Direct vent clearance distances sketch - adapted from Thermo Products & NFGC Gas Appliance Direct Vent Clearances
Distances from direct gas vent to building features

  • GAS APPLIANCE DIRECT VENT CLEARANCES - CONTENTS: clearance distances required between a direct vent side wall terminal & building components, mechanical systems, windows, soffits, openings, decks, walks, etc.
  • POST a QUESTION or READ FAQs about the installation or diagnosis of sidewall vent or direct vent chimney or flue exhaust systems for heating appliances: oil, gas, other fuels firing heating appliances & fireplaces

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Direct vent exhaust clearance distances for gas fueled appliances:

Table & illustrations of the required space between a direct or side-wall vent for a gas fired heating appliance and building windows, doors, corners, gas meter, air intakes, sidewalks, balconies & decks and other building features.

This article series describes side wall vent systems for conventional & mid-range-efficiency heating boilers, furnaces & water heaters. We include for comparison, low temperature side wall vent systems used by high efficiency or condensing boilers, furnaces & water heaters.

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Clearance Requirements for Direct Vented Gas Appliances

Direct vent clearances from building components & features, adapted from codes cited (C) 2017

Exhaust Vent Termination Clearance Requirements

In a table below we provide a complete list of required clearance distances between the air intake or combustion gas exhaust vents for direct vented heating appliances.

[Click to enlarge any image]

Some highlights include:

Page top Illustration adapted from Thermo Products installation instructions - click to enlarge this or any other image or photo at InspectAPedia. [15]

Colour illustration of direct vent sidewall terminal clearance distances adapted from American Standard Furnace installation instructions that in turn cites ANSI Z223.1/NFPA 54 National Fuel Gas Code for US installations and cites CSA B149.1 Natural Gas and Propane Installation Code for Canadian direct vent gas vent installations.

Table of NFGC Recommended Clearance Distances from a Direct Vent Gas Appliance Terminal to Other Building Features

  Direct vent gas exhaust termination item clearance Distance required (U.S.) Distance required (Canada)
A Distance above grade (ground surface), balcony, deck, porch, veranda 12 inches [note that in areas of deep snow this clearance may be inadequate and thus unsafe] 12 inches (30 cm)
B Distance to a window or door that is operable (can be opened) 12 inches [Note 2] or 6 to 36 inches depending on BTUH

6 inches (15 cm) for appliances =/< 10,000 Btuh (3 kw),

9 inches (23 cm) for appliances > 10,000 Btuh (3 kw) and =/< 50,000 Btuh (15 kw),

12 inches (30 cm) for appliances > 50,000
Btuh (15 kw)

C Distance to a permanently closed (or non-operable) window 12 inches [Note 3] [Note 3]
D Distance to a ventilated soffit (roof eaves, overhang) above the vent terminal & within a horizontal distance of two feet from the centerline of the terminal 24 inches [Note 3] [Note 3]
E Distance to an un-vented soffit 24 inches [Note 3] [Note 3]
F Distance to outside corner of the building 24 inches [Note 3] [Note 3]
G Distance from the vent centerline to a building inside corner 3 feet [Note 3] [Note 3]
H Distance to each side of centerline extended above a [gas] meter / regulator assembly 4 feet [Note 3] [Note 3]
I Distance to a [gas] service regulator vent outlet 4 feet [Note 3] [Note 3]
J Distance to a non-mechanical air supply inlet to the building or to the combustion air inlet for any other appliance

12 inches [Note 2]

6 inches (15 cm) for appliances =/< 10,000 Btuh (3 kw),

12 inches (30 cm) for appliances > 10,000 Btuh (3 kw) and =/< 100,000 Btuh (30 kw),

36 inches (91 cm) for appliances >
100,000 Btuh (30 kw)

6 inches (15 cm) for appliances =/< 10,000 Btuh (3 kw),

9 inches (23 cm) for appliances > 10,000 Btuh (3 kw) and =/< 50,000 Btuh (15 kw),

12 inches (30 cm) for appliances > 50,000
Btuh (15 kw)

