What Is Negative Air Pressure?

The difference in the air pressure in your house and the outdoors can be negative or positive.  Neither is particularly beneficial.  Let’s discuss negative air pressure as it relates to your home and specifically to your fireplace.  Keep reading to see why this subject is important.

WHAT IS IT AND HOW DOES IT OCCUR?

Stack effect diagram

Stack effect diagram

Negative air pressure can occur when the pressure inside a house is less than the barometric pressure outside.

We know that warm air rises in a home.  As this happens, a slight positive pressure is created in the upper levels of a house.  This can lead to air being forced out of the house.  Negative pressure can develop in lower levels.  Often there is no easy way for replacement air to re-enter the home.  When the home tries to pull air in, instead of pushing it out, the result is negative air pressure.

In serious situations, negative air pressure can actually out-muscle the draft in a chimney and sucks that “make-up” air down the chimney.  Needless to say, the problem with this is the difficulty of getting a fire established in your fireplace, stove or insert and the smoke filling the house!  With any volume of outside air being pulled down your chimney, it will be difficult to get any sort of draft established.

Negative air pressure will increase your energy and heating costs, too.  It draws cold air in, through the paths of least resistance.

Bathroom exhaust fans, clothes dryers, kitchen exhaust hoods and central vacuum cleaners add to negative air pressure issues when they’re being used.  They are removing air from inside the house while they operate.

WHAT CAN BE DONE?

As we mentioned, neither negative or positive air pressure is good for your house.  The exterior walls, or the building envelope, allows air to leak to and from your home.  Depending on the outdoor temperature and humidity levels, the air leakage will vary seasonally and will have different effects on the comfort inside the house.  It’s worth noting that negative air pressure is much less common with older homes than it is in newer houses.

Most of us are very conscious about reducing air infiltrating our homes.  We know the importance of sealing and weatherstripping doors and windows, insulating sidewalls and the ceiling, insulating basement walls and the sill box area.  But, with today’s construction materials and building techniques, homes are now being built exceptionally tight.  The goal, of course, is to keep interior and exterior environments as isolated as possible, regardless of the season.  In other words, keep the outdoor temperatures and humidity out, while maintaining a comfortable, controlled, conditioned space, in.   In newer homes, pressure concerns and outside air exchange can normally be addressed with an outside air make-up system installed by a knowledgeable HVAC contractor.

An outdoor air source, supplied directly to the inside of the fireplace, is standard equipment on many new models today.  And if a unit doesn’t come standard with an outdoor air kit, spend the few extra dollars for it.   One will be offered as an optional accessory to the fireplace.  It’s required by code in most areas.

WIND GUSTS

Don’t get wind gusts confused with negative air pressure.  A high gust of wind from a certain direction may cause a periodic downdraft.  But a negative air pressure scenario will draw a constant stream of spillage into the room.

GAS FIREPLACES AND NEGATIVE AIR PRESSURE

Direct vented (DV) gas fireplaces, stoves and inserts do not have a problem with negative air pressure.  DV equipment uses a sealed combustion system.  Unlike a wood fire that often uses room air for combustion purposes, a direct vented gas unit, uses 100% outside air for combustion to occur.  This is done through a co-axial vent pipe.  That is, a pipe within another pipe.  The larger outer pipe brings outside air into the firebox for combustion and the smaller inner pipe removes the by-products from combustion.  The only room air that interacts with a DV gas model is the air that’s drawn into the convection air chamber.  This room air is heated and returned back to the room via a blower fan.

AN EASY TEST

If you have noticed back-drafting of the chimney in your wood burning fireplace, here’s a quick and simple way to test the pressure.  While the chimney and fireplace are cold, attempt to get a fire burning with a little kindling and a few wads of newspaper.  If you notice the smoke is backing up into the room, simply open a window or door several inches and see what effect it has on the fire and draft.  By opening a window or door, you are simply supplying plenty of “make-up” air to the house and the smoke should be easily pulled up the chimney.

