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Dryer vent query

I

Inspector Gadget

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Joined
Mar 5, 2020
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Location
New Brunswick
Note this is a Canadian question.

Our office faced an interesting question recently. The issue - as I understand it - is that a clothes dryer has been vented through (according to the client, haven't seen it myself yet) 25' of pipe, with five turns. That seems mighty problematic to me. (Searching Ontario building commission/BC code interps/BC Code Commission rulings gave me nada.)

NBC 9.32.1.3 states that dryers shall be vented "directly" to the exterior, with no definition of "directly."

Table 9.32.3.11-A is the duct airflow/diameter/length matrix. I feel it applies - anyone disagree? If so, why?

Presuming 9.32.3.11-A applies, a residential dryer generates about 150-200 CFM, or about 82-94 L/S.

It's about here where I get lost, because I'm not sure how to determine a dryer's static air pressure. My gut at the moment would be to determine the dryer manufacturer/model, and work from there. I'm presuming it's 'murrican with fan pressure in column-inches that I can convert to Pascals and work things through from there. Based on some interweb stalking, it seems the static pressure of a dryer is usually no lower than 75 Pa.

Presuming a 4" (100mm) duct and a 75 Pa fan pressure (as a start) I'm calculating a 1-3m duct limit. This seems remarkably small, so I assume I'm off the deep end.

Help?
 
2015 IRC

M1502.4.5 Duct Length
The maximum allowable exhaust duct length shall be determined by one of the methods specified in Sections M1502.4.5.1 through M1502.4.5.3.

M1502.4.5.1 Specified Length
The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from the connection to the transition duct from the dryer to the outlet terminal. Where fittings are used, the maximum length of the exhaust duct shall be reduced in accordance with Table M1502.4.5.1. The maximum length of the exhaust duct does not include the transition duct.

TABLE M1502.4.5.1
DRYER EXHAUST DUCT FITTING EQUIVALENT LENGTH
DRYER EXHAUST DUCT FITTING TYPE EQUIVALENT LENGTH
4 inch radius mitered 45 degree elbow 2 feet 6 inches
4 inch radius mitered 90 degree elbow 5 feet
6 inch radius smooth 45 degree elbow 1 foot
6 inch radius smooth 90 degree elbow 1 foot 9 inches
8 inch radius smooth 45 degree elbow 1 foot
8 inch radius smooth 90 degree elbow 1 foot 7 inches
10 inch radius smooth 45 degree elbow 9 inches
10 inch radius smooth 90 degree elbow 1 foot 6 inches

Continues
 
Inspector Gadget said:
Note this is a Canadian question.

Our office faced an interesting question recently. The issue - as I understand it - is that a clothes dryer has been vented through (according to the client, haven't seen it myself yet) 25' of pipe, with five turns. That seems mighty problematic to me. (Searching Ontario building commission/BC code interps/BC Code Commission rulings gave me nada.)

NBC 9.32.1.3 states that dryers shall be vented "directly" to the exterior, with no definition of "directly."

Table 9.32.3.11-A is the duct airflow/diameter/length matrix. I feel it applies - anyone disagree? If so, why?

Presuming 9.32.3.11-A applies, a residential dryer generates about 150-200 CFM, or about 82-94 L/S.

It's about here where I get lost, because I'm not sure how to determine a dryer's static air pressure. My gut at the moment would be to determine the dryer manufacturer/model, and work from there. I'm presuming it's 'murrican with fan pressure in column-inches that I can convert to Pascals and work things through from there. Based on some interweb stalking, it seems the static pressure of a dryer is usually no lower than 75 Pa.

Presuming a 4" (100mm) duct and a 75 Pa fan pressure (as a start) I'm calculating a 1-3m duct limit. This seems remarkably small, so I assume I'm off the deep end.

Help?
Click to expand...
I'm not sure I could agree that a dryer exhaust duct is considered ventilation for the purposes of 9.32.3.

9.32.1.3. is more about making sure the dryer exhaust is not interconnected with other airstreams or left to exhaust inside the building (see intent statements). It doesn't really deal with the developed length of the ductwork. OBC and BCBC have identical language.

This would be a good subject for a code change request proposal.
 
tmurray said:
Canadian code doesn't list compliance with manufacturers requirements for this section.
Click to expand...
The Uniform Mechanical Code has an overarching section that covers this situation. Installation instructions are supposed to be a part of any listing. If the installation instructions do not specify a diameter and length for the exhaust duct perhaps the manufacturer can advise.

301.2 Approval. Equipment or appliance shall be approved by the Authority Having Jurisdiction for safe use or comply with applicable nationally recognized standards as evidenced by the listing and label of an approved agency. A list of accepted standards is included in Chapter 17.

504.3.1 Domestic Clothes Dryers. Where a compartment or space for a domestic clothes dryer is provided, not less than a 4 inch diameter (102 mm) moisture exhaust duct of approved material shall be installed in accordance with this section and Section 504.0.

504.3.1.2 Length Limitation. Unless other wise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14 feet (4267 mm), including two 90 degree (1.57 rad) elbows. A length of 2 feet (610mm) shall be deducted for each 90 degree (1.57 rad) elbow in excess of two.

As you can see, we have an either or situation. The manufacturers' installation instructions are generally less restrictive than the code limits.
 
Inspector Gadget said:
Note this is a Canadian question.

Our office faced an interesting question recently. The issue - as I understand it - is that a clothes dryer has been vented through (according to the client, haven't seen it myself yet) 25' of pipe, with five turns. That seems mighty problematic to me. (Searching Ontario building commission/BC code interps/BC Code Commission rulings gave me nada.)

