Recent questions and answers about direct vent chimneys or exhaust for heating appliances.

This article series describes side wall vent systems for conventional & mid-range-efficiency heating boilers, furnaces & water heaters.

Recent Q&A on Direct Vent or Side-Wall Vent Chimneys & Flues

These FAQs were posted originally at DIRECT VENTS / SIDE WALL VENTS - be sure to review the advice given there.

[Click to enlarge any image]

The page top photo of a direct vent PVC pipe too close to ground level is discussed in the FAQs on this page.

On 2018-10-19 by Sheila

I live in northern Virginia, and we normally get snows that usually total 5-10 inches per storm but with the rare 15 or more inches.

My HVAC company installed an air intake pipe whose opening is only abut 9.5 inches from the ground. I understand that this is inadequate clearance not only because of potential rodent entry but because blowing snow (and also in my case, mud) could be blown inside the pipe.

The exhaust pipe has a hooded extension whose opening is a wide as 4.5 inches in places, which my pest control contractor says is an invitation to birds, etc. I am also concerned about exhaust being taken in by the air intake pipe. I have attached an photo of my setup. I would appreciate any feedback.

On 2018-09-29 by (mod) - I feel sick when the windows are open

it's possible. Normally 10 feet from the window should be adequate clearance. However there could be special draft or wind condition that is blowing their combustion exhaust in your window.

On 2018-09-29 by Kelly

My neighbor's house (great neighbors and I love them!) is about 10 - 12 feet from the side of my house. We both have two story homes.

They installed a new gas heater and water heater and put new venting pipes with some kind of fan that blows on the side of their house that faces mine and sometimes I feel sick when the windows are open and it blows stuff out. I also feel like I can smell something when it vents.

Can this cause carbon monoxide to build up in my house? Thanks

On 2018-02-28 by Nathan

What happened in the photo at the top of this page, with the soot on the siding?

This has happened to a friend's house, the sidewall vent top/cover appears to have burned through, and maybe some leaves fell onto/through the bird-screen (which was facing upwards).

He mentioned reading that you shouldn't use gas fireplaces (what he has) for more than 2 hours, but said he has in the past run it for ~10 hours straight. My thought is the cover metal was compromised by the intense heat, causing it to oxidize and fail, then leaves fell in to produce the soot which wasn't deflected as the cover was mostly eroded. Ideas?

On 2017-11-25 by (mod) -

LP tank?

On 2017-11-25 by Steve

Can I vent propane heater above outside tank in MN

On 2017-10-13 by (mod) - good luck on your quiz

Dave, this sounds like a test question, and one that's confusingly-written.

There are no "pros and cons" - a vent has to be properly sized for adequate venting and adequate combustion air intake.

The manufacturer's installation specifications for a direct vent system will include comment on size changes to adjust for distance runs and also will normally limit the number of elbows and bends.

On 2017-10-13 by Dave

What are the pros and cons of over sizing a concentric vent for a condensing furnace?

On 2017-09-30 by Tim Collins

How far do furnace vents have to be from tankless water heater vents

On 2017-09-26 by (mod) - how far apart does each terminations must be - follow the codes & the heater manufacturer's instructions.

Mike:

Good question. Typical code language just says follow the manufacturer's instructions. (So it'd help to know the brand and model of your three direct-vent gas boilers). Then looking at a typical gas boiler installation manual we found this:

Proper clearances to combustibles must be maintained per UL and vent manufacturer requirements. The UL, National Fuel Gas Code (ANSI Z223.1/ NFPA54)1 and CSA B149.1-10 guidelines are often the basis for state and local codes.

AERCO's recommendations follow the guidelines of these agencies, unless more stringent codes govern the installation site.

The venting and combustion air systems must meet all applicable code requirements.

All Canada installations must comply with CSA B149.1 installation code.

At GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES we provide a ather complete list of required clearance distances between the air intake or combustion gas exhaust vents for direct vented heating appliances. that pertain to fireplaces and also to other direct-vent gas appliances.

