Negative Pressure

Ever feel cold air coming out of your fireplace when it’s not in use? Special guest Jerry Isenhour discusses what causes this problem.

Clay Lamb
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4 thoughts on “Negative Pressure

  1. I have a negative pressure problem in a fireplace in a 2 story great room. Both heating and air returns are in the room one in the ceiling and one downstairs. When both units go on, I have negative pressure draw in the fireplace. What can be done?

  2. @Chris Gormley – This sounds like what our industry refers to as being a possible thermal syphoning issue!

    Air goes up one chimney and is sucked back down more often than not into the basement or lower lever fireplace! Negative pressure air balancing is both an art and a science.

    Cold air infiltration in many cases means there is warm air exiting the house somewhere. Personally not being able to physically see your situation, I would seal up the envelope of the entire home first.

    “But” you need to consider that most all mechanical appliances actually need fresh air supplied to them (ie. gas furnaces hot water, fireplaces, etc…) Don’t forget that cathedral ceilings, large stair wells, bathroom and attic fans, kitchen range hood, can also cause huge negative air pressure problems within your home.

    I have seen in the past that even a clogged or dirty air filter caused air to be pulled off of the basement floor. I had one customer install a small screen louver in the glass block window located in the basement as a solution to their pressure issues.

    Another customer had a back puffing problem every time someone opened the front door. Sorry but I don’t have a “fix all” solution for you, just experiences from my customer’s unique house issues.

    Remember gas logs are not a solution, as the Carbon Monoxide problems will roll back into your home!
    Again, resolution of house pressure problems, are both an art and a science. Keep testing and documenting your findings as you go! More often than not there is a solution.

    I wish that I had a magic product or solution as this is a major problem for both heating and chimney contractors

  3. I am interested in installing a wood stove in my basement with a double walled pipe that will vent out the side of the house and up. I’ve been warned that wood stoves in basement don’t work well because of negative air pressure. Any fix to this?

  4. I think you hit the nail on the head. The whole house air pressure is very fragile to deal with to find the proper balance. Its has been my in case, it’s always a matter of opening the door, opening up blocked windows with venting, or an outside air source.

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