Chimney Liners and Extensions
By Stephen Varone, AIA and Peter Varsalona, PE
Our co-op is planning to convert from No. 6 heating oil to a gas-and-oil system. Our engineer told us that as part of the project we will have to line—and possibly extend—our chimney at an additional estimated cost of $300,000. Is this a requirement, and if so, what does it entail?
Because of the high price of oil relative to gas and the New York City Department of Environmental Protection regulation that requires buildings owners burning No. 6 heating oil to convert to a cleaner fuel by 2015, many co-op and condo boards have been converting their heating plants to a gas-only (firm gas) system or to a dual-fuel system. A dual-fuel system, also known as interruptible gas, burns gas almost all of the time, and No. 2 heating oil only when gas demand is very high, such on extremely cold days.
Property managers and board members are often surprised to learn that converting their building’s heating plant from oil to gas can require changes to the chimney. Most chimneys were built for oil heat, not gas. If this is the case with your building, a chimney liner will be needed to accommodate the new heating plant before initiating gas service, per the 2008 New York City Field Gas Code and 2013 New York City Building Code. In addition, your chimney may also need an extension or an offset.
Chimney liners protect the flue from the acidic condensate produced by burning natural gas, as the condensate can corrode the chimney’s interior masonry. In addition to protecting the masonry, the liner prevents the chimney from overheating and keeps toxic gas from infiltrating the building.
Types of Chimney Liners
There are several types of chimney liners, each characterized by its material and how it is installed or applied. Thick-gauge (10 gauge or heavier) stainless steel is the most common type of liner and can be used in flues of all heights and diameters. The liners, which are typically transferred to the site in approximately four-foot sections, are welded together as they are either lowered into the chimney from above or hoisted into place from the cellar. Because stainless steel liners can weigh several thousand pounds, they need to be braced at intervals, and the existing building structure, including the foundation and floor framing, may require reinforcement.
Light-gauge (24 gauge or lighter) stainless steel factory-designed chimney liners are also readily available. Some manufacturers offer up to 15-year warranties for their systems. These lighter gauge systems are typically fastened together with pre-designed collars, straps, ties, and supports. Although these systems are lighter and less expensive to purchase, they require engineered supports at frequent intervals, which can make them impractical for relining chimneys with difficult-to-access interiors.
Many chimneys need a liner
to accommodate a new
gas heating plant.
Another common liner is a ceramic flue sealant, which is sprayed onto the interior of the masonry chimney. The spray, a ceramic compound with a consistency equivalent to unformed concrete, hardens to form an impenetrable surface that improves the chimney’s resistance to extreme heat. Compared to the steel liner, the spray-applied liner may greatly reduce the need for structural reinforcement because its relatively limited weight is directly transferred to the masonry chimney.
Ceramic liners, however, are limited to chimneys up to approximately 250 feet in height because of the equipment used for the installation and manufacturer recommendations. Some spray-liner manufacturers, such as Thermocrete, claim they are working on overcoming the height limitations and will soon be able to install their liners in chimneys up to 400 feet tall.
Less common are masonry liners, which are composed of fire bricks or clay tile. Masonry liners aren’t well-suited for repair or alteration work because, given the tight space, it is extremely labor intensive to safely and efficiently install the bricks or tiles (which must comply with New York City-Building Code) along the inner chimney wall. In addition, bricks and tiles add a considerable amount of weight to the chimney. Also, masonry liners are not structurally self-supporting, so typically they are not suitable for chimneys that require an extension.
Design Considerations
The major factors in deciding which type of chimney liner to install are cost and the feasibility of installation. Welded stainless steel liners cost roughly 25% more than spray alternatives, and depending on height may require support at intervals. But because your building is 35 stories tall, a ceramic liner is probably not feasible.
Other factors to consider include the height and interior dimensions of the flue, the condition of the chimney, the building’s heating schedule, and changes needed to meet current building codes. If the construction work will be done during the heating season, your board may want to opt for a liner with a shorter installation period to minimize the shutdown time for the building’s heating plant (which will require the use of a temporary boiler) or wait until spring to begin the construction work.
Extensions and Offsets
If the buildings adjacent to your cooperative were completed after your building was constructed—or an extension was added to your building— your chimney may need an extension or offset to meet code. According to Section 503 of the 2008 New York City Fuel Gas Code and Section 802 of the 2008 New York City Mechanical Code, the chimney needs to exceed the height of the highest point of construction, typically a bulkhead, parapet wall, or penthouse. How much taller depends on the construction type of your building, the fuel your building uses for heat, and the chimney’s dimensions. Your engineer will specify the exact dimensions required to comply with code.
If the chimney is too close
to an adjacent building,
it will need to be offset.
If the chimney is too close to the adjacent building, the chimney will also need to be offset—i.e., extended away from the building’s wall—to meet code. Because it’s usually not feasible to relocate the entire chimney, only the portion of the chimney that extends beyond the roof level and is too close to the nearest construction will have to be offset. How much clearance is required is determined by code specifications similar to that of extensions. In addition to having sufficient clearance from the adjacent structures, the extension must withstand loads from gravity and wind, along with rain, ice, snow, extreme changes in temperature, and even earthquakes.
Like liners, chimney extensions may be constructed from steel, concrete, or masonry. The most appropriate material will depend on the height of the extension and aesthetic concerns. Masonry extensions are relatively expensive and are usually reserved for limited alterations or when aesthetics is a priority.
Landmarked buildings and those located within a designated New York City Historic District will need to receive approval from the Landmarks Preservation Commission (LPC) before construction work begins. The design engineer/architect should consider how the alteration will affect the building’s aesthetics and design the chimney extension or offset to preserve the historic look of the property, considering its appearance from the street, if applicable.
Special Inspections
Special Inspections take place at various points in the construction process and are conducted by a Special Inspection Agency registered with the New York City Department of Buildings. All new and altered chimneys require Special Inspections to verify that the work complies with the approved construction documents and that the chimney has proper clearance from adjacent combustible structures. If the construction work involves masonry wall, steel bolting, steel welding, anchors, or masonry erection, Special Inspections will be needed for those items as well.
Mechanical system work, including the heating plant, may also require Special Inspections. The inspections required depend on the type of liner specified and the material choice for the chimney extension.
DOB Inspections
In addition to Special Inspections on the chimney and liner, the oil-to-gas conversion work itself must undergo inspections by the Department of Buildings to ensure it meets code. The DOB’s Plumbing Division inspects the gas piping and gas meter room, and the Boiler Division the boiler, burner, and related equipment.
The oil-to-gas conversion, chimney liner installation, and chimney extension/offset, whether completed concurrently or successively, are usually undertaken as part of the same project. Typically, the mechanical work begins before the liner and extension work gets underway, but logistics and scheduling issues may require delays between project phases.
Regardless of the order of the installation, the building cannot begin burning gas until all of the work is completed and passes DOB inspection. Even then, because of the backlog of buildings being converted from oil-to-gas, it can take up to several months before Con Edison runs the gas line to the building and provides a gas meter for installation. Until then, the heating plant must continue to run on oil, so boards should plan accordingly.
A chimney liner and an extension or offset can add a considerable cost when a building is converted from oil to gas, but the payoff is a safer heating plant and the potential for long-term savings on heating costs.
Stephen Varone, AIA is president and Peter Varsalona, PE is principal of RAND Engineering & Architecture, DPC. This column was originally published in the October 2014 issue of Habitat Magazine.