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Negative Air Pressure ............................ and the energy efficient airtight house 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;

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.


"Indoor ventilation and air quality"


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!

Is Your House Sick?

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.

Think of your house as a living, breathing thing.

"Houses need to breathe"...... and 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. TOP


The neutral pressure plane is often, but not always, located at the vertical mid-point of the house. A house with similar leakage rates at all levels will have a neutral pressure plane at approximately its mid-point.

A house with a well-sealed basement but a leakier upstairs will tend to have a neutral pressure plane higher than the mid-point, and a house with a leaky basement and sealed upstairs will have a lower neutral pressure plane.

The neutral pressure plane tends to move towards the leakiest level of the house. This movement of the neutral pressure plane explains why opening a basement window can improve chimney flow and prevent back drafting in a basement woodstove or fireplace. The open basement window represents a large enough leak to bring the neutral pressure plane down to basement level, reducing or temporarily eliminating the negative pressure the chimney has to work against.

If you experience down drafting open a door or window for a few minutes and watch how easily this works to change the neutral pressure plane and prevents that unpleasant smoke filled room if you do it before you light the fire.

The first two suggestions are simple ways to test if you have negative air pressure before lighting your fire and the third is a solution for temporarily eliminating the problem.

1) hold your hand inside the fire box and up near the damper (make sure the damper is open) and see if you feel cold air coming down the chimney

2) Light a good size sheet of paper and hold it in that same position up near the damper; if the fire goes out or the flames are being blown back the stack effect is happening.

3) Open a window or door to balance the air pressure in the room; light another piece of paper and hold it in the fire box the flames should draw up the chimney if the pressure has been equalised (leave the window or door open until you determine that a good draw has been established in the chimney)

So now you understand the stack effect in your house and you are be able to temporarily eliminate the
problem of lighting a fireplace or wood stove in the basement. (although in an inefficient way) But remember the warm air in a house tends to rise, producing a stack effect similar to the draft in chimneys. The resulting negative pressure in a basement can cause venting problems in all combustion appliances located there; so what about your furnace that cycles on and off continually, the above tests and remedies will not be a practical solution.


A chimney installed on the outside wall of a house and serving a basement
installation is the most susceptible to back drafting caused by the stack effect. At standby when there is no fire or heat from the appliance the air in the flue can cool to outside temperature.

With no temperature difference, no draft is produced in the chimney, and even
minor negative pressure acting on the air inlets of the appliance can readily cause reverse flow in the chimney.

Back drafting at standby is clear evidence of the stack effect in buildings. Such back drafting may also be caused by other exhaust ventilators such as bathroom and kitchen fans, central vacuums or your dryer using up air and contributing to the creation of negative air pressure.

It is sometimes suggested that reverse flow in a chimney can be cured by holding a burning piece of paper or a hair drier at the base of the chimney to heat the flue.

But heating the flue only treats the symptoms of the problem, not the problem
itself. Remember, a chimney that back drafts at standby can also back draft
during a receding fire and also as your furnace cycles on and off, especially in cold weather or when an exterior chimney is severely chilled. Back drafting
during a receding fire spills poisonous carbon monoxide into the house!!

You cannot eliminate the stack effect in a house it is a natural phenomenon, but you can eliminate the effect it has on the venting of combustion appliances by introducing fresh outside makeup air. Click here to go directly to our solutions below.


When diagnosing a draft-related problem in a basement installation, always keep in mind that negative pressure induced for any reason or by the stack effect can be a contributing factor.

The following symptoms can be caused by negative air pressure or the stack effect:


Energy conservation measures are making houses more and more airtight. Sealed vapour barriers, caulking, and carefully installed weather-stripping doors and windows all reduce the leakage of air into and out of houses (infiltration and exfiltration, respectively). The shell, or envelope, of such houses resists airflows created by exhaust ventilators. (appliances that exit air when functioningeg. clothes dryer – fireplace)

Fuel-burning appliances are exhaust ventilators, as are kitchen and bathroom
fans, clothes dryers, and central vacuum systems. All these draw air from the house and exhaust it outside. When a fuel burning exhaust ventilator operates in a well-sealed house, it may not get all the air it needs to function properly.

When two or more exhaust ventilators operate at once, they may compete with each other for available air. In a competition for air, mechanical systems such as kitchen fans usually win out over natural draft systems such as chimneys creating a very dangerous situation.

The operation of a clothes dryer or high-volume kitchen exhaust fan can cause back drafting of a fireplace, other wood burning systems and the furnace. In theory, all exhaust ventilators should be supplied with an adequate source of outdoor air.

