"Good to hear you have clean dryer ducts Don.
The dryer duct issues that we run into are predominantly upper story dryers that are vented out through the roof. Installers use a roof-cap with a screen and the lint packs up inside the screen. This can…"
"I never checked that before. Checking now...
Section M1502.4.2 of the International Residential Code prohibits screws or other fasteners that protrude more the 1/8" into a clothes dryer duct. M1502 also requires manufacturer instructions to be…"
Thanks for that response. Because of your warning, I just went down to the basement and disassembled my 4 inch diameter metal dryer duct, joined with screws (and taped), and peered down it with a flashlight. It has probably been up for 10…"
DRYER VENT: screws bad idea, possibly prohibited by code.
METAL DUCT: must be screwed together or other mechanical connection S/Drive etc
FLEX for conditioned air or ventilation: Panduit strap is preferred mechanical connection.
"Static pressure drop through a straight length of pipe is a function of friction rate, and friction is largely a function of surface smoothness. Like metal ducts, PVC pipes have a relatively smooth surface.
Here's a friction loss calculator…"
"Thanks David - I was going to look at PVC for the HRV but was cautioned against it, not because of the offgassing (which would not be relevant for dryer), but because the static build up leading to a high resistance to air flow."
"Great post, Sean. I agree that screws are wise when joining metal ducts, but its also true that screws can be problematic in dryer exhaust ducts. For this reason, I used thin-walled drain & sewer PVC for my dryer exhaust in my previous home,…"
"Various studies have indicated very little air flow along surface of duct (for ventilation - have not studied forced air). So if this is for venting, the screws would not be an issue at all as the pressures are to low.
"Hi Don. We have never considered screws as impeding airflow, but I can see how in some ducts (e.g. dryer exhaust) they would catch lint etc. We always look for am minimum of two screws per joint in round duct. In cases where there are high solids…"
A question came up on exhaust duct connections. I have always considered screws necessary for mechanical fastening of one duct to another. I have been reminded recently that screws impede airflow and catch particles and fibers, all of which is probably true. My source then said that, in their opinion, all ducts should be joined solely by either tape or mastic, or a combination of the two. Is this common practice? Does this increase the time of installation? Does it hold up over time, especially…See More
HVAC design, Manuals J, S, T, & D, Duct leakage, Air flow, ENERGY STAR new home requirements, and more. Since heating & cooling are such a big part of home energy use, understanding HVAC is critical.See More
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