Venting requirements for gas-fueled water heaters:

This article outlines 15 key gas fired water heater flue-ventilation safety checkpoints for both LPG or propane and natural gas.

We include building code citations for gas water heater venting and we quote excerpts from manufacturers' water heater installation manuals, U.S. and Canadian model building codes, and other sources and water heater venting standards.

We also illustrate improper and unsafe gas fired water heater venting installations.

The natural gas fueled water heater shown at page top is improperly vented, lacking the recommended minimum 12" of vertical rise before the elbow and vented directly into a large masonry flue where it cannot develop adequate draft. This heater installation may be unsafe.

Proper & Safe Exhaust Vent Codes & Standards for Gas Fired Water Heaters

Summary of Good Venting Practices for Gas Fired Water Heaters

Water heaters must be vented using a listed and approved venting system that provides adequate size, height, and draft.

Otherwise such vents may be unsafe, venting combustion products, including dangerous carbon monoxide, into the building.

Illustrations of proper gas fired water heater venting using Type B- double wall vent pipe through a roof (above) or through a chimney (below on this page) include details for the flue vent connector such as the requirement of a minimum vent connector upwards slope of 1/4" per foot of horizontal run.

These illustrations are adapted

from WHIRLPOOL RESIDENTIAL GAS WATER HEATER MANUAL [PDF] (2015) retrieved 2018/03/05, original source: http://www.whirlpoolwaterheaters.com/media/99595/100263111.pdf

[Click to enlarge any image]

Watch out: regarding these clearances, see

the SAFE GAS B-VENT CLEARANCE DISTANCES CLARIFICATION by Charles Buell near the end of this article.

1. Watch out: Carbon Monoxide Hazard.
   
   Gas fired water heaters like those illustrated here must be supplied with adequate combustion air and the heater's exhaust gases must be vented to outdoors.
   
   Failure to properly vent a gas-fueled water heater can result in severe injury or death from carbon monoxide poisoning.
   
   The vent system must be installed by a qualified person. Examples of a qualified person include gas technicians, authorized gas company personnel, and authorized service technicians.
2. Carbon Monoxide Detector(s):
   
   To reduce the risk of carbon monoxide poisoning, install a fuel gas and carbon monoxide detector. Install and maintain the detector in accordance with the manufacturer’s instructions and local codes.
   
   Review the location of the CO detector to be sure that it will protect building occupants. More information:
   
   CO DETECTION OPTIONS
3. Clearance to combustibles:
   
   for gas fired water heater vents: 6" minimum clearance from single-wall vent pipe or flue-vent connector to any combustible material.
   
   Single wall vent pipes cannot pass through a ceiling, floor, firewall, or wall. [An exception is made for non-combustible walls such as solid masonry or concrete.]
   
   Clearances for double-walled B-vent piping are given by the manufacturer and can be found also
   
   at TYPE B-VENT CEILING FLOOR WALL CLEARANCES. Typically a double-walled metal B-vent chimney section is stamped as requiring 1-inch clearance to combustibles.
   
   If you cannot meet the 1-inch B-vent clearance you may be able to use a zero-clearance chimney material. More information:
   
   CLASS A CHIMNEYS, MetalBestos™
4. Code compliance:
   
   The vent system for a gas fired water heater must be installed according to local and state codes, or in the absence of local or state codes, the current edition of
   
   the NATIONAL FUEL GAS CODE, ANSI Z223.1 (NFPA 54) [link to 2012 edition].
5. Draft hood:
   
   use the manufacturer-provided draft hood. Don't omit it as shown in the photo below.

7. Draft hood connection to flue vent connector:
   
   provide at least 12" vertical inches of flue vent between the draft hood outlet and the first elbow or sloping flue vent connector.
   
   This is a manufacturer-recommended detail to improve the flow of exhaust gases [we have not found this in the model codes].
   
   But in effect this 12-inch rise before the first elbow is a building code requirement because the model and adopted building codes require that the installation follow the manufacturer's installation instructions.
   
   See details at BUILDING CODE REQUIREMENT to FOLLOW MANUFACTURER'S INSTRUCTIONS
8. Horizontal flue vent connection length & slope:
   
   Horizontal distance:
   
   no more than 75% of total vertical height of the entire chimney assembly
   
   Horizontal slope:
   
   no less than 1/4" per foot upwards slope per foot of horizontal run.
   
   A portion of the vent pipe (up to 75% of the total vertical height) can be horizontal, but the termination must be vertical. For the horizontal section, install without dips or sags with an upward slope of at least ¼ inch per foot. Install pipe avoiding unnecessary bends.
   
   Pipe joints must be fastened
   
   by sheet metal screws or other approved means.
   
   Support the flue vent pipe
   
   to maintain clearances and to avoid separation of joints or other damage.
   
   Vent pipe must be accessible
   
   for cleaning, inspection, and replacement. Running vent piping through a concealed space or inaccessible space is improper and unsafe.
9. Existing Vents: If using an existing venting system:
   
   Inspect the existing vent system for obstructions, corrosion, and proper installation. Repair or replace the existing flue vent connectors and chimney components if necessary.
   
   The existing vent system must be UL listed Type B double wall or single wall metal vent pipe of either 3 inch or 4 inch diameter and installed according to the vent manufacturer’s instructions and the terms of its listing.
   
   More information: B-VENT CHIMNEYS.
   
   Do not use other materials such as dryer vent hose.
   
   Local codes may be more restrictive and may not allow single wall vent pipe.
   
   Single-wall vent pipe cannot be used for water heaters located in attics
   
   and may not pass through attic spaces, crawl spaces, or any confined or inaccessible location.
   
