Fuel Pellet Adapter for a Wood-burning Fireplace (or Stove)

Welcome to another kick-ass Instructable from Disc Dog!

I have a wood-burning fireplace/stove in our house. By and large it supplies most of the heat for the house during during the evening in the colder months; it's a small house (about 850 sqft). When I bought the stove (about 4 years back) Pellet Stoves were coming out in full force, but [having an abundance of free wood lying about] I didn't savor the idea of having to buy a $5 bag of wood pellets every day just to have a fireplace. (MOst pellet stoves burn about 3/4 to a bag a day) True, they are efficient and, depending on where you live, cheaper than running most heating systems but still, it's hard to compete with 'free'.

Inevitably there would come a long-enough winter to exhaust my chopped, dried wood supply but I figured that we spend enough time outdoors during the day that I wouldn't see that long, indoor period for a number of years.

Then came Covid...and the quarantine that kept us indoors aaallll daaaaay looooong, months on end. This year I ran out of wood before we ran out of cold, wet days. Time to think outside the box...

(The other issue I have with pellet stoves is that they need electricity to run! A wood burning stove that needs electricity to work doesn't do you a lot of good during a power outage, especially when you need heat the most!)

I have a friend who welded up a cage [from expanded metal] to fit in his fireplace. (He has an open fireplace) He would just dump a 40 lb. bag of wood pellets on evenings when he wanted a fire, light it off and enjoy a nice fire. It was expensive [but as he put it] he "didn't have the hassle of cutting, storing, burning and dealing with the mess of burning cut wood in his fireplace". I did a little research and found that you can buy these wood baskets on line for anywhere from $20-$60, and that some of them are modified to deal with just wood pellets. I decided I could build a better, more efficient adapter that would only burn about 10 lbs. of pellets every 4 hours and STILL put put out a good, steady amount of flame (and heat) to warm the house up very nicely.

You'll need a section of 'machine netting' (rabbit-hutch screen) big enough to fold up and fit inside your fireplace/stove. Your screen section should be made of steel, as stout as you can get, and should have very small holes (most rabbit-hutch screen has 1/4" holes, and that works fine). If you can find the smaller, 3/16" or 1/8" netting so much the better.

Measure your fireplace/stove floor. Get a piece of netting that is 1-1/2 times longer and wider than the floor of the fireplace. My wood-burner is very small, and only measures about 30 cm x 20 cm [on the inside], so I bought a piece of 60 cm wide netting. I needed about 90 cm for the box so I had the store cut me a piece about 1 meter (100 cm) long.

(I originally use a piece of steel sheet-rock corner bead but it didn't last long because I let the fire get too hot. Read more about that on the last step) Use heavy gage steel construction angle or shelving angle [as shown] to make the base of the pellet box. (Do not use plastic or aluminum). You will need to use a right-angle grinder with a metal cutting wheel to cut up your angle for the base

You'll also need some thin, pliable steel wire [typically used in construction work for temporarily tying up or securing things together].

That's it; less than $8 worth of supplies.

You'll need a measure, a felt-tip pen (for marking the netting wit) and a couple of pliers to weave, twist, bend and/or cut the wire with. Make sure you have a good pair of diagonal cutters (pictured above) to cut the netting with.

It took me a bit less than an hour to put the first version together and then another 30 minutes to modify it. All-in-all, It should take you less that 2 hours to put one together. It took me another hour to modify it with the better base.

Image how a card-board shoe box is constructed...you'll build your box the same way (but without the folding lid). You will only cut lines in the netting at the corners and fold the box up around your cuts. This way you will only make 4 cuts, 2 at each end.

(If you have any doubts about your steps (or your measurements) cut the first one using thin cardboard and scissors then fold it together to make sure it's the size and shape you want. Make a scale model out of a used cereal box if need be.)

I wanted my box (wire cage) to be about 15-17 cm tall so I cut the box dims accordingly; each wall was either 17 cm or 35 cm tall (which I folded down to 17 cm tall).

I measured out 90 cm along the length of the netting and cut off the last 10 cm (saving it for later). Since I needed a box that was 25 cm wide x 17 cm deep (for a loose fit in a 30 cm wide x 20 cm deep fireplace) I bent up the two long edges at 17 cm each and then folded them up to form the sides. Look at the pictures above for reference. I measured out 17 cm along each end, marked it with the felt-tip and used the diagonal cutters to cut the ends along the fold.

I then folded up the ends such that the ends with exposed/cut netting were inside the box. That way I didn't poke my hands each time I handled the box; this also ensures that the top edges are constructed solely of bent edges.

After I folded it up the way I wanted, I used a couple of zip-ties to hold it in form so I could wire-weave it together.

Don't worry about reinforcing the base; the grate you will make (in one of the following steps) will do that.

Using the steel wire and the needle-nose pliers, run a few weaves up and down both ends securing all flaps of the box together. Twist the wire ends together and use the flat-nosed pliers to get them nice and snug. Cut the ends of the wire twists down to the last twist with the diagonal cutters, then tuck them into the netting using the needle-nose pliers.

You'll note that I didn't bring the side walls up to full vertical; that way the grate [that you will build to go into this wire box] slips in and out easily.

