The Right Way to Thermally Insulate a Fireplace

thermally insulate fireplace

Of all the things I could have chosen to write about, never would I have guessed I would write on something so ironic. Fight fire with fire, eh? However, before you fall into the same trap I did, remember that many crazy things happen in life. And thermally insulating a fireplace, once you think of it in detail, makes sense.

Not so long ago I wrote an article on thermally insulating an old house. Just like a fireplace, the interior of the house presents one or more heat sources. And. ultimately, much of the fuel used to heat the interior is wasted if the house doesn’t have proper insulation. The same principle applies to the fireplaces, more so if they are ”the” heat source of a room. So into the fray, we delve once again, today’s topic: how to thermally insulate a fireplace.

Types of fireplaces

Fireplaces are something whose spirit and atmosphere are incredibly hard, by any means, to replicate. They exude a kind of feel that nothing can beat on a cold, rainy, or snowy day. Although, there is a recurring trend nowadays. Many old houses have had their fireplaces removed by their owners in order to switch to a more modern lifestyle. However, many have found out afterward that it simply isn’t the same without them, so they go to reinstall them.

The thing is that times have changed and, more diverse types of fireplaces have emerged on the market. This diversity ranges from construction materials to the types of fuel used for burning. But, ultimately, the results are always the same: a cozy, burning flame and hopefully, not the house.

Wood Burning Fireplaces

  • Traditional open fireplaces
  • Zero-clearance/enclosed fireplaces
  • Fireplace inserts
  • Wood burning stoves

Gas Burning Fireplaces

  • Direct-vented built-in fireplaces
  • Ventless built-in fireplaces

Ethanol Burning Fireplaces

  • Fireplace conversion
  • Wall-mounted fireplaces
  • Tabletop fireplaces

Electric Fireplaces

  • Mantel electric fireplaces
  • Electric fireplace TV stands & entertainment centers

About fireplaces and why they require insulation

The insulation of a fireplace is critical for the safety and comfort of your home, but there are specific ways to do so even if it means not making the prettiest bonfire around. And hear me out. You would think that insulating the inside of the wall around the chimney vent is the way to do it. Remember the bonfire? This is how you get bonfires. These materials, due to being mostly dry, are also incredibly flammable. Thus, they should never come into direct contact with the vent pipe.

Most of the types of fireplaces mentioned above are modern in nature; thus, they were designed with thermal insulation in mind. This means that most of them already come with closable panels that act as protection from the outside cold when unused. What I will be talking about today will be the classic masonry type and the zero clearance type due to their similarities. The reason I will talk only about the two is that most the other types are either similar or come to win incorporated insulation.

Why is insulation so important?

Fireplaces, despite being lovely as they are, are incredibly inefficient. Fire results in heat and heat mean energy, and you and I both know that energy (in this case heat) isn’t prone to stay in place.

When burning, warmth, heated air, gasses, and other pollutants exit the chimney into the atmosphere. Despite heating the inside of the house, once it has cooled off, it will automatically start to draw out the heated air. This gradually will cool off the house overnight, making it colder than in the beginning.

The problem is that you cannot simply ”resolve” this issue by closing the damper, especially if there are embers still burning. This will place you at risk of suffocating with carbon monoxide. On the other hand, keeping it open will allow more warmth to leave the chimney. Doomed if you do, doomed if you don’t. But, don’t worry because there is a solution for insulating your fireplace.

How to insulate

1.    Classic masonry chimney

Fireplaces, due to being integrated into the structural design of the house, are pretty impossible to remove; that is without causing crippling damage to structural integrity. However, there are ways around this. There are products on the market specifically designed to insulate those old fireplaces properly without you having to remove them.

Take note that for the classic type, insulation actually means: ”how to insulate when not using it”?