   Single-wall vent pipe cannot pass through any interior wall.
   
   [Exceptions may be made for non-combustible walls such as solid masonry].
   
10. Power Vent Sharing - Common Venting: Do not share a power-vented-appliance flue:
    
    Do not common vent a natural-draft gas fueled water heater with any power vented appliance.
    
    The sketches below, adapted from the Whirlpool installation guide we have cited, are examples of vent pipe system installations and may or may not be suitable for your specific application.
    
    Consult the NATIONAL FUEL GAS CODE, ANSI Z223.1 (NFPA 54) [link to 2012 edition], a current edition and your local building & fire codes.

[Click to enlarge any image]

11. Venting through existing chimney: [Illustration above]
    
    An unused chimney flue or masonry enclosure may be used as a passageway for the installation of the water heater vent pipe.
    
    Watch out: Before connecting a vent to a chimney,
    
    make sure the chimney passageway is clear and free of obstructions. The chimney must be cleaned if previously used for venting solid fuel appliances or fireplaces.
    
    Also consult local and state codes for proper chimney sizing and application or, in the absence of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1(NFPA 54)-current edition. 

12. Termination of flue vent connector at an existing chimney: [Illustration above].
    
    This item refers to terminating the flue vent connector for the water heater right in the chimney, without extending the vent upwards through the chimney interior, relying instead on the existing chimney flue.
    
    If local codes allow, some [manufacturer specified models] gas-fueled water heaters may be terminated into an existing chimney using the instructions below.
    
    Otherwise, this water heater’s vent must terminate vertically (sidewall or other horizontal terminations are not allowed).
    
    Watch out: Do not terminate the vent pipe in a chimney that has not been certified for this purpose.
    
    Some local codes may prohibit the termination of vent connectors in a masonry chimney. [We warn about this just below].
    
    Common (combined) venting is allowable with vertical Type B vent systems and lined masonry chimneys as long as proper draft for the water heater is established under all conditions of operation.
    
    

    As you can see in this photo, this gas-fueled water heater vent was installed without the manufacturer-recommended 12" vertical rise in the flue vent connector before the first elbow.
    
    Below we show a close-up of heat damage around the draft hood of a gas-fueled water heater installed in a Minneapolis home.
    
    As the homeowner pointed out, that's because this water heater is essentially TOO TALL for this LOCATION [photo of the entire Rheem gas-fired water heater below a low ceiling].
    
    But in our OPINION even with a 12" vertical rise this heater would not vent adequately because it is directly-vented into a large, otherwise unused masonry flue.

    Watch out: in our experience and opinion, the direct termination of a gas fired water heater into a large masonry flue, as illustrated just above, is likely to give serious venting problems, particularly in cold weather when the heater is the only appliance venting into the chimney.
    
    The lower-BTUH of a gas water heater (compared with a heating furnace or boiler) will very often be unable to heat the chimney interior sufficiently to develop a draft.
    
    The result is a back-draft of combustion products out of the water heater's draft hood and into the building.
    
    Such installations are potentially unsafe and risk carbon monoxide poisoning.
    
    See CARBON MONOXIDE - CO.
    
    Do not install the flue vent connector from the water heater into the very bottom of a chimney.
    
    The vent pipe must be installed above the extreme bottom of the chimney to prevent potentially blocking the flue gases.
    
    The vent pipe must be firmly attached and sealed where it enters the chimney
    
    in order to prevent it from falling out, to prevent air leaks into the chimney - reducing the effective draft, and to prevent flue gas leaks out of the chimney. To aid in removing the vent pipe, a thimble or slip joint may be used.
    
    The vent pipe must not extend beyond the inner edge of the chimney a
    
    s it may restrict the space between it and the opposite wall of the chimney.
    

13. OK to vent into a shared B-vent chimney?
    
    Common (combined) venting is allowable with vertical Type B vent systems and lined masonry chimneys as long as proper draft for the water heater is established under all conditions of operation. Do not common vent this water heater with any power vented appliance.
14. Vertical Termination with Listed Chimney Cap:
    
    The gas vent must be terminated in a vertical position to facilitate the removal of exhaust gases.
    
    Vertical exhaust vents must terminate with a listed cap or other roof assembly and be installed according to their manufacturer’s instructions.
15. Vent dampers: Do not install a vent damper
    
    anywhere in the venting system of natural draft gas fueled water heaters.

Gas Fired Water Heater Chimney Codes in the U.S.

See the National Fuel Gas Code, Chapter 24, Fuel Gas, that includes discussion of venting requirements in Section G2427 p. 360, Venting of Equipment (cited at the end of this page).

G2427.3 (503.3) Design and construction. A venting system shall be designed and constructed so as to develop a positive flow adequate to remove flue or vent gases to the outdoor atmosphere.

G2427.6.5 (503.6.6) Gas vent termination. A gas vent shall terminate in accordance with one of the following:

1. Above the roof surface with a listed cap or listed roof assembly. Gas vents 12 inches (305 mm) in size or smaller with listed caps shall be permitted to be terminated in accordance with Figure G2427.6.5, provided that such vents are at least 8 feet (2438 mm) from a vertical wall or similar obstruction.

All other gas vents shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and at least 2 feet (610 mm) higher than any portion of a building within 10 feet (3048 mm).

G2427.7.3 (503.7.3) Termination. Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected equipment draft hood outlet or flue collar.

Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm).

(See Figure G2427.5.) An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [Also see Section G2427.7.8, Item 3.]

G2427.7.6 (503.7.6) Installation. Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space or floor.

The installation of a single-wall metal pipe through an exterior combustible all shall comply with Section G2427.10.15.

