Chimney Installation

A proper chimney installation allows a chimney to perform two functions: it removes smoke and flue gases from the furnace, and it allows the induction fan to provide the proper “draft” for the fire. Draft is the term used to describe the suction that occurs when hot air rises and creates a vacuum in the firebox. The induction fan along with the chimney draft draws fresh air into the firebox and feeds combustion of the wood. No furnace can operate properly without adequate draft.

The following instructions are guidelines only. A qualified HVAC/Chimney contractor should determine the specific chimney installation requirements for your furnace and insure that it complies with local building codes and ordinances.

  WARNING: The furnace must connect to a code-approved masonry chimney with a flue liner or an appropriately sized factory-built chimney that conforms to type HT (High Temperature) requirements of UL 103 or CAN/ULC-S629 and complies with Chapter 11 of NFPA 211, Standard for Chimneys, Fireplaces, Vents and Solid Fuel Burning Appliances. The chimney and flue pipe must be clean and in good condition.

Chimney Size

The chimney flue is a vital part of your furnace installation. A properly built and maintained masonry chimney or factory-built double wall insulated flue will assure that the induction fan provides a consistent draft under a variety of weather conditions.

Flue Diameter

The flue adapter that ships with the Frontier CX can be used with a 5” (127mm) or 6” (152mm) diameter flue. A 6” flue will require use of a stove pipe reducer such as the 24 gauge 6” to 5” Imperial Stove Pipe Reducer sold by Ace Hardware (Product UPC 0634672300069).

Chimney Height

The Frontier Series is a forced draft system which means the induction fan will control the draft through the flue. Regardless, the flue must meet your local codes for height and provide for adequate draft. This typically requires a minimum height of 12 feet (3.65 meters) from the base of the furnace.

Connecting to an Existing Chimney Flue

You may connect the Frontier Series to an existing flue or chimney subject to the following conditions:

  1. A qualified professional has inspected, repaired (if necessary), thoroughly cleaned and determined the chimney installation is suitable for use with a residential heating appliance that burns solid fuel.
  2. Avoid using exterior chimneys (i.e., a chimney with one or more walls exposed to the outside below the roofline). If it is necessary to use an exterior chimney, the chimney flue size area must not exceed two times the minimum flue area for the furnace and may require a chase.  If an internal chimney is used, the chimney flue size area must not exceed three times the minimum flue area for the furnace.

Furnace                        Min Flue                                   Max Flue Area                                   Max Flue Area                                                                                           Diameter                                Internal Chimney                              External Chimney

Frontier CX            5 in. (12.7 cm)                     58.90 sq. in. (380 sq. cm)                  39.27 sq. in. (253.4 sq. cm)


3.  If your chimney flue exceeds the maximum area allowed, it must be lined with a suitable flue liner that complies with the requirements of Chapter 11 of NFPA 211 3-1.2 — Standards for Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances.

4.  The minimum height of the chimney should be 12 feet (3.65 m) measured from the base of the furnace.

5.  Do not share a chimney flue with another furnace, appliance or fireplace. Do not use a flue that already provides make-up air to the cellar or basement.

6.  Tightly close and seal the cleanout opening in the base of the chimney.

Connector Flue Pipe

The connection between the Frontier Series flue adapter and the chimney must be 24-gauge stovepipe or thicker. Maintain a clearance of at least 18 in (45.7 cm) between the connector and combustible surfaces as shown on the following illustration.

                                                      Minimum Chimney Installation Clearances (Side View) Note: If it is necessary to use an exterior chimney, the chimney flue size area must not exceed two times the minimum flue area for the furnace and may require a chase. If an internal chimney is used, the chimney flue size area must not exceed three times the minimum flue area for the furnace.

Observe the following rules when installing the connector stove pipe.

  1. Where possible, use only corrugated (non-adjustable) elbows. Use 90-degree elbows only as required and never more than two (they reduce the draft of the chimney).
  2. Make sure all horizontal runs of connector pipe have a minimum outward rise of 1/4” (0.6 cm) per horizontal 12” (30.5 cm).
  3. If the connector stovepipe must go through a combustible wall before entering the masonry chimney, consult a qualified mason or chimney dealer. The chimney installation must conform to local building and fire codes and latest edition of NFPA 211.
  4. Insert the crimped end of the stovepipe inside the outlet collar of the Frontier series flue adapter. Install additional pipe and elbows with the crimped end towards the furnace.
  5. Seal the connector pipe to the chimney with furnace cement.
  6. Securely support the connector pipe and fasten joints with a minimum of three sheet metal screws or rivets per joint.
  7. In all cases, follow the manufacturer’s chimney installation instructions.

Installation of the Connector Pipe into an Existing Chimney

When attaching the connector pipe to the chimney, do not push it into the chimney (it may plug the chimney and impede the draft). The following illustration shows proper installation.

