Asked on Feb 28, 2013

Chimney down drafts

RockfordChimneySupplyWoodbridge Environmental Tiptophouse.comBetty


We have a wood burning fireplace. and we have had issue with when it is real windy have a down draft and blowing smoke into the room. Will chimney caps prevent this from happening. Also the upstairs bedrooms on the back of the house same wall as chimney. sometimes when we have a fire and if we go up stairs to these bedrooms they are very smoky. Does our chimney need to be taller.
6 answers
  • i would have the chimney inspected professionally for structural defects. if o.k. raising the chimney 2-4 feet above the roof peak shouldnt hurt. another option might be installing a wood or pellet or gas insert with a chimney liner

  • Betty
    on Mar 1, 2013

    What about the chimney cap will that help with the downdrafts?

  • A few things can cause poor draft. Chimney height, is one. Chimney location in regards to peak of roof. Chimney exposure to cold air. Undersized flue in chimney for size of stove. Missing or damaged smoke shelf in fireplace opening. The height of the chimney is the most common issue. As the interior of the flue heats up the velocity of the flue gasses increases and a greater draft is pulled up and out. This also has a lot to do with chimney exposure. If the chimney is entirely located on the outside of the house, such as one on the end of the home. The exposure of the brick or block surface is such that cold air cools down the heat within the chimney and slows this movement down. If the chimney is located near the peak of the roof, air currents can flow up the roof and create a down draft on the opposite side. If the chimney is located on the down wind side of the roof, these down drafts can pull the smoke down and into the windows, and will slow the draft down as well in the process. So a higher chimney may be needed, or perhaps a good quality chimney cap that prevents the air from blowing down the flue pipe. A undersized chimney flue can prevent enough air from going up the chimney and mimic a poor draft. While it is really not a poor draft, it simply does not have enough free air to pull the smoke up. With your issue combined smoke in windows and poor draft, I would think your issue is the chimney is not high enough and down drafts are pushing air back down the flue and down the house into the windows. Or combined with a poor smoke shelf inside. Another issue can be the size of the fireplace opening as compared to the size of the flue liner. If the ratio of the opening of the fireplace is to large for the flue the pulling effect across the front of the fireplace opening will be less then if the opening was smaller. This is why many times people install doors to make the opening smaller so more air will be pulled into the face of the fire pulling the smoke up rather then around the front top of the fireplace front. Lastly be sure before you try anything that you get the chimney examined by a professional chimney sweep. Doing something wrong can cause safety issues and burn down your home.

    , This shows the locations of chimneys ones located within the house are the warmest and pull draft the best, A chimney extender can be used but this should be done only as a last resort if all else fails Only a pro should install this as well, this shows the components of the chimney The smoke shelf which when combined with a properly operating damper prevents smoke from coming back down the chimney, This is a sample of how high the chimney should be in relation to the roof peak Also note the type of chimney cap It prevents air from blowing down the flue but allows the flue gasses out the sides, This shows the smoke shelf and how it works combined with damper
  • RockfordChimneySupply
    on Mar 19, 2013

    Great points Woodbridge. There are quite a few things that can cause a poor draft. If you need any help 'troubleshooting', feel free to call us - we'd be happy to help you figure out the issue.

  • Here is a sample of not what to do when raising a roof on a house. In order for the owner to save a few dollars the builder did not raise the chimney when they added a third level to the house. What resulted in a chimney located way below the ridge of the roof. In the background you will see another chimney that was installed on another addition on the house that was installed to the correct height. We have instructed the owner not to use the fireplace until they have the chimney raised for safety. You can see in the other photo a PVC vent that we installed for a new high efficiency furnace. We raised this to the proper height so when they raise the chimney we do not have to come back and raise our flues again.

    , Note higher chimney in back, Owner wondered why they had leaks around chimney after heavy snows Water collected on the top and around flashign causing leaks Lots of silicon was noted on flashing, Our new PVC vent and fresh air intake for new 95 5 efficiency furnace
  • RockfordChimneySupply
    on Mar 20, 2013

    Those are great pictures. PVC will work for venting the high efficiency furnace. But if you are venting a chimney liner and need to extend the flue, you will need a stainless steel flue extender. Below is a link if you'd like to see what one looks like:

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