# Natural vs. Mechanical Ventilation in Auto Repair Shop



## Keith

Where IBC 406.6.3 requires mechanical ventilation per IMC,

If .75 cfm/ft the basic air exhaust requirement per IMC table 403.3, can I use the wind/gravity turbine vents to achieve this?

If motors are not running, per IMC 502.14, can I use the 4% of floor area rule for natural ventilation? (assuming roll up door is open enough when occupied)

Thanks


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## mn joe

Hi Keith,

If you have adopted the IBC then the mechanical ventilation is the requirement. I would not consider the turbine as meeting this requirement.  You can't regulate or adjust the flow rate with the turbine.

 By the way, welcome to the board. Why don't you do a post to introduce yourself.

Joe


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## Keith

IMC 502.14 exception 3

Joe,

Thanks for the welcome and reply. I'll definitely post to the welcome forum and introduce myself.

IMC table 403.3 specifies .75 cfm/sf min. mechanical exhaust for auto repair.

Can there be a fan through the ceiling that runs when the lights are on, using the roll-up door as the intake?

Doesn't exception 3 below exempt such a condition from section IMC 502.14 "mechanical ventilation shall be provided..." ?

IMC 502.14 Motor vehicle operation. In areas where motor vehicles operate, mechanical ventilation shall be provided in accordance with Section 403. Additionally, areas in which stationary motor vehicles are operated shall be provided with a source capture system that connects directly to the motor vehicle exhaust systems.

Exceptions:

1. This section shall not apply where the motor vehicles being operated or repaired are electrically powered.

2. This section shall not apply to one- and two-family dwellings.

3. *This section shall not apply to motor vehicle service areas where engines are operated inside the building only for the duration necessary to move the motor vehicles in and out of the building.*

Thanks,

Keith


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## klarenbeek

The .75 CFM would still be required because it is a requirement of section 403 (ventilation for repair garages) as well as of section 502.14. What exception 3 allows is to not have the source capture system.  A jiffy lube needs the .75 CFM general exhaust but not the source capture system.


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## kluth

klarenbeek said:
			
		

> What exception 3 allows is to not have the source capture system.  A jiffy lube needs the .75 CFM general exhaust but not the source capture system.


Disagre with that. The entire section (502.14) does not apply for a Jiffy Lube. As long as the vehicle is run only to get it in and out of the building (exception 3), the .75 cfm of mechancial ventilation does not apply. Natural ventilation (4%) through the doors would suffice.

If it is a repair facility where the motor vehicle must be operated, the specific provisions for mechanical ventilation apply (includig the source capture system). When these project come through our department for plan review, the owner must document the use of the space. We specifically require them to answer/detail the business plan in order to verify compliance.

Kirk


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## earshavewalls

The OP is in California, which is under the California Mechanical Code, which is still based on the Uniform Mechanical Code. The results are a bit different, as MECHANICAL makeup air is not mentioned. CMC section 505.3, Makeup Air, only states that it shall be provided to replenish air exhausted by the ventilation system.

I have seen several paint booth plans come in that used louvered openings in the walls and/or turbines on the roof, to provide makeup air. The only thing I asked for was calculations to verify that the amount of openings were adequate to provide enough makeup air to the space. These were all passive systems. (we do see many WITH makeup air fans, but the passive systems also show up).

Until California catches up with the rest of the Country (and world, for that matter) and gets onto the IMC and IPC, there will remain several differences in interpretation of how these systems should work.

Hope this helps a little bit.....


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## RJJ

Interesting post! I have the same issue and in fact and architect is arguing that the building / repair garage complies because the garage doors are open all the time and thus meets the 4% natural ventilation> Code section 402 IMC 2006. My feeling is that mechanical ventilation is needed under 403.3.


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## jar546

The doors won't be open when it is 4 degrees outside and the wind is blowing.  Can't rely on that, no exception pointing to that either.


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## RJJ

I agree! would like to see other comments with reasons why natural doesn't apply!


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## Builder Bob

Do not forget the hazardous classification of wiring required if mechanical ventilation is not used......just food for thought.


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## TJacobs

This is one of the reasons that national codes need regional amendments, because what works in Tucson won't work in Chicago.


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## RJJ

I agree in Part! And Jeff is correct in the winter time around here. The argument is that the doors are opened all the time to allow for fresh air exchange. Ok for summer,but not winter.  Builder Bob raises a great point and I will look into it. The second part of the argument is that even in winter the doors are open quite often. Well maybe.

I believe three parts of the code apply. Natural ventilation 4%of the floor, Mechanical Ventilation & Hazardous conditions.  Fumes/Gas!

Most cars and trucks today have fuel pumps in the gas tank. The tanks need to be drained and removed to change the fuel pump.

May understanding of this area of code is that the mechanical ventilation is a must to maintain safe conditions for both workers and the shop condition to avoid a problem.

Add in Brake dust fluid etc it becomes a harsh environment.


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## Dr. J

Here is my take:  First of all, I assume the OP is based on the 2009 IMC, since Table 403.3 in IMC 2006 does not have the .75 cfm/sf exhaust requirement for repair garages.

3 non debatable points - IBC 406.6.3 requires mechanical ventilation in accordance with the IMC; IMC Table 403.3 requires .75 cfm/sf of exhaust; and IMC 512.14 does not apply due to exception 3.

So, can the overhead door be used as the make-up source for the required exhaust fan?

