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  1. #1
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    Default Is outdoor air vent required?

    New house insulated to new energy code. Spray foamed and sealed everywhere.
    What is the requirements for general ventilation to prevent "sick building" syndrome? How to they determine if the bath fans exhaust only is necessary or if an HRV is required?

    Also, HVAC unit in the un-vented attic. Would there be a special requirement for draft and combustion air.
    How do they determine that and what is the code?

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  2. #2
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    Default Re: Is outdoor air vent required?

    "HVAC unit in the un-vented attic. Would there be a special requirement for draft and combustion air."

    Carbon Monoxide is Heavier than Air and finds it's lowest level.

    Gas Fired Appliances Require Combustion Air to operate Safely as intended.

    Your blanket statement defies both of these requirements.

    It Might have Choked Artie But it ain't gone'a choke Stymie! Our Gang " The Pooch " (1932)
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  3. #3
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    Default Re: Is outdoor air vent required?

    Ken

    If the house is sealed it would require make up air, such a home should be fitted with HRV(s) to exchange stale air for fresh air. Exhaust fans require make up air, hence another reason for the need of HRV.


  4. #4
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    Default Re: Is outdoor air vent required?

    Sealed and unvented attics do not affect required ventilation air.

    Just because a house is sealed does not mean it requires outside ventilation air ... houses have been sealed for decades.

    One needs to know how many ACH (Air Changes per Hour) the leakage rate is.

    A house should not have more than 5 ACH ... and if it has less than 5 ACH ... then it requires outside air ventilation.

    Jerry Peck, Construction / Litigation Consultant
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  5. #5
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    Default Re: Is outdoor air vent required?

    Homes have been sealed for decades? You lost me there.

    Any new homes I am inspecting up here have HRV installed because the whole idea is to prevent uncontrolled air infiltration particularly in winter months. And those homes are not R2000 energy rated they have conventional insulation.

    Also noted the comment about CO being heavier than air.

    http://www.ncbi.nlm.nih.gov/pubmed/21536403


  6. #6
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Jerry Peck View Post
    Sealed and unvented attics do not affect required ventilation air.

    Just because a house is sealed does not mean it requires outside ventilation air ... houses have been sealed for decades.

    One needs to know how many ACH (Air Changes per Hour) the leakage rate is.

    A house should not have more than 5 ACH ... and if it has less than 5 ACH ... then it requires outside air ventilation.
    That's informative - thanks. I was reading the 2012 IECC code summary from our state and it was a bit confusing. They state that the ventilation rate can be controlled by EITHER using bathroom fans (w/no make up air) or HRV units. I was trying learn a little more about it.

    But what about the HVAC unit in the attic. It's a natural draft type horizontal unit and get's combustion and draft air from the "Sealed and unvented attic space". How does one determine if this is adequate?

    Ken Amelin
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  7. #7
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Ken Amelin View Post
    New house insulated to new energy code. Spray foamed and sealed everywhere...
    ...Also, HVAC unit in the un-vented attic. Would there be a special requirement for draft and combustion air.
    How do they determine that and what is the code?
    Yes, you need to provide combustion air for THAT furnace.
    That furnace is not a high efficiency model that can draw outdoor combustion air through plastic pipe so the combustion air must come from the room enclosure where it is located.
    Dumb arrangement. In my opinion only a sealed combustion unit that draws all combustion air directly from outdoors should be used in a sealed attic. Punching holes in the sealed attic to provide combustion air for a low efficiency unit is stupid and negates much of the benefits of sealed attics.
    Normally in a vented attic, combustion air is not a problem since the space communicates freely with outdoors. I doubt the sealed attic provides enough combustion air to satisfy the combustion air requirements unless it is a really large attic and/or a really small furnace.
    See G2407 in the IRC
    Since I assume this is tight construction, G2407.5.2 should be used for ALL appliances in the "room" using >/= either 15 or 21 cubic feet divided by ACH per 1,000 BTU formula. Good luck in applying that since it requires knowing the "ACH" (Air Changes per Hour) and the volume of the room.
    If it is of "unusually tight" construction, I would defer to HVAC specialist other than the one who installed it.

    Last edited by Jim Luttrall; 07-01-2015 at 05:06 PM.
    Jim Luttrall
    www.MrInspector.net
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  8. #8
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Raymond Wand View Post
    Homes have been sealed for decades? You lost me there.
    Yep.

