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  1. #1
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    Default Can furnace combustion air be pulled from attic

    Hi everyone
    I've visited this site a couple times but this is my first post.
    I have a goodman 93% high efficency natural gas furnace located in my single story home in the utility room. Utility room is not closed off in any way to the rest of the house.

    Original installers used pvc to vent the furnace to the roof but combustion air for the furnace is pulled from inside the house.

    Could the combustion air for the furnace be piped in with pvc pipe from my attic area? Of course routed above insulation. The attic has 1 vent on the north side of the home, and 1 on the south side of the house, and 3 roof vents.

    just wondering if this is acceptable practice.

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  2. #2

    Default Re: Can furnace combustion air be pulled from attic

    Combustion air for a cat1 furnace can be pulled from the attic, so I don't see why your furnace could not. I've just never seen it done. It's better to pull combustion air from the attic than from inside the home (inefficient).


  3. #3
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    Default Re: Can furnace combustion air be pulled from attic

    brandon
    thanks for your reply.

    I figured from roof is prefered but since attic is well vented it would probably be acceptable, as long as it is a good 18 inches to 24 inches above existing insulation it should be a problem. Like you said better than pulling air from inside of home.


  4. #4

    Default Re: Can furnace combustion air be pulled from attic

    I figured from roof is prefered but since attic is well vented it would probably be acceptable, as long as it is a good 18 inches to 24 inches above existing insulation it should be a problem. Like you said better than pulling air from inside of home.
    I'm kinda thinking that pulling from the attic would be better than pulling from the exterior in that crud is not falling down into the pipe. I can't really think of any negatives of pulling the combustion air from the attic. Someone please chime in if there are any.


  5. #5
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    Default Re: Can furnace combustion air be pulled from attic

    i had done some research prior to posting and the only 2 things I read was

    1. the threat of bugs / critters / other debris (which anyone could have by having the air pulled from the living space)

    2. something about different pressures from the intake and exhaust. However i still don't see how that is a big difference since it was pulling from the living space to begin with.

    I would love to hear others thoughts.


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    Default Re: Can furnace combustion air be pulled from attic

    Ryan,

    It is much more efficient to use outside air for combustion air. If your furnace draws combustion air from inside the house you are using air that you have already heated; that air is replaced by cold outside air that will then need to be heated.

    "Baseball is like church. Many attend but few understand." Leo Durocher
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  7. #7
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    Default Re: Can furnace combustion air be pulled from attic

    bruce,
    Thanks for your input, i appreciate it. I had read that, which is kinda what made me start looking into fresh combustion air for the furnace.

    However, I am not that handy enough to cut a hole in my roof and what not, even more so this time of year (snow expected tonight and all week) so i'm not going on the roof. And I am currently knee deep in $$ on other home projects right now so really am looking for the next best solution that is still safe and accepable.

    That is why I was wondering if I could get by with air from the attic space. Not too much different than getting air from the other side of the roof.. I just was not sure of the "code" acceptance of my thinking


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    Default Re: Can furnace combustion air be pulled from attic

    Pay attention to where the air is being pulled from.
    I caught one this summer that was pulling in air from an attic filled with vermiculite.
    It was a new gas furnace.

    The return should be cut into the ceiling below in my opinion.


  9. #9
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    Default Re: Can furnace combustion air be pulled from attic

    how did you know it was vermiculite? That is a form of asbestose, did you report on that? Put a box with a screen if you are worried about animals and crud going into the pipe


  10. #10
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    Default Re: Can furnace combustion air be pulled from attic

    If the utility room is on an exterior wall, why not locate the intake on the outside of the wall?


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    Default Re: Can furnace combustion air be pulled from attic

    FIELD CONTROLS, LLC - CONTRACTOR PRODUCTS Combustion Air Systems
    Check this out before getting too involved.


