Alex's Operate a Rocket Log

This log will document my effort in completing Operate a RMH for One Month BB. Note that all temp recordings will be in deg Fahrenheit.

I arrived at Base Camp the night of Dec 7. Shane, a boot here, was already running the rocket in the Fischer Price house. Interior temp got up to 78deg by ~7p. At ~8:30p, I closed the bricks above the intake to the point where I could still see the embers but it was mostly closed. At 9:15p, I put the cap on the intake to close it completely when the fire had gone out. The kids said that it was too hot to go to sleep - I thought that it was comfortable.

Dec 8 7a, it's 71deg inside and 31deg outside. It's comfortable. I've been cooking soup all morning and there's been a lot of traffic in a out of the house for the cleaning blitz. By 12:40p, it's 70deg inside and 38deg outside.

My son helped me restock the wood on the shelves. I'm curious to see how often we need to restock these shelves to heat this RMH for a month. Likely a lot of them are too large to fit in the intake. This rocket is an 8in system but the draft was so strong when it was built that it would put out the flame so it's since been modified to have a 6in intake. Less volume of feed apparently equates to less of a draw. This was surprising to me since the flow rate will increase when the CSA decreases. I think there were additional changes made to the system, I'll have to inquire more.

I was told that if the outside temps were in the teens and 20s, then it's necessary to hold a 3hr burn every day and a half. I anticipate that it won't be necessary to run the RMH until tomorrow morning.

I purchased a smart thermo-hygrometer that I plan on setting up this evening and validating over the next few days before relying on it for temp data. It'll be fun to have more detailed temp data to report!

Hello Alex!  


I am so happy for you to get to be at Wheaton Labs and play with your family!


Please post lots of pictures of all your adventures there!


Happy winter!

On 12/9, day 2 I started the RMH before breakfast when it was 65deg. It was quick to start since I didn't need to do a cold start. I started with cardboard and smaller pieces of wood, then quickly moved to larger pieces of wood. Lesson learned, don't move to large pieces of wood too quickly. I found that the radiator got hot but never too harsh to stand next to. I wanted the temps to be steady instead of spike for a slow burn. I definitely achieved that because it took about 6 hours for the temps to get to 75deg. I thought that it would take 3-4hrs. This required me to return to the FP house many times to check on it but the embers never died in between visits because I was burning the largest pieces of wood. pros and cons. There wasn't much cooking today and I would suspect an average amount of foot traffic.

temps for 12/9:
time inside outside
0646       65        30        
1241 75        37
2010 74        34

On 12/10, day 3 it was 68deg at breakfast, ~0645, which was comfortable for me but Shane was chilly so I got the RMH going even though I wasn't anticipating running it until the afternoon at the earliest. Getting familiar with the temp preferences of everyone here is part of the process that will help me refine my operating schedule. Today I plan to use smaller pieces of wood and see if that equates to longer term warmth. Stephen has noticed that the hotter the burn (the smaller the wood), the hotter the radiator and the more the mass heats up. I was surprised because I think that the hotter the burn, the more instant heat comes out of the radiator and the less the heat gets stored by the mass. I suspect we could both be right if the quantity of wood isn't kept constant. I'd like to prove this out but I'd need to find a way to measure the fuel. I'll table more detailed experiments/observation for next week after I get a better sense of the basic routine.

I should also mention that I had an oopsie when starting the RMH in the solarium yesterday. I was way too quick to transition from kindling to large pieces of wood. In hindsight, I was being way too hasty on a cold system in a cold room. I'll need to take much better care in the future. Because of this, Shane insured that I had more supervision when starting the FP house this morning. He advocated for a lot more kindling than I thought was necessary for a warm system - I'm learning that I had a lot more to learn than I thought!! I'm glad to have this opportunity!

temps for 12/10:
time inside outside
0749        70        24  

That's it for now but, of course, there's a lot more to convey.

A few days have passed since my last update. I initially included the numbers but I edited this post removing the numbers because the formatting is too strange. Plus, the temp sensors have been on point since I turned them on and the temp data collected throughout the day is more interesting to look at. I plan to merge the manual and upload the sensor data to make fun graphs next week.

