Rocket Mass Heater for my home

[Nirky]

Manny, I only have it half built as I haven't had time for the mass, but I love this thing! It uses less than half the wood of my Quarda-fire woodstove. The feeding every 15 minutes is less than optimum, thus my interest in Matt's batch box. But once I have the mass done I figure I only need to burn for 3 hours at night so that it's still warm in the AM. Now, with no mass, I'm waking up to 55 inside while it's 19 outside. A little chilly, but this small house only has R-19 in the ceilings, and it's 2x4 construction instead of the necessary 2x6 up here in northern Idaho. So I'm pleased with a half-working RMH, will be very pleased I'm sure once I have the mass up.

[mannytheseacow]

That's awesome, Nirky. I'm glad you're loving it. These things do use so much less wood. The constant feeding is something that literally took me a year to get used to. For me, my first stove was undersized, so there was a bigger learning curve. Once I made an 8" (my house sq.ft. is nearly triple yours), I burn a load in the morning, and then burn as much as I'm home at night. My temps are similar to what you have in N. Idaho (my wife lived in N. Idaho for several years). Once you have that mass I think everything will settle into place.

Don't get me wrong, I'm pretty intrigued by the batch box, too. That's just so far down on my list of priorities. I think once you get that mass together you will be burning even less and your house will be much warmer. You almost need to live with the J box for a good season just to understand how to utilize the batch box to its full potential. Along with that, you'll probably find you need an even larger mass to combat the temperature swings and utilize all the heat coming off. I think there's a balance point, be it the J tube or the batch box, and once you find that balance with your home and your heating system, you won't be feeding it very much wood at all.

[matt walker]

Yeah, what Manny said. I'm not convinced it's any better than my 8" J, just different. The J was way nicer to sit next to and stare into and feed and wiggle the sticks and stuff. And yeah Nirky, these things aren't good wood stoves, but they are great mass heaters. In other words, the short burn time isn't an issue when you have the big flywheel, without it though, they don't make a whole lot of sense. Not picking on you, I know you understand this, just saying it's going to get a lot better once you have the mass online.

[ByronC]

I know what you mean. There is something very satisfying about tending a fire. But sometimes there are chores that call one away from the stove. I'm still on the fence about which way to go for my indoor system, J-tube or batch. So I've been contemplating each.

Pros/cons of J-tube vers. batchbox

8" J-tube

* simplicity in construction
* wood miser
* open fire box to tend, look into, listen to
* wood loads in higher up off the floor than a batchbox
* not big chunks of gnarly knotty wood friendly
* works best with finely split wood

6" Batchbox

* a little more difficult for a novice to construct
* requires a firebox door (that gets really hot)
* burns a bit more wood
* more or less no fuss no tending load and burn
* wood loads in lower to the floor than a J-tube
* accepts larger less finely split wood
* able to take larger gnarly wood pieces that would choke a J-tube

Did I miss anything? Matt, did your straight/ unmodified batchbox dump a lot more radiant heat out of the barrel than your 8" J-tube, tending to overheat the room faster?

[matt walker]

I would say that's pretty good Byron. I would argue that the batch actually uses less wood in practice, since it's just as if not more efficient and since you aren't sitting there trying to stuff fuel into it you tend to settle into a less fervent wood feeding cycle.

The ability to use different format fuel is a biggie in favor of the batch for me.

The big one you missed in the J is the inherent safety of the thing with regards to burns and kids and stuff. My friends, even my slightly nervous friend, had no problem with his 6 year old sitting inches from the thing poking wood into it when it was going full tilt. Batch has more normal wood stove risks, at least on the face.

To answer your question, um, well, with the batch the barrel did jump right up to max temp every time, but if you are cruising low and slow with a J you aren't really doing it right anyway. Not that I didn't do that, I did, often. But you could do the same with the batch, mix wood, load less than full, etc.

[matt walker]

Here's a followup video to my conversion and bench addition. Long and rambling, but I just sorta go over my thoughts at this point...

[ByronC]

Matt, many thanks man, for your comparison comments batch/J-tube. Been following your secondary air experiments too. Thanks for the update video on your home system. All good stuff!

Silence on my end will always indicate being super busy with something. I.e. I've since opened up a sizable hole in the wooden lofted floor along a wall common to the LR/DR/kitchen (all one open space, about 25'x20') and poured a reinforced concrete pad down in the crawlspace (last weekend). For the past week I've been laying up block to bring the RMH foundation on up to floor level, and that step is now complete. This weekend the final/top concrete pad will be poured. Then, finally, the real fun can begin, building my indoor RMH.

[matt walker]

That's awesome Byron! Can't wait to see the build, sounds like it's off to a good start. It also sounds like a lot of work!

[mannytheseacow]

So what's the story on the conversion? Did you end up with any decisions on the best air supply methods?

I've also been curious- I regularly clean some ash out from the bottom of the heat riser, with a batchbox does the port restrict access to cleaning that area? Does it ever clog up? Oh, I should probably just build one already!

In the spring.

[matt walker]

Good questions. I've been meaning to write a follow up and just haven't been feeling like writing much lately, although I've been marshaling my thoughts on this thing, and getting an incredible amount done around the 'stead lately. I'm remiss in all sorts of updates! Anyway...here's a quick answer to your questions and I promise I'll do a thorough follow up soon to this thing. It's kinda overwhelming as there's so much I want to cover.

So, for the Pre Port air, after much experimenting, for now I've settled on what I was referring to as v5. About 10% secondary/9% primary. The tube is the rectangle stock for secondary intake along the floor, and the vertical output side is 2" round pipe with a 3/8" slot and no top. I built a door, what a pain in the ass! Made a huge difference in performance. The primary comes in just at the lower mid section of the fuel, and there is a plenum under the window that shoots air wash up across the window. That puts on an awesome show, I need to film it for you guys. Here's the door...



...and I tiled more of the bench...(your favorite Manny!)


...and I built this wood dolly/ottoman/fire-tending stool thing. Really cleaned up the hearth, and keeps all the chips and dirt contained. I love this thing!....






As far as the bottom of the riser goes, this heater is barely blowing anything past the port. I cleaned it last night as a matter of fact, as I was feeling guilty since I hadn't even really looked in there for a couple weeks. It was really clean, not much in the port/riser at all. It is a pain to clean back past the port, but you can stick a little shovel or stick in there no problem and pull stuff back. As you know, it doesn't need to be perfect, just remove any build up once in a while. I take out my secondary air tube and this thing cleans much easier than the J overall, although the process is a bit dirtier. About the same as shoveling out a wood stove, with way less volume.


Part of the reason the update has been slow is that this thing is an incredible heater. I am continually blown away by just how good it is. And then I will have a bad start or a cold load and I will smoke out my whole yard! And then an hour later I'm like, dang this is an awesome heater! So, it's amazing, and it's finicky. I'm curious to open up the flues when things warm up. I definitely have more smoke events than I did with the J, and occasionally it will take me a few minutes to get over it. And then it's warm and it's the best heater I can imagine. Overall, I'm amazed at this thing. It is just a great, great heater. After running it for a while I was thinking it wasn't doing so great on the numbers just based on guessing from watching it over the weeks. I put a load of fuel in one night, nothing special, just a regular nightly load of fuel from my stacks, and stuck the Testo in it. Same flat line chart, CO down below 10ppm, efficiency at around 90%. So, yeah, I'm endorsing it for sure, but it's going to require a good operator and good fuel to be a success. Here's the latest Testo chart.