Direct Vent Gas Fireplace Venting: How It Works, Wall vs Roof vs Chimney, and B-Vent vs Direct Vent
A direct vent gas fireplace or stove breathes entirely outdoors. One sealed pipe-within-a-pipe pulls combustion air in from outside and sends exhaust back out, so the fire never touches the air in your room. That's why it can vent straight out a side wall, up through the roof, or up an old masonry chimney, and why it needs no chimney at all. Every Napoleon vent part below ships with No Sales Tax in any state.
Quick answer: Direct vent venting is a sealed, two-layer (co-axial) pipe: exhaust goes out the inner pipe, fresh air comes in through the outer one. It can end at a wall terminal, a roof terminal, or the top of an existing chimney.
- Use only the vent pipe and terminals your appliance's manual lists. Napoleon appliances use Napoleon 4"/7", 5"/8" or 8"/11" venting depending on the model.
- Through the wall is usually the shortest, cheapest run. A small stove like the Napoleon Arlington GDS20NNSB can go out a wall with a GD-220 flex vent kit and a GD-222 wall terminal.
- A gas insert in an old fireplace vents up the chimney through two flexible liners, a co-linear vent kit, capped with a co-linear terminal.
- The outside terminal needs clearance from windows, doors and the ground. Your manual's clearance chart is the one to follow.
No Sales Tax in any state, free shipping on orders over $300. Send a photo of where your appliance will go to info@stovesource.com or text it to 1-888-866-8206 and we'll put the vent parts list together.
How direct vent venting works
The vent pipe is two pipes, one inside the other. Napoleon describes them by their two diameters, so "4"/7"" means a 4" inner exhaust pipe inside a 7" outer pipe.
- Inner pipe: exhaust. Hot combustion gases rise out through the center.
- Outer pipe: fresh air. Outside air flows in through the space between the two pipes to feed the burner. On the way in it cools the outer pipe and picks up some heat from the exhaust.
- Sealed glass front. The firebox is closed off from the room by fixed glass, so no room air is used and no exhaust can spill into the house.
Because the system draws its own air, a direct vent appliance works in a tight, well-sealed house and doesn't pull warm room air up the flue. It's also why the vent can run sideways: the exhaust and intake are balanced at the terminal, so it doesn't rely on a tall chimney to create draft.
Direct vent vs B-vent vs vent-free
There are three ways a gas fireplace or stove can deal with its exhaust. They are not interchangeable: each appliance is certified for one.
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| Direct vent | B-vent (natural vent) | Vent-free | |
|---|---|---|---|
| Combustion air | From outside, through the outer pipe | From the room | From the room |
| Exhaust goes | Outside through the inner pipe | Up a double-wall Type B pipe, out the roof | Into the room |
| Can vent sideways out a wall | Yes | No, it has to rise vertically | No vent at all |
| Front | Sealed glass | Usually open or with doors | Open |
| Best for | Most homes; heating a room | Older installs and some log sets | Backup heat where codes allow it |
B-vent appliances use room air and rely on hot exhaust rising up a vertical pipe, so they lose more heat up the flue and need a run that goes up through the roof. Direct vent is what most new gas fireplaces, inserts and stoves use today. If you're weighing a fireplace with no vent at all, read are ventless gas fireplaces safe? and our guide to ventless gas stoves such as the Buck Townsend II. For log sets, see ventless vs vented gas logs.
The three ways to run a direct vent
1. Out through the wall
The most common install. The pipe leaves the back or top of the appliance and goes straight out an outside wall to a horizontal terminal.
- Rear vent: the shortest possible run, when the appliance sits right against an outside wall. Napoleon's FRV47 (4"/7") and FRV58 (5"/8") rear vent kits are made for this.
- Top vent: the pipe rises off the top of the appliance first, then turns out through the wall. The vertical rise is what lets you run further horizontally. Napoleon's FTV47 and FTV58 top vent kits cover the usual layout.
- The wall itself: where the manual calls for them, Napoleon's 24" through-the-wall vent kits (GD-176 and GD177) handle the pass-through.
Every manual has a chart of how far you can run horizontally for a given vertical rise, and how many elbows are allowed. As an example, the Napoleon Arlington's manual allows up to 20 ft horizontal and 40 ft vertical, with more rise needed as the horizontal run gets longer. Go outside the chart and the appliance won't draft properly.
2. Up through the roof
When there's no outside wall nearby, or the wall terminal would land too close to a window, deck or walkway, the pipe goes straight up through the ceiling and roof to a roof terminal. A vertical run needs a firestop where it passes through each ceiling, roof flashing matched to your roof pitch, and a storm collar. Very tall vertical runs can over-draft and make the flame lift or run lean. Napoleon's fix is a vent restrictor plate, fitted when the manual calls for one.
3. Up an existing chimney
A direct vent gas insert slides into an old masonry fireplace and uses the chimney as a chase. Two flexible aluminum liners run up the flue, one for exhaust and one for intake air, and join at a terminal on top. That's a co-linear system:
- Napoleon co-linear vent kits come as two 3" liners or a 2" and 3" pair, in 20 to 45 ft lengths. Your insert's manual says which pair it needs.
- The top is finished with a co-linear terminal, either the universal GDI-229 or the high-wind GDI-223.
The chimney should be swept and inspected first. Any wood-burning creosote left in the flue will smell when the insert runs. If you're replacing a wood fireplace with a wood insert instead, that's a stainless liner job: see our chimney liner guide.