Exhaust ventilators operating on natural draft cannot usually compete with mechanically-powered ventilators. The chimney serving a wood stove or furnace may back draft when the negative pressure produced by mechanical ventilators (fans) overcomes chimney draft.

It is possible, however, to bring in just the right amount of outdoor air to compensate for air removed by exhaust ventilators and continuously-operating ventilators such as woodstoves and your furnace. (See our solution below)

To see why you should also be concerned about bringing clean purified air intoyour home see the added benefit of UV purification. TOP


For reliable operation, all combustion appliances installed in well-sealed houses
should be provided with an adequate source of air.

Fireplaces present a particular problem because they consume so much room air, especially when the doors are open. Even with doors closed, most fireplaces need large amounts of room air.

Fireplaces also tend to be more prone to back drafting. For this reason, it is always a good practice to provide a fireplace with close-fitting glass doors and ensure a good source of air for combustion.

Negative Air Pressure.................... and the silent killer

"Houses need to Breathe"

"Change bad air for good" the CO question

I GREW UP sleeping in bedrooms with the heat cut off and the windowcracked open, even on the coldest of nights, because my father decreed, "It's safer that way."

POISONOUS CARBON MONOXIDE gas escaping from a faulty-operating furnace was what he feared. His concern was well-founded.

I heard stories then, and still do, about whole families perishing in their sleep or becoming deathly ill from carbon monoxide fumes.This gas is a colorless, odorless killer. Its victim's flue-like symptoms make the source of illness difficult to detect. Each generation must be acquainted anew with the dangers.


Carbon monoxide (also called CO) is an odourless, colourless, tasteless gas that is very toxic. When we breathe it in it interferes with the body's ability to absorb oxygen.

What are the symptoms of carbon monoxide exposure?

Exposure to carbon monoxide can cause flu-like symptoms: headaches, nausea, fatigue, dizziness, drowsiness, burning eyes, confusion, disorientation and even unconsciousness. In very severe cases, carbon monoxide poisoning can cause brain damage or death.

Be alerted that, if members of your household have these symptoms at home, but feel better away from home, CO or other pollutants in the home may be suspected. However, there could be many other causes for these symptoms. If you see a doctor about suspected CO exposure, request a CO blood test.

Is everyone affected equally?

People may react differently to carbon monoxide exposure. The elderly, children and people with heart or respiratory conditions or compromised immune systems may be particularly sensitive to carbon monoxide and may feel the effects sooner.

What are the sources of CO?

Carbon monoxide is a by-product of the incomplete combustion (burning) of fuels such as wood, propane, oil, natural gas, kerosene, gasoline, diesel fuel, coal or charcoal. Tobacco smoking also contributes small amounts of CO into the air.

Carbon monoxide detectors

They are available at many local retail stores please be sure that it has been approved under the CSA Standards.

Conditions that may cause CO;

Be aware of these danger signs:

If your carbon monoxide detector alarms:

Some tips to safeguard your home:

All Fuel-burning equipment needs air to operate safely.

See our solutions and find out how to equalize the air pressure in your house and prevent CO spillage by bringing in the exact amount of outside air needed and distributing it throughout the house with your forced air heating system. TOP

Is Your House Sick?

The stack effect and negative air pressure, what to do:

First some history of suggestions we have used in the past before Plusaire:
One way to overcome the stack effect in woodstoves is to provide a directly ducted source of outside air to the combustion air inlet of the appliance. This isolates the combustion and venting systems from the rest of the house.

When an appliance is installed in a basement has a fitting to accept an outdoor air duct,"always" connect the duct to prevent possible backdrafting.
Indirect sources of outside air are possible but not usually desirable. A hole in the basement wall may serve as an entry combustion air, but the air flowing through the hole would mainly compensate for air leaking out the upper parts of the house.

Only a small proportion of the incoming air would be used for combustion in the appliance The effect of creating the opening is similar to that of opening a basement window - it lowers the neutral pressure plane and therefore reduces the negative pressure in the basement.


Pure Air Plus can correct the following;

All this with the installation of a Plusaire residential ventilation system providing your house with fresh air every day. What is needed is an efficient source of make-up air to equalize the negative air pressure in your home. This is what "Pure Air Plus" can provide using a "Plusaire" residential ventilation system with the added benefit of UV purification, filling your home with fresh pure air every day!

Plusaire residential ventilation systems are designed to correct the problems caused in an airtight house and the stack effect, but can be equally effective in a drafty house. The system works in two ways. Firstly it uses a distribution system you already have, the furnace and its ductwork..

Secondly Plusaire brings in air both when the furnace is in its active heating/cooling mode and also when the furnace is in its passive mode, reacting to the continually fluctuating indoor air pressure bringing in air as the house is exhausting it through various methods including fans and appliances even when the furnace is not running.

