10 Common Reasons For Center Built Fireplaces to Leak

A fireplace can be the focal point of an entire room, bringing a cozy feel and warmth to the atmosphere of a design scheme. With a center-built fireplace, you can reap those benefits in more than one room, as the dual-sided hearth provides a semblance of division in an open floor plan. Center-built or see-through fireplaces are a popular choice among those seeking to purchase or build a new home, but aren't entirely problem-free in some cases. These are ten of the most common reasons for a center-built fireplace to leak, along with a few remedies to ensure that you get full enjoyment of your new home with no worries about pesky and even dangerous leaks.

1. Drawing Issues – Two-sided fireplaces are aesthetically pleasing and give you a double bang for your buck by providing a hearth and open-flame view in separate rooms, but they're inherently prone to drawing issues. Because they're facing a draft from both sides, they can leak copious amounts of smoke. Installing glass doors on both sides of your center-built fireplace can reduce smoke leakage, which contains dangerous carbon monoxide.
2. Short Chimneys – Ideally, a chimney will project at least three feet above the roof and two feet higher than anything within a ten foot radius of the structure. Older homes that feature a center-built fireplace are frequently designed with an insufficient height, causing dangerous smoke leakage into the rooms containing the two-sided fireplace.
3. Lack of a Chimney Cap – Smoke and soot aren't the only things that can leak into your home through the see-through fireplace. When your chimney has no cover or cap, it's easy for rain to flow straight into your home causing a rainwater leak. As an added bonus, a chimney cap will help to prevent birds and small animals from roosting in your chimney.
4. Improper Flue Sizing – Traditionally, the size of a fireplace flue is calculated by using a formula in which the cross-sectional area of the flue is at least one-tenth the size of the fireplace opening. In some cases, a dual-sided fireplace that leaks smoke back into your home can be repaired by adjusting the size of an ill-fitting flue.
5. Poor Flashing Maintenance – The flashing that's designed to seal off the edges of your roofing material where it meets the face of your chimney only prevents water leakage into your center-built fireplace if it's maintained properly. It's important to check the flashing on a regular basis to ensure that it's in good condition, and should be the first thing you look at if you're encountering water leakage into your home from the fireplace.
6. Non-Functional Dampers – Fireplace dampers can be a major source of cold air leakage into your home, even if they're closed. The fit and closure of a fireplace damper is almost never airtight, so you could be dealing with air leakage and drafts as a result of your damper, whether it's open or closed.
7. Cracked Crowns – The cement on top of your chimney is called the crown, which will keep rain and snow from falling straight into the large opening that is your chimney. When these crowns become cracked or shrink as a result of normal alteration in the cement, you may find that your center-built fireplace is also a source of drips and leaks during wet weather.
8. Loose Bricks or Mortar Joints – Loose, cracked and chipped mortar, damaged bricks or compromised joints is a very common cause of water and moisture leakage into the home via chimneys and fireplaces. In older homes with large fireplaces that play a prominent role in the home's design, these leaks can be significant.
9. Overhanging Trees – One of the most appealing amenities to potential home buyers is a proliferation of mature trees. When those trees are overhanging the chimney, however, they can cause leaks as rainwater and and moisture run off of the foliage and are funneled into the chimney.
10. Depressurization – Exhaust fans in your kitchen can cause smoke to leak into the room if the centrally-located fireplace is subjected to mechanical depressurization from those fans. If the negative pressure draws the exhaust from your fireplace back down the chimney, back-flow of smoke is a very real possibility. Before you worry about larger and potentially more costly problems with your two-sided fireplace, make sure that exhaust fans and ventilation fans in the center of your house aren't affecting the pressure around the hearth.

Center-built fireplaces can be prone to leakage, but are less likely to cause problems if they're properly installed and maintained. Before making an offer on a property that includes a see-through fireplace or including one in your new construction's design, be sure that you speak with an experienced, professional contractor that can help you avoid these issues.

Resources:
http://www.highschimney.com/articles/reasons-chimney-leaks/
http://www.doityourself.com/stry/5-common-problems-with-a-two-sided-fire...