Chimney Breast Vent 101

Chimneys are vital to any home with a fireplace. If you’re in the process of either retrofitting or closing off a fireplace, knowing how their ventilation works is vital to a good job. A chimney breast vent is very common (as they should be) in older homes and they serve multiple jobs. Their most important job, however, is to prevent moisture from making its way into your home. Damp can cause a number of problems that, if left unaddressed, can cause serious issues down the line.

Chimney breast vents are vital to ensuring your home is not damaged by moisture.

Let’s talk a bit more about them, yeah?

Chimney Breast Vent – Why?

First things first – why would you even use a chimney breast vent? If the chimney is still in use, it would stand to reason that the top of the chimney serves as proper ventilation, right? Well, not quite. Moisture has this pesky habit of finding its way everywhere. If left to just kinda find its own way, you’re running the risk of it going where you don’t want it.

This means that, as time went on, people made a habit of installing a place for that moisture to go. Nowadays, chimney vents are usually installed at the top and bottom of the chimney, to provide a good path for moisture to escape your home. Chimney ventilation is also common is homes that use solid fuel fires (wood fire), stoves, or gas heaters. It allows airflow to keep everything working as intended.

But if you’re in a home with a bricked up fireplace, it’s very likely that the vent was covered as well. This is because, from an insulation and heat-retention perspective, why wouldn’t you? It’s literally a vent to the outside – that doesn’t exactly bode well for keeping heat inside and moisture out. The real issue, however, is that without the ventilation, moisture will eventually make its way into the walls and/or ceiling of your home.

This has led to some homeowners choosing to install an insulated pipe that goes into the chimney. It theoretically allows ventilation while keeping the room as temperate as possible, though I cannot vouch for this.

What Can Go Wrong?

Beyond the obvious answer of moisture making its way into your home, you run the risk of soot bleeding! That’s because, believe it or not, soot is generally all over a fireplace. And you know what’s water-soluble? That’s right, soot.

So best case, you get a moisture spot in your drywall or plaster. Worst case, you get a wet spot that’s pitch black thanks to soot bleeding with the moisture. That’s why if you troll through the various online professional forums about chimney ventilation, you’ll see one point regurgitated over and over. It goes something like, “Even if the homeowner says they don’t want ventilation installed (maybe it’s ugly, maybe they just don’t want it), do it anyway. They’ll thank you later.

Further issues you may encounter spring up when the chimney is attached to multiple fireplaces. If you’re bricking up a single fireplace but want to keep the one in your living room (for example), you’ve got to be careful. Without a good deal of additional work to seal off the chimney meeting point, you could smoke out your other room! This is where things get really complicated.

Making a Choice

The complication lies in making a choice – do you brick up both fireplaces and make the sacrifice of not having a nice, cosy fire, or do you make a bunch of extra work, and leave one open? If you opt for the former, you’re left with a colder home until you can have central heating installed. And that’s got its own list of complications (but that’s another article for another day). The other option is to fully brick off a single part of the chimney and install ventilation.

Regardless of your choice, it’s vital that you have it done by a professional. Talk to them about what local regulations say, what their advice is, and how to best go about sealing off your old chimney. Chances are that no matter how much research is done, you’ll find that a vent or two are needed.

What If the Chimney is Sealed?

If your chimney is already sealed at the top, things change a bit. The top cover (cap) will minimalise the moisture buildup, but a vent is still needed. This can be achieved with an air brick. These are specialised pieces of masonry that are designed to cover this exact issue. Rather than opening up a sealed chimney to install a vent, you can have some of the masonry replaced with air brick.

For the uninformed, air brick is a hollowed or perforated brick with grated sides. It allows you to do two things:

  1. Keep the traditional masonry look in your home without an ugly metal vent
  2. And properly ventilate a sealed chimney.

Generally made with clay or cast iron, they’re good looking and will withstand the outside weather. More modern ones are made with a plastic composite that can be installed inside. This allows greater airflow and higher durability.

The one downside to air bricks is that they’ve got larger holes than a standard vent. This can allow pests to enter in if not meshed off – which is highly recommended, at least on the outside. Installing a little bit of metal mesh can prevent unwanted guests from finding their way into your home.

Final Thoughts

Chimney breast vents are vital to the health of your home. They provide proper airflow for fires to burn safely, but more importantly, they prevent moisture damage. Damp can make its way into just about every spot imaginable, meaning it will find a way to damage your home if not accounted for. Whether that means that you use a traditional metal vent, or an air brick, it’s needed.

And seriously – this is one of those jobs where I tell you that you really shouldn’t try to DIY. Sure, you can, but if you miss something important, you run the risk of future damage to your home. Or worse, you could accidentally smoke out your home – that’s not only dangerous but really just a drag in general.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.