Negative house pressure is a common problem that can cause fireplaces and wood-burning appliances to smoke, and gas appliances to backdraft deadly Carbon Monoxide gas. This is probably the least understood house issue, but one that usually can be easily corrected.
All houses have a positive pressure plane, a neutral pressure plane, and a negative pressure plane.
The planes move constantly according to pressure changes that occur when someone opens a door or window, or turns a fan or appliance on or off.
House pressure is something that can’t be seen with the eye, but the effects are obvious –once a person knows what they are looking for.
Signs of negative house pressure include stale air, mold or mildew in bathrooms, unexplained illness among family members or pets, smoking fireplaces or appliances, and condensation on windows.
An inadequate amount of fresh air getting into the house can be a severe health hazard, as well as a smoking fireplace problem.
Tight or well-insulated houses have a better chance of having a negative pressure problem. Larger homes with multiple stories are also likely candidates, however, any house can have a negative pressure problem.
The issue is often first detected by a professional chimney sweep. This is due to the fact that smoking fireplaces are a huge annoyance, and either the sweep will find the problem during a routine inspection, or the homeowner thinks that there is a problem with the fireplace or chimney.
If after checking for proper chimney construction, including proper height, the flue and smoke chamber sized to code, and stack effect (house taller than the chimney) the next thing to look for is negative house pressure.
How to check if your heater is Negative Pressured
There are simple techniques to check for negative pressure as well as complicated methods.
First, house pressure should only be tested during cold weather in order to see what is happening when the house is closed up and the heating appliances are used.
Place shredded lengths of tissue paper or a newspaper over the fireplace opening. Open the damper and watch what happens to the paper.
Now open a window in the room very slowly and watch the paper, which should switch to moving inside the fireplace at some point.
Measure the window opening and this is the amount of air needed for the fireplace to operate without smoking.
If the house does have a negative pressure problem the next step is to correct or decrease the problem.
Other things must be taken in to account are other appliances that use air for combustion and take air from the house like:
Signs of Negative House Pressure:
Solution to the problem may include the installation of a fresh air inlet for your wood heater.
A number of wood heaters have this standard, or as an additional option
What is this ?
Heaters that have this standard, have a designated inlet that allows you to run a duct to outside to bring fresh air in for the fire
These Fresh Air Inlets are manditory for Homes in the UK and North America, and are becoming an industry standard for Australia now