Depending on the manufacturer (brand) and model, the required offset between vent terminations will typically be 24" to six feet - depending on brand/model.

We may not find an exact specification for your case as it's not anticipated in any of the installation manuals I reviewed. So the "right answer" for you, I'm sorry to have to say, is "it depends ... " on what the manufacturer of your boiler brand and model says when you call their technical support.

If that contact were impossible I'd look at specifications that make sure that for vents that combine both intake air (for combustion) and exhaust, that no vent will interfere with the air intake of one of the other boilers. For example, an Aerco boiler installation guide wants you to keep these clearances

Aerco Boiler Installation Guide on Vent Clearances to Grade

a. At least 12 inches (30.5 cm) above finished grade, or at least 12 inches (305 mm) above the normally expected snow accumulation level in geographical areas where snow accumulates.

With a vent termination clearance of at least 4 feet (1.2 m) from any air openings into a building.

Massachusetts Guide on Sidewall Vent Griound Clearance Distance

In Massachusetts, when side-wall venting is used, the vent termination must be located a minimum of 4 feet above grade.

For detailed information pertaining to side-wall venting within the Commonwealth of Massachusetts, see pages 11 and 12 in GF-128 (Innovation) or GF-147 (ReCon).

b. At least 3 feet (0.9 m) above any forced air inlet located within 10 feet (3.1 m). [I interpret this to include air intake for each of the boilers]

c. At least 4 feet (1.2 m) horizontally from electric meters, gas meters, regulators and relief equipment.

Also take a look

at DIRECT VENT INSTALLATION, SNAFUS & SPECS

where I will add any other specifications I can find.

On 2017-09-26 by Mike

I'm installing 3- direct gas fired boilers how far apart does each terminations must be

On 2017-09-11 by (mod) - Direct Vent Termination Clearance Distances, Codes, Specifications

Terry,

You will want to review GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES Separate Table for Direct Vented Gas Appliances
at https://inspectapedia.com/chimneys/Gas-Heater-Direct-Vent-Clearances.php

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.

Goodman GMVC96 IO Manual on Vent Termination Clearance Distances

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

the vent pipe diameter
the number of bends or elbows

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

3 elbows 85 ft

4 elbows 80 ft

and so on, dropping another 5 ft. in length for each elbow up to a maximum of 8 elbows and 60 ft.

You can find the manual I mention at our list of HVAC manuals provided

at GOODMAN HVAC MANUALS

On 2017-09-10 by Terry - I want to move the direct vent exhaust - is that OK?

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

On 2017-08-08 by Russell - My idea was to gas through the chimney and intake under the porch.

I am changing all to propane. New furnace (96% & 100,000BTU) with 2 inch vents; New Tankles water heater (98% & 199,000BTU) 3 inch vents. Replacing an Oil Burner.

I don't care where it's vented. 2 story home with full basement and attic.

Chimney is central to structure, straight as an arrow with an 8" flue. The house has a half wrap around porch with 3' of clearance and surrounded with open latice.

My idea was to gas through the chimney and intake under the porch. Or can I do both under the porch? Or I have a straight run through the crawl space 30 feet to the non-porch side of the house--seems this might be the easiest way.

On 2017-04-15 by (mod) - clearance from a mechanical air intake and an operable window?

Yes Jake, those clearance distances are given in GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES - table of clearance distances

On 2017-04-15 by jake

Does anyone know if there is a clearance from a mechanical air intake and an operable window?

Specifically I have an outside air intake connected to the return ducting on the furnace

. It is about 2 feet from a operable basement window. I'm remodeling the basement and if i could slide that ducting closer to the window that would be incredibly helpful (no problems with joists or anything like that so easily moved).

Anyone know how close I could put it? It doesn't seem like there should be a minimum to a window.

On 2017-03-27 by (mod) - what is the MAX. DISTANCE of a gas water heater (conventional) to the exterior wall (vs. power vent)?

