DIY Stovepipe Heat Reclaiming Rings

There's something about a wood burning stove that's just warm and inviting. Cozy is probably the word I'm looking for.

One downside is the heat is all pretty localized and takes awhile to soak into the rest of the house. To try and address that I've added a heat powered fan and it's been a great way to passively help spread the heat from the stove. But this is 2024, we can do better right?!

So while browsing for ways to increase the efficiency of the wood stove a little more I stumbled onto heat reclaimers. Some of them looked a little gimmicky but I mean it sounds good on paper so who knows… While looking into them more, I had a bit of an "Ah Ha!" moment with cross over from another project I was working on. Those heat reclaimer rings look an awful lot like corrugated metal... I wonder...

1. Corrugated metal roofing
2. This was a leftover from another project of mine. https://homedepot.sjv.io/0ZoDEE (affiliate link)
3. Check places like Craiglist to find offcuts free-cheap.
4. Some way to mark straight-ish lines on the metal
5. I used a yardstick and sharpie
6. A way to cut the metal
7. I used tin snips, very similar to these https://amzn.to/48TdGDC (Affiliate link)
8. An angle grinder with a cutoff wheel would also work
9. White Vinegar
10. We'll use this to strip off the galvanized coating on the roofing material
11. A non-reactive container to put the vinegar and metal in
12. I used an old crock pot that I have for cleaning things in the garage.
13. Gloves
14. The edges of the metal are sharp. I realized this before cutting myself this time, guess I'm finally getting better at working with me!
15. Angle grinder and flap disc
16. The edges needed a quick deburring
17. PPE for the grinder - hearing protection and eye protection and if you have it a respirator isn't a bad idea
18. If you don't have a favorite angle grinder or flap disc yet the Makita variable speed grinder https://amzn.to/3wKaqNj (affiliate link) is fantastic and Empire Abrasives is my go to for grinding discs.
19. *High temperature paint*
20. I'm out of LOPI stove touchup paint right now, when I deep clean the stove for spring I'll paint everything the same color. So instead of painting them twice, I left them uncoated for now. If they do start to rust badly before I get to the deep clean stage, I have some Rustoleum high temp BBQ/stove paint I'll hit them with https://homedepot.sjv.io/0Zo5rJ (affiliate link)

*My posts may contain affiliate links to products I use and feel comfortable sharing. Which means when you click the marked product links in my Instructable nothing changes on your end, and I earn a small % on qualifying purchases. Thank you for your support!*

OK, lets get organized and do some quick research.

Heat reclaimers look to have a couple different types. We'll call them internal and external types. The overall goal of the product is use more of the heat escaping out of the stove and up the pipe.

The plan for today is to make something similar-ish to this https://amzn.to/48MBBEC (affiliate link) which I'd classify as an external heat reclaimer because it goes on the outside of an existing stovepipe. The intent of the external heat reclaimer is to increase the surface area of the outside of the stovepipe and therefore increase the amount of heat transfered from the stove into the everything else.

An internal heat reclaimer works on the same principle of increasing surface area, but does it on the inside of the pipe where things are hotter. This style also typically includes a fan to help push the heat out of the reclaimer and into the room. This is an example of an awesome "internal" heat reclaimer: https://www.instructables.com/Wood-Stove-Heat-Reclaimer/ I think this style will probably have a larger effect than the external heat reclaimer, but I'm not commited to this project enough to cut up my stovepipe... yet?!?!

And now we come to our first downside of using reclaimed materials - The corrugated metal is steel and it's galvanized. We know that galvanized steel + enough heat = bad things. Specifically toxic fumes from the zinc in the galvanized coating. But how hot is too hot?

Quick research shows the max continuous use temperature for galvanized steel is 392*F/200*C https://galvanizeit.org/hot-dip-galvanizing/how-long-does-hdg-last/in-extreme-temperatures

How hot does a typical stove pipe get?

Trying to find average temperatures ratings for stovepipes was a bit frustrating but "generally" it seems the temperature of the stove pipe can range from 200*F - 600*F. I didn’t really get the warm fuzzies with that data since it was all over the place so I also consulted the LOPI wood stove manual. In the manual there’s no specific guidance on outside temperatures of the pipe, but the manual specifically says not to use galvanized steel pipe because it can give off toxic fumes and that on “high burn” the stove itself can operate at 600*F. Not looking good...