NBC 9.32.1.3 states that dryers shall be vented "directly" to the exterior, with no definition of "directly."

Table 9.32.3.11-A is the duct airflow/diameter/length matrix. I feel it applies - anyone disagree? If so, why?

Presuming 9.32.3.11-A applies, a residential dryer generates about 150-200 CFM, or about 82-94 L/S.

It's about here where I get lost, because I'm not sure how to determine a dryer's static air pressure. My gut at the moment would be to determine the dryer manufacturer/model, and work from there. I'm presuming it's 'murrican with fan pressure in column-inches that I can convert to Pascals and work things through from there. Based on some interweb stalking, it seems the static pressure of a dryer is usually no lower than 75 Pa.

Presuming a 4" (100mm) duct and a 75 Pa fan pressure (as a start) I'm calculating a 1-3m duct limit. This seems remarkably small, so I assume I'm off the deep end.

Help?
Click to expand...
Unfortunately, I do not think the language in Pt9 is going to help you with this. You may be able to fall back on "good engineering practices" or "manufacturers instructions". If the proponent does not agree, tell them to put in a building code interpretation request, and they can wait 6 months for the answer.
 
ICE said:
The Uniform Mechanical Code has an overarching section that covers this situation. Installation instructions are supposed to be a part of any listing. If the installation instructions do not specify a diameter and length for the exhaust duct perhaps the manufacturer can advise.

301.2 Approval. Equipment or appliance shall be approved by the Authority Having Jurisdiction for safe use or comply with applicable nationally recognized standards as evidenced by the listing and label of an approved agency. A list of accepted standards is included in Chapter 17.

504.3.1 Domestic Clothes Dryers. Where a compartment or space for a domestic clothes dryer is provided, not less than a 4 inch diameter (102 mm) moisture exhaust duct of approved material shall be installed in accordance with this section and Section 504.0.

504.3.1.2 Length Limitation. Unless other wise permitted or required by the dryer manufacturer’s instructions and approved by the Authority Having Jurisdiction, domestic dryer moisture exhaust ducts shall not exceed a total combined horizontal and vertical length of 14 feet (4267 mm), including two 90 degree (1.57 rad) elbows. A length of 2 feet (610mm) shall be deducted for each 90 degree (1.57 rad) elbow in excess of two.

As you can see, we have an either or situation. The manufacturers' installation instructions are generally less restrictive than the code limits.
Click to expand...
This is interesting. So if someone changes a dryer, do they need a permit? What if the dryer higher requirements than the previous dryer? Do we need to relocate the dryer to shorten the ductwork? Who is responsible for evaluating this and ensuring compliance?
 
tmurray said:
This is interesting. So if someone changes a dryer, do they need a permit? What if the dryer higher requirements than the previous dryer? Do we need to relocate the dryer to shorten the ductwork? Who is responsible for evaluating this and ensuring compliance?
Click to expand...
We make them label it:
M1502.4.7 Length Identification
Where the exhaust duct equivalent length exceeds 35 feet (10 668 mm), the equivalent length of the exhaust duct shall be identified on a permanent label or tag. The label or tag shall be located within 6 feet (1829 mm) of the exhaust duct connection.
 
Thanks for your input folks. I realize that this matter may hinge on a loosey-goosey interpretation of "direct."

Found the dryer in question; manufacturer does not make recommendations (not that we can enforce those in this instance.)
I may loop back with details after I lay eyes on the duct in question.
 
Welllll..... so we showed up and found the contractor had re-routed the dryer vent to something easily acceptable.
The pre-existing layout was a proper mess. We'll leave it at that.
 
In absence of a code definition of "directly to the exterior", I presume it to mean that that a clothes dryer in room A should not be ducted in such a manner as to terminate into the atmosphere of room B, even if room B itself is also equipped with its own really great exhaust fan system.
 
Yikes said:
In absence of a code definition of "directly to the exterior", I presume it to mean that that a clothes dryer in room A should not be ducted in such a manner as to terminate into the atmosphere of room B, even if room B itself is also equipped with its own really great exhaust fan system.
Click to expand...

Aye. Maybe. I mean, it's pretty obvious you've got to vent it to the exterior...

But if everyone did what was obvious I'd be out of a job.

For my part, we're going to have a sit-down and try to - in the absence of a definition of "directly" at least adopt a general guideline of how we're going to interpret the word.
 
Inspector Gadget said:
Aye. Maybe. I mean, it's pretty obvious you've got to vent it to the exterior...
But if everyone did what was obvious I'd be out of a job.
Click to expand...
I recently saw an older apartment building where a laundry room was fashioned out of an unused corner of a subterranean parking garage.
The property manager had the clothes dryer exhausting into the garage.
 
Yikes said:
I recently saw an older apartment building where a laundry room was fashioned out of an unused corner of a subterranean parking garage.
The property manager had the clothes dryer exhausting into the garage.
Click to expand...
One of my early inspections - maybe three-four months into what was a very part-time gig:

Dryer was located away from an exterior wall. I traced the outlet pipe. Up through a wall, into the ceiling. Into the attic.
That's where it ended. (!)
 
Inspector Gadget said:
One of my early inspections - maybe three-four months into what was a very part-time gig:

Dryer was located away from an exterior wall. I traced the outlet pipe. Up through a wall, into the ceiling. Into the attic.
That's where it ended. (!)
Click to expand...
Some of the reason the new code language introduced in the 2015 version was to deal with that (exterior means outside, not attic). In earlier versions, there was no guidance provided for dryer ductwork.
 
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