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    5 Common Mistakes Made by Fireplace Contractors

    Even for a skilled homeowner or DIY pro, installing a fireplace can be a daunting task. The installation involves attributes from many trades, including electrical, plumbing, and framing. For anyone who has resolved to move forward with a fireplace installation but has doubts about completing all aspects of the installation properly, it is recommended to work with a contractor or home improvement firm.

    5 Common Mistakes Made by Fireplace Contractors

    Installation requirements for fireplaces differ across product lines. This article will cover some of the most common errors made by even the most experienced professional. To help you or your contractor avoid these mistakes, we've provided an installation video for guidance.

    1. Selecting the Proper Valve

    One of the first things to establish when purchasing a fireplace is the type of appliance you wish to install. In the case of a gas fireplace installation, there is a long list of the different valve and burner systems to choose from. Among the choices in the gas fireplace category are millivolt and electronic gas valve systems. While they both perform the same basic task, they operate very differently. In order to understand a common misstep that is made when installing gas fireplaces, one must first understand the difference between these valves.

    A millivolt valve system, also commonly called a standing pilot system, is a type of valve that uses a pilot assembly with a small standing flame that burns at all times. The gas valve contains a series of small electromagnets that hold open springs within the valve, allowing gas to flow to both the pilot and burner circuits. When manually lit, the pilot flame will heat a device known as a thermocouple, and using resistance between dissimilar metals within the thermocouple, a small amount of voltage is generated to power the magnets in the valve. Unlike an electronic gas valve system which requires a 120-volt power source, millivolt systems require no outside voltage supply to operate. The pilot flame generates all the power that will be required.

    With the increasing interest in efficiency and conservation, there has been an increase in the popularity of electronic systems that save gas by eliminating the standing pilot. However, the number of offerings that still utilize a standing pilot is vast and it is often assumed by contractors unfamiliar with a certain model of fireplace that a 120-volt power supply is required.

    5 Common Mistakes Made by Fireplace Contractors
    Figure 1

    Figure 1 depicts a typical millivolt style of gas valve. Note the black terminal block with wire leads connected. This is a classic indicator of a millivolt style of valve, but if there is any doubt, we encourage you to contact a technician at to verify specifics of your model. As shown in the image, a contractor has improperly connected a 120-volt power lead to the terminal block. When energized, this can cause a dangerous charge to be passed through the valve, damaging it, the pilot assembly, and other components linked to the valve. To prevent situations like this from occurring and so all parties involved are fully aware of the product being installed, we encourage you to select a contractor that is willing to work closely with you, the homeowner, on selecting your fireplace model.

    2. Clearances Between Vent Pipe and Wood Framing

    As if often the case when adding a fireplace to a house, the appliance installation is part of a larger addition or remodel project. The decision to add a fireplace may have come while the project is well underway and as a result, structural modifications may need to be made to accommodate the vent pipe from a wood or gas burning fireplace.

    5 Common Mistakes Made by Fireplace Contractors
    Figure 2

    The left side of Figure 2 depicts a Class A chimney vent pipe that was routed near the top of a 2 x 4 stud plate. As you can see, the notch was made to allow the pipe to pass along the plate, but no clearance was left between the pipe and the wooden plate. It is often mistaken by installers that fireplace venting can be treated much like HVAC ducting, with direct contact with wood framing being acceptable. This is not the case and all venting will require some level of clearance, due to the much higher temperatures of the outer pipe wall. On the right side of Figure 2, it can be observed that the pipe would have passed too close to the plate, so the notch was made to gain the proper 2 inches of clearance to combustibles that Class A vent pipe requires. While a great number of installers understand the importance of these clearances, it is a simple mistake that can easily be made during the course of a much larger project. Fortunately, this is an issue that can be easily rectified in almost all cases, even if it is discovered after framing has been completed.

    3. Properly Insulating the Fireplace

    Mentioned earlier was the increasing interest in greater energy efficiency of a home as a whole. For many contractors and homeowners alike, this means the increased use of insulation and sealing the home tightly so that outdoor temperature swings have a minimal effect on the indoor environment. With the increased dependence on insulation, a scenario like the one depicted on the left of Figure 3 is often encountered.

