Are Vent Free Fireplaces Dangerous? 


Vent-free heating appliances are one of the most interesting pieces of hearth inventions. 

Installing them doesn’t require venting to pass through a wall or through your roof. It’s neat because even without a venting option, ventless fireplaces still achieve near 100% combustion to relieve the burden of venting. 

But are they safe? 

This post will look into that. We’ll provide scientific background to help you separate the facts from fiction and help you choose if it’s the best option for you.

Table of Contents


Common Complaints


Air Quality


Property Damage


Risk Causes from Vent Free Appliances


Vent Free Hearth Appliances


Proper Installation

Common Complaints

We’ve seen a spike in popularity in ventless appliances in the last couple years. And people in the industry longer than us tell us that it’s been that way for about 20 years now. 

With more users come more complaints. Some complained of soot, while others complained of condensation and mold. 

Some complained about bad smells

People began to have serious concerns about their breathing. And it’s no wonder when you find reports of burning eyes, itchy throats, and sinus problems. 

We’ve even seen reports of headaches, lethargy, dizziness, and disorientation. 

Most of the complaints about vent-free hearth appliances come down to concerns about indoor air quality and property damage. 

You should be concerned about both.

Air Quality

Indoor air quality is all about what makes it into our bodies through our lungs. 99% of what we breath in is oxygen (21%) and nitrogen (78%). The rest is a combination of other gases and particles. 

Luckily, most are harmless. 

But there are many that can cause a lot of problems. These are particles and Gases. 


Solids and most liquids that float around the air are collectively just called particles. Some occur naturally. Others are from manufacturing or fabrication processes.

Some are released when things are burned incompletely.

Wherever they come from, particles are concerning because they can become lodged in our lungs.

Our lungs have natural defense mechanisms in place to guard against normal amounts of particles.

But when the mechanisms are overwhelmed, the results can range from irritation to damage.

Some kinds of particles, such as creosote, are even known to be carcinogenic, which means that these particles contribute to the formation of cancer.

Particles are classified by their sizes.

Coarse Particles

Coarse particles are ten times smaller than fine grains of beach sand, or about five times smaller than the diameter of human hair.

These are the largest airborne particles.

They include dust, pollen, and mold spores. I have cat’s and the cat dander is a form of coarse particle.

Fine Particles

Fine particles can be between 4-10 times smaller than coarse particles. These are formed from gases or combustion and are one of the more concerning forms of air pollution.

High enough concentrations of fine particles have actually shown to decrease lung capacity.

Ultrafine Particles

Ultrafine particles can be up to 25 times smaller than fine particles. This means they’re smaller than the little filter hairs on the cells of your lungs!

These are the newest category of particles. And scientists are researching if they’re being absorbed right into your cells and what happens if they do.


You know what a gas is. 

Gases are free molecules that remain separate from each other without condensing into a liquid or solid. 

Just like with particles, gases become part of the air that we breathe. But while some gases are irritants, others actually make it into our bloodstream and affect how our bodies function. 

Here are a few that occur with the vent free appliances.

Nitric Oxides

Nitric oxides are naturally occurring gases. They’re produced when lightning strikes or even when something burns in normal air.

They aren’t very common in normal air.

But in large quantities it can burn your lungs and eyes.

Carbon Monoxide

Carbon monoxide comes from incomplete combustion of fuel gasses. Carbon monoxide can cause headaches, dizziness, nausea, and even death.

It prevents your blood from carrying oxygen.

Carbon Dioxide

Carbon dioxide is what comes out of your lungs when you breathe out. You’ll get it from complete combustion of fuel gas.

It’s always present in the air around you.

At normal concentrations, it’s relatively harmless. But if you have too much of it, you’ll feel sleepy and dull.


When we breathe, we’re pulling in oxygen to our lungs. The concern is when you don’t get enough oxygen.

Combustion consumes oxygen in the air. This could cause the air around you to not have enough oxygen making it hard to breathe.

Without oxygen you could become confused or lose your coordination. And eventually you could suffocate.

Water Vapor

The humidity in the air affects how comfortable it is to breathe. It can also affect how dry or muggy we feel.

Water vapor created in the combustion of fuel gasses affects both.

Also, too much water vapor can promote nasty mold growth.

Property Damage

When our health isn’t in jeopardy, you’ll need to consider the condition of your home. You don’t want a home in disrepair.

Remedying a damaged home is tiresome, timely, and expensive.

The two biggest property damage concerns are soot deposits and mold damage.

Soot Discoloration

Soot can badly stain areas around a fireplace, like your mantel and ceiling.

But it can also get onto your upholstery, clothes, and sometimes in your lungs. Since it floats around in the air, it usually takes a few days to settle down.