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    Wink Re: Can furnace combustion air be pulled from attic

    I agree with everyone else on drawing air from the attic for combustion purposes (no problem) as long as the attic is sufficiently ventilated. Just make sure if there is any ductwork up in the attic that it is well sealed (and should be insulated). I've seen disconnected ductwork many a time up in attics. Furthermore, when you stub up your PVC vent thru the ceiling and into the attic you could direct the pipe close to one of your roof vents (closest one to where the pipe will be coming into the attic). You don't have to run it up tight to the vent but just say a few inches away (this would be the more effective). You might want to put a screen on the end to prevent critters from getting into it.

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  13. #13
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    Default Re: Can furnace combustion air be pulled from attic

    Combustion air locations on direct vent 90% furnaces are completely up to the listed manufactures installtion instructions. Our opinions while we are entitled to our opinions do not make any difference in the location of combustion air.


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    Default Re: Can furnace combustion air be pulled from attic

    The State of Minnesota prohibits (through an amendment to the code) taking combustion air from an attic. You can't see if the opening has been plugged, plus you are pulling nasty materials form the attic into the home. 2006 IFGC Section 304.11, item 5, prohibits screening a combustion air duct terminating in an attic. The screen will get fouled with floating dust and insulation and get blocked.
    The combustion air duct should terminate to the exterior, would you rather breathe fresh air, or the air in the attic?


  15. #15
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    Default Re: Can furnace combustion air be pulled from attic

    I think there may be some confusion about combustion air.
    This combustion air is for a closed system furnace, it should just suck it in for the burner and then exhaust the rest out of the roof. no?

    The return air for the furnace to heat and then put back the heated air into the living area will still come from inside the house. So from my understanding I will never breathe in a breath of this air, it will only be used to fire the burners in the furnace and then exhausted to the roof.

    I think I am just going to call an hvac guy and have him give me a quote. Better just to be safe.

    Last edited by Ryan Vega; 12-07-2009 at 07:41 AM.

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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Ryan Vega View Post
    I think there may be some confusion about combustion air.
    This combustion air is for a closed system furnace, it should just suck it in for the burner and then exhaust the rest out of the roof. no?

    The return air for the furnace to heat and then put back the heated air into the living area will still come from inside the house. So from my understanding I will never breathe in a breath of this air, it will only be used to fire the burners in the furnace and then exhausted to the roof.

    I think I am just going to call an hvac guy and have him give me a quote. Better just to be safe.
    That should not be an issue.

    As long as the roof is vented well.

    Of course they have their own issues such as drain pans ,Filter access,condensate line if it is a split system,etc.


  17. #17
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    Default Re: Can furnace combustion air be pulled from attic

    bob,
    thanks for your reply, but not sure if i understand.

    they each have their own issues? filter access? condensate line?
    The furnace location within the living area utility room would still be the same.


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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Cobra Cook View Post
    how did you know it was vermiculite? That is a form of asbestose, did you report on that? Put a box with a screen if you are worried about animals and crud going into the pipe
    This is what it looked like.
    vermiculite [1024x768].jpg

    Yes I reported on it and wished the HVAC guy had not be up there disturbing the stuff.

    I reported it should be tested.

    The client walked because of a number of issues ,with this being one of them.


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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Ryan Vega View Post
    bob,
    thanks for your reply, but not sure if i understand.

    they each have their own issues? filter access? condensate line?
    The furnace location within the living area utility room would still be the same.
    I do not know how accessible the attic is ,but if the filter is at the unit ,or it needs any servicing you have to go up there.

    I would also make sure those vents are well insulated as the attic temps are more extreme and should be with in several degrees of the outside air.

    Do not get me wrong as it is done all the time and I had this done 7 years ago where they had to cut a hatch to gain attic access.The spacers sure beat the old space heater.