Ways to do it:

  • Purchase a fireplace sealer. There are three types out there:
    • Balloon-shaped sealer
    • Fireplace plug
    • Decorative cover

Balloon-shaped sealer

The balloon-shaped sealer is a balloon-shaped, inflatable seal that comes in any size required by your household chimney. It acts as a giant vacuum that sucks all the air out of your home. Remember what I told you earlier about energy and heat loss?

Now, these sealers reverse the process entirely. They suck out the cold air while simultaneously blocking the chimney from allowing warm air to escape. This also means that no cold air will enter. Furthermore, it will stop anything from the outside from entering uninvited like debris, Santa, and dead squirrels.

For its best use, make sure to install it either above the damper or at the bottom of the smoke shelf.

Fireplace plug

A fireplace plug is similar to the balloon sealer in function and design, despite being rectangular rather than round. More precisely, it is an inflatable urethane plug that is easy to install, preferably under the damper level. It works with most fireplaces and can be installed in less than 5 minutes.

It works by having 5 little areas that can be cut to provide an opening for the damper handle. Once it is inflated, it will seal itself around the damper handle, thus sealing the opening.

Decorative cover

A decorative cover is less a commercial commodity and more a personal matter of customization. Namely, you can either buy a metal panel fitted somehow (screws, magnets, etc.) to the metal screen of the fireplace, or you work with an improvised similar solution. Avoid rubber and other materials that can create deadly circumstances from heat and gasses. Metal should be your go-to genre of insulation (get it?).

2.    Zero clearance fireplace

Due to being pre-manufactured, more efficient, and designed much better than their classic counterpart, they are easier to install/take apart. This is because their building materials eliminate the need for a buffer zone, allowing it to fit much better in tighter spaces. Regardless, they will need to be properly insulated for them to function at maximum capacity. This is how you do it:

Materials and tools required

  • High-temperature caulk
  • Caulk gun
  • Silicone caulk
  • Spray foam
  • Batt insulation
  • House wrap
  • Construction stapler
  • Construction staplers
  • Screws (2-inch ones)
  • Screw gun
  • Plywood
  • Circular saw
  • Stapler

To achieve proper insulation, you will need to follow 4 simple steps:

Step 1

First, you have to take the precise measurements of the chase and recess of the fireplace ventilation shaft. This will tell you how much plywood you need to cut in order to fill the outside space of the chimney case. After, screw it, preferably with 2-inch screws (optimal length), while making sure that each piece fits tightly with each other.

Then, you have to take out the caulk (the silicone variant) and apply it vertically on the seams. Follow by installing the batt insulation to the underside of the chase with a stapler. From your remaining plywood, cut out a section able to fit under the chase and attach it with some screws. Finish up by applying caulk to the seams around the bottom of the chase area.

Step 2

Second, you have to address the issue regarding the outside of the fireplace chase. To do that, you have to take a continuous piece of house wrap and wrap it (duh) outside of the fire chase. After wrapping, make sure to secure it with some construction level staples. Make sure that every corner and inch has been sufficiently covered, including the underside of the chase’s belly. Once again, follow up by finishing off the joints and the sidings with caulk.

This process is necessary for you to be able to install any exterior sidings of your choice. Because let us be fair, looks and function are separate, but boy do ugly fireplaces not function the same.

Step 3

Third, it is now time to take out the batt insulation and attach it between the studs inside of the fireplace. It is advisable that you do this before the drywall and the fireplace units are installed. Install the drywall and, if necessary, this is when you should install the gas and electric facilities, but do not install the fireplace yet.

Step 4

Finally, caulk the remaining seams in the drywall, as well as the places it will connect with the floor and ceiling. For good measure, make sure to foam-spray the gas and electric pipes/lines to protect them. Finish up by applying the high-temperature caulk to the wall thimbles. And this should do it.

In conclusion

Ultimately, nobody can deny the importance of proper chimney insulation. Not only will it save you from a steep expenditure on fuel and heating, but it also will probably save your life. Remember that if left unchecked, fires present great risks to your personal safety and your belongings. So make sure to insulate your chimney today because you must always keep in mind that ‘Winter Is Coming’.

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