Mold Damage

Not only can mold accumulate on surfaces you can see, but it can also grow in spots you can’t, like the inside of your walls.

When the damage is too bad, you’ll need to rip out and replace surfaces like drywall instead of just cleaning them out.

Risk Causes from Vent Free Appliances

When the vent free appliance is just sitting there turned off, it’s likely only a tripping hazard.

Any potential risks you’ll have won’t show up until we fire it up. In other words, what happens when we burn things or heat them up indoors?

They either combust or volatize.


Combustion is the process where oxygen combines with a substance so that it releases heat energy.

Complete combustion adds all the oxygen to a burned substance that it can hold.

Complete combustion of natural gas or propane only produces carbon dioxide, nitrogen dioxide, and water vapor.

But incomplete combustion is where things haven’t burned all the way through.

Oxygen couldn’t attach as strongly to the burning substances. So this will create some of the nasty chemicals that we don’t want in our home. Such as carbon monoxide and nitrogen oxide.


It’s even possible for other substances we wouldn’t normally think of to produce air pollutants.

When dust flies into your fire, it will create a source of particle pollution. That smell you smell when you turn on the heater for the first time is dust burning.

Vent Free Hearth Appliances

Vent free appliances rely on burning fuel gasses nearly completely. But even complete combustion uses up oxygen and produces water vapor and carbon dioxide.

And we need to account for what comes from the tiny portion that comes from incomplete combustion that happens when something burns in the atmosphere.

When an appliance company is producing vent-free fireplaces, they check for any irritants the appliance produces. It turns out, you can’t avoid all pollutants. But you can certainly minimize them.


Our bodies can deal with trace amounts of impurities.

But there’s a level that we can’t deal with in a healthy manner.

Even if pollutants always exist, we’re lucky that ventilation keeps them in check. In the process of fresh air coming in and diluting the concentration of pollutants and carrying them away.

You might be thinking: “but this is about vent-free appliances.”

Well, ventilation happens indoors too.

Most buildings aren’t perfectly airtight. Outside air comes in through tiny holes in windows or the roof. And pushes the inside air out.

Proper Installation

All indoor vent free hearth appliances need to be listed to the American National Standards Institute standard Z12.11.2. This certifies that they’ve been tested to perform within accepted IAQ limits.

Plus, you should make sure that you are hiring a CSIA certified chimney sweep to install the appliance.

This way you know that the installation is performed to the National Fire Protection Association’s Gas Codes (NFPA 54) and the International Fuel Gas Codes.


Hire a Skilled Technician

The best thing that you can do for your fireplace, even with ventless options, is to hire a professionally trained chimney technician.

You can easily reach out to your local chimney company and have a done-for-you solution in no time!

But navigating through all of the chimney companies in your city can be a chore all on its own. And it makes sense, too.

Hiring anyone to come into your home to install something like your fireplace shouldn’t be a task you take lightly. So I created a list that you can use to make sure you make the right decision when you need someone to help you in your home.

Questions to Ask

When you’re hiring a chimney company, you should always ask the following questions before allowing them to come into your home:

  1. Can the company provide references? 
  2. Does the company carry a valid business liability insurance policy? 
  3. Does the company ensure that a certified chimney technician will be on the job? 

If they guarantee all three of those, then you are in a good spot. The technicians don’t necessarily need to be certified by the CSIA, but I do recommend putting in a bit more due diligence before accepting a certification that’s not by the CSIA. 

This is because certifications are a tricky thing, especially in an unlicensed industry like ours. Any company can craft a list of job-related questions and sell them as an exam and certify those who pass.


I recommend you take a few extra minutes in your research before making your hiring decision to learn more about the certification the company has. Here are a few tips to make sure the certification is reputable: 

  • Is the word “certified” just part of the business name or is it an earned designation? 
  • Is the certifying body a for-profit business or non-profit? 
  • Does the certification need to be maintained and renewed through continuing education as the industry evolves, or is it well enough to be certified through a one-time exam? 
  • Is the certifying body well-established or are they relatively new to the scene? New doesn’t mean “bad” but you should make sure the requirements for certification are more or at least equally stringent as those of more established certifications
  • Is the mission statement of the certifying body focused on educating and protecting homeowners or is it more focused on making it easier to earn a certification? 
  • Does holding the certification require following a code of ethics? 

If you can answer all of these questions, then I think it will be safe to allow the company in your home to work on your chimney. 

It doesn’t matter if you are in Roanoke, Lynchburg, Blacksburg, or some other city anywhere in the USA — if you have any questions about the safety of hiring a chimney company, please don’t hesitate to email me at or call me at 540-225-2626. I’m happy to help!

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