Code: DV must be 10ft over walkway?

D107

Checking into new boiler, either mod con or sealed combustion cast iron. Installer tells me according to national code (NFPA?) the exhaust/fai vent termination must be minimum 10ft over a patio, deck or any area where people are likely to congregate or pass. I had never heard this --only that it must be higher than the likely snowline and have certain clearances from windows, doors, other vents, etc. There is no residence I know of that has a side that no one might pass by. A DV out of my basement's highest point would be only 3 ft above grade, So then we'd have to come out of the house and do a 90el, then up 7ft and then another 90 to face outwards? That extended run outside would pose a condensation problem, no? At this point it would be major problem for me to do the vertical run inside the house. Anyone ever heard of this or is he misunderstanding a commercial code?

Thanks,

David

Paul Pollets

Direct Venting

The venting requirements are set by the local administrative authority, depending upon which codes they subscribe to. The manufacturer of the boilers also have requirements. generally, 3 ft or 4 ft from any opening door or window, 1ft above grade or anticipated snow level; within 6ft of a mechanical vent; 3ft from gas meter; cannot terminate under a deck or porch; less than 7ft above a paved sidewalk or driveway located on public property.
I'd call the local boiler dept. or mechanical inspector to assure you're in compliance.

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D107

Thanks Paul

Apparently our village is subject to the Uniform Fire Prevention and Building Code (nys, county of westchester) so i guess I'll have to get the book or ask the relevant village dept.

Thanks,

David

Of course many wallies seem to prefer pvc venting to the roof, but maintenance access would seem to be the issue there.

Mark Eatherton

Most AHJ's refer to the manufacturers[ instructions

8' sticks in my mind...

Who's boiler?

ME

D107

buderus gb-142/24

Thanks Mark. Below is what the install manual says and it's similar for the GA-124 which i'm also considering. I would interpret public walkway (requiring 7ft clearance above) to mean an area regularly walked through--entranceway, sidewalk, driveway. In my case the vent would terminate about 3ft above grade about 3 ft horizontally from the beginning of a patio, so perhaps it's an issue if someone is seated at a picnic table--but in summer the boiler's on only occasionally for HW so maybe it's not an issue.

The instructions say: "Do not extend exposed vent pipe outside the building beyond recommended distance." can't find what that distance is.

Provisions for combustion and ventilation air must be made in accordance with section 5.3, Air for Combustion and Ventilation, of the National Flue Gas Code, ANSI Z223.1, or Sections 7.2, 7.3 or 7.4 of CAN/CGA B149, Installation Codes, or applicable provisions of the local building codes.

The termination shall be at least 4 ft (1,220 mm) for the U.S. and 6ft. (1,830mm) for Canada away from a gas utility meter, service regulator or the like (for room air applications only). The termination shall terminate at least 4 ft (1,220mm) below, 4 ft (1,220mm) horizontally from, or 1 ft (305mm) above any door, window, or gravity air inlet into any building. Vent must be at least 12 inches (305mm) above grade, anticipated snow line or roof surface (Canada 18” (457mm) minimum) (see fig.16). Vent termination must be at least 7 ft (2,135mm) above apublic walkway (see fig. 17). Vent must be 3 ft (915mm)above any forced air intake within 10ft (3,050 mm) (see fig.17). Do not extend exposed vent pipe outside the building beyond recommended distance. Condensate could freeze and block vent pipe. Vent should terminate at least 3 ft (915mm) away from adjacent walls, inside corners and 5ft (1525 mm) below roof overhang (see fig.17). It is not recommended to terminate vent above any door or window, condensate can freeze causing ice formations. Do not use chimney as a raceway if another boiler or fireplace is vented into or through chimney.

Thanks,

David

Mark Eatherton

Tough call...

If you ask the local AHJ, they are going to be conservative and tell you that it needs to be high.

The reason they caution you on running too much pipe outside is due to the possibility of the condensate freezing and blocking the pipe. If you insulated it, then it is different, but the aesthetics of your house will suffer.

Generally speaking, our AHJ looks at it from the stand point of REGULAR and CONTINUOUS walk thoroughfare. i.e. public walk way, or public sidewalk. A drive way, or a walk way that is occasionally used between the front and the back of the home is not considered a regularly used walk way, but bear in mind that you probably will have condensate drip occurring from the vent termination, AND the products of combustion can travel horizontally away from the vent termination.