  20. #20
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    Default Re: Can furnace combustion air be pulled from attic

    Fred, I hope you do not have to breathe in the combustion air after it has gone through the burner as you will turn a pretty color of blue real quick, then you will start to rot unless it is in a sub zero location. Combustion supply air, though it may be the same air we breathe inside or outside, it is not to be confused with the supply air in the house. They are two separate entities.
    Drawing combustion air from a well vented attic is really no different than drawing it from outside, either way it is more efficient than drawing already conditioned air from the inside of your house. The same logic comes about from putting a vent to draw outside air into your fireplace so as to lessen conditioned air from going up the chimney. I am sure there are safety consultants bursting with all kinds of scientific reasons that make it a dangerous issue, most likely to justify their position and high paying jobs.
    In my earlier post I said to put a box with a screen to protect from animals and bugs, simply putting a screen on a four inch would not work as well but, there is one more item to consider, the ridge and eave vents should already have a screen and the soffit vents contain very little holes to prevent big insects or animals from entering the attic. If missing that should be part of your inspection report.
    As far as terminating a combustion air vent into an attic I hope every one can understand what can happen in that case, it is totally opposite of installing a combustion supply air vent.



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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Cobra Cook View Post
    Fred, I hope you do not have to breathe in the combustion air after it has gone through the burner as you will turn a pretty color of blue real quick, then you will start to rot unless it is in a sub zero location. Combustion supply air, though it may be the same air we breathe inside or outside, it is not to be confused with the supply air in the house. They are two separate entities.
    Drawing combustion air from a well vented attic is really no different than drawing it from outside, either way it is more efficient than drawing already conditioned air from the inside of your house. The same logic comes about from putting a vent to draw outside air into your fireplace so as to lessen conditioned air from going up the chimney. I am sure there are safety consultants bursting with all kinds of scientific reasons that make it a dangerous issue, most likely to justify their position and high paying jobs.
    In my earlier post I said to put a box with a screen to protect from animals and bugs, simply putting a screen on a four inch would not work as well but, there is one more item to consider, the ridge and eave vents should already have a screen and the soffit vents contain very little holes to prevent big insects or animals from entering the attic. If missing that should be part of your inspection report.
    As far as terminating a combustion air vent into an attic I hope every one can understand what can happen in that case, it is totally opposite of installing a combustion supply air vent.
    One of the things I like about this site is that everyone thinks they are smarter than everyone else

    Combustion air: Air neccessary for complete combustion of a fuel, including theoretical air and excess air. 2006 IFGC. This is not "combustion products", which is what is being vented through the flue. If breathing the combustion air is going to turn me blue, then it does not contain enough oxygen to support combustion.

    Terminating is the word the code uses, in other words, ending the combustion air duct in the attic. The installation of the duct requires a start point, at the furnace, and an end point, its termination point.

    A direct vent furnace can, as in the case of the OP, take its combustion air directly from the space in which it is in (like the OP), in this case the combustion air is freely communicating with the air you're breathing. Or it can have a dedicated duct connected to the furnace pulling air from another space, in this case you are not breathing the combustion air.
    The other way to provide ducted combustion air is a duct starting in the room with the appliance, not connected to the appliance (think of an atmospherically vented water heater), in this case you are again breathing the combustion air - before the appliance uses it. As far as "they are two separate entities", my lungs, and the furnace, do not know what the air they are using is intended to be used for, which is why you need to account makeup air, combustion air, and ventilation air.


  22. #22
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    Default Re: Can furnace combustion air be pulled from attic

    ok i may have created my own confusion on this one

    I am asking this.

    Can i use a pvc pipe directly connected to the combustion air intake on the furnace and terminate it in my vented attic space about 18 inches above the insulation?

    the combustion air would come in through the pvc pipe and run directly into the furnace.

    Is this very different from having the combustion pvc intake on the roof?

    sorry if there was some confusion about my question.


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    Default Re: Can furnace combustion air be pulled from attic

    Per the Indiana State Building Code, which has adopted both the 2006 International Mechanical Code and the 2006 International Fuel Gas Code
    IDHS: Codes, Standards and other Rules you can terminate the combustion air duct in the attic (it was not amended out), but it cannot have a screen over the opening.
    The combustion air duct can be pvc if it is allowed per the installation instructions. If the installation instructions prohibit terminating the duct in the attic, then you cannot terminate it in the attic (IMC Section 304, IFGC Section 618.1, appliance must be installed in accordance with its manufacturers installation instructions)


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    Default Re: Can furnace combustion air be pulled from attic

    You'll find most gas-fired furnace instructions will reference ANSI z223(.1) and/or AGA Z223(.1) and/or National Fuel Gas Code and/or NFPA 54 (all same thing) in their installation instructions. You can view NFPA 54 several different editions (depending on the date of manufacture of the furnace) on line for free after you've registered on the NFPA.org website.

