Negative Air Pressure

NEGATIVE AIR PRESSURE - What is it?

Negative air pressure is a phenomenon discovered after the energy crises in the seventy’s, and caused when houses began to be built to more energy efficient standards. An R2000 and the now R3000 homes are airtight and very energy efficient.

This type of house will show some or all of the following symptoms;

*Back drafting of combustion appliances such as the fireplace, wood stove, gas hot water heater and even the furnace
*Mold, mildew and moisture as well as condensation which shows itself around windows or on walls
*A lack of fresh air, a musty smell, lingering odors around the house
*Stagnant, stale, heavy, air causing high humidity and condensation
*A rush of air or draft when opening an exterior door.

These are all typical symptoms of an energy efficient airtight house, or sick building syndrome, but they are just that symptoms and very few people realize the health problems arising from living in an airtight house.

In a house that lacks a source of fresh air a phenomenon called negative pressure is created. This is caused by to much air is leaving the house through various sources and the inability of replacement air to have an easy access into the house replacing air and oxygen used when the living conditions such as heat rising and exhaust fans operating, combustion appliances and people are using air and oxygen. These symptoms of an energy (pic) stack.jpg+(1)enlarged efficient sick house can be eliminated. If you cure the illness with fresh air, like opening a window, the symptoms will disappear by themselves.

Since the common thread in these problems is an energy efficient airtight house then making it less airtight should solve the problem, but this kind of defeats the purpose of our concern with energy efficiency and saving heating costs.

It seems ironic that a house that has been made airtight to save energy should now be loosened up to become healthy, but that is exactly what is needed to maintain that healthy environment. But don't worry, this can be corrected in an energy efficient way with a unique system of make up air.

First some history; years ago houses were not built as airtight and these problems where less evident. At that time people still complained of drafts and cold spots in the house; these drafts although somewhat uncomfortable and annoying where actually keeping the house healthier than today's houses.

Interestingly if a similar system of make up air that we are recommending for an airtight house was placed in a drafty house many of the drafts would diminish. The reason for this phenomenon is that drafts are actually caused for the same reason stale air is circulating in an airtight home; the house even if it is drafty is still exiting more air than it can take in. This is causing the drawing effect of drafts, as replacement air tries to enter the house.

To understand how a Pure Air Plus residential ventilation system can improvethe air quality in your home and achieve a comfortable, healthy environment for your family, you need to understand your potential residential ventilation problem...

Houses need to breathe!

We all understand the value of insulating our homes to make them more energy efficient and save heating costs. However, better insulation may restricts a fresh air exchange and prevents fresh air from regularly entering the house in a natural way, trapping stale, polluted air inside your home.

As hot air naturally filtrates from your home through the ceiling it creates a vacuum causing your combustion appliances to burn inefficiently. Without a proper fresh air ventilationsource, dust, smoke, pollen and airborne pollutants constantly re-circulate throughout your house, causing a variety of lingering side affects.

Your fireplace and other combustion appliances will back draft and spill emissions back into the house, cooking odors may linger, the humidity and moisture in the air will begin to build up making the air seem heavy and indoorair quality will decline.

"Houses need to breathe"
Those that don't have an adequate air exchange are unhealthy.

Here is the problem in a nutshell;

There are too many appliances pushing air out of the house such as bathroom fans, central vacuums, range hoods, clothes dryers etc., this can be significant with no easy way for replacement air to get in. The result creates negative air pressure in the house which means the house becomes more interested in trying to suck air in than pushing air out.

This can interfere with the air supply for your furnace and other fuel-burning equipment. As air tries to enter the house through the only means available, which is the existing flues of your furnace, wood stove, fireplace and gas hot water heater, the reversal causes these appliances to spill flue gases into the house rather than exhausting them.

This makes your wood stove smoke back, your furnace and hot water heater dump carbon monoxide into the house!! What is needed is an easy efficient source of make-up air to equalize the pressure and has the ability to feed fresh air for your furnace and other fuel-burning appliances that have become starved for air. This is what "Pure Air Plus" can provide using a "Plusaire" residential ventilation systems filling your house with clean fresh air every day!

CAUSES OF NEGATIVE AIR PRESSURE - Hot air rises
THE STACK EFFECT - "Houses need to breathe"

Just as draft is created in chimneys by the buoyancy of the hot gases, a form of draft is created in houses because of the difference in temperature between the air inside the house and the outside air. The warm air inside the house tends to rise because it is less dense and warmer than the outside air.

The tendency of the warm house air to rise results in pressure differences at various levels in the house. The pressure in the basement and lower levels of the house will be less than the atmospheric pressure. This effect is similar to the low pressure at the base of a chimney. In upper levels of the house the pressure will be higher than the atmospheric pressure as the rising air pushes against the ceiling. At some point between the high and low pressure zones, the pressure will (pic) 3neutral.gif be neutral.

This point is called the neutral pressure plane. This variation in pressure is called the stack effect. The taller the house is, the greater the stack effect. The stack effect in your house can make a considerable difference in the venting and performance of combustion (fuel burning) appliances such as a wood burning fireplace or stove or an oil or gas fired furnace.

Your basement is the most susceptible to problems caused by the stack effect since it is the lowest point in the building. Wood burning appliances installed in the basement often have to operate in this negative pressure environment and are the most susceptible to a back drafting problem, but your furnace can also be affected.

In general, appliances and chimney openings located below the neutral pressure plane of the house must work against the negative pressure induced by the stack effect. Conversely, appliances and chimney openings located above the neutral pressure plane are assisted by the positive pressure induced by the stack effect.

Negative Air Pressure

ENERGY EFFICIENCY - "Houses need to Breathe"