Cristina:

• 50 feet horizontal distance for atmospheric vented gas appliances
• 55 feet horizontal distance for a Bradford White power-vented gas water heater depending on model size, btuh etc.
• Some tables for power vent systems give much greater lengths (up to 300 ft) depending on the appliance, vent design, etc.
• With a side wall power vent on a gas heating appliance, the specific distance allowed will vary as per the instructions of the manufacturer of the specific venting product or water heating product.

Bradford White Water Heater Direct Vent Specifications

Using a Bradford White water heater manual as an example, http://www.bradfordwhite.com/sites/default/files/product_literature/45917E.pdf
and excerpting:

The water heater must be located close enough to the outside wall to keep the venting distance within the maximum distance described in the installation instructions

Distances allowed vary by vent diameter (and of course water heater size and vent model and power) but are long, ranging from 30 ft. to 160 ft.

Using a Bradford White gas water heater vent article as a second model, and excerpting

BOCK WATER HEATER VENTING SPECIFICATIONS [PDF] , retrieved 2018/11/21, original source: http://www.bockwaterheaters.com/Portals/0/4-Venting_08_06.pdf

An “individual” vent is defined as a single independent vent for one appliance. “Total Vent Height” is the measured vertical distance between the flue outlet and the vent top.

The position or rise of a connector – or the location of an offset – has no effect on the “Total Vertical Height.” “Length of Lateral” is the horizontal distance or offset between the flue outlet and the final vertical portion of the vent.

The company then gives venting tables (in a separate ! document that does not load)

Damn.

Continuing to look for absolute numbers (avoided in the fuel gas code) and pasting in a few interesting examples:

Looking at an AO Smith document we're reminded that your atmospheric vent has to slope up 1/4" per foot - in a basement that alone would give a practical limit on the maximum length to vent before considering vent diameter and total distance.

Except:

This water heater is a Category 1, non-direct vented appliance. The vent pipe must be sized and installed in accordance with all local and provincial or state codes and with the latest edition of

“Natural Gas and Propane Installation Code” CAN/CSA-B149.1 in Canada,

“National Fuel Gas Code” ANSI Z223.1 (NFPA 54) in the U.S.A.  

So ultimately that's were we need to go to look at maximum length for atmospheric-vented gas appliances.

The code - subject to argument and amendment - includes

Maximum Horizontal Vent Distance

- Any angle greater than 45 degrees from the vertical is considered horizontal.

The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall not be greater than 75 percent of the vertical height of the vent. with offsets allowed if the maximum vent capacities are reduced accordingly (see 10-1.3 and 10-2.5).

The total projected horizontal distance of a vent offset (see Figure G.12), plus the horizontal vent connector length serving drafthood-equipped appliances, shall not be greater than 75 percent (or 100 percent) of the vertical height of the vent above the draft hood for single-wall (or double-wall Type-B) vent pipe, respectively.  

Amerivent's Vent Sizing Guide on Vertical Venting Height - 0 to 50 ft.

Finally, using Amerivent's

• VENT SIZING GUIDE [PDF] Retrieved 2018/11/21, original source: Amerivent, 5030 Corporate Exchange Blvd. SE Grand Rapids, MI 49512 USA, Tel: (800) 252-8467 - http://www.ameri-vent.com/files/assets/files/1366372183_Sizing26ApplicationGuide1.pdf

you'll see in tables that before considering the vertical venting height (you will have to connect to a vertical chimney or flue or the system will not vent safely) the horizontal run distances range from 0 to 50 feet depending on vent size and the total BTUh being vented.

On 2017-03-27 by cristina

what is the MAX. DISTANCE of a gas water heater (conventional) to the exterior wall (vs. power vent)?- in other words how far can air flow go freely?

On 2017-03-21 by (mod) -

Sorry I don't understand the question.

But in discussing a direct vent chimney, the installation manual for your specific brand and model will give clearance distances from windows, doors, or other air intakes or exhausts.