Now you can remove the zip-ties.

Like most fireplaces, you'll need a metal grate to put the wood over so it gets air circulation underneath it. Although your grate will have to suspend pellets.

Using the remaining piece of netting, cut it and fold it up to make a base only slightly smaller that the inside base dimensions of the wire box. My wire box had a base of about 25 cm x 17 cm so I cut, folded and wire-tied a base about 23 cm by 15 cm.

Then, using the right-angle cutters, cut the metal corner molding into enough sections to cover the base side to side (as shown). (I needed 4 each, 20 cm long sections.) After you get your lengths cut and test fitted, wire-tie them to the base of the grate. This will give the base structure.

This was my metal grate. I set the 'grate' in the base of the basket and then wire tied the entire grate/base to the base of the metal box. This will make it easier to empty and make for a more stout structure.

The first run I filled up the basket with only about 3 lbs. (1/3 capacity). I started the fire from the front (using a blow torch on 'low') and it took about 45 minutes for the flames to spread across the whole surface.

The second run I filled the basket up completely; it held about 10 lbs of pellets. I also started the fire from the top. I used a small piece of kindling to help keep the flame going. I still needed to keep hitting it a few times (in the first 5 minutes) with the torch to get it to take off. Once it lit off, it took about 20-25 minutes to get going. (This stuff really doesn't want to burn.)

(I see where other YouTuber's used a small piece of a fire-starter block; put right on the top of the mound. I think this is a wise idea and plan on doing this next time.*)

The whole box burned with a nice, even flame (and put out the same amount of heat as cut wood) for about 3 hours. Compared to cut wood, it probably burned about 10% more wood by weight (if I was burning oak it would be closer to 25% more). Toward the end of the 3 hours I was left with a very hot bin of burning pellet embers; no flame, just a bed of embers. It would have kept generating a fair amount of heat for another 30-40 minutes, but not wanting to waste the embers I toss a few small pieces of cut wood on the embers. They lit right up and I got another 60-90 minutes worth of heat.

Editor's note: I have since learned a more efficient method of keeping the pellets burning longer. Read the last step.

In summary, the best part of using pellets (instead of cut wood) is that I didn't have to cut the wood, use three different steps to get it to light up, open the box every 45 minutes to stoke the fire and then feed it more logs. No more smoke just to start (or keep) the fire going, and a LOT less ash when it's all burned out...I'm sold.

I'll probably cut up a bunch of wood for future fires, but if I use them I'll just toss them on just before we go to bed to give the house another hour or so of heat.

Author's notes:

Unlike most cut-wood fires, this stuff does not benefit from a source of blowing air. If you use a stove with a door (like mine) and then open it up to fan (or blow on it) to help it along like a charcoal fire, you'll just blow it out. You will need to figure out your optimum settings for your flues.

Once I got the flame to start up (to about a 10 cm [4 inch] circular patch) I kept my flues cracked open about 1/3rd for about the first 45 minutes (just to get a good flame going) then ended up closing all flues for the duration. If you leave your flues open you'll get a really large, hot flame, but you'll also burn up your pellets in a hurry.

*A quick note: Knowing that you can use just about any cooking oil in an oil lamp, I poured about a tablespoon of peanut oil on the top of the pellet mound and set a match to it...viola! It lite right away, and sustained an nice flame long enough to get the pellets to take off. I'll grab some fire-starter next time I'm at the hardware store, but until then I'll use some cooking oil to get it started.

OK, I goofed up...the fire from the wood pellets was far more intense than I thought it would be. This gave me pause. The thin, metal corner angles I recommended in the beginning were eaten up in no time. I went back the hardware store and found a 3-foot section of thick, steel right angle [used to mount on a wall]. I could have bought some of the really stout construction angle but it only came in 8 foot lengths and I didn't need that.

I used a right angle grinder with a metal cutoff wheel to cut it up into 4 pieces and wired them to the base of the cage. This base is now lasting far longer. I also determined that the extra angles I put on top [at right angles] might be hurting me in the long run.

I figured out that by keeping the heat so hot I was sending most of the heat from the fire right up & out the chimney. So, I removed the upper right angles from the base (keeping only four on the base as shown) and then played with the flue settings such that at no time the entire pile of pellets would not catch on fire (burn) at the same time. The picture above shows the size of flame I use. This had two effects:

1) I got 4 hours of burn time out of HALF the amount of pellets. To which, I only use about 1/6th of a bag on cold nights when I want to use the stove. The flame is not as nearly as intense but the room stays just as warm, and

2) the metal at the base of the basket lasts a lot longer.

Lastly, I want to give you one more bit of great advice: after the pile of pellets as burned to the point where it no longer supports a visible flame the embers will still glow red-hot for over an hour or so. If you want another 3-4 hours of great heat toss a few chunks of hardwood firewood on top of them! I use a couple of pieces of oak, each about 6 inches long and 3-4 inches across (pictured). right after you toss them on open the flue just long enough for them to catch fire. Once they have burned for about 10 minutes close the flue back down to keep a low flame around them. Those 2 small pieces of wood will burn completely up, leave little to no ash and keep the stove hot for over 8 hours! If you use a soft wood (like Pine) you can expect them to burn up in a much shorter time.