    Starting up north where they started sealing the thermal envelope and adding more insulation, back in the 1970's. When was in Gainesville, Florida, a couple of builders moved down who built in Michigan. They were insulating their homes like they up there, and sealing them like they did up there - something 'we' (down in Florida) had not seen before and found kinda funny - turns out that all that sealing and insulation also made for a much more energy efficient home when trying to cool it with the air conditioner (heat was not as major an issue as air conditioning was).

    Any new homes I am inspecting up here have HRV installed because the whole idea is to prevent uncontrolled air infiltration particularly in winter months.
    See? Just as I described above. You guys up there in the cold *have* to do it before we down here in the heat realize it is better to do it (you *have* to do it to keep the cold out, we do it so we can keep the houses cool for less money), but many older homes still do not have air conditioning.

    Also noted the comment about CO being heavier than air.

    http://www.ncbi.nlm.nih.gov/pubmed/21536403
    I was only commenting on what I commented on, not on the entire post (I was doing it on my phone at the time).

    Jerry Peck, Construction / Litigation Consultant
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  9. #9
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Ken Amelin View Post
    I was reading the 2012 IECC code summary from our state and it was a bit confusing. They state that the ventilation rate can be controlled by EITHER using bathroom fans (w/no make up air) or HRV units. I was trying learn a little more about it.
    Correct ... sort of ... the energy code doesn't really state either a bathroom exhaust fan or an HRV (colder climates) / ERV (warmer climates), the code states, basically, the 5 ACH tipping point from being sealed 'not enough' to being sealed 'too much' and requiring outdoor air for ventilation.

    The 5 ACH is also not really a "magic number of 5.0", the "magic number" is "5", and if the code rounds the ACH off to the first significant digit, then the ACH at the "tipping point" or "magic number" really is between 4.5 ACH and 5.5 ACH (depends on how one rounds numbers off ... such as 'even numbers round up and odd numbers round down at .5', of '.5 rounds up, in which cases the upper limit would be 5.49', rounding numbers has various methods of rounding off).

    The key is, too much air leakage is bad for energy use, too little air leakage could be bad for the quality of the indoor air.

    But what about the HVAC unit in the attic. It's a natural draft type horizontal unit and get's combustion and draft air from the "Sealed and unvented attic space". How does one determine if this is adequate?
    You would need to make the same calculations for combustion air as if the air handler was in any other room or space (cubic feet of space).

    Of course, though, with well sealed houses which require HRV/ERV for ventilation because the house is too tight (<5ACH) will require combustion air per the code due to very tight construction (an often overlooked section in the code).

    Jerry Peck, Construction / Litigation Consultant
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  10. #10
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Raymond Wand View Post

    Also noted the comment about CO being heavier than air.

    http://www.ncbi.nlm.nih.gov/pubmed/21536403
    Any CO Spillage in that Attic WILL MIGRATE into the Habitable Space below.

    It Might have Choked Artie But it ain't gone'a choke Stymie! Our Gang " The Pooch " (1932)
    Billy J. Stephens HI Service Memphis TN.

  11. #11
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    Default Re: Is outdoor air vent required?

    A sealed attic is sealed to the outside and not sealed from the rest of the living area. The insulation has been moved to the roof line and the attic would be semi conditioned unless there is a vent up there in which case it would be conditioned. Actually you probably want some air circulation as sealed attics can have high humidity.

    There would be no harm putting a grill in the ceiling and allowing more air flow to the attic. Also that is a draft induced furnace and it is not likely to back draft unless it is tied in to a water heater. The back drafting would occur at the water heater as the fan is pulling air through the heat exchanger and forcing it out. If it is straight shot from the furnace out of the house you don't need to worry.

    - - - Updated - - -

    A sealed attic is sealed to the outside and not sealed from the rest of the living area. The insulation has been moved to the roof line and the attic would be semi conditioned unless there is a vent up there in which case it would be conditioned. Actually you probably want some air circulation as sealed attics can have high humidity.

    There would be no harm putting a grill in the ceiling and allowing more air flow to the attic. Also that is a draft induced furnace and it is not likely to back draft unless it is tied in to a water heater. The back drafting would occur at the water heater as the fan is pulling air through the heat exchanger and forcing it out. If it is straight shot from the furnace out of the house you don't need to worry.