On 2017-03-21 by Anonymous

What is the minimum clearance from combustibles for a 2 separate pipe system for a wall venting system?

On 2017-02-21 by (mod) -

Joc

I'd follow the table above, as there are multiple considertions; for example a blank wall isn't the same as a wall with a window. 10 feet is generally good.

On 2017-02-21 by Jocelyn

How many feet do you have to have between two houses that share and alleyway if you want to install a direct vent gas fireplace?

On 2017-02-21 by (mod) - distance to adjacent buildings

Joc

I'd follow the table above, as there are multiple considertions; for example a blank wall isn't the same as a wall with a window. 10 feet is generally good.

On 2017-02-21 by Jocelyn

Updated question:
How many feet do you have to have between two houses that share an alleyway if you want to install a direct vent gas fireplace? - See more at: https://InspectAPedia.com/chimneys/Direct_Vent_Chimneys.php#FAQ

How many feet do you have to have between two houses that share and alleyway if you want to install a direct vent gas fireplace?

On 2017-01-27 by (mod) using 45 degree angles on direct vent flue

Perhaps, Dick. Check the installation manual for your specific heater and direct vent unit as those will state the limit on number of bends and turns

On 2017-01-27 by Dick

can I use 45's to vent a power vented lp water heater down to go out an existing hole

On 2017-01-24 by George - distance furnace to first elbow

Is there any required distance coming off of the Furnace before your first elbow on 4 inch exhaust pipe

On 2016-11-26 by (mod)

Check the table above, anon, as deck clearances are included there. Please let me know if questions remain.

On 2016-11-26 by Anonymous

can you have a wood deck directly above the outside vent of a direct vent gas fireplace?

On 2016-11-23 by hankclemmer

What is the separation distance required from a high efficiency through the wall vent and a property line?

On 2016-09-30 by (mod) - extend the distance of a direct vent

Chris, there's no useful service I could offer by e-text, even with photos, that would leave me feeling that your home is safe; there are too many on-site details that one might see that won't occur to us remotely. I suggest

1. give a call to the manufacturer of the direct vent system you have installed, prepared with details about your boiler, and the distances involved, and get their suggestions on what the venting system can and cannot do safely.

2. give a call to your local fire inspector to see what help they can offer, and/or perhaps your building department to see if they'll accept a modification IF the manufacturer says it's in-spect.

On 2016-09-30 by Chris green

I have a 8,000 btu direct vent gas heater which was vented outside last year, we then boxed on the area as to have an entrance from the garage into the house with one window and one patio door. We were told by the seller and the co that it could be vented further out come fall to use again now they say no.

Do you know why or how we could proceed I could take photos and if there is a fee for your help please advise Chris g austin mnI have a 8,000 btu direct vent gas heater which was vented outside last year, we then boxed on the area as to have an entrance from the garage into the house with one window and one patio door.

We were told by the seller and the co that it could be vented further out come fall to use again now they say no.

Do you know why or how we could proceed I could take photos and if there is a fee for your help please advise Chris g austin mn

On 2016-09-18 by (mod)

Burch I'd take some photos & measurements, then contact the manufacturer of the gas fireplace you are using to ask their advice before I'd consider flipping any vent over or modifying it.

Alternatives include addition of heat shielding in the affected area. Heat shielding itself needs to be non-combustible and needs to be installed so as to permit air to circulate around and behind it. Ask your local fire inspector for help in making sure that there are not fire nor gas-intrusion hazards at the home.

On 2016-09-18 by Burch

The soffit mentioned is not a vented soffit.

On 2016-09-18 by Burch

Yes, that's my issue. The termination is to close to the soffit and causes it to become to hot. Can you turn the termination upside down and have it vent out the bottom?? Can you possibly build an extension box and place the termination at the end of the extension? Looking for ideas?

On 2016-09-17 by (mod) - vent near the soffit or roof overhang

Assuming you cannot reasonably move the vent termination, the soffit needs to be sealed against exhaust gas entry.

