# Taking outside air from a crawlspace



## earshavewalls (Feb 27, 2012)

I just got a call from a contractor asking if the required outside air for a home system could be taken from the (ventilated) crawlspace. I am in California and therefore under the 2010 California Mechanical Code, which is loosely based on the 2009 Uniform Mechanical Code. New, or modified sections of 311.0 specify sources of air for such systems, but 'crawlspace' is not mentioned. The only issue I can see would be if the furnace or other fuel-burning appliances were located in the space.

Hoping that someone else has dealt with this issue and has a quick, easy answer! Right now, it looks like they could do it. Good thing it's fairly dry around here.........

Thanks,

Wayne


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## Gregg Harris (Feb 27, 2012)

earshavewalls said:
			
		

> I just got a call from a contractor asking if the required outside air for a home system could be taken from the (ventilated) crawlspace. I am in California and therefore under the 2010 California Mechanical Code, which is loosely based on the 2009 Uniform Mechanical Code. New, or modified sections of 311.0 specify sources of air for such systems, but 'crawlspace' is not mentioned. The only issue I can see would be if the furnace or other fuel-burning appliances were located in the space.Hoping that someone else has dealt with this issue and has a quick, easy answer! Right now, it looks like they could do it. Good thing it's fairly dry around here.........
> 
> Thanks,
> 
> Wayne


IMC 701.4 it is approved


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## Gregg Harris (Feb 27, 2012)

wrong answer I missed ventilation for combustion


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## mark handler (Feb 27, 2012)

Gregg Harris said:
			
		

> IMC 701.4 it is approved


IMC 701.4 is okay for cumbustion air But not fresh air.


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## ICE (Feb 27, 2012)

311.3 Prohibited Source. Outside or return air for a heating or cooling air system shall not be taken from the following locations:

(1) Closer than ten (10) feet (3,048 mm) from an appliance vent outlet, a vent opening of a plumbing drainage system, or the discharge outlet of an exhaust fan, unless the outlet is three

(2) Where it is *less than ten (10) feet above *the surface of any abutting public way, sidewalk, street, alley or *driveway*.

(3) A hazardous or *insanitary location* or a refrigeration machinery room as defined in this code.

(4) From an area, the volume of which is less than 25 percent of the entire volume served by such system, unless there is a permanent opening to an area the volume of which is equal to 25 percent of the entire volume served.

Two ways I would say no.  One is that I wouldn't consider the underfloor area to be sanitary.  Second is that if there are any underfloor vents adjacent to the driveway the source is then not 10' above the driveway.


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## gbhammer (Feb 27, 2012)

It is a tricky question. the section says "openings _that_ terminate outdoors" not should, and is a crawl space even considered outdoors. Do the ventilation openings of the crawl space meet the demand for the outside air.

401.5 Outdoor opening protection. Air intake

openings that terminate outdoors shall be protected with corrosion-

resistant screens, louvers or grilles. Openings in louvers,

grilles and screens shall be sized in accordancewithTable 401.5,

and shall be protected against localweather conditions.Outdoor

air exhaust and intake openings located in exterior walls shall

meet the provisions for exterior wall opening protectives in accordance

with the International Building Code.


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## gbhammer (Feb 27, 2012)

The driveway would be a squasher for sure, the unsanitary is not a given.


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## mark handler (Feb 27, 2012)

Is this AIR SUPPLY or Combustion Air?


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## ICE (Feb 27, 2012)

Air supply


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## ICE (Feb 27, 2012)

gbhammer said:
			
		

> The driveway would be a squasher for sure, the unsanitary is not a given.


Ok so support the idea that the crawl space is sanitary.  I say it is too dark, damp, bug infested with rodent droppings and all manner of dust particles to even think of putting that air in my lungs.


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## mark handler (Feb 27, 2012)

IMHO

Air supply, No

Combustion Air, Yes

I do not belive there is enough "Fresh Air", under most houses.

There are always exceptions but most crawl spaces I have been in, do not have "Fresh Air"


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## gbhammer (Feb 27, 2012)

Not saying I disagree with you ICE, just saying some "crawspaces" that do not meet the def of a basement by say ceiling height are pretty sanitary/ all concrete and four or 5' tall.


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## JMORRISON (Feb 27, 2012)

Radon and other gases from soil?


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## ICE (Feb 27, 2012)

gbhammer said:
			
		

> Not saying I disagree with you ICE, just saying some "crawspaces" that do not meet the def of a basement by say ceiling height are pretty sanitary/ all concrete and four or 5' tall.


I concede that there are possible scenarios where the crawl space could be rendered safe enough for the air supply but that would be a rare exception.  I would venture to guess that the OP's crawl space isn't one of those exceptions.


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## gbhammer (Feb 27, 2012)

ICE said:
			
		

> I concede that there are possible scenarios where the crawl space could be rendered safe enough for the air supply but that would be a rare exception and more work that it's worth.  I would venture to guess that the OP's crawl space isn't one of those exceptions.


:agree Your right of course, just trying to see the OP through.