K Distance to a mechanical [systems] air supply inlet

6 feet (1.83m)

3 feet above if within 10 feet horizontally

3 feet (91 cm) above if within 10 feet (3m) horizontally
L Distance above a paved sidewalk or paved driveway on public property 7 feet [Note 4]  
M Distance below a balcony, deck, porch, veranda

12 inches (30 cm) [Notes 7,8]

24 inches [Note 3]

  Distances between a gas fireplace direct vent termination cap and other building features or mechanical systems See GAS FIREPLACE VENT CLEARANCE REQUIREMENTS

OpinionsOn Additional Recommended Clearance Distances from a Direct Vent Gas Appliance Exhaust Opening to other Building Features or Equipment

  Distance from a clothes dryer exhaust vent wall termination to the nearest air inlet point on a direct vent chimney 10 feet [Note 5] - CLOTHES DRYER VENT CLEARANCES
  Distance to an air conditioner or heat pump compressor/condenser unit to the nearest point of a direct vent gas heater exhaust 24 inches to 6 feet [Note 6]
  Distance to air intake and exahust vent openings of another direct vented gas fired appliance At least 3 feet (0.9 m) above any forced air inlet located within 10 feet (3.1 m). [Note 9]


1 Authorities/Sources:

  • CSA B149.1, Natural Gas and Propane Installation Code
  • National Fuel Gas Code, ANSI Z223.1 / NFPA 54 [8]
  • Gas Fired High Efficiency Furnace Down Flow & Direct Vent (Sealed Combustion) Thermo Pride Model CMA1-50N & CMA2-75N Installation and Service Manual" [15] [cites & recounts illustrations & clearances from the U.S. National Fuel Gas Code
  • Note 7 below

2. For non-direct vent applications such as the side-wall vent appliance shown earlier on this page, the required distance is much greater: 4 feet to the side or below the opening, or 1 foot above the opening.

Typical clearance from an operable window to a direct vented gas appliance vent outlet:

6 inches (15 cm) for appliances up to 10,000 Btu/hr (3 kW), 12 inches (30 cm) for appliances between 10,000 Btu/hr (3 kW) and 100,000 Btu/hr (30 kW), 36 inches (91 cm) for appliances above 100,000 Btu/hr (30 kW)

3. This distance requirement may vary in order to be in accordance with local building codes, the gas supplier, and the equipment manufacturer's own product installation specification

Clearance must be in accordance with local installation codes and the requirements of the gas supplier

3.a. for a gas fireplace exhaust termination cap, 3 feet (91cm) within a height of 15 feet (4.5m) above the meter / regulator assembly

3.b. for a gas fireplace exhaust termination cap, 3 feet (91cm) above - if within 10 feet (3m) horizontally

4. In direct vent applications, this clearance distance must be in compliance with local building codes, the requirements of the fuel gas supplier for the heating appliance in use, and the appliance manufacturer's instructions. For non-direct-vent applications (that is, side wall venting only), the required clearance is 7 feet.

A vent shall not terminate directly above a sidewalk or paved driveway that is located between two single family dwelling and serves both dwellings.

5. This is the author's OPINION based on other clearance distances and standards discussed in the article above.



6. This is the author's OPINION considering that heat from the gas exhaust vent blowing onto an A/C compressor unit condensing coil could impact the coil's ability to condense refrigerant back to liquid form, affecting the condenser unit's efficiency and life. I'm considering the situation in which the hot gas exhaust blows onto the air intake side of a condensing coil.

(Most modern condenser units draw cooling air in from the unit sides and push it out the unit's top).


7. Direct Vent Terminal Clearances cited in AMERICAN STANDARD GAS FURNACE INSTALLATION MANUAL [PDF] (2008), American Standard Heating & Air Conditioning, that in turn cites:

In accordance with the current CSA B149.1 Natural Gas and Propane Installation Code.

In accordance with the current ANSI Z223.1/NFPA 54 National Fuel Gas Code.

