Building A Masonry Heater
I'm building a Masonry Heater for my house based on plans from the book "Living Homes"
The core of the fireplace is built from fire brick using Refractory Mortar to glue the bricks together
and let it handle high temperatures. The design includes two secondary burn chambers to fully
burn all the gasses and causes this design to emit almost no smoke from the top of the chimney.
Then after leaving the firebox, the hot air is circulated back and forth to allow the stone to absorb
as much heat as possible before finally letting the gas escape up the chimney.
To start out, I decided to beef up the concrete pad under the fireplace. I wasn't sure how much rebar was in the original concrete slab so I will cut out a 4x8 foot section and repour it. I rented a concrete saw, gas powered, finicky, but it got the job done. This didn't cut all the way through the concrete, rather it made a nice score line to minimize edge chipping.
Ah, every big boy's dream... a jackhammer in the house!
The idea is to chip away towards the cutline, working slowly, trying to break through to the bottom of the concrete. Once I break through, it should get easier, as the concrete will have a hole to fall into.
Just about to break through in some areas. Never knew a jackhammer could be so much fun! Not nearly as hard as I thought it would be to use it.
Punched through and moving faster now. And I actually found there was "some" rebar in the slab. Doesn't look like the spacing is very close, but it's nice knowing there's something holding my floor together.
Now things are moving along nicely. It makes a big difference having the open hole for the concrete to fall into.
Time to get a move on and return the jackhammer before the rental store closes. I'll clean up the rubble and cut the edges with a masonry blade in my cutoff grinder when I get back.
Now that I've got the hole cleaned up, I laid down new rebar and wired it together. This, along with some high strength concrete, should support the 4000 pounds oops, make that at least 14000 pounds (7 tons!) I'm putting on top of it. As I keep buying brick, the weight keeps growing ;)
I bought a mixer from Home Depot since I'll be mixing a lot of mud/stucco/plaster in later parts of the build and in other projects I have planned for the home.
The pour is complete and the surface trowled smooth. give it time to set up and figure out how to layout the base of the fireplace.
I started off using Refractory "Cement" on the firebrick, but found that wasn't the best product. What I needed was Refractory "Mortar". The cement had aggregate and little fiberglass fibers in it which made it great for filling large spaces or for pouring into a mold but not so good for buttering bricks. Also note in the photo that I drywalled up the door into the bedroom behind the fireplace. I am converting the two bedrooms into a single master bedroom with a large walk-in closet. Also notice the hollow cinder blocks against the wall. I will turn these on end to allow vertical airflow behind the fireplace to keep the back wall cool.
I found some Refractory Mortar called "HeatStop". Great product, just mix with water to a pancake batter consistancy and dip the edge of the brick in it and put in place. If you look at the two ends of the fireplace, there are square holes where the air will come into the bottom of the firebox. I had the option of running pvc pipe from outside to the fireplace to allow outside air to flow through the fireplace and out the chimney, but my house isn't the most air tight and the fire will burn fast and hot for a short time so I wasn't too worried about "negative air pressure" in the house. I will probably plan for outside air if I build this into a new house next time.
The next layer of bricks is installed. Now you can see the start of the firebox and how the two sides allow the air to flow into the bottom of the firebox.
A close-up of the air inlet. The air comes in from the bottom/sides and flows into the square chamber where it mixes with the gasses from the fireplace in the secondary burn chamber, then they flow into the bottom of the fireplace to feed the fire.
This is as far as I can go on the sides until I build the arch over the firebox. Building any fireplace is always a question of how well it will "draw" so I paid close attention to the air chambers, making sure they were well mortared and smooth to keep the air flowing nicely.
A front view of the fireplace to this point.
Now I need to figure out how to support the arch as I build it. I've seen other people fill the inner cavity with sand to the shape they want, so my first thought was to fill the interior with bricks and sand or maybe magazines and paper to make the shape. But I hadn't bought any sand and getting a smooth shape would be challenging with other materials.
So I looked around the garage and found some old pvc water pipe and figured I could make a nice arch shape with that.
Add some used carpet, wire it together and 'viola!' an arch. Now to be truthful, I actually didn't use the arch to support the bricks, but rather built each layer using the arch as a guideline to make sure I was building each side evenly. The angle of each next layer was small enough that I could hold the bricks in place while I packed in the mortar and it would hold in place.
