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Is it possible to have too many air intake vents in house?

barryeross | Posted in Green Building Techniques on

Is it possible to have too many return Air vents in house? Of course I guess anything is possible.
But I believe it was someone on this site, that responded to an issue I have with a Lennar home.. IT was build as part of their “green’ series. I lived in the house for 9 months and after my second trip to the emergency room due to air quality or lack there of in the house… I moved out… And I have been trying for 2 years to fix it.

The house always felt like there was no oxygen, and you would just need to step outside to breath.. Once I moved out of the house, I went from near death to perfectly normal..

I installed an attic fan, which did help with Air flow… but what has seemed to completely transform the air flow(quantity) in the house was putting ‘contact paper’ over 7 of the 9 air return vents in the home (2600 sq ft). The two remaining are filtered, the other 7 are not…

I have read some articles on your site that talk about the possible air imbalance if you don’t have enough return air vents. is it possible the house was pulling too much air through these return air vents and not replenishing it?

I also saw where you talked about an issue where air from the attic could be pulled if there were not enough return air vents.. but I am wondering if that is actually what was happening in my house.. but having too many return air vents, was actually pulling the attic air into the return air vents…

The only time I used to be able to stay in the house without getting sick or passing out.. was with windows and doors open… There were no funny odors or smells.. Just smelled like a new home..
I had air quality testing done several times.. and no one found anything…

The only thing I would notice is my CO2 meters would start to go off without windows and doors open.. they would go from 400 ppm to 1100 ppm within about 2-3 hours.. without a window or door open…

The whole experience ruined my life.. but I am desperate to figure out what the root cause is.. and If it is the return vents.. Can I just leave them covered.. Seems like a bad idea.. Or should I get an expert(not the people who installed this.. to review the whole system…

Any comments greatly appreciated.. the one person who commented and recommended covering those return vents… might have saved this house…

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  1. GBA Editor
    Martin Holladay | | #1

    In general, covering return air grilles with contact paper is a terrible idea. Return air grilles are an essential part of your forced-air heating and cooling system.

    Note that if your forced-air heating and cooling system is properly installed, it usually doesn't introduce any outdoor air into your home, or expel any indoor air from your home. All it does is heat or cool the air that is already in your home.

    Of course, it's always possible that your forced-air heating system has unbalanced ductwork or leaky ductwork. The only way to find out if that's the case, however, is to test the airflow through your ductwork with a flow hood, a Duct Blaster, or similar test equipment.

    If you think there are problems with your duct system, by all means have the system evaluated. You should contact a certified home energy rater (one certified by RESNET or BPI). Explain your problem. Tell them that you want the ducts connected to your forced-air heating system to be evaluated for leaks and balancing issues.

    In the meantime, take that contact paper off your return-air grilles.

  2. Reid Baldwin | | #2

    What ventilation system, if any, does this house have?

  3. barryeross | | #3

    The house has 7 ridge vents... The builder (Lennar) double checked after my many complaints of being sick (symptons similar to High Altitude sickness... I also installed an attic fan, in March of 2014.. 6 months after I moved out from living there full time...

    I have had the builder inspect the HVAC and ductwork, the company who installed it, as well as an independant company... But no one ever said they looked at the return air ducts.. I just assumed it would all be the same...

    I know there is something wrong.. because the house just became magically breathable again... I have neighbors who would not even come into the house.. it was so bad..

    I am going to track down another independant party to inspect the duct system.. Thanks for mentioning those certifications.. that helps.. I have spent 2 years trying to fix this.. and this is as close as I have come... Had every inspection done you can think of.. It s not mold, chinese dry wall, Co2, Co1, radon, VOCs, etc, etc... The one thing I will say is.. that if I put an air freshener in this house.. within in minutes all 2600 sqft feel like you are trapped in an elevator with someone wearing way too much cologne... I have a 450 sq ft condo I used for testing... and I can put the same air freshener in there for days and have no issue..

  4. BillDietze | | #4


    The ridge vents are not for exchanging internal air with the outside. Do you have a HRV or ERV? Turn them up! (more air exchange).

    No? Then do you have bath fans? Run the baths fans on high and repeat the air freshener test. Does it help? If so them you may need a better ventilation strategy.

  5. GBA Editor
    Martin Holladay | | #5

    Ridge vents help ventilate an attic. But I think that Reid Baldwin was asking a different question: does your house have a mechanical ventilation system -- for example, a heat recovery ventilator (HRV), and exhaust-only ventilation system that keeps a fan running for 24 hours a day, or an outside air duct connected to the return air plenum of your furnace?

  6. Reid Baldwin | | #6

    My question about ventilation was not about how the attic is ventilated, but how the house is ventilated. Is there an ERV or HRV, bathroom exhaust fans, supply ventilation via the furnace? The fact that the CO2 goes up quickly and things get better when you open windows sounds like poor ventilation.