    5 Common Mistakes Made by Fireplace Contractors
    FIGURE 3

    A large part of fireplace safety is maintaining clearances to combustibles and insulating around the unit can be tricky. Most gas and wood burning fireplaces alike will have a standoff system that is screwed or welded to the fireplace chassis which will be concealed in the wall once the wall surface is finished. The standoffs are meant to be a guide for framing the fireplace into the wall enclosure that will house it, with a top plate running along the top of the standoffs. Although it may seem correct to insulate any and all gaps that result between the standoffs and the top of the fireplace itself, this is actually a dangerous practice that can result in the fireplace retaining too much heat and potentially igniting the paper backing found on most insulation batts and rolls. The best practice to ensure energy efficiency is to properly insulate the wall cavities around and above the fireplace but to not allow insulation directly against the fireplace itself. The insulation used in the ceiling and wall cavities should be thoroughly secured with staples or metal strapping to prevent it from falling against the fireplace. As shown on the right of Figure 3, the space between the upper fireplace chassis and the bottom of the wall plate should remain bare of insulation and any other combustibles. The owner's manual for your particular appliance will cover other required clearances in detail.

    4. Selecting the Proper Vent Pipe

    A large part of a successful gas fireplace installation is the selection of the proper vent pipe to route the burnt exhaust gases to atmosphere. Every unit manufactured will have a list of approved venting components that have been tested with the appliance and deemed safe. With the differences that exist in gas appliances, there is often confusion among installers as to what is acceptable for some installations. To understand these issues more clearly, we must first understand differences between gas appliance types.

    A large part of a successful gas fireplace installation is the selection of the proper vent pipe to route the burnt exhaust gases to atmosphere.

    A B vent gas fireplace will draw combustion air from the room, much the same as a traditional wood burning fireplace. Exhaust gases are vented to the atmosphere via a two-ply galvanized vent pipe known as Type B venting. This is the same type of venting used for many gas furnaces and water heaters. Because they are not efficient, B vent fireplaces are not as popular as they once were. Direct vent fireplaces will use a pane of tempered or ceramic glass to seal the combustion chamber from the room. To allow the fireplace to receive air for combustion, a double-walled vent pipe will be used. The inner tube will vent the exhaust to the atmosphere, while the outer tube will pull combustion air from outside. The outer tube will also help to keep the entire vent system cool by enshrouding the inner exhaust tube.

    5 Common Mistakes Made by Fireplace Contractors
    FIGURE 4

    Shown in Figure 4 is the vent collar of a direct vent fireplace. Note the outer and inner vent collars. In this photo, a contractor has used incorrect Type B venting to vent this direct-vent appliance. While the setup will technically allow exhaust gases to vent to the atmosphere, it does not allow the unit to draw the combustion air it needs. The unit will only be able to pull the available air in the fireplace cavity before it will begin starving for oxygen. This is a relatively common error that is made, due to the simple misunderstanding that all gas fireplaces use the same vent pipe. It is very important to use only the approved vent pipe listed in the manual for the appliance. When in doubt, contact a professional NFI certified technician at for guidance.

    5. Materials and the Fireplace Front

    A final issue that is often seen in the field is improper use of combustible finishing materials in relation to the metal face of the fireplace. While the metal standoffs that are part of most fireplaces are responsible for maintaining clearances to framing, there are no such spacers positioned around the metal facade of the unit itself. Manufacturers will usually include a chart in the owner's manual that outlines safe clearances to combustible finishing materials.

    Figure 5

    Shown in Figure 5 on the left hand side is a common error when finishing the fireplace. Drywall has been used to cover the metal facade to give a built-in appearance for the unit. Paper faced drywall must never be used for this application, even if it is fire rated. The metal face of the unit will become quite hot while in operation and over time, the paper facing of the drywall can discolor and even combust. Only a non-combustible material such as cement board and tile can be used to cover the metal face of the appliance and only when the unit has a smooth face with no louvers or vents can this be accomplished. Any unit that uses a louvered face must always have its louvers uncovered unless the manufacturer explicitly states otherwise. Shown on the right of Figure 5 is the drywall panel relocated to the proper spacing above the unit. A trim kit can be used to cover the gap for an all drywall application or cement board can be used to span the gap to the upper edge of the fireplace.

    Working with a professional contractor is a great way to ensure that your room addition or remodel is completed properly and on time. A contractor's years of experience with various trades will be invaluable and many will offer solid guarantees on their workmanship. When it comes to the intricacies of the fireplace installation, we strongly encourage you to reach out to the professionals at to coordinate the purchase of the appliance. Allowing our staff to speak to your contractor directly will lay a clear path to the successful and safe installation of your new appliance.

    About the Author

    Collin Champagne

    Approaching his 10-year work anniversary, Collin is one of our National Fireplace Institute (NFI) certified technicians and content manager for the eFireplacestore, eCanopy, and EliteDeals brands. He is a Master Hearth Professional, which means he is certified in all three hearth appliance fields—wood, gas and pellet.