    Some additional thoughts are protecting the attic/roof assembly i.e. separations/blocking/sealing, air quality and energy (efficiency) instructions/ratings & codes/ordinances, etc. New/replacement appliance may require updating to newer code adoptions.

    You sure PVC (and not CPVC) was used to vent exhaust through the roof?

    93% considered high efficiency for a furnace not so sure anything above 88-90% can be achieved gravity only or power combustion, so this would be a condensing furnace right? You'd also have to know the rating/requirements of the furnace and the size/volume of available airflow/air exchange in the attic space. Two openings seems doubful creating negative pressure in attic. NFPA 54 outlines using indoor space of the appliance room calculations with sufficient infiltration/air exchange or direct venting terminating outdoors for combustion and dillution air. What does your installation manual say for the make, model, and vintage furnace on the subject? Attic air will be cold too.

    Last edited by H.G. Watson, Sr.; 12-07-2009 at 03:10 PM.

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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Ryan Vega View Post
    ok i may have created my own confusion on this one

    I am asking this.

    Can i use a pvc pipe directly connected to the combustion air intake on the furnace and terminate it in my vented attic space about 18 inches above the insulation?

    the combustion air would come in through the pvc pipe and run directly into the furnace.

    Is this very different from having the combustion pvc intake on the roof?

    sorry if there was some confusion about my question.
    Short answer is yes ,Ryan.


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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Bob Elliott View Post
    Short answer is yes ,Ryan.

    Good answer, but wait, there's more . . . .


    The high efficiency furnaces that I have installed seem to be pretty tempermental when it comes to the pressure differential between the combustion air intake and the vent.

    I have installed many furnaces with the combustion intake in the attic but the installation manual required that I add two elbows so the intake is facing down AND the added pressure drop equals the longer vent pipe length.

    As far as a plugged intake resulting in a safety issue . . . I doubt it. All of the furnaces that I have installed would trip an alarm and shut off at the slightest hint of a plugged air intake.


  27. #27
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    Default Re: Can furnace combustion air be pulled from attic

    thanks for all your input. Just to be on the safe side I'm having my hvac guy come and take a look to see what he recommends and to get a price.. I need help with venting my dryer anyways (i can't figure out a way to do it while keeping the dryer as close to the wall as possible *space issues along with stackable washer and dryer*)

    but thanks it seems like there are just many possiblities that could happen, I don't like headaches so I'll probably play it safe and just have it done out the roof


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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Ryan Vega View Post
    thanks for all your input. Just to be on the safe side I'm having my hvac guy come and take a look to see what he recommends and to get a price.. I need help with venting my dryer anyways (i can't figure out a way to do it while keeping the dryer as close to the wall as possible *space issues along with stackable washer and dryer*)

    but thanks it seems like there are just many possiblities that could happen, I don't like headaches so I'll probably play it safe and just have it done out the roof
    Ok ,just make sure to use Corrugated sheet metal venting.


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    Default Re: Can furnace combustion air be pulled from attic

    Perfect world cold attic: same RH (or drier), same temp, and equal pressures (and quickly equallized as the wind blows, etc.) as the outdoors. Sealed and separated from the living space, no moisture or heat migration from living activies below. Reality is there is usually some (or a great deal of) moisture migration and heat migration. Lower temperature air at same or even higher RH = lower absolute moisture content/humidity than higher temperature air. That cold (drier) air enters sealed chamber, ideal combustion/dillution air would have a low absolute moisture content for most efficient firing/heating, they'll still be moisture to condense from the firing of the NG.