  7. Reid Baldwin | | #7

    Looks like several of us were typing at the same time.

  8. GBA Editor
    Martin Holladay | | #8

    I think that three nearly simultaneous posts, all saying exactly the same thing, may be a new GBA record.

  9. sfriedberg | | #9

    What kind of heating system does this house have? And, have you had the house tested for carbon monoxide levels?

  10. barryeross | | #10

    I do not have a ERV or HRV... These are itmes I need to understand better.. This is a builder grade system.. I did try to run all the bathroom and kitchen exhuast fans 24-7 ... no impact...

    I did have someone recommend a fresh air return.. but I live in Florida and someone else said that I could get Mold into the system..

    The house was tested for Carbon Monoxide... And Carbon Dioxide..

    This is really great input.. Thank You..

  11. jeffwatson | | #11

    How are your humidity levels within the house?

  12. barryeross | | #12

    The humidty level in the house.. I have 3 monitors.. is between Low 40's and high 50's with windows and doors shut... Once I open the windows and doors.. it is usually between 60-80 percent.. Mind you it is florida.. and I never wanted to keep a door or window open because of mold.. Lennars expert told me to open my windows and doors every other day for 15 minutes... And the house would feel completely normal after that..

    The heat in the house has probably only be on 4 times.. and each of those was during inspections and testing... If the outside temps dropped below 60 degrees the house still stays warm/hot...

    Ill try to attach a photo of the air handler with specs..
    Im calling around trying to find someone with the certifications a previous poster mentioned..

  13. barryeross | | #13

    Here are the photos of the unit

  14. Expert Member
    MALCOLM TAYLOR | | #14

    Michael D,
    What a good summary of the pertinent issues!

  15. user-4310370 | | #15


    From your questions it seems that you lack a basic understanding of the systems involved. This is not a negative comment but it leads me to think a) you should hire a professional to help you and b) you should spend some time learning about the basics of a house, its systems and envelopes to help you better interact with the professionals helping you. This site has many excellent resources that can help with the basics.

    But to help clarify you are talking about several systems and areas that do usually interact.

    First, your attic and roof vents. Since it has roof vents you have and unconditioned attic - this means it is more part of the outside environment than the inside and is therefore a) separated via insulation and air barriers from the rest of the house - air and heat/cold is not meant to move between your attic and the rest of your house therefore attic more vents, attic air fans etc. will not likely cause or help address your issue (small caveat if your ducts and/or hvac system is located in the attic there may be unwanted interaction) b) it is vented - meaning air is meant to move freely between the attic and the environment. The temperature should be closer to the outside temperature than the interior.

    Here are links to articles on the building envelope and on a conditioned attic (the opposite of what you have but it has good basics and links to other articles)

    Second, your HVAC system. Since you have registers it is a safe assumption you have a forced air system. This system is typically only supposed to pull air from your rooms heat it or cool it (and remove humidity) and then return the air back to the rooms inside the building envelope. Since it is really only moving air around your house changing the number of return air registers will likely not address your issue either. Imagine being in a boat with a bucket of fresh water- no matter where you move it in the boat that water will not get salty since it is not interacting with the water in the ocean. Also your HVAC system should not change the pressure of your house as it is operating within the envelope not forcing air out or drawing it in (again typically). An imbalance in your HVAC system should only effect how well/hard your furnace blower is working to move air not the quality of air inside the house.

    Sometimes a furnace and blower and/or ductwork can be in a houses unconditioned attic with a lot of insulation around the ducts, this is inefficient but generally not a cause of health issues unless something unusual occurs (mold due to moisture etc.)

    Where an HVAC system can be a cause of health issues due to combustion air - the air that burns with the gas must exit the house and as it does it will pull air into the house to make up for that. Older non-high efficiency systems were installed with the assumption that the house is leaky enough that it is not a worry. Newer high efficiency systems have their combustion chambers sealed and separated from the house envelope and have a pipe to pull in air from the outside and a pipe out to vent it after the burn. If your health issues are year round and not only during heating season then that is not likely an issue.

    Third, what most people are asking questions about are fresh air systems (HRV/ERV) . They pull fresh air in and push stale air out in a balanced way while attempting to keep the temperature of the air coming in as close to that going out as possible. Fresh air systems are not in 90% of the homes today as older homes have so many holes in the envelope that enough fresh air comes in naturally to be comfortable. If your builder did a great job air sealing it is possible you need a fresh air system. (This can be an HRV/ERV or even a pipe from the outside to your furnace's)

    There is a way to test this - a blower door test which will tell an expert how easily air is moving between your house and the outside.
    FYI - 1100 CO2 is a bit high but not necessarily dangerous. I have an old leaky house an it is at 900 as I type. 1000 is considered a threshold between normal and poor but is not unhealthy in the way you discuss above - occupied office buildings are often in 1000's.