In both cases the system tempers the fresh air by mixing it with furnace air before it enters the cold air return in the furnace and is delivered throughout the house with existing ductwork. The whole house is now supplied with fresh makeup air to eliminate all the symptoms mention previously throughout this site. This continually creates a healthy comfortable indoor environment.

Here is how Plusaire will help you and your family experience a healthy home free from negative
air pressure issues and the fear of CO contamination!!

Eliminate the negative pressure inside your house caused by heat rising in cold climates and prevent carbon monoxide spillage from fuel burning appliances by bringing in the exact amount of outside air needed to make
your home healthy and distributing it through your forced air heating system.

Solutions From: Pure Air Plus
Improving air quality one house at a time

Affordable residential Ventilation Systems featuring "Plusaire"

What actual benefits can you expect from your "Plusaire®" system

Easier than opening a window

Give your family the gift of a healthy environment- “Plusaire gives fresh air for life”.

The first completely natural and automatic, inexpensive superior clean air whole house system improving your indoor environment in 48 hours by filling your home with fresh clean
air every day!

We want you to enjoy Plusaire risk free so we are offering you a money back guarantee.

And as an added bonus – All our prices are quoted in Canadian dollars for our Canadian customers and giving our US customers the dollar exchange benefit.

So now that you know we stand behind our product and there are no hidden costs how will it fit into your home and which size do you need.


Plusaire® can only be install on a forced air system and will require access to an outside wall from the furnace room, it comes in 4 sizes to suit the size of your house. The exterior air intake vent needs to be 20 inches up from ground level to prevent snow cover from blocking the vent. If you have less than a 20 inch clearance you will require a snorkel to raise this to an appropriate level see snorkel in accessories.

Use our sizing page to determine the size of Plusaire unit you require click here to automatically go to the unit sizing page and find type of Plusaire required for your house.

Now that you know the size of the unit you need for your house you have four easy ordering options for self installation or call us at 519 942 9721 for installation prices for the southern Ontario area.
1) The fastest way to place your order is directly on line using PayPal and the credit card of your choice just click the order link next to the size you need.

2) For personal service you can email your order to pureairplus@sympatico.ca

3) Call us at 519 942 9721 and place an order by phone

We have provided everything you will need

1) Plusaire Unit
2) Complete installation instructions
3) Complete installation kit
4) Fresh air vent and wall sleeve

All this bundled into our internet introductory offer at one low price. This complete package assures you that that you can easily install your Plusaire Unit yourself giving your family the gift of fresh air.

To take advantage of our internet introductory offer and get your Plusaire Unit complete with fresh air intake vent and self installation kit and shipping all included.

choose from the unit sizes below or

Use info from sizing chart at the link above

BME size # 2 Air Unit & Kit…………………….…995.00
BME size # 3 Air Unit & Kit…………………….…1095.00
BME size # 4 Air Unit no kit…...………….…995.00

Larger sizes are available through custom orders call 519 942 9721



Snorkel to raise exterior air access…………………….........140.00


Order Now and get your Plusaire unit fresh air vent self installation kit and shipping all included for the above low internet price.

An email will be sent confirming your order

We want you to enjoy Plusaire risk free so we are offering you a one year Money back guarantee

Email us at pureairplus@sympatico.ca to get your free report CMHC Combustion Gases in Your Homei

Isn’t your family’s health worth it….No price can be placed on your health!!

Plusaire Units have no moving parts and provide a lifetime of fresh air.
Remember Plusaire is engineered to always bring in just the right amount of air as dictated by the negative pressure in your house and is energy efficient, exits no air so heat recovery technology is not required …..… easy installation you can do it yourself!!!

Thankyou for your interest in air quality.

Maiken Crole
Pure Air Plus

15 Amanda St.
Orangeville Ont.
L9W 2J9

Try it Risk Free Money back guarantee excluding shipping

Contact us atpureairplus@sympatico.ca
Business 519 –942 9721
Fax 519 – 941 0033

"Pure Air Plus" can provide your family with a unique experience in residential ventilation systems using "Plusaire®" continually creating a healthy comfortable indoor environment and filling your house with pure fresh air every day!

Those who have had the system installed and where suffering from breathing disorders or asthma and those with smokers in the home have noticed the most immediate and significant difference with symptoms being reduced by 50% or more.

Just think how different your home environment can become if you reduce the toxins and introduce fresh air into your home, the results are nothing short of remarkable and your family will feel better and have more energy and an improved quality of life.

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"Is your house sick"



Energy efficiency................... "Houses need to Breathe"

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.