    Have a Sch. J done. Was the dryer present when the furnace was installed? Some dryers can be side vented with a manufacturer's kit, keeps the unit's back up against the wall, don't know if that would help in your situation, but threw it out there, since you mentioned it.


  30. #30
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    Smile Re: Can furnace combustion air be pulled from attic

    Rod, good post. Fred, "The combustion air duct should terminate to the exterior, would you rather breathe fresh air, or the air in the attic?" Fred did yer ferget what yer earlier post said. How is what air that is going to be used for combustion that originates from the attic going to intermingle with the air u breath?
    Realistically unless the furnace has a combustion air blower it will be almost impossible to prevent some inside air from being used for combustion unless the furnace is located out side the house. As far as getting a furnace, boiler or hot water to burn at 100% good luck.
    Do you know that natural gas does not contain any carbon? It is actually a distilled oil by product, then how is it perceived to give off Carbon Monoxide?




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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Cobra Cook View Post
    Rod, good post. Fred, "The combustion air duct should terminate to the exterior, would you rather breathe fresh air, or the air in the attic?" Fred did yer ferget what yer earlier post said. How is what air that is going to be used for combustion that originates from the attic going to intermingle with the air u breath?
    Realistically unless the furnace has a combustion air blower it will be almost impossible to prevent some inside air from being used for combustion unless the furnace is located out side the house. As far as getting a furnace, boiler or hot water to burn at 100% good luck.
    Do you know that natural gas does not contain any carbon? It is actually a distilled oil by product, then how is it perceived to give off Carbon Monoxide?
    Cobra Cook:

    Had to save that gem. Too funny. On what basis to you declare natural gas (not a distilled oil byproduct) or for that matter any hydrocarbon product contains no carbon atoms?

    Hydrocarbon molecules burning with less than sufficient combustion & dillution air = incomplete combustion.

    Incomplete combustion means burning in a lack of air (not enough oxygen).
    If there is not enough oxygen available
    for all the carbon to turn into carbon dioxide (complete combustion),
    then some or all of the carbon turns to carbon monoxide.
    This happens with any hydrocarbon - we shall take methane as an example.
    During incomplete combustion methane gas burns with a yellow flame
    (unlike the clear blue flame seen in complete combustion).
    Carbon particles (sooty marks) may also be seen.
    methane + oxygen carbon monoxide + water.
    2CH4(g) + 3O2(g) 2CO(g) + 4H2O(l)

    Complete combustion happens when
    the hydrocarbon burns in an excess of air.
    An excess of air means that there is more than enough oxygen
    to cause all of the carbon to turn into carbon dioxide.
    The methane gas burns with a clear blue flame.
    methane + oxygen carbon dioxide + water + energy
    CH4(g) + 2O2(g) CO2(g) + 2H2O(l)
    The reaction is exothermic (gives out heat).
    Perhaps someone has been drinking the C2H5OH rather than burning it?


    Last edited by H.G. Watson, Sr.; 12-07-2009 at 05:03 PM. Reason: formatting

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    Default Re: Can furnace combustion air be pulled from attic

    Cobra Cook: Look up: Hydrocarbon


    Natural Gas:

    Methane is composed of a molecule containing one carbon atom and four hydrogen atoms.

    Other contents: Propane, ethane, butane and pentane.

    Natural gas is an abundant, naturally occurring gas, which is found deep beneath the earth’s surface, in large pockets that are located inside porous rock. It is called a fossil fuel because scientists believe it to have been created by the gradual decomposition of ancient organic fossil matter, such as plants and tiny sea animals. Layers of this organic matter built up over time until the pressure and heat from the earth “cooked” this mixture into natural gas.

    The principal chemical ingredient of natural gas is methane. Very small amounts of other gases also are contained in natural gas, including ethane, propane, butane and pentane.

    Learn more:

    AGA: What Is Natural Gas?

    Last edited by H.G. Watson, Sr.; 12-07-2009 at 04:32 PM.

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    Default Re: Can furnace combustion air be pulled from attic

    " It is actually a distilled oil by product, then how is it perceived to give off Carbon Monoxide? "


    What!!!!