    I hope this at least helps with the basics. I am no building pro like many of the others here so I won't even take a stab at your issue but I wish you luck in finding and fixing it.

  16. nvman | | #16

    I too am curious about the amount of cold air returns required in a forced air heating system. We just went to a high efficiency furnace and do our cold air returns really howl! It as if they are starved for air. With the new system, does it mean that there is not enough air being 'returned'? Does this mean that to make up for the lack of return air, the furnace will suck any old, dirty available air? Even though our home has been renovated, the ducting structure is 58 years old so and does not have returns in the bedrooms.

    As an aside, the installer did come back and reduce the fan speed a bit plus I installed high flow grilles.

  17. GBA Editor
    Martin Holladay | | #17

    Yes, duct systems can be unbalanced. And yes, it's far more common for a duct system to have an undersized return air system than an undersized supply air system (although some houses have both).

    In general, the size of your main return air duct needs to be at least as big as your main supply air duct. (But this crude comparison is no guarantee, of course, that your ducts are properly sized.)

    For more information on these issues, see All About Furnaces and Duct Systems.

  18. barryeross | | #18

    These are all grest responses thank you... My current task is really centered around trying to get the right level of expert in... I have had 5-6 different companies in trying to help with the issue.. but what I am finding is.. they are HVAC people recommend duct cleaning because that is all they can sell... Air quality people recommend air purifiers and Ozone machines because that is what they sell. Insulation people recommend more insulation.... General building inspectors - recommend calling the people above... So it is very frustrating.. and Yes I have bought and tried evverything these people are selling... None of it worked... The key thing I am finding is I need to get the right kind of expert... and someone put some certificaitons above.. so as I am screening people that is helping.. because I am extremely frustrated and basically am giving up.. this is my last effort.. before letting the house go... It is not worth my health...

  19. charlie_sullivan | | #19

    Barry, it sounds like you are heeding Martin's advice: "You should contact a certified home energy rater (one certified by RESNET or BPI)." I think that is your best bet and should help you avoid scenario you are describing contractors recommending what they sell and inspectors recommending contractors rather than helping you figure out what you need.

  20. GBA Editor
    Martin Holladay | | #20

    If you visit the RESNET website and the BPI website, you'll see that the sites allow you to search for certified energy raters in your geographical area.

  21. barryeross | | #21

    Thanks again for the websites.
    This is going to speed this process up... fingers crossed..

  22. jeffwatson | | #22

    Barry, please let us know how it all works out. I'm in a situation very similar to yours & your description on your experience with hiring people to look at stuff is on the mark! Very disconnected, a lot of redirection, and lots of "just buy this."

    I hope your experience with RESNET/BPI is better than mine (they've unfortunately fallen into the same group). It sounds like your goals match mine - you think you have an IAQ issue & you want somebody to tell you what's causing it. However, once the infrared guns come out, the focus on the issue at hand diminishes & it simply becomes an air-sealing point-out party. Let us know how it goes.

  23. barryeross | | #23

    Thanks Jeff... Sorry to hear you are having this issue as well.. Definitely the worst experience of my life.. Thanks for the heads up on BPI... I have only talked to one of them over the phone so far.. have a call set up today.. I get the feeling I am going to have to call several different people.. because the RESNET contact referred back to HVAC...

  24. charlie_sullivan | | #24

    BPI or RESNET certified doesn't guarantee a high skill level, but it least it points you towards a pool of more likely candidates.

  25. OxygenGuy | | #25

    This is a little late, but I think the problem is the CO2 level, which rose to 1100ppm in a few hours. Extended occupancy would push it even higher. Headaches are an early sign of oxygen deprivation (aka 'altitude sickness') which starts at 1000ppm. My company built a new lab where we did hot/cold reliability testing. Liquid nitrogen was used for cooling in the test chambers. We complained of headaches for about 3 years before the company installed an oxygen level test system. When the chambers went cold, liquid N2 was vaporized and entered the chamber. This pressurized the chamber so nitrogen leaked into the lab, which reduced the oxygen content. We found the company had modified the original design by not installing external chamber vents and an outside air intake on the HVAC return to save money. The solution was to install an external vent on the return duct, per original design, providing positive pressure and fresh air (oxygen.) This is a problem when contractors seal a home so tight it's like breathing into a bag; you're rebreathing your own exhaled CO2 because it has no escape from the house. Keeping ALL the nasty hot/cold/polluted outside air sounds like a great idea, but it can suffocate the inhabitants. More return air is not the cure; it's part of the problem. Make sure your HVAC contractor understands ALL the requirements, i.e. enough external air.

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