Downdrafts & Smoke Backup Causes

smoky fireplace, amhurst NHFireplace/chimney systems are pretty basic until something goes wrong. When you’re experiencing smoke backing up into your home, you may not have a clue why it’s happening. Fortunately, there are only a few possible causes for backdrafts or downdrafts, and most are fairly easy to fix.

Drafting basics

In order for smoke to flow up the chimney, five things are required:

  1. Sufficient positive air pressure in the room where the wood-burning fireplace is located
  2. Air within the chimney that isn’t excessively cold
  3. A flue that’s free of obstructions
  4. The “normal” amount of smoke from the fire
  5. A fully open damper

Common causes of fireplace smoke backups

Negative air pressure

Air-tight homes are notorious for insufficient air pressure inside them to push smoke properly up the chimney. Air-pressure issues also are common when the fireplace (or stove) is located in a basement or a lower floor of the home.

This problem usually can be solved by cracking a window in the same room as the appliance. You may need to do this with several windows – try different approaches and see which works best.

Cold flue air

Cold air is heavier than warm air. If the air in your flue is particularly cold when you start a fire, it may prevent warmer air from rising and exiting the chimney. This is a problem seen in regions with very cold winter temperatures.

To warm up your flue air before getting a fire going, try lighting a rolled-up newspaper and sticking it up past the damper for a minute or so. Once the air begins to warm up, you can start your fire.

Obstructions in the flue

Excess creosote and soot, which are byproducts of smoke condensation in the flue, as well as tree leaves and twigs and nesting materials of small animals all can narrow the flue and cause smoke to back up into your home.

Having your chimney cleaned by a CSIA-certified chimney sweep will remove all types of drafting obstructions. Creosote should be cleaned out once a year to reduce the chance of a chimney fire. As to foreign debris, installing a custom, full-width chimney cap will solve the problem.

Excess smoke from wet wood

Wood that hasn’t had time to cure (dry) is too moist to be burned in a fireplace. It will produce large amounts of smoke, often too large for your chimney to effectively draft.

A rule of thumb is to let wood logs dry for about six months, and keep them free of rain and snow while doing so. Test logs by banging two together: a dull thud means there’s too much moisture; a cracking or popping sound means the logs have dried out.

damper, manchester nhDamper is closed

This is the easiest backdraft/smoke backup problem to solve, and it’s a problem you’ll know about immediately. The damper must be fully open to properly vent your fireplace. If it’s rusted or damaged, it may only partially open. Have your damper inspected, if you suspect this is the reason for smoke backing up into your home.

Black Moose Chimney & Stove of Antrim, NH, provides CSIA-certified chimney sweeping, chimney inspections, and all manner of chimney repair, modification, and rebuilding work. When you have excess smoke – or any other problem – we have the solution. Call us today at (603) 525-7905.


First Thing

John RantaJohn Ranta
17:01 22 Mar 24
They arrived on time, worked quickly and showed me the results. Prfessional throughout. jr
william greenwilliam green
23:21 14 Mar 24
Really helped me out can't say enough good things highly recommend!!!! The young man that came to my home was very knowledgeable and friendly great attitude all around answered all my questions and left me stress free best of all left no mess.🤙🏻🤙🏻
Michael Dell'OrtoMichael Dell'Orto
18:39 14 Mar 24
Jaime ConleyJaime Conley
17:13 14 Mar 24
Sarah GilliattSarah Gilliatt
01:46 13 Mar 24
A very thorough and careful job done! Thank you.
Larry CookLarry Cook
15:11 07 Mar 24
I wanted to give 5 stars but they are very busy which meant I had a good wait for both the inspection/cleaning, then for a quote on repairs and then for the repairs. Their prices seemed a little high to me but I have nothing to compare with as they were highly recommended by someone I trust and other companies had plenty of negatives reviews which kept me from getting additional quotes. I am happy with the work and they promptly returned to fix a mistake that had been made. Chris the inspector, Jennifer in the office, and Alex and his repair crew were all pleasant and took the time to answer all of my questions. Alex and his crew even took their shoes off (it was winter) before entering my house without even being asked! So if you are not in a rush and want to ensure you chimney is as safe as possible then I think you'll be happy with Black Moose.
Rebecca DeFuscoRebecca DeFusco
22:35 21 Feb 24
After a recent sweep of our chimney, it was discovered that our flue tiles were cracked. Black Moose techs were hard working, detail oriented and professional! Nice jobs guys! See you next year for my cleaning!
Karen CKaren C
14:52 14 Feb 24
Excellent I highly recommend Black Moose Chimney and Stove; Kelly and Liam are awesome, they did a great job. Extremely professional, arrived early, went through everything with a fine tooth comb ensuring pellet stove was thoroughly cleaned. They also were respectful of my home, conscientious and cleaned up after themselves. Made sure stove worked prior to leaving and told me to call promptly if anything came up afterward. Will definitely use them again.
Denise ClarkDenise Clark
16:32 31 Jan 24
We've had Black Moose clean our chimney for a number of years.But recently, we had an emergency situation at our home involving our chimney & oil furnace flue, which was caked full of soot from a malfunctioning furnace. They came & cleaned out both flues in no time, even going up on the roof with snow on it! They cleaned up after their work in the interior rooms where the oil furnace and the woodstove are located. Great work. Reasonable prices. Very nice people. You can't go wrong with Black Moose.
Joe GJoe G
18:30 24 Jan 24
Goods: The technicians know their business, very efficient in cleaning/inspection along with cleaning up after the 'dirty work'.Others: Communications could be more effective. Despite early coordination about scope of work (multiple flues within same chimney) the estimate provided did not reflect this and the final invoice was significantly more than the estimate provided.Quote for follow-on chimney relining was significantly more than that offered by other companies in the area (and far more than neighbors experienced for similar work accomplished by other companies)