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

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    Default Re: Can furnace combustion air be pulled from attic

    Do you know that natural gas does not contain any carbon? It is actually a distilled oil by product, then how is it perceived to give off Carbon Monoxide?
    Cobra, you need to either explain that or do a little research on the subject.
    Natural gas around here is produced from natural gas wells, not as a by product of oil production. My understanding is that most all fossil fuels, including natural gas, are carbon based fuels. Natural gas when burned properly produces carbon dioxide and water vapor or carbon monoxide if burned with a lack of oxygen.

    Jim Luttrall
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    Cool Re: Can furnace combustion air be pulled from attic

    ~75% of all NG comes from NG wells via a refinery to scrub out impurities such as propane, ethane, butane, iso's, etc. and 25% from refining crude oil. ~75% of all LP gas comes directly from refining crude oil and 25% from refining NG

    HG explained the chemistry correctly so I'm really at a loss where you came up with your theory about CO and NG.

    The best setup for a Cat. IV furnace is to pull combustion air from the same zone and the discharge, which is outdoors. While some allow pulling air from the indoors, it will depressurize the CAZ and could result in an imbalance in the venting. The attic is also subject to weird pressure regimes WRT the vent discharge outdoors so even if *approved*, it is a poor choice and yes, you would need to be concerned about airborne *stuff* getting down the intake.

    An intake would not 'terminate' but 'originate' in an attic or outdoors---it terminates at the appliance.

    Bob

    Keep the fire in the fireplace.

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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Bob Harper View Post
    ~75% of all NG comes from NG wells via a refinery to scrub out impurities such as propane, ethane, butane, iso's, etc. and 25% from refining crude oil. ~75% of all LP gas comes directly from refining crude oil and 25% from refining NG

    HG explained the chemistry correctly so I'm really at a loss where you came up with your theory about CO and NG.

    The best setup for a Cat. IV furnace is to pull combustion air from the same zone and the discharge, which is outdoors. While some allow pulling air from the indoors, it will depressurize the CAZ and could result in an imbalance in the venting. The attic is also subject to weird pressure regimes WRT the vent discharge outdoors so even if *approved*, it is a poor choice and yes, you would need to be concerned about airborne *stuff* getting down the intake.

    An intake would not 'terminate' but 'originate' in an attic or outdoors---it terminates at the appliance.

    Bob

    You're absolutely correct. Mea Culpa (call it concentric confusion or brain *art).


  37. #37

    Default Re: Can furnace combustion air be pulled from attic

    You sure PVC (and not CPVC) was used to vent exhaust through the roof?
    H.G. -- PVC is pretty much the go to exhaust pipe material for cat IV furnaces, around here at least.


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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Brandon Whitmore View Post
    H.G. -- PVC is pretty much the go to exhaust pipe material for cat IV furnaces, around here at least.
    Schedule 40


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    Default Re: Can furnace combustion air be pulled from attic

    if you are going to all the trouble of running an intake pipe from the attic. Why not just take the extra staep and do it right, which is intake exterior air. Through roof vent, through soffit vent, easy install.
    Another thought for you is that if you have recessed lighting in the attic. The draw from the intake in the attic will pull hot air from the house up into the attic.
    Do you want to lose heat?
    Oh and when you have an intake pipe installled into the attic it does not terminate in the attic it terminates at the combustion unit. I think you may have confused some who insist on literal translation of every word and sentence


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    Cool Re: Can furnace combustion air be pulled from attic

    Hey, to extend PVC out the roof from the attic is going to cost about $4.50 for the roof jack and about $0.40/LF for the PVC----that really adds up! Might cost at least an additional $15.00 in materials.

    Seriously, it sounds like a plumber didn't want to get on the roof to cut a hole (which can be cut from the underside if need be) and extend the pipe through the boot, attach candy cane and cement it in place. On new construction, he can leave the boot flashing up off the roof unsecured for the roofer if he gets in there early enough.


