Dryer Vent Through a Brick Wall — Complete Installation Guide
Drilling through brick for a dryer vent is a different job than drilling through wood-framed walls. The core bit size matters. The fire-stop requirement is non-negotiable. And the cap selection for masonry is a different short list than for vinyl siding. Here's exactly how to do it right.
Tools and Materials You'll Need
| Item | Specification | Notes |
|---|---|---|
| Rotary hammer drill | SDS-Plus or SDS-Max, 1,000+ watts | A regular drill will not work in brick. Rent if you don't own one — $40–60/day at most tool rental counters. |
| Diamond core bit or carbide hole saw | 4-5/8 inch (see sizing section below) | Diamond core bits are faster and cleaner. Carbide core bits work but generate more heat and may need water cooling. |
| Center punch and masonry bit | 1/4 inch or smaller | For the pilot hole to anchor the core bit guide. |
| Rigid galvanized steel duct | 4-inch diameter | Smooth-wall preferred; must extend through the full wall thickness. |
| Fire-stop sealant (intumescent) | UL-listed caulk or putty | Required at penetration. Non-fire-rated silicone caulk is NOT an acceptable substitute. |
| Termination cap | Masonry-compatible, no mesh | See cap selection section below. |
| Mortar or hydraulic cement | Quikrete or equivalent | For patching the annular gap if the core hole is oversized. |
| Painter's tape | Any width | For marking cut line on brick; helps reduce edge chipping on the face course. |
Core Bit Sizing: The Right Diameter
This is where most guides give wrong or incomplete information. The correct core bit size depends on both the duct diameter and how the duct will be finished at the wall face.
| Approach | Core Bit Size | Reasoning |
|---|---|---|
| Duct slides through; fire-stop caulk fills gap | 4-5/8 to 4-3/4 inch | Just enough clearance for the duct to pass through without binding; small gap is easily fire-stopped with caulk. This is the cleanest finish. |
| Duct with masonry penetration sleeve | Per sleeve manufacturer specs (typically 5 to 5-1/2 inch) | Some installers use a purpose-built masonry sleeve with an integral fire-stop collar; size the hole to fit the sleeve. |
| Loose fit / mortar fill | Up to 6 inch | Acceptable if the gap is filled with mortar and a fire-stop collar is installed. Less preferred — more work and harder to get right. |
The most practical approach for most installations: use a 4-5/8 inch diamond core bit. This leaves approximately 1/8 inch clearance around the 4-inch duct, which is easy to fire-stop with intumescent caulk and provides a clean, professional-looking finish at both the interior and exterior faces.
Step-by-Step: The Complete Installation
Plan the hole location
Mark the exterior wall location from outside using measurements taken from inside. The hole should be centered horizontally in a mortar joint where possible — cutting through a mortar joint rather than through brick face reduces the risk of cracking the brick and produces a cleaner cut. Confirm the wall location clears any electrical wiring, plumbing, or structural elements inside the wall. Use a stud finder on the interior side to confirm there are no hidden obstacles.
Apply tape to the brick face
Apply two layers of painter's tape around the planned cut area on the exterior face of the brick. This reduces edge chipping on the exposed face course — a purely cosmetic benefit but worth the two minutes it takes.
Drill the pilot hole
Using a small masonry bit (1/4 inch) in the rotary hammer, drill a pilot hole at the center of the planned penetration, going all the way through the wall. This lets you verify the interior exit location before committing to the full core cut. Step outside and confirm the pilot hole exits where you intended.
Core from the exterior inward
Set up the diamond core bit, using the pilot hole to center it. Cut from the exterior face toward the interior. Cutting from outside in produces a cleaner face at the most visible surface. Apply gentle, steady pressure — do not force the bit. For a 4-5/8 inch hole through 8–12 inches of double-wythe brick, expect 15–25 minutes of cutting time. Have a helper vacuum the dust or use wet coring to control dust and heat.
Clear the core plug
The masonry core plug often does not fall free cleanly. Use a cold chisel and hammer to break it out from inside, working carefully to avoid cracking the face brick. Wear eye protection — masonry fragments are sharp.
Insert and position the duct section
Insert a section of 4-inch rigid galvanized duct through the wall. The duct should extend slightly past the exterior brick face — typically 1/2 to 1 inch — to provide a surface for the cap to mount against. Confirm the duct is level or pitched very slightly toward the exterior (this prevents condensate from running back toward the dryer).