Connecting to a New Factory-made Chimney

A properly sized and installed chimney flue will ensure adequate draft at all times for optimum performance of the furnace. For a new chimney installation, use an insulated stainless steel system that conforms to type HT (High Temperature) requirements of UL 103 and ULC S629 and complies with the requirements of Chapter 11 of NFPA 211, Standard for Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances.

The factory-made chimney can be routed straight-up through the roof or routed through a side-wall and then straight-up. The height of the chimney must be at least 12 feet (3.7 m).

Furnace                                                  Min Flue Diameter

Frontier CX                                            5 inches (12.7 cm)

  Warning: Solid wood burning furnaces should NOT be side vented.

Note: When installing a new chimney flue, be sure to observe local building codes and the National Fire Protection Association ( rule: The top of the chimney must extend at least 3.0 feet (0.9m) above the highest point where it exits the roof and be at least 2.0 feet (0.6m) taller than any point of the roof within 10.0 feet (3.04m).

Supplying Make-up Air

Fireplaces, other furnaces, clothes dryers, exhaust fans, and other appliances, all draw air from the room in which they are located. The Greenwood Frontier adds to that draw, so it is important to make sure there is an adequate source of fresh air to offset these demands. Otherwise, you may create negative pressure in the room and starve combustion in the furnace. Intake air temperature should be 40°F (4.5°C) or above.

To determine the requirement for makeup air:

  1. Determine the volume of space (cubic feet/meters) in the room. Include in the calculation adjacent rooms and areas not closed-off by doors.

Volume (CF) = Length (ft) x Width (ft) x Height (ft) or

Volume (CM) = Length (m) x Width (m) x Height (m)

2.  Determine the fuel input requirements of all appliances in the space. Add them and round the total to the nearest 1000 BTU (0.29 kw) per hour.

3.  Determine whether the space is “confined” or “unconfined” by dividing the total volume of the room by the total fuel input requirement for all appliances in the room.

  • If the result is greater than or equal to 50 CF (1.42 CM)/1000 BTU (0.29 KW) per hour, then consider the space “unconfined.”
  • If the result is less that 50 CF (1.42 CM)/1000 BTU (0.29 KW) per hour, then consider the space “confined.”

4.  For an “unconfined” space in a conventionally constructed building, the fresh air infiltration through cracks around windows and doors NORMALLY provides adequate air for combustion and ventilation, so no additional make-up air is required.

5.  For a “confined” space or an “unconfined” space in a building with unusually tight construction, an additional source of make-up is required. Please refer to the table below and consult an HVAC professional to determine the best way to supply make-up air for your installation.

Frontier CX Required Makeup Air

Confined Space                      Open Area                   Screened Vent Area                   Filtered Vent Area

<500 ft2 (<141.6 m3)       24 in2 (155 cm2)              60 in2 (387 cm2)                      120 in2 (774 cm2)

Note: If fans are used in the fuel storage area, they should be installed so as not to create negative pressures in the room where the boiler is located.

Measuring and Adjusting the Draft
Draft is a function of the chimney flue and the induction fan on your Frontier Series. The draft can be affected by several factors including chimney height, temperature of flue gases, cross-sectional area of the chimney, chimney wall insulation value, dilution air, and total volume of flue gases.

Symptoms of an improperly designed or installed flue include visible smoke out the chimney, smoke escaping into the room, creosote buildup in the flue, and/or poor heating performance.

The following procedure describes how to measure draft using a manometer—a device that measures draft:

1. Close all windows and doors in the building and turn on all appliances that remove air from the home (e.g., heat pump, air conditioner, exhaust fan, clothes dryer, fireplaces, etc.).

2. Drill a hole in the connector pipe (just large enough for the tube of the manometer) at least 1 foot above the furnace outlet collar.

3. After all chimney connections, plumbing and wiring is complete, build a fire and allow the furnace to settle into stable operation. If the boiler has been installed in conjunction with a Type A flue pipe, take the draft reading after 1 hour. For all chimneys other than Type A flue pipe, take the draft reading after 2 hours.

4. Using the manometer, measure the draft in the flue. a. If the draft measurement is below .05” WC (12.45 Pa) at full fire, there is too little draft and corrective measures are required to avoid incomplete combustion. Excessive draft (over .07” WC) may result in frequent cycling of the Frontier CX dampers and an inconsistent burn.

5. Once needed adjustments are complete, seal the hole made for the manometer tube with furnace cement or a screw.

Your installer should have a manometer for completing these measurements. Some installers may recommend to permanently install a manometer on the furnace to assist the owner in monitoring the draft. A decrease in draft, for example, can signal a dirty boiler if it coincides with an increase in stack temperature.


Sources of Equipment*

1. Manometers and other measurement devices can be found at

2. Chimney flue components: local building supply store or

3. Other Chimney products: and

More Information

1. Chimney Safety Institute of America (

2. All About Chimneys (

3. National Fire Protection Association (

4. American Society of Mechanical Engineers (

*NoteGreenwood Clean Energy provides these supplier references for your convenience only. We do not endorse the vendor, the equipment they sell, or their prices. Other suppliers may offer similar or identical components and we encourage you to comparison shop.

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