Unsatisfied with my first revision, I ordered a different duct on Amazon, and waited. It shipped from Mira Loma, 41 miles east of here, on Sunday. Monday was Christmas, so they get a free pass. Late Tuesday night it arrived in South Gate, 12 miles south of here, having gone straight through Monterey Park along the way. Amazon was still saying it would be delivered by 10:00 pm Thursday. So naturally it was waiting on the doorstep when we returned from yesterday’s adventures.
I ordered this particular duct because Amazon said there was a layer of insulation between the metal inside and PVC outside, which I needed to prevent a fire hazard with all the stuff stored under the bed. As soon as I started working with it I knew this wasn’t true. It was way too thin and flexible to have insulating material sandwiched between the layers I could see. However, at 16 feet long, I was able to run the duct exactly where I wanted it, and place the outlet at the head of the bed without sacrificing storage space under the bed. I fired up the heater to see how hot it got. While not as hot as the bare metal duct I used before, it was still far too hot for my comfort level, confirming the lack of insulation inside.
So I raided my stash of spare Reflectix and wrapped the duct in it, using duct tape to seal the gaps. This is the first time I think I’ve ever used either of these for their original intended purpose. I zip tied the wrapped duct into position, then cranked up the heater. Once up to full temperature, plenty of hot air came out the outlet, but the outside of the Reflectix was still cool to the touch, just the way I wanted it. It got slightly warm in the sharp bend right behind the heater itself, which isn’t surprising, but not hot enough to worry about like it was before. I think this is going to work, at least well enough to repack underneath the bed and prepare to head back to Quartzsite.
Yesterday’s adventures are worth a post on its own, as well as what we’re doing today. I’ll get to those, but for now, I’m off to have adventures in LA before heading back to the desert. I’ve enjoyed it here, but I miss my desert friends, and I have mail and packages starting to pile up in Quartzsite. After today’s trip, it’s time to make preparations for warp speed.
Smokey Da Van 
I see you ordered the 3″ diameter. Why not order a 4″ diameter and tuck the original inside, creating a definite air/metal/plastic insulation layer around the other. Just be sure to secure the ends, somehow, since I would think your hose clamps might not handle it. You could maybe nick the 4″ ends and tuck it down to the hose clamps, but you’d probably need to tape it really good to prevent tearing. Just a thought. (Because of your original post, I ordered one of these, cuz they’re prettier and a bit better, to replace the one on my dryer. Yah, fancy-RV problems! Heh.)
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That could work, too, though I’m not sure how I’d keep the inner duct suspended inside the outer one to preserve the air gap. If the two are touching then heat will transfer anyway. Reflectix seems to be working well, though I need to make some revisions in the routing for more gentle angles. My heater is complaining about overheating, which indicates insufficient airflow through the duct. I suspect the sharp turn straight out of the heater.
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