Dryer vent heat shedder

I can’t call this a heat exchanger, as it doesn’t exchange any heat. It just sheds some of the heat from the dryer duct into the room. I am trying to keep some of the heat I paid to create, in the house, where I tend to hang out when it’s cold outside.

I know I’d get better return on the money I spent by feeding the dryer outside air, but I wanted to give this a try. A friend gave me the heat sinks, so I wanted to see if I could find a noble use for them. I love DIY projects anyhow. I kinda liken it to a homemade energy themed work of art.

A picture is worth a thousand words, so here’s a 25k word novelette. (Hey, technically these stereoscopic photos are 2 photos each, so they count double. Just cross your eyes to get your word-count’s worth.).

The parts needed for my dryer heat exchanger
The parts needed for my dryer heat exchanger. I spent $56 at the hardware store last night to get the bulk of it. The heat sinks a friend gave me, because they had my name on the boxes “FREE”.
A friend of mine gave me boxes of new, unused computer heat sinks.
A friend of mine gave me boxes of new, unused computer heat sinks.

I currently have 20 of these heat sinks. I fiddled around with them for a while to see how many I can fit on my duct, and I came up with 74. Two rows of 15 down the long, wide face with 14 spaced in between and a row of 15 down each side.

Laying out the heat sinks on my ductwork to see how many I would need total
Laying out the heat sinks on my ductwork to see how many I would need total.

I figured I’d start with the 20 I have, and see if it does anything for me at all before I mangle that many heat sinks.

The center row of heat sinks is spun 45 degrees so they fit better
The center row of heat sinks is spun 45 degrees so they fit better. I have them upside down to keep the goo from getting everywhere.

I rather like this dense arrangement. I’ve knocked all the cooling fans loose for now. I may re-install some of them. Possibly just down the center row maybe? A larger box fan running off the dryer’s timer may work better in the end.

2 hours measureing and marking to get the layout I wanted
2 hours measuring and marking to get the layout I wanted.
Took me a while to figure out the best way to drill the holes
Took me a while to figure out the best way to drill the holes.

I ended up drilling all the holes with a drill bit from the back side where I had my layout marks. I then de-burred the holes from the front, pushing hard, so I dimpled each hole. This flexed the metal so that the screws would tighten the sheet metal up to the heat sink.

positioning the heat sinks and holding them while screwing them on was tricky
Positioning the heat sinks and holding them while screwing them on was tricky. Duct tape for Duct work FTW!

The screws I used where some pan head self tapping sheet metal screws. Ended up not needing the self tapping feature as I had to pre-drill all the holes to keep the metal bits from preventing the heat sinks from coming up tight to the metal. Live and learn. I just ran them between the fins on the heat sink. They seem to hold tight. I hope that if I ever disassemble this thing, I can reuse the heat-sinks in the future. Maybe. Please?

The heatsinks came with some thermal paste, but I added extra for good measure
The heatsinks came with some thermal paste, but I added extra for good measure

It’s actually surprising how heavy the assembled unit is. A lot of light weight parts makes for a heavy finished product.

20 heat sinks screwed to some ducting. how silly is that?
20 heat sinks screwed to some ducting. how silly is that?

Carbon Monoxide poisoning is a risk when doing something like this, so the whole contraption is sealed up tight. I’d feel really bad if I killed myself trying to save a buck.

This fancy tape was the most expensive part to buy! What do you mean, I can't use duct tape on duct work?
This fancy tape was the most expensive part to buy! What do you mean, I can’t use duct tape on duct work?
The screws are all sealed with silicone sealer good for 400 degrees
The screws are all sealed with silicone sealer good for 400 degrees

I tried to keep the inside of the duct as smooth as possible to not collect any lint and cause a fire hazard. I am hoping the shallow screw heads will create just enough turbulence to keep mixing the hotter air with what’s already shed some heat to the walls.

Ready to wire up and mount on the wall!
Ready to wire up and mount on the wall!

 

Now I just need to add 2 stainless steel housed thermistors so I can monitor the air intake and exit temperatures. If I see a temperature difference, that means it’s working. I can use a 55 gallon plastic bag to figure out the air flow of the dryer. Some magical maths will tell me how much heat I am dumping into the house vs throwing out with the wash-water (clever, eh?). If I get any good results at all, I will try to collect enough heat sinks over time to finish this project.

54 more heatsinks needed. New price for these appear to range between $10 and $100 (Seriously?!?). Glad I am not damaging the heat sinks too bad, but the dollar value of this project kinda makes me a little sad.