I also took some of my own measurements (fun excuse to play with a thermal camera!) and I saw temperatures up to about 350*F on the outside of the stove with an average fire burning. Looking specifically at the stovepipe where we plan to install these - I have a double wall pipe coming out of the stove and it saw temperatures of around 150*F.

So what’s the take away from all that data?! While it's unlikely the stove pipe will exceed 350-400*F, it is possible to reach that temperature so:

My take away is that we should err on the side of caution and remove the galvanized coating if we’re going to continue with this material for the project.

PS - Doggo did good helps on this step! She was an excellent control subject to verify the thermal camera was operating in the expected range.

PPS - If you're curious, I'm using a Seek Thermal Camera, specifically this one https://amzn.to/3Tq03Ho (affiliate link) I've had it for quite a while and it works great for me. It's been an awesome tool to troubleshoot things like my 3D printer heatbed to the furnace in my house to finding that annoying cold draft from one of the windows. And yes, it's fun to use just because too...

OK, do we switch materials or remove the coating?

I thought about using aluminum cans, but that would be a lot of work to cut up and form them.

Next I played with some aluminum foil and aluminum duct work tape, and while I think they could work, they'll be more prone to falling apart over time. 

We could get some aluminum or copper sheet and make some forming dies and then make some cool rings. And we could even make them in fun shapes, and we could and we could and we could and we could and we could and we could and we could and we could and we could and we could and we could and we could…

Woah there turbo! 

Slow down, we’re not even convinced these things are worth the $35 the Amazon’s wants for them, lets not overcommit just yet… Lets just stick with the original plan and remove the galvanized coating, it’s not that hard to do and we already have all the materials.

OK, now that we’re back on track…

#1 - The ol’ eyecrometer thinks the corrugated sheet I have is wide enough but what does the maths say? The corrugated panels are ~25” wide, the maths says the circumference of a 6” pipe is C=2𝝅r, so C=2*3.14*3 or 18.84”. Perfect, we’ll call it 19” plus wiggle room.   

(Side tangent, there's also an instructables 𝝅 contest going on right about meow!)

Now that the maths is settled, lets cut a few strips off the corrugated metal sheet. I used a yardstick and a sharpie to mark a few straight lines on the metal and then cut them off with tin snips. The strips are 1.75" wide because that's how wide the yardstick is and it looked about right proportionally. This took less time to do than it did to write the last step 😂

I should probably grab gloves… Yeah lets grab gloves… 

So how’s this thing actually line up on the pipe? Hey! Look at that, the corrugations line up like it was meant to be! Score one for team keep going with the project!

Lets keep the attachment method simple and just cut two slots in the strip where they meet like so. I marked where they overlapped when wrapped around the pipe with a sharpie. The material is a little bit “springy” so there’s some wiggle room and I made the slits slightly pie shapes so they’ll be easier to get started sliding into each other. I took my time to make sure things fit flush but didn't overcut the length of the slots. (And so I didn't accidentally cut the slits on the same side of the strip... That sounds like something I'd do when I'm in a hurry...) Have a look at the pictures if that got a little wordy and doesn't quite make sense.

Alright, that’s looking pretty dang good!

Now that we know everything fits and how to attach them to the pipe lets get that galvanized coating off.

To remove the coating the strips will be soaked in white vinegar. There are other ways to remove galvanized coating, this is the least toxic way I've found that works reliably.

I have an old crockpot in the garage for cleaning things like this, but a tupperware container would also work fine. Put the strips into the container and fill until the parts are fully submerged.

OK, now we wait. I ❤️ waiting…

I left the strips overnight in the vinegar and then checked on them. It’s working, but I think another day’s soak is needed. You can see in the picture how three of the strips are really dull and more grey than silver compared to the strip that hasn’t been soaked. 

I rinsed off the strips with water, put them back in the crockpot, topped up the vinegar and left them overnight again. 

To be honest, I was starting to second guess my decisions again at about this point... This was turning into more work than expected. But I'm pretty much committed at this point right?!

Fortunately the second vinegar bath went well. Now the strips all have a uniform dark grey coating instead of the speckled coating they had yesterday. This is what we want. This means the coating has been removed. There are a couple tiny spots of galvanized coating left (like smaller than a dime spots), I'll remove them with the grinder in the next step.

Rinse off the parts with water and save the vinegar to use on the next metal cleaning project.