Special cases
- Terminal would be below ground level. In a basement where the vent exits below grade, a periscope (snorkel) raises the terminal so it sits above the ground outside.
- Very long or awkward runs. Napoleon's GPV power vent uses a fan in the terminal to pull the exhaust out, allowing 10 to 110 ft runs and terminations above or below the fireplace. It needs a model-specific adaptor kit.
- Vinyl siding. Hot exhaust can warp vinyl. Napoleon's GD-222 wall terminal includes a vinyl siding shield; whatever terminal you use, fit the shield or standoff your manual calls for.
Napoleon direct vent parts we sell
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| Part | Sizes / part numbers | What it's for | From |
|---|---|---|---|
| Direct vent wall terminal | GD-222, GD-222R (4"/7"), GD422R-2 (5"/8"), GD822R (8"/11"), ST47U, ST58U-1 Silhouette | Ends a horizontal run on the outside wall | $268.99 |
| Silhouette terminal screen (STS4758) | For ST47U and ST58U-1 | Guard where people can touch the terminal | $248.99 |
| Direct vent roof terminal kit | GD-112 (4"/7" flat), GD-810, GD-811, GD-812, GD-813 (8"/11") | Ends a vertical run on the roof | $358.99 |
| Direct vent flex vent kit | GD-220, GD-345 (4"/7"), GD-445 (5"/8"), GD-820, GD-830 (8"/11") | Flexible pipe between appliance and terminal | $138.99 |
| Top or rear vent kit | FTV47, FRV47, FTV58, FRV58 | Complete short horizontal run kits | $348.99 |
| 24" through-the-wall vent kit | GD-176, GD177 | Wall pass-through | $378.99 |
| Direct vent periscope | GD-201 (4"/7"), GD401 (5"/8") | Raises a below-grade wall terminal | $678.99 |
| Gas insert co-linear vent kit | Two 3" or 2" + 3" liners, 20–45 ft | Vents a gas insert up a masonry chimney | $168.99 |
| Co-linear vent terminal | GDI-223 high-wind, GDI-229 universal | Caps a co-linear chimney run | $308.99 |
| Vent restrictor plate | RP4, RP5, RP6, RP8 | Tames over-draft on tall vertical runs | $48.99 |
| GPV power vent terminal | GPV, plus a model-specific PVA adaptor | Long or awkward runs, 10–110 ft | $1,368.99 |
Napoleon vent parts are model-specific. Check the venting section of your appliance's installation manual for the exact part numbers before ordering. Browse everything in Napoleon fireplace parts and accessories.
Direct vent termination clearances
Where the terminal sits outside matters for safety: exhaust must not drift back in through a window or door, and the terminal must stay above snow and clear of anything flammable. The national fuel gas code (NFPA 54) sets the minimums below for direct vent wall terminals. Your appliance's manual often asks for more, and when it does, the manual wins.
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| Clearance from the terminal to | Code minimum |
|---|---|
| Finished ground level (bottom of terminal) | 12" |
| Any opening into the house (window, door, air inlet), appliance up to 10,000 BTU/hr | 6" |
| Any opening, appliance 10,001–50,000 BTU/hr | 9" |
| Any opening, appliance over 50,000 BTU/hr | 12" |
Your manual's clearance diagram also covers soffits, inside corners, decks and porches, gas meters and regulators, and walkways. Those vary by appliance, so lay the terminal out from that diagram before you cut the hole. In snow country, keep the terminal above the usual snow line, not just 12" above the lawn.
Common direct vent mistakes
- Mixing brands. Use the pipe and terminals your manual lists. Some Napoleon manuals approve certain other brands' rigid pipe with an adaptor, but only the ones named. Never mix pipe from different makers in one run.
- Too much horizontal, not enough rise. Every manual limits horizontal run against vertical rise. Plan the run on the manual's chart first.
- Running horizontal pipe flat or downhill. Horizontal sections should rise slightly toward the terminal, as the manual specifies.
- Terminal too close to a window or under a deck. The most common inspection failure. Check the clearance diagram.
- Skipping firestops and wall thimbles. Required wherever the pipe passes through a wall, floor or ceiling.
- Using a direct vent appliance on B-vent or a bare chimney. It needs its own sealed co-axial or co-linear system.
Gas appliances must be installed by a qualified gas technician, following the installation manual and your local code. If your gas fireplace is installed and won't light, see gas fireplace won't light. Switching fuels? See converting a gas fireplace to propane.
Frequently asked questions
Does a direct vent gas fireplace need a chimney?
No. It vents through its own sealed pipe, which can go straight out a side wall or up through the roof. An existing chimney can be used as a chase for the vent liners, but it isn't required.
What is the difference between direct vent and B-vent?
A direct vent appliance takes combustion air from outside and sends exhaust out through a sealed two-layer pipe, and it can vent horizontally. A B-vent appliance takes air from the room and sends exhaust up a vertical Type B pipe through the roof.
How far can a direct vent run horizontally?
It depends on the appliance and how much vertical rise comes first. Each manual has a chart. The Napoleon Arlington, for example, allows up to 20 ft horizontal, with more rise needed for longer runs. A power vent such as the Napoleon GPV allows much longer runs.
How close can a direct vent terminal be to a window?
Under the national fuel gas code, 9 inches for appliances from 10,001 to 50,000 BTU/hr and 12 inches above 50,000 BTU/hr. Many manufacturers require more, so check your manual's clearance chart.
Can I use a different brand of vent pipe?
Only if your appliance's manual lists it. Direct vent appliances are certified with specific venting systems, and using unlisted pipe can void the certification and warranty.