Obviously, you cannot leave the windows open during the heating season, but it’s a good first-step to determine precisely what the problem is.  There are other tests that can be used to determine how to effectively correct and balance the air supply through proper ventilation.  Equipment that measures the difference in air pressure is called a differential pressure sensor or a manometer.  Remember that good diagnostic testing will consider exhaust fans, clothes dryers, kitchen exhaust hoods and the force of the wind on the upwind or downwind side of the house.

Your WE LOVE FIRE dealer and/or a knowledgeable HVAC contractor is the best place to continue the evaluation process.

Below is a list of fireplace and grill stores that service ()

Auburn, AL

Top Hat Chimney Sweeps
1280 Financial Ct.
Auburn, AL 36830

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Elk Grove, CA

Custom Fireside Shops
9097 Elk Grove Blvd.
Elk Grove, CA 95624

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Sacramento, CA

Custom Fireside Shops
5455 Auburn Blvd.
Sacramento, CA 95841

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Durango, CO

Durango Outdoor Living
140 Rock Point Drive
Durango, CO 81301

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Durango, CO

Four Corner Stoves & Spas
3001 Main Avenue
Durango, CO 81301

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Grand Junction, CO

Stove Depot and Chimney Works
330 North Ave.
Grand Junction, CO 81501

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New London, CT

Family Hearth and Patio LLC
571 Broad Street
New London, CT 06320

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Ridgefield, CT

Yankee Doodle, Inc.
71 Ethan Allen Highway
Ridgefield, CT 06877

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Dover, DE

Byler's Stove Shoppe Inc.
1368b Rose Valley School Rd.
Dover, DE 19904

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Destin, FL

Doodlebuggers Service Network
36054 Emerald Coast Parkway
Destin, FL 32541

Bettendorf, IA

Fireplaces Plus, Inc.
1745 State Street
Bettendorf, IA 52722

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Post Falls, ID

Quality Stoves & Home Furnishings
569 N Syringa St
Post Falls, ID 83854

Rockford, IL

Advanced Chimney Systems, Inc.
3486 Lonergan Drive
Rockford, IL 61109

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Wauconda, IL

Grass Roots Energy, Inc.
28751 N Route 12
Wauconda, IL 60084

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Evansville, IN

Firemaster, Inc.
5300 E Morgan Avenue
Evansville, IN 47715

Jeffersonville, IN

Olde Towne Chimney & Fireplace Sales
915 Nachand Ln
Jeffersonville, IN 47130

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Overland Park, KS

Kansas City Fireplace Center
10470 Metcalf Avenue
Overland Park, KS 66212

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Erlanger, KY

TateBuilder's Supply, LLC
3511 Dixie Highway
Erlanger, KY 41018

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Littleton, MA

Woodstove, Fireplace and Patio Shop, Inc.
60 White Street
Littleton, MA 01460

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Seekonk, MA

The Fireplace Showcase
775 Fall River Ave
Seekonk, MA 02771

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Sudbury, MA

Woodstove, Fireplace and Patio Shop, Inc.
348 Boston Post Road
Sudbury, MA 01776

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Duluth, MN

Duluth Stove & Fireplace
2431 W Superior Street
Duluth, MN 55806

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Minneapolis, MN

Woodland Stoves & Fireplaces
2901 Franklin Ave. South
Minneapolis, MN 55406

Oakdale, MN

Energy Savers of Minnesota
6298 Highway 36 Blvd N
Oakdale, MN 55128

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Rochester, MN

Brekke Fireplace Shoppe
1904 S. Broadway
Rochester, MN 55904

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Walker, MN

Wilkening Fireplace Company
9608 State 371 NW
Walker, MN 56484

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Fargo, ND

Home Heating, Plumbing & A/C Inc.
701 28th Street South
Fargo, ND 58103

Omaha, NE

Fireplace By Design
13913 R Plaza
Omaha, NE 68137

Epping, NH

The Stove Shoppe
285, Calef Highway Rte. 125
Epping, NH 03042

Windham, NH

The Stove Shoppe
25 Indian Rock Road
Windham, NH 03087

Hamilton, NJ

Bowden's Fireside - Hearth & Home
1731 Nottingham Way
Hamilton, NJ 08619

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Voorhees, NJ

Rettinger Fireplace Systems, Inc.
