Why Are Cigar Lounge Owners Told They Need a DOAS?
The answer, more often than not, is one BIG Misunderstanding! You see, most mechanical engineers know the 60 CFM-per-person number. They see “smoking lounge,” go to the official ventilation table (IMC 4-3.3.1.1), do the math, and pretty soon you are looking at a very large outdoor-air system and a very large bill.
What those engineers and local inspectors are forgetting is that the International Mechanical Code (IMC) has more than one page.
They treat the official ventilation table like it is the entire law. But there is an exception to this rule; it’s known as Section 403.2. It is as valid as the rest of the IMC code, which tends to be law of the land.
Section 403.2 explicitly provides a legal exception that allows air to be recirculated within the same room if it is properly treated with engineered source control. A city inspector or plan reviewer does not have the legal right to choose which sections of the code they feel like enforcing. If a licensed Mechanical Engineer (PE) stamps a design utilizing the 403.2 exception, the municipality is legally obligated to approve it.
Explaining IMC 403.2
IMC 403.2 the EXCEPTION
Exception:
Where the (1)registered design professional demonstrates that an (2)engineered ventilation system design will prevent the (3)maximum concentration of contaminants from (4)exceeding that obtainable by the determined in accordance with Section 403.3, the (5)minimum required rate of outdoor air (6)shall be reduced in accordance with such engineered system design.
- Registered Design Professional ~ typically the mechanical engineer responsible for the design.
- Engineered ventilation system ~ the complete design, which may combine LakeAir air cleaning, carbon filtration, outdoor air, exhaust, and energy recovery
- Maximum concentration of contaminants ~ the indoor air quality target the system must control.
- Exceeding that obtainable by the determined in accordance with Section 403.3 ~ the engineer must show that the proposed design controls contaminants at least as well as the prescriptive outdoor-air approach.
- Minimum required rate of outdoor air ~ for a smoking lounge, the prescriptive path can be 60 CFM per person.
- shall be reduced in accordance with such engineered system design. ~ if the engineer proves the engineered design provides equivalent or better contaminant control, the required outdoor-air rate is reduced according to that design.
Key Takeaway: 403.2 does not ask the engineer to ignore the code. It gives the engineer another code-compliant way to meet it.
403.2 Is a Right, Not an Entitlement
IMC Section 403.2 Is a Code Path, Not an Automatic Approval
The exception in IMC Section 403.2 is not a suggestion. It is part of the mechanical code, just as the prescriptive outdoor-air rates in Section 403.3 are part of the code.
Section 403.2 begins with the prescriptive rule: the minimum outdoor-airflow rate is determined in accordance with Section 403.3. But it then provides an engineered alternative:
“Where the registered design professional demonstrates that an engineered ventilation system design will prevent the maximum concentration of contaminants from exceeding that obtainable by the rate of outdoor air ventilation determined in accordance with Section 403.3, the minimum required rate of outdoor air shall be reduced in accordance with such engineered system design.”
That word—shall—matters. When the registered design professional demonstrates that the engineered design meets the exception’s stated contaminant-control standard, the design cannot be rejected simply because a reviewer, contractor, or owner prefers the prescriptive 60-CFM-per-person approach.
At the same time, Section 403.2 is not a free pass or an automatic reduction in outdoor air.
The engineer must demonstrate that the proposed system prevents maximum contaminant concentrations from exceeding the concentrations that would result from the Section 403.3 outdoor-air rate. For a cigar lounge, that normally means documenting the room, design occupancy, smoking load or contaminant assumptions, outdoor-air and exhaust rates, pressure relationship, contained recirculating airflow, filtration performance, gas-phase odor-control media, controls, maintenance, and the calculations used to establish equivalent contaminant control.
This is where LakeAir can help. Randy Bush, owner of LakeAir, has spent years working with IMC 403 on real smoking-room projects. He has testified before the Wisconsin Senate and worked with engineers and inspectors across the country. If a project gets hung up on ventilation or 403.2, Randy gets involved. He helps look at the code path, the engineering, and how the project is being framed so everyone is working from the same set of rules.”
The code official may review that analysis, request supporting documentation, question assumptions, and determine whether the submitted design actually satisfies the adopted code. The official’s role is to evaluate whether the documented engineered system meets the exception—not to disregard the exception because a large DOAS is the familiar prescriptive solution.
Key takeaway
Section 403.2 creates a legitimate engineered path to reduce outdoor-air ventilation when the required demonstration is made. It does not guarantee approval before the engineering is submitted, reviewed, and found to meet the adopted code.
What Does Your Cigar Lounge Look Like Under 403.2
Under 403.2, your cigar lounge looks much like any other well-designed lounge from your customer’s standpoint. From your vantage point, though, you see something different. You see good protection for your customers and staff. You notice you are not spending huge dollars every month conditioning massive amounts of outdoor air. The air balance feels right. Smoke stays where it belongs instead of drifting into non-smoking areas. The room feels comfortable, the system is doing its job, and you are not paying for more mechanical equipment than the project actually needs.
That is really the point of 403.2. The customer should not walk in and think, “This lounge is using an engineered ventilation exception.” They should just think, “This is a nice place to sit and enjoy a cigar.” The engineering is working quietly in the background, controlling contaminants, maintaining pressure, and supporting the environment without becoming the environment.
Let's take a Look Under the Hood at Your new 403.2 Modified System
A 403.2 system is pretty much what you originally imagined your cigar lounge would have. Your HVAC system provides the heating and air conditioning that keeps you and your customers comfortable. Then you add commercial air purification to remove smoke particles and reduce odor.
A 403.2 design gives us a good standard to build from. From there, we can expand the system to fit the kind of lounge you want to create. The LakeAir approach gives you room to build a straightforward Standard lounge, step up to a more refined Premium experience, or create an Iconic destination lounge where comfort, air quality, and atmosphere become part of what customers remember.
Ventilation Does not Disappear
Using 403.2 does not mean we stop bringing outdoor air into the lounge or stop exhausting air from it. Ventilation is still part of the system.
Air purification can remove smoke particles and reduce odor, but it does not solve everything. Carbon monoxide and carbon dioxide still have to be managed through ventilation.
An ERV can fit very naturally into this design. It brings in outdoor air and exhausts stale air while recovering much of the heating or cooling energy that would otherwise be lost.
So now the system starts to come together:
- Your HVAC keeps the room comfortable.
- LakeAir air purification handles smoke and odor.
- The ERV or ventilation system brings in outdoor air and removes stale air.
- The system is balanced to keep smoke where it belongs.
- The engineer sets the ventilation rate required by the 403.2 design.
Ready to see what a code-compliant, budget-friendly design looks like for your space? Input your dimensions into our Cigar Lounge Environment Planner below to calculate your customized layout.”
The Planner lets you take those pieces and start shaping the actual lounge: how many people you expect, how much air cleaning you want, how much ventilation you need, how much negative air pressure you want in the room, and what kind of customer experience you are trying to create.
Key Takeaway: 403.2 gives us the engineering path. The planner helps us turn that path into a real cigar lounge.