As part of our commitment to help ensure your protection, please be aware that the National Fire Safety standard requires that a Level II Internal Chimney Inspection be conducted whenever a house is bought or sold. (NFPA 211). The internal elements of the chimney fall outside the scope of your home inspection. Chimney repairs can be very expensive.
A Level II Inspection will be able to show you these conditions
Lugar Inspection Services offers visual inspection and does not conduct repairs so there is no conflict of interest.
Here are some simple scientific fundamentals to explain how and why a chimney works – or maybe why it doesn’t. This information is designed to make it easy to follow along with the procedures a knowledgeable F.I.R.E Certified inspector will use to diagnose smoking or odor problems with your chimney.
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 airflow. 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 renovated, have been made 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 recessed light fixtures and window frames. At the same time replacement air is trying to enter in the lower part of the building to make up 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 fireplaces, 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 pressure 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 (leeward) side will depressurize the house and increase the likeliness of backdrafting from chimneys or vents. Backdrafting 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 necessary make 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 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 to 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 airflow 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.
When most American homeowners think of their chimneys, living room fireplaces immediately come to mind. While those fireplaces most likely have chimneys, your home’s primary heating system also is very likely to have a chimney or chimneys to carry heat, smoke, and dangerous flue gasses out of your home. Whether you heat your home or your fireplace is fueled by gas, oil, wood or pellets, you most certainly want to keep your chimney and venting system in mind as an integral part of an efficient system.
The Chimney Safety Institute of America and many other fire safety organizations, including the National Fire Protection Association(NFPA) recommend that chimneys and vents are inspected annually and maintained as needed. This section of our website was designed to help you learn more about your chimney and venting system and what to expect when you call a chimney professional so you can make educated decisions about your chimney and venting system.
Annual chimney inspections by a qualified professional can prevent carbon monoxide intrusion and chimney fires and can also help you identify potential system issues to address them before they become costly.
In the United States, numerous agencies and organizations now recognize the importance of annual heating system inspection and maintenance in preventing carbon monoxide poisoning. The U.S. Consumer Product Safety Commission, the U.S. Environmental Protection Agency, the National Fire Protection Association, and the American Lung Association – are some of the organizations that now encourage the regular maintenance of home heating systems and their chimneys in order to keep “the silent killer” at bay.
A well-tuned furnace or boiler – connected to a venting system or flue that is correctly-sized, structurally sound, clean and free of blockages – will operate efficiently and produce a warm and comfortable home. An overlooked heating system can produce death and heartbreak.
Considering the risks involved when gas or oil systems are neglected – and the benefits that accrue when they are properly maintained – you would do well to have your chimneys checked annually by a F.I.R.E. Certified chimney inspector and swept or repaired as needed.