If there are heat and fire hazards that's a different situation - just say so and we'll comment.

On 2016-09-16 by Burch

Just found out my gas fireplace vent termination is to close to an unvented soffit. How can I remedy this?

On 2016-08-24 by (mod) - venting a direct vent condensing gas fired water heater out through the crawl space ?

(mod) said:

Gary: about venting a direct vent condensing gas fired water heater out through the crawl space:

Probably you can direct vent a condensing water heater down and outside PROVIDED you follow the details in the specific heater's installation instructions.

Typically a downwards slope, shortest possible runs, and minimal number of elbows or bends are critical considerations as is clearance above ground, veranda, porch, deck, or balcony (12") for the vent termination. .

I would want to see the installation instructions for the *specific* brand and model of water heater to be direct-vented, as the manufacturer will tell us what routing, distance, slope, etc. are considered safe and effective. Also significant is whether the vent is operating by natural draft (venting down will NOT work in that case) or whether it uses a power vent.

Navien Condensing Water Heater Venting Instructions

For example Navien's condensing water heater venting instructions include these remarks:

For best results, keep the venting system as short and straight as possible.

Locate the water heater as close as possible to the vent termination.

Do not connect the water heater vent to a vent for any other gas water heater or vent stack.

For horizontal runs, slope the horizontal section upward toward the vent termination at a rate of 1/4" per foot (2% slope).

Create an airtight seal at each joint in the exhaust and intake air pipes from the water heater collar to the vent termination.

To avoid moisture and frost build-up and to maintain clearances to openings on adjacent homes, 45° elbows, 90° elbows, or tees may be attached to the end of the termination vent pipe to direct the exhaust plumes away from buildings, as long as the total allowable vent lengths, maximum number of elbows, and distances to air intake restrictions are observed.

Do not store hazardous or flammable substances near the vent termination.

If this water heater will be installed in areas where snow is known to accumulate, protect the vent termination from blockage.

Ensure that the vent termination is at least 12" (305mm) above ground, or as required by local codes.

Support the vent pipe with hangers at regular intervals or as required by local codes.

Exhaust and intake air pipes must be supported at least every 4 feet (1.2m).

The vent for this appliance shall not terminate over public walkways; or near soffit vents or crawl space vents or where condensate or vapor could create a nuisance or hazard or cause property damage; or where condensate or vapor could cause damage or could be detrimental to the operation of regulators, relief valves, or other equipment.

When using direct venting, maintain the following venting clearances, as required by

• ANSI Z21.10.3 and the National Fuel Gas Code,
• ANSI Z223.1/NFPA 54, and
• CAN/CGA B149.1 Natural Gas and Propane Installation Code.

On 2016-08-24 by Anonymous

For a condensing direct vent water heater with PVC exhaust, can the exhaust be routed below the heater through a crawlspace and then out the side? It seems exhausts should be higher or parallel.

However, IF it were feasible to run it below the heater into the crawlspace and out a sidewall, this would afford me the perfect space to install a small tankless unit on the main level below some stairs.

Question: Strong winds may overcome exposed direct vent chimneys or flues for heating appliances?

Concerning sidewall power vent to one of my residential gas furnaces. It is a proper code compliant side vent sloped properly with condensate drain etc. However, it is on a wall exposed to a wide open area - thus winds can be strong against the house.

Do I need to install something like an open vent collar to reduce the back pressure variations caused when winds are heavy? - Sack from VA 12/2/12

Reply:

Sack

Interesting question, I don't know but if you can tell us equipment brand and model we will research the question - or you can all the the manufacturer who can tell us.

I've never seen a power vent with wind protection installed, and we have presumed that the blower fan that provides positive draft for the direct-vented heating appliance is designed & tested by the manufacturer to provide more than adequate draft provided that you have followed the manufacturer's installation instructions.

Those instructions typically state that

The combustion air intake shall be installed upwind of the vent outlet when exposed to prevailing winds.

