4

I’m looking for an authoritative source that would detail where a 4" dryer vent duct can and cannot pass, and what it can or cannot touch. Is there such a "code" for (residential) dryer vents where all the prescriptions are laid out?

I’m trying to relocate my dryer vent, and would like guidelines to follow to ensure everything is "up to spec". Things I worry about are: burning things, melting things, and adding condensation/corrosion.

The knowledge seems to be spread out on this forum, i.e. one question for each specific situation and material. I've listed partial answers I've found in References, but I wish there was a comprehensive guide.

To be specific, I'm hesitating between

  1. passing the duct over the 2x4 and left of the drain ptrap (which appears to be cast iron, supported by steel strapping and with rubber hose-clamped gaskets). There is no clearance there, the pipe has to be slid over the 2x4, squeezed oval a bit to clear the drain (but not to the point of kinking), and has to remain perfectly horizontal. I could maybe make a 1/2" notch in that stud if I needed to add insulation (it's not load-bearing, it's just framing for the bulkhead that hides all this mess).

  2. passing the duct on the right side of the drain's ptrap, and left of the pipe. Barely any clearance there, but it feels odd to pass a hot pipe right next to cold water. I'm (perhaps overly) concerned about condensation.

all around the vent

  • I'm in Vancouver BC,
  • The existing vent goes straight out the building side wall (4-5 feet away). I'm re-routing the parts of the vent that are indoors.
  • It's in a ceiling / bulkhead.

References:

Tidbits of knowledge I've pieced together.

  1. Touching fiberglass is okay: Is insulation around a dryer vent hose safe?
  2. Behind drywall is okay (I imagine touching drywall is okay): Is It Okay to Put Dryer Vent Behind Drywall When Finishing Basement
  3. A possible code to adhere to: International Residential Code (IRC) SECTION M1502 appears to be cited a lot: This one
  4. Touching ABS pipe is okay (in fact apparently under-the-floor dryer vents can be made of ABS): Can dryer vent touch ABS pipe?
  5. Confusion about Dryer Vent temperatures. They are cited to be around 130°-165°F (54°-74°C), yet they still seem to cause fires and melt plastic dryer exhaust hoses.
  6. Vent passing near/through wooden beams is okay: Dryer vent passing through two wooden beams. Is it safe?
  7. Vent touching hot water pipe is okay, but might need foam around duct to prevent galvanic corrosion and or noise: Dryer vent pipes touching copper hot water pipe
  8. The vent can be strapped to joists, so presumably it can touch joists: How to hang a dryer vent in a basement ceiling?
  9. Condensation is something to be concerned about: Can I clean my under-the-floor dryer vent?
  10. Dryer vent slope is a concern. Goal is to have gentle slope towards dryer, but that's apparently not in code (citing IRC 2009): Is it a problem if my dryer vent slopes uphill through a crawl space?
4
  • 3
    The normal temp is 130-165. But the problem is that if you have lint buildup then (a) the temperature increases because the hot air can't get out fast enough and (b) the lint catches fire. A quick search shows lint ignition anywhere between 250 F and 511 F. The lower end could happen inside a clogged duct. The higher end would be inside the dryer with a clogged lint screen (which is a slightly different problem, but related). Feb 9, 2023 at 2:35
  • My experience has been that the dryer vent clogs closer to the machine and then the temperature cut off causes the dryer to stop mid cycle and you know your dryer vent is likely clogged. Really even if the dryer vent clogs toward the end of the vent if the air can't move the heat will build in the dryer and it should cut out. Maybe old dryers didn't have the thermal cut out or the thermal cut out are sometimes defective? Feb 9, 2023 at 5:51
  • In my country, the authoritative source for what is “acceptable” is the fire department - the architects work to their requirements and changes, builders as well, and everyone else. The fire dept had us change our design during build because they wanted it different even though they had originally signed off on it, so it got done. Nobody relies on the internet…
    – Solar Mike
    Feb 9, 2023 at 7:30
  • I had not thought of consulting my fire department's resources. that's a good one. I got lost trying to swim in my city's online resources.
    – init_js
    Feb 9, 2023 at 9:43

1 Answer 1

2

There's a maximum length (incl. accounting for elbows), code for how it should be assembled (tape, no screws) and code for how it can penetrate the exterior wall and vapour barrier, but no code for clearances or slopes, also none for insulation in the mildest of climate zones.

There is separate code for how and where you can notch joists and studs to accommodate the pipe. This is for BC, Canada.

However, electrical cable cannot touch the hot pipe, and insulation or clearance for the cable is required.

If you could be more specific about what clearance you need further information about for your case, perhaps someone else can chime in with the pertinent (building) code.

As an aside, dryer vents are usually aluminum; round HVAC ducts can be aluminum or galvanized steel, and rectangular trunk ducts are galvanized steel.

4
  • 1
    I may have been suckered into buying steel? I have "galvanized pipe" and I assumed it was steel. I didn't think there was such a thing as galvanized aluminum homedepot.ca/product/…
    – init_js
    Feb 9, 2023 at 2:22
  • 1
    @manassehkatz-Moving2Codidact yes for trunk and plenum; for round I've also seen and used aluminum
    – P2000
    Feb 9, 2023 at 5:27
  • I'll try to figure out which code applies. I'll make some calls to the city / fire dept. I've updated my question with specifics.
    – init_js
    Feb 9, 2023 at 9:45
  • @init_js yes you can include the fire dept, but ultimately in BC it is the city's building code that matters. It is available at your local library. You can also call a local HVAC company and ask to speak to a tech. For very specific concerns I often do a walk through with a local carpenter and pay them for their time. Codes vary by city.
    – P2000
    Feb 9, 2023 at 14:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.