How Do You Install a Chimney Through a Cathedral Ceiling?

You install a chimney through a cathedral ceiling by running stove pipe from the appliance up to a ceiling support box, then switching to Class A insulated chimney pipe (UL 103 HT) for everything that passes through the roof. Because there is no attic, the support box mounts directly to the ceiling framing, and the chimney exits straight through the roof above.

The steps below cover system layout, support requirements, roof penetration, clearance rules, and final safety checks per NFPA 211 and typical manufacturer instructions. This guide is written for single-story homes with vaulted or cathedral ceilings and no accessible attic space above.

What does a cathedral ceiling chimney installation mean?

A cathedral ceiling follows the slope of the roof with no flat attic space between the ceiling and the roof deck. That means the chimney runs vertically from the appliance straight through the roof without passing through an attic.

Because there is no attic to rest a ceiling support on horizontal joists, the chimney must be supported at ceiling level using a cathedral ceiling support box (sometimes called a "square ceiling support box"). This box attaches directly to the roof framing and carries the full weight of the chimney system above it. The installation is simpler in some ways than a through-attic installation, but the support box choice and correct clearances are just as important.

Stove pipe vs Class A chimney pipe - what goes where?

A safe installation always uses two different pipe types. Mixing them up or running the wrong pipe through a ceiling or roof is a code violation and a fire hazard per NFPA 211.

Rule: Stove pipe connects the appliance to the support box inside the room. Class A insulated chimney pipe takes over from the support box upward through the roof and outside.

What components do you need?

A typical cathedral ceiling chimney system includes these parts (exact components vary by brand and diameter):

• Stove pipe sections (single-wall or double-wall connector) to connect the appliance to the support box
• Appliance adapter (if required by the stove manufacturer)
• Cathedral ceiling support box - carries the chimney load and creates the transition from stove pipe to Class A
• Class A insulated chimney pipe sections (UL 103 HT) for the roof penetration and above
• Roof flashing matched to your roof pitch
• Storm collar to seal around the pipe above the flashing
• Chimney cap to keep rain, animals, and debris out
• Roof support straps or bracing (required when the chimney extends more than about 5 feet above the roof)

You can find complete chimney kits that include all these parts matched to your pipe diameter and roof pitch.

How do you plan the interior pipe run?

Before cutting any openings, measure and confirm:

1. Floor-to-ceiling height and the height of your stove's flue collar
2. Vertical alignment from the flue collar straight up to where the chimney will exit the roof
3. Total connector pipe length needed between the stove and the support box
4. Required clearances from combustibles along the entire run (18 inches for single-wall stove pipe, 6 inches for double-wall)

Telescoping connector sections can help fine-tune the height without cutting pipe. Make sure the stove pipe runs as straight and vertical as possible for the best draft.

How tall does the chimney need to be? (The 3-2-10 rule)

Chimney height is governed by the 3-2-10 rule, which is referenced in NFPA 211 and adopted by most local building codes:

• The chimney must extend at least 3 feet above the point where it exits the roof
• It must be at least 2 feet higher than anything within a 10-foot horizontal radius (including ridgelines, dormers, and other structures)

These minimums support proper draft and reduce fire risk from sparks landing on the roof. On a chimney kit through the roof with a steep pitch, the chimney may need to be taller to clear the ridge. Always verify your local code and the chimney manufacturer's height requirements. For more on chimney height rules, see our building codes guide.

How do you cut the roof opening with correct clearances?

When creating the roof penetration:

• Maintain a minimum 2-inch clearance from the outer wall of the Class A chimney pipe to any combustible material (wood framing, insulation, roof decking)
• On a sloped roof, the opening will be oval rather than round to maintain that 2-inch clearance on all sides
• Do not allow insulation, spray foam, or any combustible material to fill or touch the clearance gap
• Frame the opening per the manufacturer's instructions - most systems specify a specific rough opening size

This 2-inch clearance requirement is standard for UL 103 HT listed chimney systems. Some manufacturers may require more - always check your specific system's installation manual.

How do you install the cathedral ceiling support box?