8. Permitted only if veranda, porch, deck, or balcony is fully open on a minimum of two sides beneath the floor.

Watch out: there could be other more dangerous conditions: if the air intake vacuum created by the A/C compressor / condenser unit actually draws air or gases out from the nearby direct vent gas heater or from a passive-vented (atmospheric vented) gas fireplace appliance, that increased draft may impact the safe operation of the gas burner, risking dangerous or even fatal carbon monoxide hazards.

Separately, if a different compressor unit design caused the unit's exhaust to blow into the gas heater exhaust vent, that could prevent safe venting of exhaust gases. Where either these conditions are possible I'd increase the clearance distance to 10 feet or 3 meters.

9. This is an excerpt from installation instructions for an example system, the Aerco GF-5050 Innovation Series & ReCon Water Heater Venting and Combustion Air Guide [PDF] retrieved 2017/09/26, original source:

Watch out: check with the manufacturer of your heating equipment to determine their recommended clearances between direct vent openings when you are installing multiple direct-vent appliances at the same building.

For help finding the manufacturer of your gas fired equipment see these two links offering both equipment installation and operating manuals and age decoding help:



Also see

  • B-VENT SIZING, Hart-Cooley [PDF], sizing guide for Type B Gas Vents for Category 1 Appliances, All Fuel Chimney for oil-fired appliances and open-face fireplaces, Hart & Cooley, 5030 Corporate Exchange Blvd. SE Grand Rapids, MI 49512 USA, Tel: (800) 433-6341 Website: retrieved 2017/09/26,
  • Brand, L., & W. Rose, "MEASURE GUIDELINE: High Efficiency Natural Gas Furnaces", [PDF] (2012), U.S. Department of Energy, NREL, retrieved 2017/09/26, original source:

    This Measure Guideline covers installation of high efficiency gas furnaces. Topics include: when to install a high efficiency gas furnace as a retrofit measure; how to identify and address risks; and the steps to be used in the selection and installation process.

    The guideline is written for Building America practitioners and HVAC contractors and installers. It includes a compilation of information provided by manufacturers, researchers, and the U.S. Department of Energy (DOE), as well as recent research results from the Partnership for Advanced Residential Retrofit (PARR) Building America team.

    Content that can be shared with homeowners is written in a way that can be understood by that audience.
  • Dura-Vent Direct Vent Pro IO MANUAL [PDF], Venting System For Direct Vent Gas Stoves and Fireplaces, Simpson Dura-Vent, Inc. PO Box 1510 Vacaville CA 95696-1510 USA Customer Service Support 800-835-4429 retrieved 2017/09/26,
  • Thermopride HIGH-EFFICIENCY UPFLOW FURNACE INSTALLER'S INFORMATION MANUAL [PDF], retrieved 2017/09/26, original source:


Direct Vent Exhaust for Heating Flues: Installation & Inspection Questions


Question: what is the maximum allowable length for direct vent gas heater flue & how many elbows can I use?

20917/09/11 Terry said:

I have a Goodman 60,000 BTU high efficiency Direct venting

my fresh air vent is about 3 feet below the window

my exhaust vent I want to move just right around the corner of the house approximately a total distance of about 48 inches

can I do this if not how far to the right of the window and below the window can I be with The exhaust vent thank you

This question and reply were posted originally at DIRECT VENTS / SIDE WALL VENTS


You will want to review GAS APPLIANCE DIRECT VENT CLEARANCES Separate Table for Direct Vented Gas Appliances - above on this page.

Where you will find a table of all of the required minimum clearance distances from the vent outlet (or a vent intake) and other building features like windows and doors.

In GENERAL and excerpting from Goodman's GMVC96 Installation and Operation Manual,

The vent termination of a direct vent application must terminate at least 12 inches from any opening through which flue gases may enter a building (door, window, or gravity air inlet).

AND the Installation & Operation Manual for your Goodman heater because there are individual heater model-dependent safety and functional restrictions on how you can extend and route the vent piping between the heater and the exit point: there are constraints on the diameter and length of piping and also on the number and type of bends or elbows that can be used. If you violate these the system may not vent properly and it could be unsafe.

