How to Have an Efficient Fireplace in an Air Tight Home

Modern Homes, Poor Draft

Modern homes are built so that there are not as many pinholes letting air escape. 

Open fireplaces have always been messy, smoky, and inefficient. But these issues aren’t as noticeable when there’s enough draft to pull the exhaust up and out of the fireplace. 

In addition to having poor draft, many modern fireplaces are actually just used as a design element. There are specific designs that make fireplaces work properly. And without proper training, builders aren’t able to achieve this. 

And if they do have the training, they need to stay up to date with modern techniques. Many masons and other contractors who build fireplaces use outdated design traditions that will cause more trouble in drafting. 

Building scientists understand why traditional fireplace designs work poorly. And masons, manufacturers, and hearth installers have created new products and techniques that eliminate any of these problems.

Why Your Fireplace Might Fail

We’ve seen a lot of newly built and poorly working fireplaces with some outdated techniques that have proven to be inefficient.

For example, when it comes to open fireplaces, it’s common for contractors to push the smoke shelf, smoke chamber, and the need for wide, but shallow throat dampers.

It turns out that all three of these features will work against your fireplace’s performance.

The smoke shelf and shallow throat damper will act as obstacles to straight exhaust flow.

The smoke chamber will also reduce the draft strength by slowing and cooling the fireplace exhaust. By the way, slowing and cooling the fireplace exhaust is a sure way to have excessive creosote build up.

The performance of your fireplaces can be immediately improved if you just remove the throat damper and smoke shelf. Then install a top damper that has a chain coming down so you can operate it in your home.

We’ve seen great improvements since the results are a smooth, straight path for the exhaust and less smoking when a fire burns.

Position & Location of Fireplace

The biggest source of trouble with drafting is the location of the fireplace.

You can see older houses built more than 50 years ago with fireplaces right in the middle of the house.

They’ve moved over to exterior walls or even into chases that are completely outside the house. This causes the cold hearth syndrome, which is a major source of most fireplace failures.

When you have a cold hearth, you can almost always predict a blast of cold air when the fireplace doors are opened to build a fire.

Smoke will fill the room when you try to light the kindling. This is very common.

The starting point for this is the initial decision for fireplace location. Especially with an exterior fireplace.

The cold air sucks the warmth from the fireplace and chimney structure. This causes the temperature of the air in the flue to drop.

And when flue temperature is lower than the house temperature, air will flow down the chimney and onto the hearth.

This is called “cold backdraft.” It doesn’t happen because cold air is heavy and falls down the chimney. It’s because your house basically sucks the cold air in.

Hot exhaust in a chimney produces a draft, so the warm air in your house produces a pressure difference called stack effect when it’s cold outside.

Basically, warm air is buoyant compared to the cold air, making the warm air float to the top. There will be a slight low pressure zone at the bottom towards the hearth and higher pressure at the top of your chimney.

You’ll probably experience a negative pressure from the stack effect when it’s cold outside.

As soon as the air in your chimney gets below room temperature, your house becomes a better chimney than your chimney! And that’s how a cold backdraft gets started.

Stack Effect

You know what stack effect is. At its core, it’s when warm air rises and cold air sinks.

When your chimney doesn’t extend higher than the other parts of your house, the chimney can’t compete with the taller living space. The house will create more stack effect than the chimney makes in draft when no fire burns. 

The higher pressure zone at the top of the house pushes air out through tiny holes in your windows, attic access hatches, or even ceiling penetrations. 

The negative pressure low in the house drawas cold air from outside in through low level leaks, such as your fireplace. 

In these cases, your chimney is said to have a taller effective stack than the chimney. Air will flow down through the chimney, then loop through the house to exit through the attic or top level wall leaks. 

That’s why we always build chimneys to be taller than the rest of the house. It’s always easier when the chimney is closer to the center of the house, too. 

Whatever the case may be, the cold hearth syndrome mentioned before, has two ingredients: 

1. A misplaced chimney
2. A fireplace located low in the house

If we move the chimney towards the center of the house, your problems will disappear. 

But moving a fireplace isn’t practical after it’s built. But there’s some ways that you can help minimize cold hearth syndrome simply by keeping your chimney from falling below room temperature. 

One trick is to build a sealed, insulated chase using the same materials and building techniques as your house, so that you’re effectively “tricking” the chimney to thinking it’s inside. 

The chase can be vented to the inside so that warm house air circulating in it will keep it at about house temperature.

Makeup Air

We can’t put all the blame on improper design and location. Tighter house construction and powerful exhaust fans need to take some heat, too.

By installing vapor barriers and using doors and windows that have sealing gaskets, builders have been able to reduce air leakage by more than 75% in the last 20 years!

Homes are now equipped with high-volume exhaust fans, like the one in your kitchen, that moves air out of your house at a pretty high rate.

Since tightly sealed house walls won’t allow this much air back in through leakage, you’ll have a negative pressure in your house, causing your chimney to backdraft.

A simple fix for smoky fireplaces has been to install a makeup air system that is interlocked to the range exhaust switch. This will force air into the house to compensate for the kitchen range exhaust flow.

This will take care of the depressurization and solve the smoky fireplace problem.

Controlled Combustion

Your fireplace’s design plays a big role in the efficiency and satisfaction that it can provide.

The internal features that produce efficient, smokeless combustion tend to be the same as those that produce reliable chimney venting and easy operations.

The more air a fireplace demands for normal operation, the fussier and spillage-susceptible it will be.

Open fireplaces are the worst because they consume lots of air, which cools the system. And reduces draft.

If you need a traditional fireplace because it fits the look you’re going for, just make sure to add some doors on it to help with this. Blocking the air to the firebox will cause the average exhaust temperature to go way up.

Higher temperatures mean a more stable draft.

If you don’t want glass doors or much heat, then you can opt for a gas hearth.

You can also get EPA-certified fireplaces. They meet the EPA’s rules for low smoke emissions and are actually more resistant to leaking smoke in the house.

Whatever you do, don’t sacrifice performance for low cost. You’ll get what you paid for, especially with your fireplace.

Some cheap units are made out of lighter, thinner materials, and are often connected to lightweight air cooled chimneys with flue diameters that are too small.

The cost savings could actually lead to more leakage and decreased efficiency.

Hire A Skilled Technician

The best thing that you can do for your fireplace, even during the building stage, is to hire a professionally trained chimney technician.

The technician will look at your chimney and ensure that the chimney is up to code and capable of drafting properly.

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 fix something like your chimney 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. 

Certifications

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.

But if you’re still unsure, 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 mitchell@patriotchimney.net or call me at 540-225-2626. I’m happy to help!