What is the condition of your dryer vent? A 2017 NFPA report states that annual dryer-cause fires average 14,630. Deaths: 9. Injuries: >420. Nearly $222 million in property damage. Leading cause: failure to clean vents and lint traps. nfpa.org/-/media/Files/… 
Clean the lint trap every load - but also check your vent to the outside. Is it direct without a lot of bends? If it's >8 feet long, is it hard-piped? Is it clear from lint? Is it vented to an outside wall (preferably >10 feet away from any air intakes like HVAC equipment?
Think it can't happen to you? This is what I found in my dryer vent (after I had some technicians from an un-named big box hardware store in to replace it!). Yes that is a bird's nest. The technician said the vent didn't need to be replaced because there weren't any holes in it.
... He said to return the new vent (he was trying to save us $$ 😐). He also kindly 'stretched out' the flex duct for us so it was a big swirly pile and then crunched it tight against the wall when he put the dryer back. Please: NEVER unnecessarily stretch out dryer vent duct.
So I fixed it myself (originally I hired them to save myself the time because I was so busy doing building science for other homeowners). Where, in one house, we found this.
That is a fire that is waiting to happen. Not to mention moisture-loading into a semi-finished basement. Always vent to the exterior!
And dryers (the BIGGEST fan in the house) can cause other problems, too. This one is in the same room as an open draft water heater. When the dryer is on and the water heater fires up, the dryer will pull carbon dioxide, nitrous oxides and small particulates into the room...
...which will get pulled upstairs to the living areas because the floor above isn't air sealed. Think I'm making a big deal out of nothing? This is eerily similar to a case we consulted on where four people almost died from carbon monoxide poisoning.
And low-dose, long term effects of all the nasty stuff can trigger asthma attacks, allergies and mess with cognitive development. Seriously. Please. Check your dryer vent or have a qualified building scientist (not someone from unnamed big box hardware store) check if for you.
*it
How to tell if a vent is ok: Best is a short, unobstructed direct path (less than 20 lineal feet) made of rigid metal ducting* with no more than two bends of 90º or less and a dampered, screened 4” deep vent outlet to the exteriorwall (not the attic, basement or roof)...
... The exterior vent should be more than 10 feet away from any air intakes (like an exterior air compressor or direct vent intake).
Flex duct is ok to use IF duct path is >8 feet in total with no more than one bend and ducting is a straight line - not tangled up or cramped.
Is this all good? Great - but make sure there are no obstructions or lint balls stuck in the venting. My birds nest was not visibly obvious from the exterior or interior. You may need to pull the dryer out and look into the duct to verify.
Any other dryer vent wisdom, horror stories or how-to's from my #buildingscience colleagues out there?
Shoot - *Carbon Monoxide (CO - not CO2)
@threadreaderapp please unroll.