G2427.7.10 (503.7.10) Termination capacity. The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached.

Gas Fired Water Heating Venting Standards for Canada

See Chapter 7 beginning at page 152 and also see "Combustion Spillage" beginning on p. 160 in this example code: B149.1HB-00 Natural Gas and Propane Installation Code Handbook

Excerpt:

Gas appliances may be vented to either a chimney flue or a certified vent or factory-built chimney.

When vents are used, they must be certified to the applicable standard and bear a label that indicates that they have been so tested and approved.

It is important not to remove these labels in order to enable field inspection. In the case of Type B or Type L vents, each length extending above the roof line must be certified for exterior use and so identified.

Excerpt:

7.14.4 A chimney shall extend not less than 3 ft (900 mm) above the highest point where it passes through the roof of a building and not less than 2 ft (600 mm) higher than any portion of a building within a horizontal distance of 10 ft (3 m).

Nowhere in these standards is there an acceptance of a short-rise, horizontally-vented, dryer-vent flapper capped or painted-screen-capped water heater vent termination.

Side-wall vented appliances, without exception, make use of some form of power exhaust, never simply atmospheric exhaust. Such vent exits and terminations, if your water heaters were power-vented, cannot be obstructed and must use a listed (approved) termination cap or cover.

Excerpting from GAS FIRED WATER HEATERS - home

Check for proper exhaust venting of combustion products from your gas fired water heater.

Gas-Fired Water Heater Chimney & Vent Codes, Guides, Standards

Above: Gas water heater direct vent clearance distances, adapted from AO Smith's Gas Water Heater's Owners Manual for Gas Models FSPH-75 270 series, cited at WATER HEATER AGE & MANUALS - for all brands.

[Click to enlarge any image]

For more details see the citations below as well as these gas water heater venting guides:

Gas Water Heater Calorifer Geyser Cylinder Codes & Guides

• Canada: B149.1HB-00 Natural Gas and Propane Installation Code Handbook [PDF] (2000) retrieved 2018/02/09, original source: http://www.tagengineering.ca/wp-content/uploads/2015/02/B149-1handbook.pdf
• Canada: CSA Standard B149.1-10 Natural Gas and Propane Installation Code [PDF] (2010) retrieved 2018/02/09, source: http://www.enefen.com/images/previews-CSA_B149.1-10_pre.pdf
• AMERICAN WATER HEATER VENT DETAILS [Illustration] retrieved 2018/02/09,
• BOCK WATER HEATERS, ENGINEERING MANUAL [PDF] retrieved 2018/03/05, original source: http://www.bockwaterheaters.com/Portals/0/Engineering%20Manuals/BWH-Eng%20Man_3-13-Web.pdf
  Excerpts, p. 28
  
  The purpose of venting a gas or oil-fired water heater is to completely remove all products of combustion and to vent gasses to the outside air without condensation in the vent or spillage at the draft hood (except in cases of downdraft or poor stack conditions).
  
  To assure correct venting, use a strong, gas-tight insulated pipe with a cross section equal to that of the flue collar or draft hood outlet and of sufficient vertical height.
  
  During vent installation, avoid sharp turns, long horizontal runs and improper pitches. Maintain proper support of vent connectors and joints, observe clearances from all combustibles, and top the vent outlet with an approved cap.
  
  Type “L” vent is double walled vent. Type “L” is stainless lined and used for oil and Power Gas heaters. Type “B”, due to its temperature rating, can only be used with atmospheric gas water heaters.
  
  All venting installations must conform with local codes. In the absence of local codes, refer to “National Fuel Gas Code” NFPA 54 and “Standard for the Installation of Oil-burning Equipment” NFPA 31 (Tables 21-33 are based on NFPA 54).
• BRADFORD WHITE GAS FIRED WATER HEATERS [PDF], retrieved 2018/02/09, original source: http://www.bradfordwhite.com/sites/default/files/product_literature/238-44219-00G.pdf
• STATE GAS WATER HEATER INSTRUCTION MANUAL [PDF] retrieved 2018/02/09,
• U.S. NATIONAL FUEL GAS CODE CHAPTER 24 [PDF], retrieved 2018/02/09,
  Excerpt:
  
  G2401.1 (101.2) Application. This chapter covers those fuel-gas piping systems, fuel-gas utilization equipment and related accessories, venting systems and combustion air configurations most commonly encountered in the construction of one- and two family dwellings and structures regulated by this code.
• WATER HEATER AGE & MANUALS - for all brands
• More citations and documents are atReferences or Citations

Examples of Improper & Unsafe Gas-Fueled Water Heater Chimneys & Vents

This discussion has moved to its own page

at GAS FIRED WATER HEATER UNSAFE VENT

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-02-24 by Adam G2427.6.4 (503.6.5) "Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (from vertical wall or chimney)

This question is in reference to a gas water heater that needs to be vented through the roof and is located near an existing chimney (cannot vent through chimney).

G2427.6.4 (503.6.5) states that "Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure G2427.6.4."

Does "vertical wall or similar obstruction" apply to an existing chimney that stands 18 inches high with and 18 inch flue extension?

Or, as an alternative way to think of this question, can a gas water heater be vented through a 4 inch pipe at the the minimum height according to Figure G2427.6.4, which would be 1 ft in my application, if it terminates within 8 ft horizontally from the existing chimney (18" by 18" and terminates 18" above roofline?

See https://up.codes/s/gas-vents for Figure G2427.6.4.

