The Benefits of an Outside Chimney

Here are some reasons that will prove to you that chimneys belong inside houses.  The facts demonstrate without question that  masonry chimneys built onto the sides of houses so their profile shows, or metal chimneys enclosed in framed chases, even though they might look alright, don’t work well at all.  In fact, I suggest that a chimney hanging off the side of a house like an afterthought is an abomination, functionally and aesthetically.

Why Chimneys belong inside houses. Fireplace-Chimney-Defects

Look around your subdivision and note where most chimneys are located. Outside chimneys are rampant. They are everywhere, hordes of them in tract developments, and ones and twos stuck on big custom houses. It’s not a class thing — the urban rich and the rural poor all seem to get outside chimneys these days.

A lot of people complain about their fireplaces being tempermental and hard to light without getting smoke in the room. Another complaint is when the fireplace is not being used, the doors and the hearth are cold. If your house have fireplace, you are aware of these complaints.

Choose the Right Location

One of the most important is: where to install a new wood stove in your home? Having space is just one of the considerations. However, the most important thing is that your stove is placed safely away from anything combustible, including flammable flooring, furniture, and walls. This precaution helps ensure that a stray spark can’t cause damage to your home. For example, you won’t want your stove to sit too close to furniture that could catch fire.

Back Drafting Chimney

Normally in a fireplace or wood stove an updraft is created that takes waste gases up and out the chimney. Those gasses are then dispersed into the outside air. Sometimes a draft may develop that moves in the opposite direction, this fills the house with smoke and poisonous gases – this is called a backdraft.

Causes of Backdrafting

There can be a number of reasons why smoke is backdrafting into your home. The main causes are:Home Inspection Required
1. Negative pressure (common in newer homes & basement installations)
2. Backdraft (common with outside chimneys, short chimneys or high-wind areas)
3. Blocked chimney
4. Burn technique / wet wood

The term backdraft describes the upward flow in a chimney that fully reverses and 100% of the combustion gases from the appliance (if it is firing) and air in the chimney flow into the building.  If the fireplace or stove is firing, it is a hot backdraft; if there is no fire on when the reversal occurs it is called a cold backdraft.  Combustion spillage, on the other hand, is when only some of the products of combustion are released into the building, such as when a loading door is opened quickly when a fire is smoldering.

Your House is a System

To minimize heat loss, energy-efficient home are sealed by a tight building envelope (which includes windows, doors, vapour barrier, roof etc). That’s a good thing. But this closed environment doesn’t allow moisture in the air to escape and that can cause air quality problems, mold and other concerns. An energy efficient home must be carefully built to minimize uncontrolled airflow, but the indoor environment must also be carefully balanced by employing advanced heating, ventilation and air conditioning design and technology.

When it’s cold outside, the warm air inside makes the house act sort of like a chimney. The warm air in the house wants to rise because it is less dense, more buoyant, than the cold air outside. So, when it is cold out the air pressure high in the house is positive, slightly higher than the atmospheric pressure outside. And the air pressure low in the house is negative, slightly lower than atmospheric pressure. This phenomenon is called stack effect. Somewhere between the high pressure high in the house and low pressure low in the house is a zone of neutral pressure which is called, rather cleverly, the neutral pressure plane.

Cold Hearth Syndrome

The cold hearth syndrome occurs with masonry fireplaces and chimneys that share an outside wall or project out beyond an outside wall. It also happens to a factory-built fireplace and its chimney that are installed in an external chase (right). In both cases, the air in the chimney is inadequately isolated from the outside cold and its average temperature falls below that of the house. Outside chimneys serving wood stoves and furnaces suffer the same failure.
External chases are usually insulated only at the back and sides of the fireplace, extending to ceiling level of the room in which the fireplace is located. It is also common for these chases to be fairly leaky. This combination of low insulation over much of its height, combined with the leakage of cold outside air into the chase, allows the average temperature of the air in the chimney to fall below that of the air in the house. If the appliance is also located below the neutral pressure plane, the cold hearth syndrome will occur.

Chimney Cleaning

Regularly cleaning your chimney is an important part of keeping your home safe for the winter months. Your home insurance company will most likely ask you how ofter you use your appliance, how often you have it cleaned and when was the last time it was cleaned. That’s because as you use your fireplace to burn wood for warmth (or just for seasonal atmosphere), a highly flammable carbon based, tar-like substance called creosote begins to build up on the inside of your chimney walls. Over time, this build up can ignite and burn at over 2000° Fahrenheit which can be extremely difficult to extinguish and quickly spread to other areas of your home. 

In fact, on average there are over 25,000 of these chimney fires every year that lead to over $125 million in property damage. (According to the Chimney Safety Institute of America

Book your WETT Certified inspection today.

Roger Frost

Barrie Home Inspector



Certified Building Code Official
Certified Master Inspector

WETT Certified Inspector

Phone 705-795-8255 

Email Roger


WETT Certified Inspections for Barrie, Alliston and Orillia