In the Goodman heater manual I use as an example (Watch out: you didn't give your heater model so this our excerpt may not be correct nor safe for you), and using a 60,000 BTUH Goodman MVC96/CVC96 Direct Vent (2 - Pipe) system, the maximum allowable length FOR THAT BTUh example depends on

  1. the input BTUH rating of the specific heater
  2. the vent pipe diameter used
  3. the number of bends or elbows
  4. specific installation instructions from the manufacturer for your heater brand and model

Assuming use of a 2" or 2 1/2" diameter vent pipe, with 1 elbow the maximum length can be 95 ft. , 2 elbows, 90 ft., and so on, dropping another 5 ft. in length for each elbow up to a maximum of 8 elbows and 60 ft.

The company warns:

Adhere to these instructions to ensure safe and proper furnace performance. The length, diameter, and number of elbows of the vent/flue pipe and combustion air pipe (when applicable) affects the performance of the furnace and must be carefully sized. All piping must be installed in accordance with local codes and these instructions. - Goodman MVC96/CVC96 Direct Vent manual cited below

You can find the Goodman furnace manual I cite at our list of HVAC manuals provided at GOODMAN HVAC MANUALS and there you will find contact information for the company so that you can be sure you have the correct instructions and the installation and operation manual for your specific heater.

Watch out: the Goodman furnace direct vent length table given below is adapted from that manual and it might not be correct for your heater and model. Check with your manufacturer or your supplier.

Example Table of Maximum Direct Vent Gas Furnace Vent Lengths

Goodman *MVC96/*CVC96 Direct Vent (2 - Pipe) and Non-Direct Vent (1- Pipe) 6

Maximum Allowable Length of Vent/Flue Pipe& Combustion Air Pipe (ft) 1, 2

Heater Input BTU Rating Vent Pipe Diameter4 Inches Number of Elbows in Total Vent Run3, 5
1 2 3 4 5 6 7 8
40,000 2 or 2 1/2" 120 115 110 105 100 95 90 85
60,000 2 or 2 1/2" 95 90 85 80 75 70 65 60
80,000 "B" 2 or 2 1/2" 75 70 65 60 55 50 45 40
80,000 "B" 3" 200 193 186 179 172 165 158 151
80,000 "C" 2 or 2 1/2" 25 20 15 10 5 N/A
80,000 "C" 3" 200 193 186 179 172 165 158 151
100,000 2 or 2 1/2" 25 20 15 10 5 N/A
100,000 3" 200 193 186 179 172 165 158 151
120,000 2 or 2 1/2" 45 40 35 30 25 20 15 10
120,000 3" 95 90 85 80 75 70 65 60


  1. Maximum allowable limits listed on individual lengths for inlet and flue and NOT a combination.
  2. Minimum requirement for each vent pipe is five (5) feet in length and one elbow/tee.
  3. Tee used in the vent/flue termination must be included when determining the number of elbows in the piping system.
  4. 2 1/2” or 3” diameter pipe can be used in place of 2” diameter pipe.
  5. increased Clearance Configurations using (2) 45 deg. Long Sweep elbows should be considered equivalent to one 90 deg. elbow.
  6. One 90° elbow should be secured to the combustion air intake connection.

Source: GOODMAN TWO STAGE GAS FURNACE CV96 & MVC96 [PDF] Installation & Operating Manual, (Type FSP CATEGORY IV Direct or Non Direct Vent Air Furnace), retrieved 2017/09/11, original source: https :// ForEmployees/ qgcOperationsTraining/Furnaces/ Goodman_GMVC96_Installation.pdf

Watch out: the installation and operation manual used as an example here includes additional vent and vent termination requirements that must be respected for safety and for proper functioning of the heating equipment.

See MANUALS for HEATING SYSTEM CONTROLS for I&O Manuals for other heating equipment brands and models.


Continue reading at DIRECT VENTS / SIDE WALL VENTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



Or see GAS FIREPLACE VENT CLEARANCE REQUIREMENTS Separate Table for Direct Vented Gas Fireplaces



Or see this

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