kitchen exhaust for the facility exceeds 5,000 cfm. Below that threshold, Table 140.9-C does not reach the hood.
Section 140.9(b) is a prescriptive requirement. The CEC's 2022 Commercial Kitchens Fact Sheet states the commercial kitchen requirements may be traded off on the performance method of compliance, so a project modeling to the performance path is not bound by the cap at all.
The condition that matters most on a remodel is the last one: the cap does not reach an existing hood retained through the work. The route it travels is worth naming, because the exception only makes sense once you see the rule it modifies. The Note to Section 140.0 says Sections 140.1 through 140.10 apply to newly constructed buildings. Section 141.1 is what pulls the applicable subsections of 140.9 into an addition or alteration in the first place. And Exception 2 to that prescriptive requirement switches the cap off for an existing hood not replaced as part of the work. So the correct reading is an exception to a rule that applies, not a rule that never applied.
Deep fryers are medium duty, and the mistake costs a size
One number in that first table trips more designs than the cap does. Deep fryers, every kind, open deep fat and donut and kettle and pressure, are medium duty under 2022 CMC Section 508.5.1.4, not heavy. Heavy duty is gas under-fired broilers, gas chain broilers, wok ranges and over-fired upright broilers. Put a broiler on a line that was drawn around fryers, and the whole hood moves to the heaviest appliance under it. Wall canopy from 300 to 400 cfm per linear foot, because the duty level of the hood follows the heaviest thing beneath it.The health department signs before the building department
Here is the part that decides who is in the room. The 2022 CMC Chapter 5, Part II obligations are real, but the gate is not the building department. Health and Safety Code 114380(e) bars the building department from issuing a permit for a food facility until the local enforcement agency has approved the plans. That agency has 20 working days, and plans not approved or rejected within 20 working days are deemed approved. Health and Safety Code 114149.1(a) then requires the exhaust ventilation to be installed and maintained per the California Mechanical Code, which is how a health agency comes to enforce a mechanical standard as a health condition.AB 671, effective January 1, 2026, added a restaurant tenant improvement clock inside that health review: 20 business days to approve or deny a complete plan, or it is deemed approved for permitting purposes. A resubmittal after a denial gets 10 business days, limited to the deficiencies already identified, with no deemed-approval language attached to it. The statute says working days in one subdivision and business days in the other, and the two are not interchangeable. And a new hood counts as a change of scope, which LA County Public Health reviews on the full 20 business days, not the 10-day resubmittal track.
Makeup air answers to three authorities, not one
Makeup air is where people misname the governing code. The rule that makeup air must equal exhaust is a health statute, Health and Safety Code 114149.1(d): makeup air provided at the rate exhausted. It is not in the mechanical code. The 2022 CMC, at Section 511.3, sets a pressure standard instead: whatever quantity keeps the cooking area from going more than 0.02 inch of water column negative, with internal makeup air on a compensating hood held to 10 percent of exhaust. The 2022 Energy Code adds a third constraint at Section 140.9(b)2A, limiting only the mechanically heated or cooled portion of that same makeup air. Three authorities, three standards, one air path. A design can satisfy the health rule and still miss the energy prescriptive path.That layering is why the hood is rarely the whole job. The 2022 CMC alone drags in duct clearances, a grease duct velocity band of 500 to 2,500 feet per minute, rooftop termination geometry, and an automatic fire-extinguishing system: Section 513.2.2 puts the UL 300 wet-chemical requirement inside the mechanical code, not only the fire code, and Section 513.4 turns its discharge into an electrical scope, shutting off fuel and power on activation. Whether a grease interceptor comes with it is a separate call, since 2022 California Plumbing Code Section 1014.1 conditions the interceptor on the authority having jurisdiction deciding pretreatment is required, sized per Section 1014.2.1 or Section 1014.3.6. A hood line item is worth catching the day it posts, because the rest of the restaurant files behind it: we read new permits across the 50-plus SoCal portals we track and score them by trade, so a Type I hood filing surfaces as the leading edge of a build carrying mechanical, suppression, and electrical scope, and that coverage runs across 18 trades on pricing posted month to month.
So the two numbers are both real, and both binding, just not at the same time on the same job. The floor governs an unlisted hood on the prescriptive path above 5,000 cfm. The cap governs that same hood's energy budget under the same conditions. Everywhere else, a listed hood, a performance model, or an existing hood kept through the work, one of the two lets go.