Gas dryer exhaust vs. mod-con intake

Gordan

Are there any clear guidelines for the proper distance between a residential gas dryer exhaust and a combustion air intake for a mod-con? I can certainly understand the recommendations for not locating the intake near a "laundry facility" but, given the infrequent use of a single-family dryer, is the ingestion of dryer exhaust really a concern?

Bob Vennerbeck

Why take a chance?

YOUR single family use of dryer may be infrequent - ours is a whole more constant than I think it should be, but I don't get a deciding vote..... particularly in the depths of winter.



Dryer exhaust is not just combustion byproducts, but more than a little bit of lint, even with the filter intact, in-place, and cleaned regularly... and that is no certainty either.



I would do my best to keep my expensive new modcon drinking the cleanest air I could give it - now you've got me worried about pollen, and spiders, and ....



Vbob

Bob Bona_4

good question

How far is far enough away from fly away lint? Clearance codes don't take particulate spray into consideration. I just recently had this dilemma, I was away enough to meet codem and added some more feet, but still wondered. I'll be watching to see what others have to say. 

Jack

I get to see

a lot of catastrophes. I usually get the call when a contractor is having a hard time. Even with a tankless, which in itself has an infrequent use, when remotely close (huh?) to each other it can create a real mess. You get into the kind of conversations about which way the wind blows, etc. No joy! Previous posters are spot on. Protect your equipment.

Gordan

Ok, so how far is far enough? Above or below?

Canadian code says > 6'. US code says... what? Not finding anything specific in any manufacturers' venting instructionsm either...

STEVE PAUL_3

A LITTLE OFF THE QUESTION

I never could get a definitive answer to the question as to whether or not a dryer vent discharges the products of combustion or if it ONLY discharges water vapor and lint.

 An appliance guy told me both, yet a PSE&G gas guy told me only vapor and lint.

 It seems to me that depending on a discharge pipe that by its very design is going to clog, to act as a carbon monoxide vent is the precise definition of dumb.

What is the answer?

Tim McElwain

A dryer exhasts it does not vent

so it is not classified as a vent. By the way if you take a combustion analyzer and do a test on what comes out of the exhaust you will get CO2, O2, CO etc plus lint and water vapor. therefore the exhaust is contaminated air and would affect combustion on equipment getting air from outdoors. We have recently had contamination problems with sprays used on shrubs getting into the air intake and corroding equipment.



There are no directions as to distance from clothes dryer exhaust that I can find. I looked in the International Code and also NFPA 54. The rule I have always followed was to get as far away as possible. Following other criteria 4 feet away from any windows, doors and other openings is good. I like the Canadian rule which I believe is 6 feet.

Robert O'Connor_12

Clothes Dryers

I'd check the manufacturer's installation instructions on both the domestic (residential) clothes dryer & your condensing boiler. Both should show minimum distances.

In the Great State of New Jersey we use the 2006 IRC (International Residential Code) & the IFG and IMC's

See 2006 IRC Section M1502.2. It says it needs to be at least 3'ft away in any direction. Also see IFGC Appendix C (Exit Terminals of Mechanical Draft & Direct Vent Systems). Other references include ANSI Z21.5.1 or Z21.2.

My advice is you do not want ANY by-products from the dryer exhaust getting any where near your combustion air intake for the boiler.



Robert O'Connor/NJ

Gordan

TT Prestige venting supplement doesn't have any mention of it

Same for the installation manual. Viessmann venting supplement does, but only in reference to the Canadian code. Dryer manual has no reference to clearance from other appliances' intakes, exhausts, or what have you.



So, if I were to go by Canadian code - 6' in any direction - is there a direction that would be more advantageous? The dryer makes quite a plume, and in cold weather it does seem to hang near the ground...

Tim McElwain

There are no codes for dryers

as too location in relation to other equipment as the dryer is not listed as a vented appliance it is a exhausting appliance.



Give us the layout of what you have by way of a little sketch. How about venting them around the corner from one another, is that possible?

Mark Eatherton

Bag filter it....

We had a modcon in a horse barn, with the air intake 30' above the barn yard, and we STILL were sucking in dust and animal dander, clogging the boiler. We installed a bag filter in the air intake pipe with a Magnehelic gage across the filter to see when it was plugging up. Worked like a champ.



Intake air was 3" PVC. Installed 4 x 3 no hub coupling, about 1' of 4" with the vacuum cleaner bag filter in the 1' section, then another 4 X 3 no hub coupling. The bag was held in place by the no hub coupling.



Maintenance on the aluminum heat exchanger was also MUCH easier after we introduced the filter.



Personally, I think ALL modcon boilers should have air filters on them... Dust and dirt in suspension, mixed with air and fuel, then burned at a high temperature makes for a hard tack crud that is tough to remove, regardless of heat exchanger construction.



ME

Gordan

What kind of bag filter?

That seems like a good precaution, unless it's likely to lead to its own issues...

Mark Eatherton

Zinger Vacuum Bag

from Home Depot.



Blue.



And yes, if allowed to plug up, it WILL create its own set of baggage, hence the need to hug your boiler at least monthly (by the HO during DHW production, full fire mode)



Observe Magnehelic gage pressure differential when new, and then use that number times 2 for replacement. So if the filter new creates .02" W.C. delta P, then replace when it gets to .04. Gage should be 1/2" WC full range, with 100ths of an inch increments.



ME

Gordan

How about one of these hooked up to a buzzer?

http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=20031&Product_ID=1410&sPageName=Ordering



A "change me" reminder.



I guess one with manual reset would be even better... could hook it up to a little indicator light.

Mark Eatherton

What ever's cleaver...