Thank you,
Adam

On 2023-02-26 by InspectApedia Editor (mod) - distance allowed from water heater to chimney connection

@Adam,

You say that your gas heater vent is "within 8 ft horizontal distance" from the chimney, but not how close to the existing chimney it actually-is. So your question is a bit tricky.

In my OPINON at 7 ft. 6" (within 8 ft) the nearby chimney might not be considered an obstruction, while if the two are quite close - say inches or a foot apart, the chimney might be an obstruction.

Your local building code inspector is the final legal authority on this gas water heater vent question, but my OPINION is that a chimney of typical dimensions above the roof line MIGHT count as a "vertical wall or OTHER OBSTRUCTION"

On 2023-02-13 by Krista - new installer of water heater did not seal the flue connection

I recently had a new water heater installed. They changed out the flue that goes into the chimney. Is it the installation companies responsibility to seal around the flue pipe that leads into the chimney?

On 2023-02-13 by InspectApedia Editor (mod) - the water heater installer must include proper flue-to-chimney seal

@Krista,

Yes. That would be part of a complete and safe installation and would typically be included in the installation directions for your water heater.

If you tell us the brand and model of your water heater, we can research this further.

On 2023-01-22 by Brian -replacing our 28 year old Lennox Whisper Heat 80% gas furnace

I am considering replacing our 28 year old Lennox Whisper Heat 80% gas furnace but must go high efficiency. I would like to keep my conventional gas hot water tank which is common vented with the furnace into a 6” B-vent to the roof 30’ above.

I believe the B-vent is too large for just the tank vent.

My question, is there an affordable option of 3” or 4” metal flex vent I can run down the B-vent as chase to my tank?

On 2023-01-22 by InspectApedia Publisher (mod) - risk of inadequate chimney draft with just water heater venting into chimney

@Brian,

Smart question. My opinion is that even at a smaller diameter vertical flue for just the water heater, the total chimney height might be too much for the heater to develop a draft.

So I would start by identifying the water heater brand and model, grab its installation manual (we provide hundreds of them here as free PDF down loads), and see what venting distances and sizes the manufacturer says are acceptable.

Also you might look into converting the water heater to a direct vent exhaust if the model permits that.

Watch out: insufficient draft at a gas fired water heater risks dangerous carbon monoxide release and poisoning of buiding occupants

On 2023-01-23 by Brian

@InspectApedia Publisher, thank you. If I go the route you suggest, could I use the then abandoned 6” b-vent to supply combustion air to the new furnace and water heater? I would like to minimize the number of holes cut through the building envelope.

On 2023-01-27 by InspectApedia Publisher (mod) - use abandoned water heater vent to provide combustion air to new furnace?

@Brian,

Probably, yes, but I would want to be sure that not just the diameter but the length of run and its orientation (vertical, bends, etc.) will never short-change the equipment of combustion air. That's why I want to start with the specific brand and model of equipment.

Standard calculations look at input BTUh when calculating chimnney and vent sizes and combustion air requirements - varying of course by equipment type.

On 2022-11-19 by Jim Y. - is this the right height of water heater vent above roof?

I have a water heater vent penetrating near the eve of a 12/12 pitched roof. If I hold to the 2’ above any part of the roof 10’ away, this means the pipe will be 12’ tall above the penetration. is that correct ?

On 2022-11-20 by InspectApedia (Editor) (mod) - required gas water heater vent height above roof

@Jim Y.,

I'm not sure we have the same view of your situation - maybe you can attach a photo or sketch.

In general the clearance is the horizontal distance from the top of the chimney to the nearest surface.

You'll also want to read Charlie Buell's comments on this page.

@Jim Y.,

Here is typical gas vent height language from the US Fuel Gas Code

Gas vents shall extend at least two feet above the highest construction, such as a roof ridge, parapet wall, or penthouse, within ten feet of the vent outlet whether the construction is on the same building as the chimney or on another building.

Here is a more-complete quote from New York's adopted version of the National Fuel Gas Code

503.5.4 Chimney Termination

Chimneys for residential-type or low-heat appliances shall extend not less than 3 feet (914 mm) above the highest point where they pass through a roof of a building and not less than 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm).

Chimneys for medium-heat appliances shall extend not less than 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm).

Chimneys shall extend not less than 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar.

Decorative shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with the manufacturer's instructions.

On 2022-11-16 by Jes - do these gas water heater vent codes apply to mobile homes?

Is this the same for mobile homes, too?

On 2022-11-16 by InspectApedia (mod) - gas water heater codes for mobile homes

@Jes,

The codes for many aspects of mobile homes are found here

BUILDING CODES & STANDARDS FOR MOBILE HOMES
https://inspectapedia.com/Manufactured_Homes/Mobile_Home_Codes.php

and there you will find the link to

MOBILE HOME WATER HEATER CODES & STANDARDS

On 2022-09-27 by Zehringer David - can I use existing power exhaust for another device to also vent my new gas water heater?

I’m replacing a 50 gal 40,000 btu NG water heater with another same size. Can I take the “power exhaust” off old same sized old unit just four screws

Then install on new “natural draft” unit of same size? Saves me $400

On 2022-09-27 by InspectApedia (Editor) - don't vent a natural draft water heater through a power-exhaust vent system

@Zehringer David,

Sorry but I don't understand how you could possibly vent a "natural draft" water heater out through what was a power-exhaust vent system.

Typically a power-exhaust vent uses a fan to blow the combustion products out through a side-wall.

Watch out: For a natural draft water heater, excessive draft causes by a power vent risks improper and unsafe water heater operation.

A natural draft gas appliance relies on the draft developed in a properly-sized metal (or other) chimney to safely vent combustion products..