On Day 4, I decided to see how the rocket performed differently with smaller pieces of wood. The fire was easier to start, ran much hotter faster, and took less overall time to run. What a huge difference! So I proceeded to take all of the wood off the shelves, chop it, and return it to the shelves. See photo of shelf update.

I enjoy the fact that I can have a wood fire going, take a walk or work outside and not smell anything gross. It smells so nice outside that I forget that I have a wood fire going altogether!

It's now day 7 and this RMH is starting to feel more familiar and predictable. Though, I'm glad I'll be here for a month to continue to observe and learn. Now that the wood feed pieces are much smaller, I've been starting the fire with mostly cardboard, paper, and a few small pieces of wood. When the wood pieces have definitely caught, I fill the entire feed with wood on the smaller side. Once most of the wood has burned, I repeat, maybe using slightly larger pieces. Then I do a final feed with slightly larger pieces. I'll upload pictures of the feed at the next update.

Alexandra Malecki wrote:On Day 4, I decided to see how the rocket performed differently with smaller pieces of wood. The fire was easier to start, ran much hotter faster, and took less overall time to run. What a huge difference! So I proceeded to take all of the wood off the shelves, chop it, and return it to the shelves. See photo of shelf update.

One thing I'm loving about mine is that we are using all the little bits of wood that no-one else bothers to pick up and take home. Pine trees fall near the road and the main trunk is removed by the owner while the branches get left behind. So months later we dutifully pick them up so they don't pose a fire risk. We prune fruit trees and I sit down with a pair of loppers and cut the sticks into the right length for the firebox. I find branches by the side of the road while I'm out walking the dog and drag them home. Mostly the rmh runs on the stuff that nobody else wants, and for the most part I don't even have to chop it!

I uploaded the temperature sensor data and overlayed it with my manual data collection. I much prefer the sensor because it will give me a more accurate average temperature; it collects data every minute and collects temperature data to the hundredths. Looking at the overlay, my manual data entries are rounded to the nearest whole number and the electronic sensor is located approximately 40inches away from the existing wall mounted sensor that I was collecting data from which is why there are discrepancies.

Take a look at the pretty data below!

So far
--the Average temp is 72.12degF (above 70deg)
--the Min temp collected was 65degF (at the requirement)

On day 15, I relocated the sensor (refer to attachment below for visual) because of a temperature spike oversight. When I was validating the recorded data from the automated thermo sensor, I compared the manual data entries to the automated entries to confirm alignment but I didn't glimpse at the localized highs. First, to address the manual to automated misalignment, the automated thermometer sensor records non-integer data to the hundredths while the manual temp readings using the wall mounted temperature display records integer data (I suspect that the data isn't rounded). The error in data I attribute to the dissimilarity of precision in data collection. With the temperature spikes being brought to my attention, it appears that the temperature spikes occur for a short period of time right when the rocket is ignited. When I first placed the thermometer sensor, I didn't suspect that radiant heat would effect the readings since it's not within line of sight. Upon closer inspection, it is possible that a corner of the sensor was in fact ever so slightly within line of sight. Radiant heat intensity is inversely proportional to the square of the distance from the source. However, if the rocket was operating for an hour, then I would have suspected that the temperature spike would last an hour. After pondering this temperature spike longer to try to evaluate if the sensor was reliable, it occurred to me that as part of my routine, I ignite the rocket and within 15 mins, I turn fans on to circulate and distribute the heat throughout the house. I suspect that the automated temperature sensor is recording localized temperature spikes since it's located closer to the rocket.

I typically operate the rocket until the wall mount temp indicator reads 74degF if I plan to be in the kitchen cooking that day or over 78degF if I plan to leave for the day. I’ve found that if it’s ~71degF when I retire for the evening, then it will be ~67degF when I awake.

So on Day 15, I relocated the sensor 33inches farther from the rocket, closer to the wall mounted thermostat display and have been validating the temp highs in real time. The readings are now consistently in alignment (of course, the differences in precision aside).

Aside from all of the sensor chatter, I've now spent almost 3 weeks operating the FP rocket. I even spent '15 mins recording a quick podcast' that turned into a nearly 2hr podcast with Paul and Stephen: https://permies.com/wiki/271512/Podcast-Christmas-RMH-Special-Part#2843201 and Part 2 has yet to be released.