Getting closer!

Now we need to deburr the edges and address the small spots of galvanized coating that's still left. An angle grinder with a 80 grit flap wheel works great.

The corrugated metal is very thin, so be sure to put on your carfuling pants for this step. Start by lightly running the grinder over the edges of the metal, rounding off the sharp points and edges.

Next lightly grind out the galvanized spots, you know the drill here - good ventilation and a respirator are your friends.

Now stack all the parts on top of each other and mark where we need to make our notch cuts (hey, look how evenly I managed to cut everything! I'm usually pretty terrible with tin snips, go me!). Cut the notches out like we did in step 3 and now we're FINALLY ready to install these!

OK, we're in the homestretch now! The rings were easy to install on the stovepipe (no surprise, we did a fit check in step 3). I spaced them even-ishly apart and it was time to light a fire!

Is it working yet?

And how do we actually quantify if it's working / better than it was before?

Well... that's a good question. At this point I can confirm it's not, not working...

I was a little surprised how visible the strips were in the thermal camera and I was really surprised how much cooler the strips were compared to the pipe. I could easily touch the strips with my hand but the pipe was uncomfortably hot to the touch. I believe this confirms that the strips are taking heat from the stove and dissipating it into the room faster than just the bare stovepipe is capable of. So that means it is working, ie doing what it's supposed to do.

For curiosity I also strapped an aluminum heat sink onto the stovepipe to compare it to the rings. This is definitely and apples to oranges comparison, the heat sink is a different material and has larger fins to dissipate the heat. At first glance it appeared the heat sink was performing worse, AKA it was hotter than the reclaimer strips. The side view was pretty interesting though, we see the temperature at the tips of the heatsink to be about the same as the heat reclaimer strips. So it is working the same or better than the heat reclaimer strips.

Overall, subjectively I didn't really notice a difference. That said there's a lot of variables at play and my sample size so far with them installed is small. I can say that this week I used about the same amount of wood as usual, overall the house got to about the same temperature as usual with a fire going and the rate at which the stove heated up/cooled down was pretty normal. I'm not sure if I can get away with setting up a datalogger in the living room for very long... and while the dog was impressed with the thermal camera, I'm not sure how impressed my significant other was at having the everything thermal camera'd at dinner so...

So, I assume the #1 question is - Do they work?

Short answer: Yes-ish.

I plan to keep them installed and make a couple more so take that for what it's worth. While I'm not convinced they will significantly impact the amount of fire wood I need to cut in the future, I do think they're doing more good than not. I'd say get a heat powered fan first, then maybe consider makeing or purchasing a set of heat reclaimers.

I'm guessing the next question is - Did we save money?

Eh, if we were to buy the parts instead of using leftovers and if we factor in labor... and assuming we're only after 6 or fewer of these rings - No, we really didn't save any money. We're about even on DIY vs. Buy. Technically I have enough material to make about 36 of them, but that would be a ridiulous amount of rings to put on the stovepipe and would probably make it a PITA to disassemble for cleaning out the pipe.

Overall, in my instance I had no direct out of pocket cost and I had fun making them. So yeah it was worth it.

Bonus question - Why haven't you painted them yet?

I'm out of the LOPI stove touchup paint right now, when I deep clean the stove for spring I'll paint everything the same color. So instead of painting them twice, I left them uncoated for now. If they do start to rust badly before I get to the deep clean stage, I have some Rustoleum high temp BBQ/stove paint I'll hit them with.

Might not have been on the radar question - What the heck does P.S. and P.P.S. mean?!

PS stands for postscript. It's like notes at the end of things. PPS is, yep you guessed it post postscript. It's also a short note at the end of a piece of writing. https://dictionary.cambridge.org/us/dictionary/english/pps

Alrightly, thanks for playing and that'll do it for today!

________________________________________________

If you'd like to see what I'm up to when I'm not Instructable-ing you can also find me at these places:

My Website: https://www.makerneer.com/blog

Instagram: https://www.instagram.com/makerneer

YouTube: https://www.youtube.com/@makerneer

My Etsy Shop: https://www.etsy.com/shop/Makerneer

Note: My posts may contain affiliate links to products I use and feel comfortable sharing. Which means when you click the marked product links in my Instructable nothing changes on your end, and I earn a small % on qualifying purchases. Thank you for your support!