Just venting out through a wall or through a too-short chimney is very dangerous, risking backdrafting and dumping fatal carbon monoxide gas into the building.

Check the installation manual for your new water heater and follow its venting instructions.

On 2022-09-28 by Zehringer David

I currently have a 50 gal 40,000 btu NG hot water heater And I have a unused 180,000 btu. Furnace with a built in water heater the same furnace unit that STATES it will also produces 135 gals hot water per hour, are these two output comparable outputs given different types of units? Or does the tank unit out produce hot water in a long use application.

There are two bathrooms, two kitchens and two laundry rooms currently handled fine with the 50 gal tank. Can the tankless 135 gal per hr keep up like the 60 gal tank unit ??

On 2022-09-29 by InspectApedia-911 (mod) - can I take old “power exhaust” off then install new “natural draft” unit?

@Zehringer David,

Since we don't have the brand and model of your heating boiler, and just using the data that you've provided, I think it's likely that your heater, that is the one that you've not used, is including a tankless coil that can produce hot water at the rate of about two and a half gallons per minute. That's a flow rate not necessarily a total quantity even though that total quantity was given.

On 2022-09-27 by Zehringer David

The power vent system must draw a specific amount of combustion air through the burner, for a 40,000 btu burner a constant, X this is in-order to properly fire a 40,000 btu heater, this correct.

Therefore, changing the burners should not create any excess or any deficiency in the air flow from unit to unit, if the units ratings are properly stated and correct.

Therefore changing the water heater unit shouldn’t present any back draft hazard then should it.

Power vented units are used primary where 2000 square feet of available air space is not available to draw on for combustion air and B. a side vent is needed.

On 2022-09-27 by InspectApedia (Editor)

@Zehringer David,

Thanks for the discussion - though I'm not sure we have all that's been said quite correct.

I agree that a system may use a blower to obtain combustion air but as you doubtless know there are many designs that vent out through a sidewall and plastic venting whose exhaust vents could not then be used safely for an atmospheric vented gas water heater.

Watch out: to be safe, Let's name the water heater brands and models involved so that we or anyone can look at their installation requirements as given by the manufacturer.

On 2022-08-30 by Dell - gas water heater vent slopes "down" to the chimney

My slope is 2” downward before going upward is that dangerous on my gas water heater

On 2022-08-31 by InspectApedia-911 (mod) - is 2” downward before going upward dangerous on gas water heater

@Dell,

Watch out: It's very possible that your heater isn't venting correctly.

Check the draft hood for burn marks or to see if you feel exhaust spilling out there. If you do, it's definitely unsafe.

Watch out: even then, I worry that in changing weather conditions, such as in cold weather, the heater may not vent properly. The risk is fatal carbon monoxide (CO) gas poisoning.

On 2022-06-09 by Declan - larger vent pipe if I add another water heater?

I have two 40 gal gas water heaters venting into a 4" vent pipe i want to add a third water heater. Do i need to increase the size of my main vent pipe which as said is 4". Thank you

On 2022-06-10 by InspectApedia (mod) - increase the size of main vent pipe

@Declan,

Almost certainly yes.

Usually with each additional water heater after one, each successive flue pipe is one size larger.

But of course the length of the run and then input btus are important.

Identify the brand and and model, pick up through IO manual, and see what the manufacturer says about shared flues. Or post that information here and we'll see what else we can find.

Watch out: as perhaps you already understand, inadequate venting can be very dangerous and can even produce fatal carbon monoxide gas in the building.

On 2022-05-17 by Laura - Is this water heater vent pipe installed correctly?

Is this installed correctly?

On 2022-05-17 by Friedmandaniel911 (mod) - check owner's manual for proper installation of this gas water heater

@Laura,

We can't say that a water heater is installed properly from just a partial snap of a portion of the equipment.

If your only question, considering you're posting on a water heater vent page, is about the vent - we can't see all of it, and can't even see underneath that foil tape to assure that the metal exhaust flue vent connector is properly mounted to the draft hood over the water heater.

When the heater is running do you feel hot exhaust spilling out at that vent opening? If so, the vent isn't working properly.

Do you have working CO and smoke detectors properly installed, located, tested in your home?

Do you have a copy of the installation and owner's manual for your water heater? If so, you can certainly check the installation requirements given there.

see WATER HEATER AGE & MANUALS - for all brands - live link at Recommended Articles on this page.

Beyond that,

What I can see doesn't raise a serious concern though I'd want to know

• that there are appropriate shutoff valves
• that the vent is completed properly and safely
• if you're in an earthquake zone that seismic restraints are in place
• that the heater temperature is set to a safe level
  etc.
  

On 2022-04-27 by Tom

Can I connect my water heater to an existing attic vent cap

On 2022-04-27 by Inspectapedia Com Moderator

@Tom,

Sorry I don't understand the question.

"Attic vent cap" - what's that? Perhaps you could attach a photo or a sketch. Use the "Add Image" button.

On 2022-04-01 by Matt

Can I vent both a LP water heater and LP furnace through the same schedule 40 PVC sidewall vent (chimney) if both appliances are located on the same floor (basement) and in close proximity to each other?

On 2022-04-01 by Inspectapedia Com Moderator - each direct vented appliance should have its own intake and exhaust vents

@Matt,

I wouldn't try that.

Typically each direct vented appliance expects to have its own intake and exhaust vents.

You don't give a diameter or length or other features of your exhaust system but it's possible that you would not be providing adequate the combustion air or exhaust, either of which could cause unsafe conditions even risking a carbon monoxide poisoning hazard.

We are pretty much obligated to stick with a manufacturer's installation instructions.