Before arriving here, I suspected/expected that I'd have my routine and technique refined by now but I find that I'm still experimenting.

There are a lot of variables:
--thickness of the wood: too large causes too slow of a burn (and you need to get the system ramped up fast to reach full combustion temps) and too small can cause a competing chimney effect. I think the ideal state is for the first round to be primarily cardboard (or other quick burning fuel), with some magic dust (small bits of wood). The second round, fill the belly with a load of primarily smaller sticks (but not tooo small). Then the next round use a combination of large and small sticks. Repeat a combination of large and small OR use 2 large chunks to sustain a slow burn. Cork it.
--how full to fill the belly: if the wood pieces are too tight in the feed then they won't naturally fall to keep the feed low which causes the fire to rise up the sticks. For the majority of the time I've been operating this rocket, I think I've been over packing the feed. You do want the feed to be full to increase the air velocity but not too full.
--positioning of the wood: place the smallest sticks farthest from the barrel in the feed because you want the entire load to burn at the same rate.
--positioning of the bricks and cork to limit air intake - I think explaining this requires some visuals of the air flow. Basically, you want the air to go through as many sticks as possible, not bypass the sticks. Remember that fluids will take the path of least resistance so if given the opportunity, the air will bypass the sticks and then your fire triangle won't be optimized.
--strategy for when to use cardboard, shorties (short pieces of wood), and skinny pieces of wood: cardboard burns way hot for a short time, shorties will extend your burn time without sticking out of the intake. Shorties can be used to block an air bypass and keep the air velocity strong. Skinnies should be used at the back of the feed.
--ash removal: if you forget to remove ash before you ignite the rocket, then your bed of coals will be high and your sticks will be proud of your feed. You can't remove ash easily after starting your first fire.
--timing for refilling the feed: you don't want to add prematurely when the bed of coals is too high (sticks will be proud of feed) but you don't want to wait until the coals have died or you'll have to restart your fire.
--using the poker to fiddle or not to fiddle with the wood - use it sparingly. Apparently I'm still researching this.
--first in, first out (for using the driest wood): I can't quantify how much this matters but I suspect that the wood on the shelves inside have been drying while the wood stored outside in the wood racks are comparatively less dry. Using dryer wood is always preferred to ensure your system operates more efficiently.

to consider for optimizing the performance or even optimizing for convenience (are you going to be there in 15-20 mins or do you prefer a longer burn so that the embers are still hot when you return?).

Lately I've been trying different strategies for keeping the fire low. A low fire indicates a strong draw and lack of a competing chimney -- optimized performance. In being hyper-focused on this as a desirable outcome, I found that I've been fiddling with the feed way too much and causing issues. In trying to optimize the configuration of the wood, I was incidentally caused too much flow turbulence in the wood feed and/or clogged the entry to the burn tunnel. Yesterday I felt like the rocket and I weren't getting along and the house got a little bit smokey so I needed to open the door and burn the rocket longer than I would have needed to to compensate for the lost heat. After reflecting more on my failure, I recalled that I also forgot to remove ash before igniting the rocket so I was constantly struggling with wood sticking too far out of the feed -- to exacerbate this, I even burned WAY more paper and cardboard (as a result of Christmas wrappings), so the ash buildup was way higher than normal.

Today, I decided that I need to restrain myself and not fiddle with the wood after filling the belly -- I experienced 0% of the issues that I had yesterday and I attribute that to clearing the excessive amount of ash and not fiddling with the wood after filling the feed.

That's all for now...

The month started out dry and cold, then got warmer with intermittent, light snow, then got colder with a lot of snow.

With the added humidity in the air, I've been running the rocket to hotter temps in the morning than usual to ensure that the temps don't drop to below my requirement in the night. I'm not sure if that was necessary but we've all adjusted to having the house running pretty hot. We even made snow cones to cool down one hot morning using snow from outside!