Avoid locating the vent terminal on a wall facing prevailing winds and wide-open areas. When impractical, choose a location that protects the vent from strong winds, such as behind a fence or hedge. [15]

Do you have a copy of the installation instructions and can you give the brand and model of your heating appliance?

Watch out: the manufacturer's instructions for some direct vent installations such as gas fireplace vent terminations we have reviewed warn that wind-resistant vent terminations are not permitted for certain heating appliances.

See GAS FIREPLACE VENT CLEARANCE REQUIREMENTS

Thanks to Alan Carson, Carson Dunlop Associates, Toronto, for assistance with this topic.

Vertical direct exhaust is a similar installation to the sidewall direct exhaust vented vertically, typically up through the building roof.

This heater venting system, typically for gas fired boilers, is used only by certain heating appliance models such as Weil-McLain's CGs boilers.

Image at above left courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. [Click to enlarge any image]

Question: neighbor's power vent 18" from power line

(Mar 8, 2014) James S said:

My neighbor just installed a power vent for his furnace on the outside of his house.

The house is 18" from the property line (this is a grandfathered non-conforming setback), but the new very loud power vent extends a further 10" into the space, so stops 8" from the property line.

Is it ok to extend into the non-conforming set back like this when the code says they can't build 3' from the property line?

Reply:

James,

Good question, for which I don't have a sure answer; this is a question for your building department.

Most communities indeed have restrictions on just what can be close to the property line, with variations depending on whether you're considering a front, side, or rear property boundary. Keep me posted.

Question: clearance distance from direct vent furnace exhaust to clothes dryer exhaust vent

(Apr 8, 2014) Paul T said:

what is the clearance for a direct vent furnace to a dryer exhaust vent?

Reply:

Paul I'm not aware of a clearance specification between the furnace and a dryer exhaust vent, and I'm not sure if your question is distance to the vent pipe or distance from the direct vent furnace combustion air intake or distance from its exhaust, or distance from the heating appliance itself.

But I'd say that ANY dust emitting source close to any fuel burning appliance is a concern if the dryer lint can enter or clog combustion air inlets (very dangerous where carbon monoxide may be produced) or other air vents such as cooling vents on equipment.

I can suggest two approaches to getting past speculative arm-waving:

1. if you see dryer lint in or on the appliance that's a potential safety concern that needs to be addressed

2. Check with the appliance manufacturer directly, for the particular brand and model of heater, starting with a review of its installation instructions and if needed a call to the manufacturer.

Watch out: if your clothes dryer were a model whose air intake were at risk of drawin in combustion products that would be a dangerous situation.

...

Continue reading at DIRECT VENTS / SIDE WALL VENTS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see DIRECT VENT / SIDE WALL VENT FAQs-3 - more-recently-posted questions and answers about direct-venting heating appliances.

Or see these

Recommended Articles

• DIRECT VENTS / SIDE WALL VENTS
  • DEFINITIONS of Sidewall or Vertical Direct Venting compared with Direct Exhaust
  • DIFFERENCES Between High Efficiency Condensing Boiler vs a Mid-range or Conventional Heater Venting Requirements
  • CLEARANCE REQUIREMENTS for Direct Vented Gas Appliances
  • SLOPE REQUIREMENTS for direct-vented chimneys & plastic vents
  • SAFETY WARNINGS Regarding Combustion Air Supply Source for Direct Vented Heating Boilers/Furnaces
  • SUPPLIERS of Side Wall or Through Wall Vent Chimney Systems & Equipment - where to buy it
• DIRECT VENT INSTALLATION, SNAFUS & SPECS
• DIRECT VENT WIND PROBLEMS
• GAS FIREPLACE VENT CLEARANCE REQUIREMENTS Separate Table for Direct Vented Gas Fireplaces
• WALL-MOUNTED FURNACES

Suggested citation for this web page

DIRECT VENT / SIDE WALL VENT FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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