On 2021-11-17 by William in Missouri - has improper venting made my water heater unsafe or shortened its life?

Bought a new house with a 50 gallon power vented Bradford White gas water heater.

However, the installer failed to install the manufacturer recommended condensation drain tube so condensation flowed back into the fan and tank and percolated around the hose clamps on the vent pipe corroding the vent fan chassis and the exterior of the tank all the way down to the pan.

After inspection by another licensed plumber I contacted the installer to correct and he simply added the condensation drain tube that was initially omitted.

My questions are 1) has the usable life the unit been shortened from a year of operation after improper installation, and 2) has it exposed us in any way to chronic low level CO due to the improperly vented appliance?

On 2021-11-17 by (mod) condensation of the water heater controls, components, tank, vents, piping, etc means water heater's life has been reduced

@William in Missouri,

Shown here is a Direct-Vented Bradford White gas water heater.

Thank you for an important safety and water heater life question on the effects of mis-handled condensate.

My general OPINION is that any condensation of the water heater controls, components, tank, vents, piping, etc. certainly introduce at least a reasonable risk that the heater's life has been reduced, but a more-accurate answer ought to come from a careful inspection of the equipment to see its actual condition.

The possible effects of the improper condensate drain on the heater range from trivial-cosmetic to serious, shortened life or unsafe equipment.

So let's base an answer on a bit of objective data: an inspection.

About the low-level CO exposure, we have no basis yet for claiming that there was ANY abnormal CO leakage or exposure from your water heater. To make that assertion you'd need inspecting and testing that found that such leakage was occurring.

If you had a CO detector properly installed, located (nearby) and tested to be sure it's been working, and if that device never sounded, then it's not likely that there was a measurable hazard.

A typical home / residential CO detector (Carbon monoxide detector) uses a sensor that detects very low levels of CO, down to perhaps 10 ppm.

That's to enable the detector to sound an alarm at different CO levels depending on the duration of the presence of CO that the device has measured.

Kidde, a major vendor of fire and safety equipment gives this good representative data of the response time/level of CO detectors:

40 PPM CO for 10 hours
50 PPM CO for 8 hours
70 PPM CO for 1-4 hours
150 PPM CO for 10-50 minutes
400 ppm CO for 4-15 minutes

For a healthy adult OSHA sets the maximum allowable concentration for continuous exposure for healthy adults in any eight-hour period at 50 ppm of CO.

See details at

CARBON MONOXIDE - CO

It would be helpful to know the specific water heater model about which you raised the condensate question so that we could look at the manufacturer's instructions.

On 2021-11-18 by William in Missouri

@Inspectapedia Com Moderator,

The model number is RG2PV50T6N19

I would provide the link but I don't want to impede delivery of this message

Thank you for your attention.

On 2021-11-23 by (mod) - How does mis-handled condensate in gas water heater installation affect heater life expectancy and potential CO exposure?

@William in Missouri,

For other readers, see this

• Bradford White RG2PV50T6N19 Water Heater INSTALLATION MANUAL [PDF]

and this

• Bradford White PV-SERIES WATER HEATER SERVICE MANUAL [PDF]

or see all of our Bradford White water heater manuals

at BRADFORD WHITE WATER HEATER AGE & MANUALS

Continuing: from the IO manual we have

Venting System Condensation

Condensate formation does not occur in all installations of power vented water heaters but should be protected against on installations where condensation can form in the venting system

Formation of condensation in the venting system of power vented water heaters is dependent upon installation conditions including, but not limited to:

• ambient temperature and humidity of installation location;
• ambient temperature and humidity of venting space;
• vent distance and slope;
• and product usage.

In order to effectively control condensate from adversely affecting the mechanical components of the water heater several methods may be employed:

1. For horizontal installations the vent pipe can be installed with a downward slope (not less than 1/8" (3 cm)) and away from the blower.

2. In order to prevent condensate from draining back into the blower (vertical or horizontal runs), an optional condensate kit is available as a service part (Condensate kit, p/n 239-45875-00).

A molded exhaust adapter with drain outlet is secured with one hose clamp, to the vent pipe.

Tubing is provided to drain any accumulated condensate away from the water heater and to a suitable drain.

The kit comes complete with instructions for proper installation.

What I take from this is that the company knows that in some installations, failure to adequately direct condensate out of the heater can be a concern - hence their condensate drain hose kit is provided.

A read of the IO manual and of the service manual don't give further warning about this problem nor the possible safety concerns that could arise.

We're back at my earlier advice:

The impact on the remaining life of your water heater from previous condensate backflow over some unspecified period and at an unspecified rate, isn't possible to assess from text or discussion.

But an experienced technician could certainly make a visual inspection of your water heater and could express an opinion about the nature, location, and specific components affected by any corrosion she can find.

If those are light-superficial then there's probably no measurable impact on the heater's remaining life.

On 2021-09-24 by (mod) - rooftop clearance to rooftop HVAC equipment

@Jake,

I'm not sure of just what is your concern. But certainly that's not a gas water heater, this page's topic.

Is the height your concern?

On 2021-09-23 by Jake

Can you tell me if this split system has incorrect install problems

On 2021-08-27 by (mod) - Do I need to replace the single wall pipe with 4-inch type B Vent?

@Dan,

The final legal authority is your local building inspector.

The final technical authority are the manufacturer's installation instructions for your specific water heater brand and model.

That whining and warning out of the way, no, you can use single wall metal flue vent connector pipe between the heater and the chimney as long as you're meeting clearances from combustibles.

But I think I see aluminum - if so, that's not usable; use steel.

On 2021-08-27 by Dan

I'm replacing a natural gas fires water heater with a new natural gas water heater.