Apply fire-stop sealant
Apply UL-listed intumescent fire-stop caulk (e.g., 3M Fire Barrier 2000+ or equivalent) to fill the annular gap between the duct and the masonry core at both the interior and exterior faces. The sealant must fully fill the gap around the entire perimeter — partial filling is not compliant. Tool it smooth with a wet finger or caulking tool. This material expands when exposed to heat, sealing the penetration against fire spread through the wall assembly.
Install the termination cap
Mount the exterior cap. Most masonry-mount caps use masonry anchors (plastic expansion anchors and screws) rather than nails. For a clean installation, mark the cap mounting holes, drill with a masonry bit, insert anchors, and screw the cap flange directly to the brick face. Caulk around the cap flange perimeter with exterior-rated silicone to prevent water infiltration behind the cap.
Connect the interior duct run
Connect the interior duct section to the through-wall section using a slip coupler or dryer duct collar. Seal all joints with metallic foil tape (not standard duct tape, which fails at elevated temperatures). Do not use sheet metal screws inside the duct — they catch lint and create blockage points.
Test before closing up
Run the dryer for 15 minutes. Step outside and confirm the cap is opening, you can feel warm exhaust airflow, and there is no air leakage around the cap flange or through the fire-stop. If there are no leaks and the cap operates freely, the installation is complete.
Cap Selection for Masonry Walls
Most standard dryer vent caps have flanges designed for wood or vinyl siding — they rely on nailing through the flange or caulking to the flat siding face. On masonry, you need a cap with either:
- A wide flat flange that accepts masonry anchor screws, or
- A telescoping sleeve design that is secured inside the core hole itself (common in commercial applications)
For the cap type (gravity louver vs. spring-loaded vs. pest-resistant), the same rules apply as for any dryer vent cap — no mesh, backdraft damper required. See the full Bird Guard vs. Louvered Cap Guide. For masonry walls in particular, a spring-loaded damper cap is a good choice because the more positive seal helps keep insects and rodents from finding the gap around the damper flap.
Fire-Stop Requirement: Why Regular Caulk Is Not Acceptable
Building codes require that penetrations through fire-rated wall assemblies be sealed with materials that maintain the wall's fire resistance rating. A brick wall — even a single-wythe brick wall — is a fire-rated assembly. Standard silicone caulk or foam backer rod do not meet this requirement because they burn or melt at relatively low temperatures, allowing fire to pass through the penetration.
Intumescent fire-stop caulk contains materials that expand dramatically when exposed to heat (typically 10–20x their original volume), physically blocking the gap around the duct and maintaining the wall's fire rating. This is not expensive: a tube of UL-listed intumescent fire-stop caulk costs $15–25 and is available at most hardware stores. It's a non-negotiable part of the installation.
Brick Wall Installation FAQ
Not effectively. A standard hammer drill can drive small masonry bits in hard materials, but it does not have the percussive energy (measured in joules of impact energy) needed to core through brick. Rotary hammers deliver 2–4+ joules of impact energy vs. a hammer drill's 0.5–1 joule. For a 4-5/8 inch core through double-wythe brick, you need a rotary hammer. Rent one if you don't own one — it's the right tool and the difference in time and effort is dramatic.
A cavity wall requires extra attention at the fire-stop. The cavity itself is a potential path for fire or smoke to travel between floors in multi-story buildings — a phenomenon called cavity fire spread. The fire-stop must seal both the inner and outer wythe penetrations, and ideally a non-combustible fire-stop material (rigid mineral wool, not just caulk) should be packed into the cavity section around the duct. This is a more complex installation and in many jurisdictions the fire-stop detail will be specified by a building inspector for permitted work.
A slight angle (up to 3–4°) is typical and manageable. In fact, a very slight downward pitch toward the exterior is preferable — it encourages condensate to drain out rather than back toward the dryer. If the hole angled significantly upward (toward the interior), condensate will pool inside the duct. If the angle is more than about 5° in either horizontal direction, you may need to use an offset fitting inside the wall to bring the interior duct connection back into alignment. Severely angled holes can be patched and re-drilled, though this is a significant additional effort in masonry.
After the fire-stop caulk is applied and cured, the gap between the duct and the masonry can be finished with hydraulic cement or non-shrink grout if a hard patch finish is desired, or with a trim ring/escutcheon plate for a cleaner appearance. The fire-stop caulk provides the functional seal — the cosmetic finish layer is purely aesthetic. Escutcheon rings (split rings that slip over the duct and mount flush to the wall face) are available at plumbing supply stores and make the interior penetration look professional.