476 Centennial Blvd
Voorhees, NJ 08043

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St. Henry, OH

Buschur's Refrigeration, Inc.
541 N Eastern Avenue
St. Henry, OH 45883

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Media, PA

Chimney Cricket
101 State Road
Media, PA 19063

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Rapid City, SD

Hebron Brick Company
1543 Deadwood Ave
Rapid City, SD 57709

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Sioux Falls, SD

Hebron Brick Company
2211 W. 50th Street
Sioux Falls, SD 57105-6525

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Vermillion, SD

Kalin's Indoor Comfort Inc.
710 Cottage Avenue
Vermillion, SD 57069

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Manassas, VA

Winston's Chimney Service
11301 Industrial Road
Manassas, VA 20109

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Barre, VT

Chimney Sweep Fireplace Shop
1284 US Rte, 302 Ste 10
Barre, VT 05641-2317

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Bennington, VT

Friends of The Sun
126 Hicks Avenue
Bennington, VT 05201

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Manchester, VT

Friends of The Sun
159 Depot Street
Manchester, VT 05255

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Shelburne, VT

Chimney Sweep Fireplace Shop
3113 Shelburne Road
Shelburne, VT 05482

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White River Jnct, VT

Home Comfort of New England
1255 VA Cut Off Road
White River Jnct, VT 05001

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Burlington, WI

Burlington Fireplace & Heating LLC
857 Milwaukee Ave.
Burlington, WI 53105

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Madison, WI

Top Hat
5117 Verona Rd
Madison, WI 53711

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Morgantown, WV

Rustic By Design
709 Beechurst Ave. Suite 15
Morgantown, WV 26505

Laramie, WY

High Country Stoves & Fireplaces
860 N. 3rd Street
Laramie, WY 82072


For more information, contact your local fireplace and grill store.

2 Responses

  1. This week’s wood words – Heat Wood Air
    […] https://welovefire.com/fireplaces/what-is-negative-air-pressure/https://www.healthlinkbc.ca/healthlinkbc-files/indoor-air-qualityhttp://www.pureairplus.com/iaq.html […]
  2. Mark
    We have more awareness about radon. Which is a deadly gas that sips through the ground, through your basement floor and in to you basement or whole house if it sits on a slap. My question is which chimney/fireplace system generates less or no suction ie negative pressure inside the house that it will not further affect radon suction in to the house via negative pressure. Specially for homes with a radon mitigation system. Thank you in advance for your knowledge and reply.
  3. jay vogt
    I really have a question not a comment as such other than I'm happy there is someone out there that tries to figure this stuff out. I had to install a radon removal system in my slab on grade building . ( its a garage conversion to a living space) unfortunately I was not able to get to every location where there was an airspace between the slab floor and below so I'm pulling some air (I don't know how much) from the interior spaces , down thru the floor -under the slab and outside with the radon fan. If I'm careful opening the stove door I can usually not get smoke roll back into my room ( I'm sure it helps that the windows and doors are not super tight or efficient as I'm getting outside air in that way. My space is not super tight like current new home construction). Even when there doesn't appear to be smoke in the house at all could the negative pressure I'm creating be pulling dangerous gas from the stove into my space? or is the air being circulated thru the radon pull cleaning my airspace? What do you think is probably happening and what would you recommend I do since the radon system is here to stay? I can remove the wood stove of course but would like to find a solution that allows for the ambiance of the fire. I"m currently installing a direct vent rannai propane wall heater to cover most of the heating requirements . Thankyou for reading and hopefully sharing your insights. Sincerely Jay
  4. Solutions for Your Fireplace on Windy Days - We Love Fire
    […] air pressure. A high gust of wind from a certain direction may cause a periodic downdraft. But a negative air pressure condition will draw a constant stream of cold outside air spilling into the […]

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