Is your chimney not working correctly, have everything” and nothing seems to help? Per problem lies in your chimney physics!
At first, this might sound complicated. But real Here are same simple scientific fundamentals to and why a chi many works-ir maybe why it doe…brochure is designed to make it easy to follow al… procedures a knowledge enable CSIA Certified Chirr… will use todiagnoes smoking or odor problems… chimney.
Your House as a system
Even though you can’t see it, the air in your house scantly in motion. In general, airflow tries to flow…house in the upper parts and make up air tries… your house in the lower parts of your house. The house as a system makes it easy to under stand till… that airflow. The actual flow of air into and out…influenced by a number of constantly changing including: stack effect; wind loading; interior m… systems and fuel-burning appliances such as fu… fireplaces, wood stoves and water heaters.
Is your chimney not working correctly? Have you “tried everything„and nothing seems to help? perhaps the problem lies in your
Chimney Physics!
At first, this might sound complicated, But really it isn’t. Here are some simple scientific fundamentals to explain how and why a chimney-or maybe why it doesn’t. This brochure is designed to make it easy to follow along with the procedures a knowledgeable CSIA Certified Chimney Sweep” will use to diagnose smoking or odor problems with your chimney.
Your House as a System
Even though you can’t see it, the air in your house is constantly in motion. In general, airflow tries to flow out of your house in the upper parts and make up air tries to flow into your house in the lower parts
of your house. Thinking of your house as a system makes it easy to understand the reasons for that air flow. The actual flow of air into
and out of any home is influenced by a number of constantly changing factors, including: stack effect: wind loading; interior mechanical systems and fuel-burning appliances such as furnaces, fireplaces,
wood stoves and water heaters.
Homes built in the past 25 years, and older homes that have been
retrofitted, have been made more and more airtight. This makes it
much more difficult for makeup air to enter the home.
As the saying goes,” hot air rises”, and so does the warm air in your home. When the warm air rises to the upper areas it’s called the stack effect. That trapped air creates a pressurized area and forces its way out – through even very small openings such as light fixtures and window frames. At the same time replacement air is trying to enter in the lower part of the building to makeup for the escaping air.
Somewhere in your house, amid all this airflow, is something called the Neutral Pressure Plane (NPP). Above this theoretical plane, the air pressure is slightly positive compared to the outdoor air pressure and is trying to force its way out of the house. Below the plane, it is slightly negative and the house is trying to draw air in. The location of the NPP can constantly change in response to changing conditions.
All of the factors that affect airflow in the house also influence the level of the Neutral Pressure Plane.
Anytime a fireplace or fuel-fired heating appliance (except direct vent) is below the plane, air will tend to flow into the house through the chimney or vent. A common example of this is found in homes with two fire-places, one below the other. As the upper level fireplace uses air for combustion and chimney flow, it depressurizes that level slightly causing air to flow upwards from the lower level. Since the lower level fireplace is below the NPP, it draws air into the basement through the chimney. Unfortunately, since those two flues generally exit the chimney close to each other, the makeup air can contain some smoke from the fireplace above and it can pick up unpleasant chimney odors as it passes down the chimney flue.
Wind-loading is the effect on interior house pressures caused by the wind.
When wind strikes a building, it creates high pressure on the side that it hits
and low pres-sure on the downwind side. Any open windows or doors on the windward side will help to pressurize the house, increasing chimney draft. However, openings on the downwind side will depressurize the house and
increase the likeliness of back drafting from chimneys or vents. Back drafting is
a reversal of the airflow in which the smoke is coming into the house instead of going up the chimney.
Interior mechanical devices such as clothes dryers, kitchen fans, bathroom fans, attic fans and central vacuums can also create depressurization by removing large volumes of air from the house. The result is often negative pressure in the area of a fireplace, woodstove, or other fuel-fired heating appliance making it increasingly difficult for natural draft chimneys to function as intended.
Another mechanical system that commonly removes air from the house is a forced air furnace. Many such systems are out-of-balance due to leaks in the ducts. Leaky supply ducts cause air to be blown into the attic or crawlspace. Leaky return ducts draw air from the basement or other areas they pass through.