  12. #12
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    Default Re: Is outdoor air vent required?

    More information would help. What is the energy source for the furnace? Is it is fuel gas or fuel oil? Is the furnace a sealed combustion chamber, induced draft unit?

    The installation of the sprayed foam insulation on the underside of the roof deck and the lack of ventilation in the attic area leads me to wonder if the home was designed and built with a conditioned attic.

    Also, check with the current occupants or, if possible, the builder to determine if it's meant to be a conditioned attic. Some links to websites with information about conditioned attics are provided below.

    Understanding Attic Ventilation | Building Science Corp

    http://energy.gov/sites/prod/files/2...ics_011713.pdf

    http://www.nepaenergysmart.com/pdfs/...ed%20Attic.pdf


  13. #13
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Robert Hronek View Post
    A sealed attic is sealed to the outside and not sealed from the rest of the living area. The insulation has been moved to the roof line and the attic would be semi conditioned unless there is a vent up there in which case it would be conditioned.
    The term used to be 'semi-conditioned' as that makes sense in that it is not 'conditioned' yet is acclimates to approximately the same temperature and humidity as that of the actual conditioned space - however, that was not a recognized term (from everything I have learned, heard, and been advised). There was a time when some actually installed a supply up in the attic part, but that just lead to mildew on things so that was stopped. Being as the space acclimates to within a degree or two of the actually space with the supplies in it, the 'conditioning of the environmental air in the space' (even without supplies in it) makes it 'conditioned space', just not calculated into the heat or cooling loads.

    I still prefer 'semi conditioned' as it makes sense and is easier to understand, but I have been converted over to just calling it an 'unvented' or 'sealed' attic and try to leave the 'conditioned' term out of it - but, as compared to an unsealed attic which has outside air circulating through it ... the sealed attic area is 'conditioned space' (especially when you think of it as compared to an unsealed and vented attic).

    Jerry Peck, Construction / Litigation Consultant
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  14. #14
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    Default Re: Is outdoor air vent required?

    Thanks, Jerry, your points are, as always, interesting and your distinction between semi-conditioned and conditioned is informative. I was unable to find any agreed upon operational definition for or distinction between semi-conditioned and conditioned attic spaces as the terms seem to be used interchangeably.

    I think that the primary issue here is helping home inspectors understand the pros and cons, the rationales, and the physical dynamics attendant to this particular construction method. The concept and its implementation arose as a method of improving the overall cooling and heating energy efficiency of homes by reducing the potential for cold or hot attic air to infiltrate the living space of homes and to provide a narrower temperature differential between the living space and the attic.

    It will be interesting to see if the concept proves to work well enough that, barring few or no adverse unintended consequences such as tight building syndrome, accelerated aging of some roof covering materials, etc., it will become an increasingly common construction practice.


  15. #15
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    Default Re: Is outdoor air vent required?

    Quote Originally Posted by Ken Amelin View Post
    New house insulated to new energy code. Spray foamed and sealed everywhere.
    What is the requirements for general ventilation to prevent "sick building" syndrome? How to they determine if the bath fans exhaust only is necessary or if an HRV is required?

    Also, HVAC unit in the un-vented attic. Would there be a special requirement for draft and combustion air.
    How do they determine that and what is the code?
    Suggestions to prevent back-drafting and other combustion safety hazards:
    3 Ideally, install direct vent (outdoor air for combustion) equipment
    3 If direct vent equipment is not feasible, install induced draft or power vented combustion appliances
    3 Exhaust-only whole-house mechanical ventilation may not be appropriate where natural draft and induced draft appliances are installed
    3 Confirm that combustion appliances including fireplaces are installed and commissioned in accordance with code and
    manufacturer instructions
    3 Perform worst case depressurization testing, as required, in accordance with industry standards, such as from the Building Performance
    Institute (BPI 2012), Air Conditioning Contractors of America (ACCA 2011), The Energy Conservatory (TEC 2012) , or other
    approved tests.

    Link to the above suggestions http://www.homeinnovation.com/~/medi...n_10252013.pdf

    and several additional documents Building and Fire Codes Overview

    And it may be useful to know in the 2015 IRC Table M106. provides the minimum duct diameter and length for the fan to perform in accordance to its rated cfm.

    Hope this helps


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