Here's one of the sides starting to take shape. The gap in the bricks at the top row is where the gasses will be allowed to recirculate from the firebox into the secondary burn chambers. Note, at this point I am back to using the "Refractory Cement" I had originally purchased, since it is perfect for filling the larger spaces between the bricks.
I've got both sides nearly finished. I will let these set up overnight before I try to cut and place the "keystones" which will hold both sides together. I'm pleased with how well it's coming together.
Keystones are in and the side chambers are starting to rise.
There's been one thing bothering me as I look at the side holes that feed from the upper corners of the fireplace into the secondary burn chambers. My design took more layers to make the arch than the design in the book. So when I opened the space to let the air circulate, it ended up being further down the side wall than I like. I kept looking at it and decided the way to make a better airflow was to enlarge the holes. So a masonry bit, a hammer and chisel and I think it will be worth the extra effort.
A close up of the new hole. I lost some of the brick inside the firebox, but I can repatch that with the refractory concrete later.
The inside of the firebox where the bricks chipped away.
Now I'm ready to fit the bricks up against the arch. I'll do these all at once to make sure I end up level with the top of the arch. Plus it will make the other bricks go in faster since there will be no hard cuts. I mark these bricks with a sharpie and cut them before I mix the mortar.
Both sides are done with the bricks against the arch. Now let it set up over night and get both sides even with the top of the arch tomorrow. If it appears that the top bricks are offset a little, actually it's the second brick down that's inset. This is so I can place a full brick across the gap to make the top of the secondary burn chambers.
The side chambers are capped off and I'm ready to start building the baffle layers. I've still got to put the four end bricks on the sides, but I ran out of mortar and will do that next time. You can also see one of the clean out doors I bought to provide access into each of the baffle sections. You can lift up on the handle and remove the door. I will mortar these into the baffles as I go.
Baffles are started.
A closeup of the throat at the top of the firebox. I tried to round the corners to keep the airflow smooth as it enters the baffle system.
A look at the cleanout door in the first baffle. They are made from cast refractory cement and the door lifts up and out to provide access.
One full set of baffles is done and I'm working on the second set.
Two done, and the third and last turn is started.
The firebrick part of the build is essentially done. You can see the cleanout doors in the side.
But as I kept looking at the fireplace, something was bothered me... in the original plans from the book, the author mentioned that he used full bricks in most of his design to minimize the amount of cuts needed to the firebrick. But what struck my eye was the odd air spaces that would be between the firebrick and the outer layer of bricks. I think it would be best to have a flat surface, with a small air gap between the inner and outer layers, which would facilitate the transfer of heat to the outside walls. So this is the last chance I'll have to do something with the firebrick... so....
I covered the fireplace with a tarp and started cutting and grinding the protruding bricks flat. The tarp helps contain some of the dust, but it's all over the house again... sigh.
A couple different ways to cut and grind the bricks. I scored the bricks with a masonry blade on an angle grinder. Then knocked the pieces off and finally ground the area semi-smooth with a grinder disc.
Picking up the outside brick. I got a good price on some odd-shaped bricks the yard had a hard time moving. They're triple height compared to regular filler brick and I mixed it up with some regular sized concrete bricks to give me options when positioning the lintel and in building some of the curved areas.
Sadly, on the way home I shredded a trailer tire. But I was able to use the small truck jack and get a new tire in a nearby town. I'm amazed the little jack could hold the weight!
So I propped up the fireplace door I bought and used photoshop to mock up what it would look like. With as much time as I'm putting into this project, I just didn't like the rectangular glass with the arch showing through. And since a custom door would cost between $1200 and $2000, I decided to try to make my own door.
I already owned a mig welder, so $20 got me some angle iron. Let's see if I can do this.
Measure, cut, bend, weld. Even though I'll embed the door in the facing layer of brick, I can use the existing arch as a template.
I Messed up a little on this angle cut. To make both sides of the bend line up I should have made two angle cuts, rather than one straight and one angled. But I can weld in another scrap of metal and make it flat later. I'll do better on the other side. Live and learn.
Both sides tacked to a nice arch. Time to cut and bend the bottom.
Now time for some grinding, tack welding any low spots and repeat until I have a nice smooth frame.
Door frame done. Notice the round "tabs" where I will tie it into the surrounding brick