My RMH operation routine has fluctuated quite a lot but after a month, I've settled in to a rhythm. In the morning, I brew my coffee. As I wait for my coffee, I remove the cork (the cover for the wood feed) and I remove ash from the bottom of the wood feed (I learned that if I don't remove the ash, it might be trickier to operate the rocket). Every few days, I'll reach further back into the burn tunnel and remove as much ash as I can. Then I get 3 handfuls of cardboard and other kindling and stuff the wood feed, keeping the material low and ensuring that the burn tunnel has at least an inch of an opening. I then sprinkle in some small wood bits and/or bark on top of the cardboard.

Then I scoop up two handfuls of the smallest wood on the shelves, placing the largest and/or knottiest pieces first closest to the barrel. I place the largest end of the stick at the bottom of the feed. I then place the remaining sticks, orienting each so that the elongated cross-section is parallel to the direction of the air-flow. I try to avoid placing sticks that prevent air from traveling around them. I need to be so careful not to overpack the feed - I have a tendency to do this. If I overpack it then it limits air flow. I have also been trying to keep the side walls (all aside from the the front wall) clear. It seems that this configuration contributes to keeping the fire low.

Then I strain my coffee and get breakfast ready, get the kids going, and otherwise tend to other things for 15-20mins, peering into the wood feed every time I walk by it.

The next time I load the feed I get one large piece of wood and a big handful of smaller wood sticks and implement the same strategy as above. I turn on the two fans that help shed heat from the radiator and circulate air around the house. I then continue to weave in my morning chores while being able to check on the feed. I have a habit of poking the sticks more than I should but that also seems to follow my first habit of overpacking the wood feed. Things go much more smoothly when I don't overpack the feed and the sticks fall down on their own without me getting antsy about it.

I need about 3-4 rounds of feeding the rocket to get to 74/75degF which works for if I'm doing a normal amount of cooking that day. If I'm doing a lot of cooking (like Christmas Eve and Day), then I'll do 2-3 rounds to get to 72/73deg. If I'm not planning on hanging around that day because I'll be in the workshop or going in to town, then I'll run the rocket 5-6 rounds to get to ~79degs.

If I go to bed and the inside temps are above 71, then I feel pretty good about the temps not declining too much while I'm sleeping to go too close to the minimum temperature requirement. There was one evening (after being in town longer than planned) where I needed to run the rocket a second time just to ensure that the temps would be high enough.

Overall, the inside temperatures have been WAY TOO HOT. My kids and I should have packed more summer clothes for this trip. This is way warmer than I'm use to at home, using my  boiler-radiant heat system.

I'd be remiss if I didn't mention my failures: there have been 3 different times that I got smoke back (once from overpacking and twice from too much ash build up) and I've had to aerate the house by opening the front door.

For a few weeks I was using the bricks to partially cover the opening but it seems that I did that with undue caution. The radiator seems to get hottest when I don't use the bricks or the cork. At the end of the month, I now only use the bricks if the sticks are too proud of the feed, I overpacked it and need to baby it, or the wood has dropped down but it's too soon to load and I want to alter the intake air flow (I'd have to keep experimenting to see if this is justified or not).

My first 28days of operating a Rocket Mass Heater are complete! I'm really glad that I spent a month getting familiar with this 12-year, well-functioning rocket so that I can use this experience as a baseline moving forward.

I've attached temperature graphs of the data I collected.

For the inside temperature graph, note that on Day 2 the morning temperature dropped to 65deg. The minimum temperature requirement states "kept at least 65 degrees F". The manual measurements round down to the nearest integer (for example, if the temperature is 65.9 then it would read 65). Also note that on day 15, I relocated the sensor 32inches farther from the RMH so that the temperature readings wouldn't spike when the rocket was turned on. I was concerned about how this would impact the average temperature of the entire study; however, the requirements are for 3 discrete temperature readings to be taken each day so there's very little accuracy with the requirements as they are. Calculating an average monthly temperature with 84 discrete data points (and not specifying when to take the measurements; before and after starting the rocket) will have a large % error.

For the outside temperature graph, note that only day 15 had a daily low that exceeded 32degF. I'm relieved that the weather continued to be cold for accomplishing this BB!

This Rocket was operated in a 3 bed, 2 bath insulated structure.

Take a look at my BB submission here: https://permies.com/wiki/125881/pep-rocket/Operate-RMH-Month-PEP-BB#2848529