IMC 501.3 states in part "_If only a mechanical exhaust system is installed for a room or if a greater quantity of air is removed by a mechanical exhaust system than is supplied by a mechanical ventilating supply system for a room, adequate makeup air consisting of supply air, transfer air or outdoor air shall be provided to satisfy the deficiency. The calculated building infiltration rate shall not be used to satisfy the requirements of this section._."  SOMETHING has to provide make up air.  It doesn't have to be a powered make-up air unit, it could be a louver with a motorized damper interlocked to open when the fan is running.  So if it can be a hole in the wall with an open/close thingy, could the hole be the door opening, and the interlocked open/close thingy be the overhead door?  Sure - an opening is an opening and a thingy is a thingy.

OK Dr. J, what about your usual natural ventilation rant?  The issue is how is the minimum temperature provision of IBC 1204.1 satisfied along with IMC 401.3 requiring ventilation whenever the space is occupied.  In this case, the exception to IBC 1204.1 probably applies :"_Exception: Interior spaces where the primary purpose is not associated with human comfort._ ".  I would say the space's primary purpose is not associated with human comfort.  Note that if you disagree, then even the louver with damper design would need to be show that there is sufficient heat to offset .75 cfm/sf.  An open overhead door would be next to impossible to properly heat.  But again, I say the min temperature requirement does not apply.

So, bottom line, can the overhead door be used as the make up air source for the required .75 cfm/sf exhaust fan - yes if interlocked with the fan to open when the fan is on.  The Owner just needs to be aware that this requires an open door and operating fan when it is 4 degrees.  If they can't keep their workers happy, that is their issue.

As a designer, I would suggest the much smaller louver and damper solution, and if the owner really wanted to keep his employees happy, add enough heat to offset the .75 cfm/sf.  Overhead radiant heaters would be ideal.  But this is not required.


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## RJJ

DrJ: This is under the IMC 2006. But I like your thoughts.


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## Dr. J

Then what's all this talk about Table 403.3 requiring .75 cfm/sf of exhaust for Repair Garages?  That ain't in 2006.  It is part of the new "exhaust" column in the 2009 Table 403.3.


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## Dr. J

2009 really cleared it up (well "ICC clear" that is).  I can't find "repair garage" in 2006 Ch 4.  512.14 would still not apply, so find me the "required ventilation" IBC is referring to.  One might go with the parking garage requirement, but that is a stretch.

Actually, we should remember that there could be other ventilation requirements outside the IMC depending on specific procedures taking place, pits, and whether or not the sparkys want to deal with classified wiring methods.


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## mtlogcabin

2006 IMC Table 403.3

Storage

Repair garages, enclosed

  parking garages                  1.5 cfm/ft2

 Warehouses     0.05 cfm/ft2


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## RJJ

MT: I agree in Part. I suppose the argument is that have they meet the burden by natural ventilation by have doors and does that apply an over ride the need for mechanical ventilation. I would say no.


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## Paul Sweet

The doors wouldn't have to go all the way up when the fan was operating - just far enough to provide the required free area for the volume of air removed by the fans.


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## Dr. J

> 2006 IMC Table 403.3Storage
> 
> Repair garages, enclosed
> 
> parking garages 1.5 cfm/ft2


OP:



> IMC table 403.3 specifies .75 cfm/sf min. mechanical exhaust for auto repair


OPer has gone AWOL, so without further info, gotta assume this is under 2009.

Just to cover the bases, there is no requirement for exhaust in a Repair Garage under 2006 IMC Table 403.3.

2006 Table 403.3 is for "Outside Air", not exhaust.  There are a couple of occupancies with footnotes requiring exhaust.  The category "Repair garages, enclosed parking garages" Has footnote d, which states "d.	Ventilation systems in enclosed parking garages shall comply with Section 404."  A repair garage is not an enclosed parking garage.  Thus all Table 403.3 requires is 1.5 cfm/sf outside air.  There is no requirement to exhaust this air.  Well, ... you can eventually find a way to prohibit that outside air from being recirculated to other parts of the building, so that air ends up being exhausted probably, but like I said, the 2009 version is much cleaner.


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## Dr. J

> MT: I agree in Part. I suppose the argument is that have they meet the burden by natural ventilation by have doors and does that apply an over ride the need for mechanical ventilation. I would say no


While IMC 401.2 presents a choice of either mechanical or natural ventilation, IBC 406.6.3 restricts that choice in repair garages, so mechanical is the only option.  So in either version of the code, the answer to the OP is no, can't just use a wind/gravity turbine vents or an open door.  The difference between 2006 and 2009 is that 2006 requires 1.5 cfm of outside air supplied to the space, and some unspecified way of getting it out of there, while 2009 requires .75 cfm of exhaust with some unspecified means of getting make up air in there.


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## RJJ

Dr.J I have kinda hijack this OP. The issue I am dealing with is 2006 IMC & IBC. The IBC 406.6.3 I believe calls for mechanical ventilation. You have created a true on point issue in the IMC. Although the difference between 06 & 09 is the cfm's the difference I see is that it is not just a case of natural ventilation. once again ICC has left it as clear as mud.


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## jsmith14

Keith said:
			
		

> Where IBC 406.6.3 requires mechanical ventilation per IMC,If .75 cfm/ft the basic air exhaust requirement per IMC table 403.3, can I use the wind/gravity turbine vents to achieve this?
> 
> If motors are not running, per IMC 502.14, can I use the 4% of floor area rule for natural ventilation? (assuming roll up door is open enough when occupied)
> 
> Thanks


problem in ventilation need some auto mechanics, it could help you if you see some professionals on it.


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## cda

Welcome jsmith

How did you find us???


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## brudgers

cda said:
			
		

> Welcome jsmith  How did you find us???


  He just dropped in...


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