Furnaces, water-heaters, fireplaces and woodstoves are examples of fuel-burning appliances that require large volumes of air for combustion. Unless they are specifically equipped to draw air in from outside the house, such as direct vent appliances, operating them can reduce the inside air pressure. There are a variety of mechanical devices on the market that help provide the necessarymake up air to balance the air pressure needs of your house system.
Draft and Flow
Many experienced chimney professionals use the similarities between water and air to explain the way your chimney works. Although most people don’t realize it, the air moving up your chimney works
under the same set of physical principles as water flowing in a hose or pipe.
When a fire place chimney is full of hot air, it actual, through the fire box. This pulling effect is called d,, corresponds to the amount of pressure in a water only difference is that the air pressure is negative water pressure is positive (think of using a straw to instead of to blow bubbles). Thus, a chimney is dive pressure system. Increasing the draft in your like opening the faucet wider on the hose. The sir,,. To increase the draft in your chimney is to burn the hotter air is lighter, so it has more pull. Another more draft is to increase the height of your chimney when the chimney is already so tall that frictional negate the effect of the extra height.
Given the same amount of pressure, a larger pipe oily carry a greater volume of water than a small same is true for chimneys- with the same amount, (pressure), a larger flue will exhaust more smoke f,,, fireplace than a smaller one. But just as a water h,,, kinked or plugged, the airflow in your chimney ca,,, restriction that slows down the smoke flowing up ,,,, neyu. Some of the reasons for poor flow in
a chimney excessive creosote deposits; closed or plugged dar,,,,
,,,chemical devices such as clothes dryers, bathroom fans, attic fans and central vacuums ,,,to depressurization by removing large volumes ,,,e house. The result is often negative pressure in fireplace, woodstove, or other fuel-fired heating, king it increasingly difficult for natural draft function as intended.
,,, handicap system that commonly removes air from ,,a forced-air furnace. Many such systems are, cue due to leaks in the ducts. Leaky supply ducts, e blown into the attic or crawlspace. Leaky draw air from the basement or other areas they
,,, tar-heaters, fireplaces and woodstoves are fuel-burning appliances that require large vole-,,,or combustion. Unless they are specifically draw air in from outside the house, such as appliances, operating them can reduce the inside, There are a variety of mechanical devices on the ,,,ell provide the necessary make up air to bal-,,,reassure needs of your house system.
,, low
, ended chimney, use the between water, loan the way, y works. ,,,sty people it, the air move-,,, chimney works ,,,new set of phys-,,,s as water ,,,nose or pipe.
When a fireplace chimney is full of hot air, it actually pulls air through the firebox. This pulling effect is called draft and it corresponds to the amount of pressure in a water hose – the only difference is that the air pressure is negative and the water pressure is positive (think of using a straw to drink with instead of a blow bubbles). Thus, a chimney is called a negative pressure system. Increasing the draft in your chimney is like opening the faucet wider on the hose. The simplest way to increase the draft in your chimney is to burn the fire hotter – hotter air is lighter, so it has more pull. Another way to get more draft is to increase the height of your chimney – except when the chimney is already so tall that frictional forces negate the effect of the extra height.
Given the same amount of pressure, a larger pipe can obviously carry a greater volume of water than a smaller one. The same is true for chimneys – with the
same amount of draft(pressure). A larger flue will exhaust more smoke from your fireplace than a smaller one. But just as a water hose can be kinked or plugged, the airflow in your chimney can have a restriction that slows down the smoke flowing up the chimney. Some of the reasons for poor flow in a chimney are: excessive creosote deposits; closed or plugged dampers;
Improper construction; structural damage or even a dirty chimney cap. In fact, having a plugged-up chimney cap at the end of your chimney is just like having a closed nozzle at the end of a hose – you just can’t get any air flow through the chimney. Your CSIA Certified Chimney Sweep can evaluate your chimney and recommend any corrective action to ensure that it is capable of the proper draft and flow.
Chimney Safety Institute of America
2155 Commercial drive
Plainfield, IN 46168
(317) 837-5362 Fax (317) 837-5365
office@csia.org
Website:www.csia.org
|