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## Amish Electrici (May 29, 2012)

I expect that this is one of those topics where there just cannot be a single 'correct' answer. It's also an area where the designers' original intent - and it can be pretty hard to guess what someone was thinking fifty years ago - is confounded by changes made since then. Let me explain...

What is a crawl space? How is it constructed? What are the local practices, local conditions? These are questions that strike to the heart of the topic.

As we discuss this topic, over in the various 'save the world' forums they're advocating the complete sealing and insulating of crawl spaces, all in the name of 'energy efficiency.' This is ironic, as the 1980's were all about flushing air through the crawl space, to keep radon gas from reaching the house above.

Then there's the general code issues relating to fire protection, which generally frown upon connections between different vertical levels.

Even if the crawl space is ideal for use as a plenum, you need to be careful not to use it as both an 'intake' and an 'exhaust.' It simply won't do to have your cooking odors get sucked up into the bathroom.

My opinion? Well, that would apply only to a NEW crawl space. I think you need to -first- look at the existing space and see if it is adequately vented to the outside.

Assuming it is, I see plenty of 'pluses' to drawing fresh air from the crawl space. Mind you, as you draw air from the crawl, you might need to increase the venting of the crawl, Still, for incidental uses (such as fresh air for the range and water heater burners), drawing the air from the crawl space can work. Once you add a fan to the mix (furnace, range hood, dryer), it becomes more likely that you'll need more air than the crawl can readily provide.

Heck, I'd even like to use the crawl space as a source of cool air for my attic .... now THERE is a code / design challenge!

My point is that I think the code panels need to address the topic as a topic in it's own right, looking at the crawl space as part of the house as a whole. Existing code is inadequate.


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## mtlogcabin (May 29, 2012)

Even though the code allows the air in an unvented crawl to commicate with the living space the mechanical contractors experience found true Ice's concerns. A musty smell or bad air. In the long run the owner will not be happy with the make up air for his house traveling through the crawlspace first.

R408.3 Unvented crawl space.

Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where:

1. Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall; and

2. One of the following is provided for the under-floor space:

2.1. Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.9;

2.2. Conditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1102.2.9;

2.3. Plenum in existing structures complying with Section M1601.5, if under-floor space is used as a plenum.


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## conarb (Jun 3, 2012)

Amish Electric:

I'm curious, are you really Amish?  I didn't think the Amish used electricity.  And which "save the world forums" are you referring to, The Journal of Light Construction or the Green Building Advisor? Im impressed that the Amish see through this "save the earth" bull****.


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## Amish Electrici (Jun 5, 2012)

conarb said:
			
		

> Amish Electric:I'm curious, are you really Amish?  I didn't think the Amish used electricity.  And which "save the world forums" are you referring to, The Journal of Light Construction or the Green Building Advisor? Im impressed that the Amish see through this "save the earth" bull****.


No, I'm not Amish, though I am of German descent.

As an apprentice, waiting in line at the parts house, we began making up names for electrical contractors. After all, the supply house was in Sparks, Nevada     That said, we also made up slogans ("We remove your shorts")

My idea, which I actually used when I got my own license years later was "Amish Electric: No Power, No Problem!"

BTW, the "Green Building Advisor" was who I had in mind, as they most recently have been singing the 'seal up the crawl space' song. I'm also quite familiar with LEED, and a few of the 'energy' codes.

I'm currently doing a whole-house remodel, bringing a 1957 ranch into the 22nd century. You can be sure I'm considering EVERY angle, and the crawl space is quite important to my plans. 1957 houses were NOT designed to have 2012 air-tight construction. For that matter, I suspect my attic needs a lot more air flow .... but that's another topic.


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## Sifu (Aug 8, 2012)

I want ot pick up this old thread with a new question.  I found a wood burning f/p installed yesterday with a flexible air connector run to the crawl-space for combustion/make-up air.  I remembered reading this old thread and came back to it but fireplaces aren't part of the conversation.  Wondering if this would be acceptible or if the air should come from the outside.  Any thoughts?


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## north star (Aug 8, 2012)

*+ + +*

From the `06 IRC, Section R1006.2 - Exterior air intake.

"The exterior air intake shall be capable of supplying all

combustion air from the exterior of the dwelling or from

spaces within the dwelling ventilated with outside air such

as non-mechanically ventilated crawl or attic spaces.

The exterior air intake shall not be located within the

garage or basement of the dwelling, nor shall the air intake

be located at an elevation higher than the firebox.......The

exterior air intake shall be covered with a

corrosion-resistant screen of ¼-inch (6 mm) mesh."

From Section R1006.5 - Outlet:

"Locating the exterior air outlet in the back or sides of the

firebox chamber or within 24 inches (610 mm) of the firebox

opening on or near the floor is permitted.........The outlet shall

be closable and designed to prevent burning material from

dropping into concealed combustible spaces. "

Section R1006 also lists some requirements for size of the

passageway supplying the combustion air  &  clearances.

Is your flex connector able to close / shut off the outside

air?



*+ + +*


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## Sifu (Aug 8, 2012)

Much appreciated, I should have spent more time looking for myself.  The installation looks like it complies though I am not sure about being able to close off the air.  I will check the installation closer next time out.


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