    Side story: I was installing B-vent for a fireplace while a nosey plumber was there telling me my business. He was working in the attic with me directly above on the roof so he could hear my hammering and see the nails penetrating. He cut into my boot with a Sawzall. Closest I ever came to hitting anyone on a jobsite. Instead, I showed the inspector several of his mistakes so he had a punch list for his failed inspection. Payback.

    Keep the fire in the fireplace.

  41. #41
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by wayne soper View Post
    Another thought for you is that if you have recessed lighting in the attic. The draw from the intake in the attic will pull hot air from the house up into the attic.
    I would think the attic would have to be awfully tight and without venting to draw air from recessed lights. How many CFM's does the intake draw?


  42. #42
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    Default Re: Can furnace combustion air be pulled from attic

    recessed lights act like chimneys on their own let alone whatever CPm is involved which I admit I do not know. Anyway it was just a backup comment to do the job right and not try to Rube G it.


  43. #43

    Default Re: Can furnace combustion air be pulled from attic

    I wasn't even thinking about pressure issues in regards to terminating in the attic. I was thinking that it would act partially like HRV and pull in slightly warmer air being lost from inside the home. I doubt that it would depressure the home, but that's a pure guess and my opinion only-- assuming there is attic ventilation.


  44. #44
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by wayne soper View Post
    recessed lights act like chimneys on their own ...
    Shouldn't, at least not since 1984 (in Florida) or whenever your energy code came in. Of course, even in Florida it was not realized that the energy covered that as the wording was not straight-forward about it, but starting in 1997 the wording specifically addressed air-tight recessed lights as such.

    It is amazing how much we do not understand what is written in the codes until it is pointed out to us, and the wording changed slightly so we can understand what it was telling us all along.

    Last edited by Jerry Peck; 12-09-2009 at 06:07 PM. Reason: fixing quote bracket
    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  45. #45
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Bob Harper View Post
    Hey, to extend PVC out the roof from the attic is going to cost about $4.50 for the roof jack and about $0.40/LF for the PVC----that really adds up! Might cost at least an additional $15.00 in materials.
    .

    I understand your point Bob, but there is more to it than the $15 in material.

    I can think of one example where the roof was very steep and a LONG ways from the ground. The owner bit and chewed at my price to the point where $15 mattered and frankly getting on that roof more than what was necessary was worth a lot more than the dollars.

    Yes you could use a concentric vent/CA fitting, but not for $15.

    Then there is the issue of more roof penetrations. Many architects (and builders and homeowners) do NOT want more roof penetrations, or ANY roof penetrations.

    A properly ventilated attic is not a detrement to the home quality and attic combustion is a very practical application.


  46. #46
    David Bell's Avatar
    David Bell Guest

    Default Re: Can furnace combustion air be pulled from attic

    The standard for combustion air is 1 cubic foot open of area for 1000 btu of combustion. Direct vent furnaces dont really care where the air comes from as longs as they can keep the secondary heat exchanger in a negative pressure,thus the pressure switches on all this type of furnace. I do agree that pulling outside air is the best and all manufacturers offer a concentric venting kit that allows for just one termination point whether it be sidewall or rooftop


  47. #47
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by David Bell View Post
    The standard for combustion air is 1 cubic foot open of area for 1000 btu of combustion. Direct vent furnaces dont really care where the air comes from as longs as they can keep the secondary heat exchanger in a negative pressure,thus the pressure switches on all this type of furnace. I do agree that pulling outside air is the best and all manufacturers offer a concentric venting kit that allows for just one termination point whether it be sidewall or rooftop
    Good post as you are absolutely correct.

    I have never seen one used this way, but just downloaded a PDF for concentric vent install on Cat 4.