I have about four feet of 4-inch,, single wall vent pipe that connects the water heater flue to a Type B vertical exhaust stack.

Do I need to replace the single wall pipe with 4-inch type B tubing? There are no combustible materials in

 

On 2021-06-04 by (mod) - building code requirement for 12 inch rise in gas vent before first elbow or bend

@A Plumber,

Thanks for a helpful question.

Please find it repeated and my detailed reply also now at:

BUILDING CODE REQUIREMENT to FOLLOW MANUFACTURER'S INSTRUCTIONS https://inspectapedia.com/plumbing/Gas-Water-Heater-Venting-Codes.php#ManufactCode

About the 12 inch rise of vent before the first elbow, the article above states:

This is a manufacturer-recommended detail to improve the flow of exhaust gases [we have not found this in the model codes].

But remember that as codes require the installation to comply with the heater's manufacturer's installation instructions, that makes the 12 inch rise a defacto code requirement as well.

This example text is an example from the Whirlpool gas water heater IO manual cited in the article above

Vent Installation

To improve the flow of exhaust gases, we recommend that a minimum of 12 inches of vertical vent pipe be installed on the draft hood prior to any elbow. A portion of the vent pipe (up to 75% of the total vertical height) can be horizontal, but the termination must be vertical.

Here is an example building code citation requiring that the manufacturer's instructions be followed.

This example is from the 2014 New York City Mechanical Code which is, of course, an adoption of the model codes like the National Mechanical Code

NYC Mechanical Code Section 304 Installation

304.1 General

Equipment and appliances shall be installed as required by the terms of their approval, in accordance with the conditions of the listing, the manufacturer's installation instructions and this code. Manufacturer's installation instructions shall be available on the job site at the time of inspection.

304.2 Conflicts

Where conflicts between this code and the conditions of listing or the manufacturer's installation instructions occur, the provisions of this code shall apply.

Exception:

Where a code provision is less restrictive than the conditions of the listing of the equipment or appliance or the manufacturer's installation instructions, the conditions of the listing and the manufacturer's installation instructions shall apply.

So you can see that by inclusion the manufacturer's instructions in fact become a "code requirement" where the "code" is less-restrictive,

therefore the 12-inch minimum vent connector rise before the first elbow is required by the model as well as adopted building codes even where it is not explicitly stated in the code itself, as long as it appears in the installation instructions for the gas-fueled equipment that you are installing.

Of course your local plumbing or building code compliance inspector is the final legal authority.

On 2021-06-04 by A Plumber - authoritative source for the 12" minimum vent connector rise before the first elbow

I am having trouble finding an authoritative source for the 12" minimum vent connector rise before the first elbow.

While I understand this is best for priming the vent and establishing flow, it seems impossible to convey this to other plumbers, since our code book and the NFPA makes no mention of any minimum.

It seems very much a best practice, and not a hard rule.

On 2021-03-26 - by (mod) -

@julie, sorry I don't quite get the question. Do you mean a 3-foot rise across the three feet of horizontal run? Of course not. Perhaps you can clarify what three foot rise we are discussing

On 2021-03-26 by julie

If you have a 3" vent pipe on a hotwater heater that exits into the chimney with a 3' pipe to the wall do you need a 3' rise?

On 2021-03-25 - by (mod) -

@Anonymous, I'm not sure I understand your situation exactly but in general we never connect heating appliances on two different floors to the same flue.

On 2021-03-25 by Anonymous

can you vent a hot water tank from the crawl through the floor and connect to a furnace witha T on the next floor then vent to the roof

On 2021-03-16 - by (mod) -

@Manuel,

You will want to check the installation instructions from the manufacture of that A.O. Smith water heater as most likely the manufacturer limits the number of turns and bends that you can make in the vent system. Too many turns and bends means that the venting may be in adequate and unsafe.

On 2021-03-25 by (mod) - are the section-connections in my my water heater flue vent safe?

@Bob,

With the obvious reclama that no one can perform a safety inspection by text alone, what you describe sounds secure to me with three screws and foil tape holding the connection between two metal flue vent Parts together.

On 2021-03-24 by Bob

Water heat 4" venting pipe connected to elbow appears short, only about 1/2" is inserted into elbow and 3 screws holding. Seam is covered with foil tape. The overall vent pipe is secure with ceiling clamp and does not move. Question is whether the 1/2" insert into elbow is okay with 3 screws and foil tape?
please advise
Thanks
Bob

On 2021-03-14 - by (mod) - some water heaters are designed to vent through a side wall, others, not.

@Alesia,

Certainly, there are both tankless- and tank-type propane and natural gas (shown below from AO Smith as its Signature 40-Gallon Short 6-Year Limited 38000-BTU Natural Gas Water Heater) that can be vented directly out through a side wall.

Check with your local plumbing or building supplier

On 2021-03-13 by Alesia

We have a propane hot water tank in our basement that the previous owner vented out the side of the basement wall.

Apparently the hot water tank is one that is suppose be vented through a chimney. Is there a replacement propane water heater that we can get that vents through the wall and if so what would you suggest and what would we need to get it installed properly?

On 2021-02-02 - by (mod) - Venting a gas water heater inside of an enclosure is dangerous, could kill someone,

MB

Watch out: Venting a gas water heater inside of an enclosure is dangerous, could kill someone, and even if nobody is inside the enclosure to be killed, risks improper and unsafe operation, inadequate combustion air, production of fatal carbon monoxide, and perhaps other hazards.

A gas water heater must be vented to the outdoors.

If cutting through the roof is inconvenient or difficult, probably possible to vent out through a side wall and then up to an adequate height above the roofline.

