Converting or Closing Up a Fireplace in a Center City Rowhome
Many Center City rowhome owners want to switch a wood fireplace to gas, or safely close one they no longer use. Both touch the chimney, and both go wrong when the flue is ignored.
Why the fireplace question keeps coming up downtown
In a Center City rowhome, the original wood-burning fireplace is often more trouble than the owner wants. It needs a tall flue swept regularly, it draws cold air and loses heat up the chimney when it is not lit, and in a tightly finished modern interior the mess and the maintenance can outweigh the occasional fire. So owners reach one of two decisions. They want to convert the fireplace to gas, for the convenience of a flame at the flip of a switch with far less upkeep, or they want to close up a fireplace they never use and stop it from leaking air and inviting problems. Both are reasonable choices, and both run straight into the chimney, which is exactly where they tend to go wrong.
The mistake people make is treating the fireplace as a self-contained appliance and the chimney as a separate thing that does not need to be part of the decision. It is not separate. A gas conversion changes what the flue has to carry, and the exhaust from a gas appliance behaves very differently from wood smoke in an old masonry flue. Closing up a fireplace changes how the flue and the stack breathe, and done carelessly it can trap moisture in the chimney. Whichever direction you are going, the flue and the stack are part of the project, and the right way to start is by understanding what you actually have before you change it.
Switching a wood fireplace to gas
Converting a fireplace to gas is popular for good reasons, but the flue is the part that decides whether it is done safely. A gas appliance produces exhaust that is cooler and more acidic than a wood fire's, and in a large old masonry flue sized for wood smoke, those cooler gases condense on the way up, depositing moisture and acid that eat at the liner and the mortar over time. The flue that vented wood smoke fine for a century is often the wrong size and the wrong condition for gas exhaust, which is why a conversion frequently requires a correctly sized liner dropped into the existing flue to match the new appliance. Skip that step and you can end up with condensation damage and a draft that does not vent properly.
The starting point, then, is an inspection of the existing flue, by camera where access allows, to establish its condition and size before anything is converted. That tells you whether the flue can serve a gas appliance as it stands, whether it needs relining to the right size, and whether the existing masonry and crown are sound enough to carry the new arrangement. A conversion planned around the actual condition of the chimney is straightforward and safe. A conversion that assumes the old flue will simply work is the one that produces problems a season or two later, and untangling those after the fact costs far more than getting the flue right at the start.
Closing up a fireplace the right way
Closing up a fireplace you no longer use sounds like the simplest possible job, and done thoughtlessly it creates problems that outlast the convenience. The fireplace and its flue are part of how the chimney and, on a rowhome, the party-wall stack breathe and shed moisture, and simply sealing the firebox opening without thinking about the flue above it can trap moisture in the chimney, where it has nowhere to go and works on the masonry from the inside. An open flue at the top with a sealed firebox at the bottom is a recipe for a damp, deteriorating stack, and a fully sealed chimney with no provision for moisture is little better.
Doing it right means treating the whole chimney, not just the visible firebox. Typically that involves capping the flue at the top to keep rain and animals out, providing for the chimney to breathe and shed moisture so it does not rot from within, and closing the firebox in a way that can be reversed if a future owner wants the fireplace back, which on a historic home is worth preserving the option of. The details depend on the specific stack and whether it is shared, which is why this too starts with a look at what you have. A fireplace closed up properly stops costing you air and maintenance without creating a hidden moisture problem in the chimney, and that balance is the entire point of doing it carefully.
The decommissioned flue that was never closed up
There is a third situation that catches a lot of Center City rowhome owners, the fireplace that has already been abandoned by a previous owner but never properly dealt with. Somewhere along the way someone stopped using it, maybe blocked the firebox with a decorative cover or stuffed something up the flue to stop the draft, and the chimney has simply sat that way for years. From inside the room it looks settled and harmless, but a flue that was casually abandoned rather than properly decommissioned is often quietly taking on water at the top, holding trapped moisture in a half-blocked stack, or serving as a nesting site behind whatever was used to plug it. The previous owner's quick fix becomes the next owner's slow problem.
If you have inherited a fireplace like this, the sensible step is to find out what was actually done before deciding what to do next, because the right course depends entirely on the current state of the flue and the stack. An inspection establishes whether the chimney is taking on water, whether the flue is genuinely blocked or just covered at the firebox, and whether the masonry above the roofline is sound, and from there you can choose to properly close it up, restore it to use, or convert it to gas with open eyes. The point is that an abandoned chimney is not a neutral, do-nothing condition, it is a chimney that was left in an unfinished state, and on a historic rowhome that unfinished state usually keeps costing the owner until someone deals with it deliberately.
Whether you want to convert a Center City fireplace to gas or close one up for good, the chimney is part of the decision, and the way to get it right is to start with an inspection of the flue. We will tell you honestly what your stack needs to do either one safely. Call 215-618-4699.
Phone 215-618-4699 whenever you want it inspected, no pressure, no sales pitch.