  48. #48
    Phillip Bates's Avatar
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    Default Re: Can furnace combustion air be pulled from attic

    Good morning:Wow!Thats a lot of reading as a result of your posted question.The issue of installation of intake & exhaust pipes- no matter whether you live in the US or Canada - is covered by the furnace manufacturers installation instructions(a certified document that our gas code up here enforces, as probably does yours).Having both terminate within the same pressure zone ensures you don't have nuisance no-heat calls due to the affects of wind/blowing snow,etc on either pipe which then affects the pressure/air switch wired into the system.The manufacturer will not honor a warranty if the installation doesn't meet their specs(including if combustion air is taken from the furnace area which may be inside a laundry room with its chlorine products, hence a corrosive atmosphere).Also the intake/combustion air pipe should be fitted with 90 degree elbow, so nothing should ever fall inside it.Install screen but as no dimension may be smaller than 25mm you will always risk small insects making a home there during your off season.I suppose you can run it to your attic if you must, & perhaps the exhaust termination isn't currently affected by prevailing winds, etc. so all will run without problems for you if you do so(I'm referring to the issue of different pressure zones).Good luck.


  49. #49
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Phillip Bates View Post
    Good morning:Wow!Thats a lot of reading as a result of your posted question.The issue of installation of intake & exhaust pipes- no matter whether you live in the US or Canada - is covered by the furnace manufacturers installation instructions(a certified document that our gas code up here enforces, as probably does yours).Having both terminate within the same pressure zone ensures you don't have nuisance no-heat calls due to the affects of wind/blowing snow,etc on either pipe which then affects the pressure/air switch wired into the system.The manufacturer will not honor a warranty if the installation doesn't meet their specs(including if combustion air is taken from the furnace area which may be inside a laundry room with its chlorine products, hence a corrosive atmosphere).Also the intake/combustion air pipe should be fitted with 90 degree elbow, so nothing should ever fall inside it.Install screen but as no dimension may be smaller than 25mm you will always risk small insects making a home there during your off season.I suppose you can run it to your attic if you must, & perhaps the exhaust termination isn't currently affected by prevailing winds, etc. so all will run without problems for you if you do so(I'm referring to the issue of different pressure zones).Good luck.
    Phillip,

    Please note that there is a space bar, typically located along the bottom of the keyboard below the letter keys, it makes "spaces", like this " ", and makes it much easier to read posts.

    Also, there is a enter key, also acts as a return key, which is used for making paragraphs between sentence, like this (hit enter key twice)

    and now you have separate paragraphs, which makes it MUCH easier to read posts.



    Jerry Peck, Construction / Litigation Consultant
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    www.AskCodeMan.com

  50. #50
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    Default Re: Can furnace combustion air be pulled from attic

    Quote Originally Posted by Bob Elliott View Post
    Pay attention to where the air is being pulled from.
    I caught one this summer that was pulling in air from an attic filled with vermiculite.
    It was a new gas furnace.

    The return should be cut into the ceiling below in my opinion.

    Hi Bob,
    Can you fill me in a little bit more about this comment please? Where was the home located..the City or State? Do you encounter vermiculite in attics or walls very often? Do you know the origin of the vermiculite Libby or South Carolina? Do you have standing protocols for dealing with vermiculite when you encounter it or do you just wing it since you know?

    I notice you commented further below so I will read through all of that as well. I just joined this site to chat with you regarding this comment, and do not know how the site works yet. If it will send me an email when you respond or not. If you would be so kind as to drop me an email at ttrent1 at juno dot com...I would appreciate it.
    Thanks TT

    - - - Updated - - -

    Quote Originally Posted by Bob Elliott View Post
    Pay attention to where the air is being pulled from.
    I caught one this summer that was pulling in air from an attic filled with vermiculite.
    It was a new gas furnace.

    The return should be cut into the ceiling below in my opinion.

    Hi Bob,
    Can you fill me in a little bit more about this comment please? Where was the home located..the City or State? Do you encounter vermiculite in attics or walls very often? Do you know the origin of the vermiculite Libby or South Carolina? Do you have standing protocols for dealing with vermiculite when you encounter it or do you just wing it since you know?

    I notice you commented further below so I will read through all of that as well. I just joined this site to chat with you regarding this comment, and do not know how the site works yet. If it will send me an email when you respond or not. If you would be so kind as to drop me an email at ttrent1 at juno dot com...I would appreciate it.
    Thanks TT


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