No way of getting it to the roof eh...

ME

D107

yes we do have internal chimney

two adjacent 8x13 flues (inside meas. 7x11), 33ft high, the last 10ft through the attic which someday will be foamed and unvented). fireplace and current gas boiler flue. I had hoped to free the boiler side flue up for small ac ducts someday (currently have large ducts on attic floor.) Roof is probably best route but then what tech is going to go up on roof to maintain termination points annually on our steep roof? I guess a certified chimney sweep could do it.

Probably boiler could be placed on chimney wall just under breeching so one 90el takes pvc right into chimney. the installer told me he did that but had to take off some terminal endpiece due to condensation and icing.....that doesn't sound right.

For this situation do you prefer a concentric?

Thanks,

David

Mark Eatherton

Do this...

THe GB is allowed to pull inside air if I'm not mistaken.

Run 3" inside of the chimney to the roof. There really isn't any maintenance to be done to the vent termination. Use a 3" coupling, facing straight up, or alternately, a 3" tee, bull headed with vermin screens. Flash teh top of the chimney water tight, and let 'er rip. Make sure you observe Buderi's requirement for a drip tee on the vent right after the boiler connection to keep the stack condensate out of the boiler.

Decided to go aluminum after all eh...

ME

D107

thanks

well I really haven't decided but around here installers that know modcons know buderus and they say parts are easy to come by. It's really not the best time to do this financially given other projects.

But for me the sealed combustion (FAI) aspect is one of the chief benefits of these boilers so that I don't keep sucking cold air into my basement. Not sure why you don't recommend a concentric or separate in/out pvc lines up chimney. (cost maybe, cross contamination?)

As far as I know the cast iron noncondensing GA-124 doesn't require an adjacent exhaust/intake point so possibly I could have sealed intake out the side of my house and a stainless liner up the chimney. That adds quite an expense of course but then I'm done. If only the darn thing modulated.

Thanks,

David

Mark Eatherton

You have options....

In the GB installation manual, you can do a horizontal combustion air, and a vertical exhaust. Just make sure you are within the equipments developed length considerations, and if you will exceed them, bump the exhaust up to 4" to alleviate pressure drop.

So, you take the exhaust the the roof, where you are use to seeing steam coming from pipes, and pull the combustion air horizontally from the nearest outside wall, alleviating the negative air syndrome you are concerned about.

I actually am a big fan of real long concentric vent considerations. In your situation, I'd run the exhaust up the old chimney annulus, and draw the combustion air in through the annulus created between the PVC exhaust and the brick chimney, thereby pulling additional waste heat out of the exhaust stream, further enhancing thermal performance of the appliance as a whole.

In fact, truth be known, I have done this successfully NUMEROUS times, and was able to convince the AHJ that it was a safe and proper way to go, but have been turned down numerous times by bull headed closed minded AHJ's who could not see the forest for the trees.

Personally, I'd like to see ALL mod con manufacturers adopt this principle of providing exhaust and combustion air. The math is quite simple. You either have the required free air (difference in area between the chimney versus the PVC pipe), or you don't.

If you can take it to the roof, I would. You won't regret it.

Heres their current I&O manual http://www.buderus.net/LinkClick.aspx?fileticket=0cgZCcY9YoE=&tabid=108&mid=646

ME

D107

great idea

Mark love the chimney wall fai idea. The only possible negatives would be if the existing terra cotta lining had loose debris or dust that could enter the boiler OR, as in my case I discovered that the fireplace and boiler flues had a common cleanout at the base--something I'd correct by fully separating the flues with a mini-brick partition.

Thanks very much for your thoughts. Best of luck in your new career as consultant and teacher. I think the Obama energy team should be forced to spend a weekend with you and a few other Wallies.

David

Mark Eatherton

They wouldn't know what to do with us David....

We'd be the first entity to show up on their door step without our hands sticking out, and we'd be the first entity to give THEM advice on how to run THEIR business...

But we COULD put a dent in their energy bills though...

Good luck in your adventure.

ME