The support box is the most important structural component in a cathedral ceiling installation. It does three things:

1. Carries the vertical load of the entire chimney system above it
2. Creates the safe transition from stove pipe (room side) to Class A chimney pipe (roof side)
3. Maintains required clearances at the ceiling penetration

Fasten the support box to structural framing (rafters or added blocking) per the manufacturer's instructions. Verify how far the box must extend above and below the finished ceiling surface - this varies by brand. In a two-story house, a different support method is used because the chimney passes through a floor, but in a single-story cathedral ceiling the support box is simpler and mounts at the roofline.

How do you install the Class A chimney through the roof?

After the support box is secured:

1. Connect the first Class A chimney pipe section into the top of the support box
2. Add sections upward through the roof opening, locking each joint per the manufacturer's twist-lock or snap-lock system
3. Maintain the required 2-inch clearance to combustibles at every point through the roof assembly
4. Continue adding sections until you reach the required height per the 3-2-10 rule

How do you install roof flashing and the storm collar?

Weatherproofing keeps rain and snowmelt from entering your home along the chimney pipe:

• Roof flashing: Install a flashing cone or adjustable flashing plate matched to your roof pitch. Slide the upper edge under the shingles or roofing above the pipe, and let the lower edge overlap the roofing below
• Sealant: Apply roofing sealant compatible with your roof material and flashing. Do not create water traps by sealing the downhill edge
• Storm collar: Slide the storm collar over the chimney pipe and position it just above the flashing. Seal the top edge of the collar to the chimney pipe to shed water away from the joint

When do you need roof support straps?

If the chimney extends more than about 5 feet above the roofline (the exact threshold depends on the manufacturer and local wind conditions), you should add roof support straps or a bracing kit:

• Roof support straps reduce lateral movement from wind
• Fasten the straps into structural members (rafters or ridge beam) - never just into roof decking alone
• Follow the manufacturer's maximum unsupported height guidance

Final connection and safety checklist

Before the first fire, work through this checklist:

• All stove pipe joints are secured with screws or locking bands per the manufacturer
• Male/female joint orientation is correct (crimped end pointing down on stove pipe for condensation drainage)
• All required clearances are met - 18" for single-wall stove pipe, 6" for double-wall stove pipe, and 2" for Class A through the roof
• The support box is fastened to structural framing and carries the chimney load
• Roof flashing and storm collar are installed and sealed
• Chimney cap is installed on top
• Roof bracing is installed if the chimney extends more than 5 feet above the roof
• A local code inspection is scheduled (required in most jurisdictions per IRC and NFPA 211)

For a printable version of this checklist and more installation details, check our installation guides page.

Not sure which parts you need?

Every cathedral ceiling installation is a little different depending on your stove, ceiling height, roof pitch, and pipe diameter. If you are not sure which components to order, use our free chimney design service - send us your measurements and photos, and we will send you a custom parts list and diagram within 24 hours. You can also call us at 888-834-0880 (9 AM - 9 PM, 7 days a week) to talk it through with a chimney systems specialist.

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Need help selecting? Contact our team for a free design service.

Frequently Asked Questions

Can I use stove pipe through a cathedral ceiling instead of Class A?

No. Stove pipe (single-wall or double-wall connector pipe) is only rated for use inside the room. It must never pass through a ceiling, floor, wall, or roof. Class A insulated chimney pipe (UL 103 HT) is required for all penetrations. This is a hard requirement under NFPA 211.

What clearance do I need around the chimney pipe in the roof?

Class A chimney pipe requires a minimum 2-inch clearance to all combustible materials (wood framing, insulation, roof decking). Some manufacturers require more, so always check your specific system's installation manual before cutting the opening.

Do I need a ceiling support box if I have a cathedral ceiling?

Yes. Because there is no attic floor to rest a standard ceiling support on, a cathedral ceiling support box (or square ceiling support box) is used instead. It attaches directly to the roof framing and carries the full weight of the chimney system above it.

How high does my chimney need to extend above the roof?

The 3-2-10 rule applies: at least 3 feet above the roof penetration and at least 2 feet higher than anything within 10 feet horizontally. On steep cathedral ceiling roofs, the ridge may be close, so measure carefully. Local codes may have additional height requirements.

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