    When not at work, he spends time with his wife, Lindsey, and his sons, Samuel and Eli, on their ranch enjoying their many animals. Completing projects around the ranch and spending quality time with his family are among his greatest joys. 

    Questions About This Article

    All customer questions are answered by our NFI Certified Specialists free of charge!
    11 Questions & 11 Answers
    Doug M.
    from Broken Arrow, OK asked:
    December 31, 2022
    I have a gas log fireplace, when lit on the lowest setting the heat from the fireplace melts the paint on my mantle.  How can I fix this? 
    1 Answer
    Submitted by: Kelsey C. on January 2, 2023

    Tom H.
    from Cypress, TX asked:
    February 3, 2022
    What is the cost of adding a 2nd gas valve in the FP box?
    1 Answer
    We do not have any log sets or fireplace inserts that allow a second gas valve in the firebox.
    Submitted by: Tyler M. on February 3, 2022

    from Columbus, OH asked:
    December 14, 2021
    I have a small gap between the metal fireplace unit and the cement board I put up. I feel a draft thru this gap. Can I caulk with a high heat sealer before installing tile?
    1 Answer
    Yes, you can use a high-heat sealant there and adhere any noncombustible material to fill the gap.  This assumes that the manufacturer of the fireplace does not require that gap to remain open.
    Submitted by: Tyler M. - NFI Master Hearth Professional on December 14, 2021

    Brian M
    December 13, 2021
    Do I put insulation in my new wall around the fireplace and the gap between wall and gas fireplace?
    1 Answer
    Insulation is certainly a good idea in the wall surrounding the fireplace, but there is usually a requirement for an air gap between the fireplace and certain areas around the back and sides of the fireplace, and also possibly the space above the fireplace.  The amount of space required varies from model to model. 
    Submitted by: Tyler M. - NFI Master Hearth Professional on December 13, 2021

    from Ponoka, AB asked:
    April 10, 2021
    We are converting our wood-burning fireplace with an electric insert. What type of insulation should we use to close off the chimney?
    1 Answer
    Fiberglass insulation will suffice for this application.
    Submitted by: Aaron D. on April 12, 2021

    from Michigan City, IN asked:
    September 8, 2020
    When replacing a gas fireplace with a smaller fireplace, can I put drywall on the framing or what should I to use? 
    1 Answer
    Every fireplace will require different "clearance to combustible materials", I would follow the instructions for combustible facing requirements found in the installation manual of the fireplace that you choose.
    Submitted by: Aaron D. on September 9, 2020

    Betty K.
    from Kill Devil Hills, NC asked:
    April 3, 2020
    Do I need to put the cement board on the interior wall? The fireplace is installed in a bump-out on the side of the house.
    1 Answer
    Cement board is not used in all applications, so we would need to have more specific information to answer this question accurately. 
    Submitted by: Will M. on April 3, 2020

    from Edwardsville, IL asked:
    March 24, 2020
    We have a wood-burning fireplace insert that is so cold in the winter. I don't think there is any insulation behind it. Are you suppose to put insulation on the outside walls?
    1 Answer
    You are most certainly supposed to insulate the three outer walls of any exterior chase to prevent the issue that you are now having.
    Submitted by: Will M. on March 25, 2020

    Dan O.
    from Boston, MA asked:
    November 22, 2019
    I have a gas fireplace and there was a bump-out built to accommodate the system. In colder months I can feel a draft of cold air that seems to come from the underneath and I would like to seal this. Do I need to allow for a certain amount of an air gap around the system?   
    1 Answer
    Your fireplace model will have a specific clearance measurement that requires an air space of a certain amount - this amount will be specified in your installation manual.  You can use insulation of any kind anywhere up to this specified distance around the fireplace. 
    Submitted by: Tyler M. - NFI Master Hearth Professional on November 22, 2019

    Rebecca C
    from Cincinnati, OH asked:
    November 12, 2019
    On most gas logs, should the electrical hook up be on the right or the left?
    1 Answer
    Most gas log sets will have a connection on the right side. 
    Submitted by: Will M. on November 12, 2019

    from Connecticut asked:
    November 5, 2019

    I would like to place tile around my contemporary fireplace that I have set into the wall, but it has a service panel underneath. Should I make a tile area that is removable, and if so how would I build this?

    1 Answer
    You are correct that the panel should always remain accessible for service and maintenance. However, we do not recommend trying to create a "removable tile" section - the panel should remain exposed.
    Submitted by: Tyler M. - NFI Master Hearth Professional on November 5, 2019

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