On 2021-02-02 by MBriggs

For a a natural gas fired water heater installed outdoors in a galvanized water heater enclosure, are you required to cut through the top of the enclosure and vent above the roofline? Or is it acceptable to allow it to vent inside of the outdoor enclosure?

On 2021-01-25 by (mod) - share common exhaust vent for two direct vent gas water heaters?

Mike:

A condensing or high efficiency heater that vents directly out through a side wall might use PVC vent materials as approved by the manufacturer, but none of those vents that I have seen or installed are shared; further, there is a required separation distance between them.

However the final word on your question should come from the manufacturer of your specific water heater brand and model.

For other readers: A conventional oil or gas fired water heater vents through a metal flue vent connector and a UL-listed chimney (metal such as a B-vent, or masonry) never through plastic.

On 2021-01-25 by Mike

Can you vent two water heater through one single PVC pipe? These are power vented water heaters

On 2021-01-22 - by (mod) - Gas water heater got wet in flooded celler

Mack:

Depending on just what got wet, I'm concerned that a previously-flooded water heater could be unsafe.

I'm unclear how you could possibly move the burner of a gas fired water heater outdoors;

But I agree it sounds as if there is an air flow or combustion air or gas orifice clog problem.

On 2021-01-22 by Mack

Gas water heater got wet in flooded celler try lightin it lights but burns out notice when remove buner to out side works fine not gettin air vent on bottom is problem. Any ideals to repair thanks mack

On 2021-01-11 by Bob

No worries Oliver lol
I didnt actually see it but the tech said that the there was some pitting on the upper end of the heat exchanger tube. I dont think he actually saw a whole but said that it likely would leak when it was heated.

Either way Im happy to get a new system since its a rental
thanks again for the help
Bob

On 2021-01-10 - by (mod) - leaks found in gas equipment: unsafe!

Thanks Bob that detail will help others.

Apologies for, like the Dickens character, asking for still more, but do you know where the drip originated?

On 2021-01-10 by Bob

Watch out: Just to follow -up, Turns out that in addition to the exhaust leak, the heat exchanger had a small leak so they are going to replace the whole unit.

The tech said the water dripping on the AF rod or near it was causing the problem.
thanks for your help

On 2021-01-10 - by (mod) - check for a flue gas spill switch

Thanks for that interesting follow-up, Bob.

Sure some water heaters have a flue gas spill switch that can shut down the heater. Attach a photo of the heater's draft hood and we may be able to point out the sensor and its wiring.

On 2021-01-10 y Bob

I just discovered an air leak from the 4" PVC exhaust pipe where it fits into the heater. Waiting on an HVAc guy to come and seal it. I wonder if the water heater has a CO monitor shutoff and that was the issue or maybe there is some other problem like with combustion air as you say.

On 2021-01-10 - by (mod) - inadequate combustion air at a gas water heater is very dangerous

Bob:

Watch out: this sounds unsafe to me; if there is inadequate combustion air the risk is fatal carbon monoxide poisoning - death of building occupants. Be sure you discuss that with the building manager and give that warning in writing as well.

And be sure that there are properly located, installed, tested CO detectors as well a smoke detectors in your apartment.

On 2021-01-10 by Bob Allen

Im living in an apartment with a direct vented tankless water heater (State GTS-540-NEH) , located in a bedroom closet. The water heater keeps shutting off with error code: 391 "Air-fuel ratio rod failure." The bldg manager is ordering a new AFR rod assembly.

I later noticed that if I keep the door cracked open the water heater works fine. My worry is that the real problem is a blocked combustion air inlet since keeping the door open seems to fix the problem.

Also the closet is not sealed with a 1/2" gap under the door. Apparently not enough to avoid the shut off but also worrysome regarding CO and fumes even if the water heater is fixed. Does the code require a sealed closet for a direct vent system?
thanks
Bob

Reader comment: Safe Gas B-vent Clearance Distances Clarification

Daniel,

Watch out: while your drawing [above] is consistent with whirlpool drawings cited, it is not consistent with fuel gas code that Whirlpool says to follow for a persons applicable area.

Charlie Buell

Charles Buell Inspections, Inc, 206 478-7371 17123 22nd Ave. NE, Shoreline WA 98155 Email: charles@buellinspections.com Website: www.buellinspections.com, WA Licensed Home Inspector #220, ASHI Member #246514 ASHI National, Technical Review Committee Adjunct faculty at Bellingham Technical College

Moderator reply:

Thank you Charlie, we'll add your detail and helpful drawing in the original article.

...

Continue reading at GAS FIRED WATER HEATER CHIMNEY & VENTING DEFECTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

GAS FIRED WATER HEATER VENTING CODE FAQs - questions & answers posted originally on this page.

Or see these

Recommended Articles

• CHIMNEY CODES & STANDARDS
• CHIMNEY HEIGHT & CLEARANCE CODE
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• GAS FIRED WATER HEATERS - home
• GAS FIRED WATER HEATER CHIMNEY & VENTING DEFECTS
• GAS FIRED WATER HEATER VENTING CODES
• GAS FIRED WATER HEATER VENT UNSAFE
• GAS HEATERS, HIGH EFFICIENCY
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• METAL CHIMNEYS & FLUES - home
• METAL CHIMNEY INSTALLATION MANUALS
• TYPE B-VENT CHIMNEYS
• TYPE B-VENT ROOFTOP CLEARANCE
• TYPE L VENT CHIMNEYS
• WATER HEATER AGE & MANUALS - for all brands

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GAS FIRED WATER HEATER VENTING CODES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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