'Cause, if you ignore it, like a red headed step child with freckles, it WILL go away... :-)



ME

Slimpickins

filters

The old Glowcores used to incorporate an inline air filter that was pretty nice. Anybody remember those?  In a lot of ways there were ahead of their time. Too bad they didn't R&D that heat exchanger design a bit more before releasing

SpeyFitter

IBC Air filter

IBC just came out with an air filter for their boilers this past year. If I'm not mistaken it's similar to the old glowcore boilers filter from what I've heard ( could be wrong).It has 2" inlet/outlet that you gear clamp onto 2" plastic pipe for the seal, and it uses a filter that appears very similar to an automotive filter. It has an easy to remove lid to check the filter and clean/replace if neccessary.

Steve Whitbeck

filter

The filter may keep out the particulate mater but it WON'T keep out the gasses and acid laden vapor.

Unknown

Tinkerer

I hear ya,,, but if the intake & exhaust are within specs what else can we do?

Should we start looking for dead people around the termination point?

Whoops,, guess I just invited Tim,,,, LOL ;-)

DanHolohan

Dave,

why are you taking shots at Tim? He's a respected member of this community. I'm trying to understand what the problem is.



Please e-mail me: dan@heatinghelp.com.

Unknown

Dan Holohan,,,

No need for a pm,,, my comments were meant as "tongue in cheek",,, I meant nothing personal indeed towards Tim!



Obviously I was wrong,,, but I meant no harm,,,,, I apologize!



Guess I`ll stay-off the Wall for awhile,,, a "self imposed" hiatus. :-)



Hope this helps!

Henry

Air intakes

I don't know were you got 6 feet in the Canadian code, which code? We looked at dryer venting and air intake on the B149.1 venting sub-committee and then made amendments to the code. The new 2010 code has this:

8.3.7

An air-supply opening shall not be located within 3 ft (1 m) of a moisture exhaust duct.air-supply opening shall not be located within 3 ft (1 m) of a moisture exhaust duct.

Note: A moisture-exhaust duct (e.g., a gas or electric clothes dryer discharge; spa exhaust) is considered to interfere with

the combustion air intake when located within 3 ft (1 m) of the air intakeA moisture-exhaust duct (e.g., a gas or electric clothes dryer discharge; spa exhaust) is considered to interfere with

the combustion air intake when located within 3 ft (1 m) of the air intake1 m) of the air intake



But what is more important as this is only a minimum, is to FOLLOW the certified instructions of the appliance manufacturer. When we write code specs, it is for the safety of the users and not an installation manual to make appliances work. It is to make sure that the appliances operate safely. The appliance manufacturer who has done may tests, provides an installation manual to ensure safety and peak performance of his equipment.

Henry

Gordan

To be honest, I'm going by a reference to CA code...

...that's in the Vitodens venting supplement.



That's the only thing that I could find in Viessmann docs. No other specification that's not code-related. The funny thing is, I'm not even installing a Vitodens, but a TT Prestige, and that one has NO guidelines on distance from dryer vents.



Henry, believe me, I appreciate what you're saying. Please consider that the reason I'm asking this question here is because I ALREADY looked at the documentation you're trying to steer me to - and then some - and failed to find the info there. If this is my fault, and not the manufacturer's, I would very much appreciate the link to a doc and page number that contains the answer to my question.

Gordan

Tim, I'm working on it...

I just have to take some measurements. I'm embarrassed that it's taken this long...

Henry

Air intakes

The Viessman supplement is not code but is a certified instruction manual that must be followed. Some manufacturers do not spend the additional time into investigating all the possibilities that can influence their appliances. I spent a few years doing R & D and appliance certification to realise this!



To answer your question regarding dryer exhaust, YES it does affect combustion air intakes of appliances. The lint is the primary problem! We used "moisture duct" because there are concerns with pools and spa exhaust that contain contaminants such as chloride which are very corrosive.



Henry

Gordan

Thanks, that answers half my question.

The other half - the meatier half - is how far, and what arrangement would be most benefical. Boiler intake at a higher elevation than dryer exhaust? Lower? Exhaust is hot so it's supposed to rise... but it is also vapor-laden, which adds weight. I've definitely seen it linger near ground level and create big ole plumes, so I would be inclined to put the boiler intake a couple of feet above the dryer exhaust, at least. I haven't the foggiest what lint does or which way it goes, so an inline filter, as suggested by Mark and others, seems like a wise precaution.

Henry

Air intakes

We use the ten foot rule for apartment blocks and smaller. For hotels and and larger laundry rooms, we look at prevailing winds and the building structure. If you can stay away from the same wall as a dryer exhaust, the better it is. We had one case at a hospital where the dryer exhaust was through the roof. It was for 3 dryers (75 pounds? each?) The lint blocked the rooftop unit that was some 30 feet away!

Each case is different and caution should apply.

Henry

Kestrel

Came upon the same question

Just came across this old thread searching for the answer to a similar problem.  In reading the I+O manual for my new Knight WHN-085, the venting section says to stay away from dryer exhausts - it says because of nasty chemicals in anti-static products - but does not give a precise minimal distance, nor a relation above/below, as Gordan was asking.



Since this thread was from 2010, any new insights in the community regarding the spatial relationship between intake ports and dryer exhaust?

Glen

regardless of the numbers -

whether its a 3, 4 or 10' - depending on code - how about the premise that if there is evidence of interference or sub standard performance caused by a vent, exhaust or other building outlet - it must be fixed. Especially in winter and the freezing of condensable vapours chokes off the air supply; like the previous post - fabric softeners also kick the snot out of flame rods etc, cause all sorts of intermittent errors.