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Intake air locations

brianandson | Posted in General Questions on

My 1970 built home has zero fresh air intake and the home has major negative pressure.  I want to add fresh air supply in my mechanical room for combustion air and I also want to add fresh air intake to my return air plenum.  My question is-  I have a dryer exhaust vent on the side of my home that I want to add the intake vent for combustion air.  Is there a minimum distance that I need to stay away from the dryer exhaust vent  for the location of my combustion air intake vent?  The place I want to put the intake vent is approx 5 feet horizontally from the dryer exhaust vent but not sure if this is allowed 
thank you for any guidance you can give me

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  1. Expert Member
    KOHTA UENO | | #1

    Here's one resource to check out:

    Info-606: Placement of Intake and Exhaust Vents

    1. brianandson | | #2

      Great thanks for the info.

    2. qofmiwok | | #15

      "Intakes must not be located within 10 feet above any paved surface or roof." This one's a puzzle. I get an asphalt roof or driveway, but what's wrong with being close to a concrete surface or a metal roof?

  2. Jon_R | | #3

    "Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) from any hazardous or noxious contaminant,..."

    If this is an electric (vs gas) dryer, I'd say the exhaust isn't a hazardous or noxious contaminant. Ie, 5' is fine.

    If not, a 3' vertical difference may be easier to achieve than 10' horizontally.

    1. brianandson | | #4

      Thank you. Looks like I need to find a new spot for my intake vents. Thank you for your reply

  3. Expert Member
    BILL WICHERS | | #5

    Make sure you keep the intake away from the driveway or garage too, you don't want to pick up any exhaust gasses from vehicles, even if only briefly. The best location for intake air is usually somewhere on a back or side of the house, away from any other vents on either your home or a neighbor's home.


    1. brianandson | | #8

      Thank you Bill. Yeah I’m thinking the back side of the house will be a good spot. I just got a dryer exhaust vent that I need to keep the air intake away from

  4. walta100 | | #6

    It seems highly unlikely that any 1970s home is now so tight that you have negative pressure. Short of someone having spent literally hundreds of hours sealing leaks building a negative pressure seems all but impossible.

    Then builder went out of their way to make and leave gaps they wanted the building to breathe.

    What problems are you experiencing?
    Do you have a fireplace and does it work?
    Do you have a gas water heater?
    Do you have a furnace that is over 90% efficient ?
    Do you have a large kitchen fan?


    1. brianandson | | #7

      Thank you Water for your reply. Yeah I moved in to this home in 2015 and I have done a lot of sealing and added insulation. I sealed all the attic penetrations and added foam at the exterior rim board. Also have done a lot of caulking and foamed all the exterior wall plugs and switches. I have a natural gas water heater, furnace and dryer in the basement. I have a door at top of the basement stairs that slams closed by itself when the furnace turns on. And I have a fireplace that the smoke gets sucked down the chimney and smokes out the house. And I also noticed our 2nd floor rooms do not get warm. So I’m assuming air is getting sucked to the basement when the gas appliances are running? but I’m not an expert. I opened a basement window and it definitely seemed to help with the door slamming closed and also with the fire place smoke from getting sucked back down the chimney. I was think fresh air I take would be more of a permanent solution. But I also do not want to bring in too much fresh air and create a positive pressure in the house. Does this seem like a good idea to you? Thank you again

  5. walta100 | | #9

    Your symptoms are concerning!

    Do you have 2 operating CO detectors in the house?

    Does the fire place work when you have a window open?

    Have you tested the draft on the water heater?

    This video does a great job of showing both a passing and a failing draft test.

    If I had your symptoms I would not operate the gas appliances until I had CO detectors in place and understood when and why it was back drafting. My permanent solution would likely be to replace the appliances with power vented equipment.

    Please do not be one of the families killed by CO poisoning


    1. brianandson | | #12

      Hi Walter. Thank you for your concern. Yes I have two working CO detectors. Having the basement window open does help. The door at the top of the stairs does not slam closed anymore and we are able to have fires without the smoke being sucked back down the chimney into the house. I have checked the draft on the water heater exhaust and it does go up thru the vent. I will look into power vented equipment. This is definitely not my area of expertise. I was hoping fresh air intake would help, but now I’m thinking I need to call a professional to come over and figure this out. Thank you again for your advice

  6. Jon_R | | #10

    A ducted furnace with unbalanced supply/returns is a common source of building pressure problems. With the furnace running, compare the pressure in every room to the rest of the living area. Also compare indoor to outdoor pressures with each appliance on and off. Do these things before adding an intake.

    Also note that stack effect means that some negative pressure is inevitable.

    1. brianandson | | #13

      Thank you Jon for your reply. I definitely think the supply and return ducts are unbalanced. The basement gets really warm in the winter and our 2nd floor bedrooms are really cold in winter. Do you have any guidance on how to compare the pressures in each room? Is there a device that measures the pressure? Or is there another trick? Do you recommend me to have a professional come over and balance the system before I add fresh air intake? Thank you for your advice and I’m thinking my best option is to hire a professional.

  7. Expert Member
    BILL WICHERS | | #11

    >"I have a door at top of the basement stairs that slams closed by itself when the furnace turns on. And I have a fireplace that the smoke gets sucked down the chimney and smokes out the house."

    Jon beat me to it: if you have a problem with your air returns, then the furnace is probably pulling air from the basement to supply the ducts. This could be what's slamming the basement door shut.

    The issue with the fireplace is back drafting, which is a bigger safety issue. If the fireplace does that, then something else (like a natural draft water heater) could also backdraft and cause CO issues. Both of these issues point to a lack of makeup air from outside to supply the combustion of the fireplace (or water heater, in my example).

    The first issue with the basement door, if it's the furnace blower, is an issue with air circulation within the home, basically a lack of, or overly restrictive, return vent system for the furnace. The second issue, with the smoke, is a lack of outdoor air intake for combustion air, and remember that any non-sealed combustion gas using devices (furnace, water heater, etc.) also need this source of combustion air.

    You probably have two different problems here that need to be addressed in two different ways.


    1. brianandson | | #14

      Thank you bill. Yeah it sounds like I have multiple issues going on in my home. I probably need to just bite the bullet and hire a professional to come over and fix the issues. I definitely agree that the duct system is unbalanced and that I need to get some combustion air for the furnace water heater and dryer. Thank you for your guidance.

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