How To Insulate a Gas Fireplace Chase? [Step By Step Process]

How to insulate a gas fireplace chase

Constructing a gas fireplace involves a number of technical and rigorous processes. For a part of the house intended to accommodate fire, it is important to make sure all safety measures are put in place.

One of the major components of a fireplace is the chase. A fireplace chase is a square or rectangular, narrow space that runs from the fireplace to the chimney on the roof.

When you look at the chimney at the top of your roof, you’ll find a square or rectangular wooden or concrete opening where the chimney pipe runs through- that is the chase. More often than not, insulation is done to keep things in check.

A fireplace chase does many things, from keeping your home warmer and reducing the risk of fire outbreaks, to properly housing the chimney pipe.

Most typical chases are built with wood, while some are constructed with concrete materials. Whatever the case insulating a gas fireplace chase is one-way homeowners try to prevent fire accidents or things like water coming in.

Whether it’s a reversed interior fireplace chase or an exterior chase, the question remains whether it should be insulated. If yes, how is a gas fireplace chase insulated?

Should Gas Fireplace Chase Be Insulated?

From experience, we realize that insulation is not exactly used in all fireplaces. The fire safety rating of a fireplace is often determined by the type of insulated metal flue pipe running through the chase.

Where this pipe is not properly insulated, extra chase insulation becomes necessary. A gas fireplace should be insulated to support other safety components like fire blocking, which can be done using OSB or ¾” thick plywood.

Another important reason why you should insulate your gas fireplace chase is if you live in a very cold region. In such cases, your chase may just act as a ventilation mechanism, allowing warm air to escape from within your home and letting in cold air.

By insulating the chase, you’ll be able to keep the chimney warm, reduce the buildup of creosote and even increase the draft. Just like the attic area, it becomes important to insulate the ceiling area of the chase to keep the warmth in and the cold out.

How To Insulate a Gas Fireplace Chase?

Before you set out to insulate your gas fireplace chase, you must be sure to consult relevant instructions.

  • Firstly, ensure you’re complying with installation instructions put in place by the fireplace manufacturer.
  • You must also comply with installation instructions that the metal chimney manufacturer provided.
  • Be sure to ascertain if insulation contact is allowed or if air space or clearance should be maintained.

Generally, there may be quite a number of materials that most people use, including cellulose, straw, fiberglass, polyurethane, and polystyrene.

However, we’ll recommend mineral wool or batt because it is fire resistant. While you should strive to keep them in place and provide clearance from the chimney pipe, there won’t be the risk of fire in case they fall on the pipe.

The outside of the chase can be drywalled and insulated the same as the rest of the house. This should be enough to keep it warm. The inside is where the issue often becomes more serious.

Find below a simple process to insulate your gas fireplace chase. Let’s begin with the tools for the job.

Required Material

To properly insulate your fireplace chase, you’ll need the following;

  • Plywood: If not already done, plywood will be needed to fit the underside and outside of the chimney chase. This will also provide brackets for fitting the mineral wool.
  • Insulation Knife: Just so you don’t damage your kitchen knives, an insulation knife will come in handy. The blade is serated for easy and smooth cutting through insulation materials like mineral wool. You can try out the Grip-Rite Stone Wool Insulation Knife.
  • Screws and Drivers: If you’re going to add some plywood, you’ll need screws and screwdriver to faster them properly and keep them in place.
  • Spray Foam: Can be used for sealing, where necessary.

Step by Step Process

  • Get the measurement of the outside and fit it with plywood. Use 2-inch screws to screw them to the chase, ensuring each piece is tightly butted to the next.
  • The next step is to caulk the vertical seams using silicon caulk.
  • Install the wool insulation to the inside of the chase using a stapler to hold it in place. You can fit the underside with a plywood using screws, then caulk the seams at the bottom of the chase.
  • Check between the fireplace studs for room to attach mineral wool insulation, with paper side facing the chase. Ensure the electrical and gas lines are fully installed before you continue.
  • Caulk all seams, including in areas where the chase meets the ceiling and floor.
  • Seal electrical and gas lines running through the chase using a spray foam.
  • If there are any wall thimbles, use high-temperature caulk.
  • To insulate the top of the chase in order to prevent leaks, you’ll need to extend the mineral wool batt insulation all the way up to the chimney metal cap that covers the chase. Ensure the insulation is touching the cap. You can use the spray foam to seal whatever unwanted opening may be left.


  • Be sure to leave a 2-inch clearance at least for proper venting to take place.
  • Push the insulation towards the inside wall of the chase to avoid contact with chimney pipe, as this can lead to to fire if heating continues for long.
  • Ensure you use a fireproof insulation material to line the chase to prevent accidents.
  • Also ensure the metal cap in the chimney is properly covering the chase to prevent water and other elements going in.
  • Identify the thermal barrier in your home and ensure the air barrier is adjacent the thermal barrier.

Tips To Protect Gas Fireplace Chase Insulation Longer

While it is almost impossible to prevent draft, chase insulation can help reduce the volume and keep your heat longer, while saving energy.

But, it is one thing to install chase insulation and yet another to ensure it lasts long. Here are simple tips to protect gas fireplace chase insulation longer.

  • Use durable insulation material such as mineral wool batts. This material cannot be destroyed by fire and is extremely weatherproof.
  • You need to also seal all leaks. Where you find cracks on the roof by the chase, it is important to seal it properly to prevent water going in and destroying the wall lining.
  • Only use high-temperature caulk that can withstand the heat in the chase.
  • Ensure insulation is fitted properly to wall and plywood in the chase to prevent falling off and touching the chimney pipe.
  • Check regularly to spot problems quickly and attend to them immediately. Regular checks can help to avert problems before they occur.

Final Words:

You’ll find that you may not need chase insulation if your chimney pipe is properly insulated and your fire blockers are in a good place.

Also, if you live in a relatively hotter region and your chimney cap is large enough to Pro good covering, you probably do not require chase insulation. But if you do and you decide to run it from roof to attic, it can be a pretty technical process.

You can simply call the experts and save yourself the trouble. But if you’re big on DIY, then this guide should prove very helpful to help you insulate your gas fireplace chase and prevent draft and keep the heat in.

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