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  1. #1

    Exhausting smelly air up the chimney?

    Hi -

    I live in a leaky 2300 sf 1 story ranch in the NE. It leaks a 'houseful' of air to the outside roughly once every hour.

    The main crawl space is 1900 sf and 5 ft high. 6 mil black plastic lines the dirt floor and runs up the side walls 4 ft. There is an active sump pump during winter and spring. In this space sits two gas boilers and 1 gas hot water tank. I have closed all fresh air vents except two. At this time, I can not close off all vents because I need the air for these combustion appliances. However, I run a dehumidifier during the summer anyway, even though it runs 24/7. For the most part, its fairly dry down there, 55 % humidity. With all this said, it smells like a dirt basement/crawl space.

    In one open vent I placed a Tjernlund two-fan exhaust fan. From the outside of the house, you can smell the offensive odder big time.

    In the crawl space, I have a chimney with three flues. One of the flues is a clear shot from the crawl space to the top of the roof. For example, I can see daylight from within the crawl space. If my house experience 'stack effect', I wish all that moist air would go up this chimney flue and not into the main house.

    Q: Is it a good idea to put in a mega exhaust fan that blows smelly crawl space air up the chimney flue? I would assume this would draw conditioned air from the first floor down into the crawlspace. I might lose energy, but my goal is to mitigate the smell. My house is leaky, would this bring in a constant flow of fresh air from the out side. If so, great! Right? Is this a good idea or bad? Any why?

    Thank you!!!

  2. #2
    Join Date
    Jul 2005
    Posts
    5,366
    Quote Originally Posted by homeowner123456 View Post
    Hi -

    I live in a leaky 2300 sf 1 story ranch in the NE. It leaks a 'houseful' of air to the outside roughly once every hour.

    The main crawl space is 1900 sf and 5 ft high. 6 mil black plastic lines the dirt floor and runs up the side walls 4 ft. There is an active sump pump during winter and spring. In this space sits two gas boilers and 1 gas hot water tank. I have closed all fresh air vents except two. At this time, I can not close off all vents because I need the air for these combustion appliances. However, I run a dehumidifier during the summer anyway, even though it runs 24/7. For the most part, its fairly dry down there, 55 % humidity. With all this said, it smells like a dirt basement/crawl space.

    In one open vent I placed a Tjernlund two-fan exhaust fan. From the outside of the house, you can smell the offensive odder big time.

    In the crawl space, I have a chimney with three flues. One of the flues is a clear shot from the crawl space to the top of the roof. For example, I can see daylight from within the crawl space. If my house experience 'stack effect', I wish all that moist air would go up this chimney flue and not into the main house.

    Q: Is it a good idea to put in a mega exhaust fan that blows smelly crawl space air up the chimney flue? I would assume this would draw conditioned air from the first floor down into the crawlspace. I might lose energy, but my goal is to mitigate the smell. My house is leaky, would this bring in a constant flow of fresh air from the out side. If so, great! Right? Is this a good idea or bad? Any why?

    Thank you!!!
    You're forcing a negative pressure in the crawl, which happens to be the CAZ for your gas appliances. The odor may be stack gasses backdrafting into the crawl.

  3. #3
    Q: Creating a negative pressure in the crawl space will prevent combustion gasses from venting out the chimney? Do backdrafting stack gasses smell?

    Let's say I upgrade my boiler and water tank to a direct-vent system.

    Q2: Can I then exhaust this crawlspace air up the chimney to mitigate the smell (which I still think is from the musty crawl space itself.) Good idea??

    Thanks.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,266
    Open vents to the outside and maintaining <50%RH is difficult. If you eliminate the wet spots and maintain <50%RH, odors will go away. I suggest a bigger dehumidifier, powered makeup fresh air, and minimal open vents. You must have enough dehu capacity to maintain <50%RH and 100 cfm of fresh air,3-4 lbs. per hour. Dehus like the 90 pint Ultra-aire 90 pint units with powered make-up air maintain <50%RH with minimal energy use.
    Keep us posted.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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