rocket mass heaters and wind

Hello Paul and everyone. You and heating costs have inspired me to build a RMH. Ive been watching the series on myths of RMH and I am loving the information and finding it very helpful. I am new to forums like these so i may need some help at first learning the site. I was still in the process of designing my fire box but was pushed to get the rest of the system together. I was also eager to see a RMH in action in person and in doing so made a few mistakes. First how important is the burn box length compared to the height of my chimney pipe inside of my barrel? I have an L and J channel combo design. would probably be considered more L channel though. The length of my burn box is approximately 15in from opening to the start of my chimney into barrel. chimney inside barrel is about 3ft give or take a few inches. Where i have my burn box placed i can change the length easily. (somewhat easily) I also in a hurry to complete left a little low hanging lip at the start of my up chimney from my burn box. to be more clear my my burn box is about 6in high, in my hurry building the chimney i left a brick too low and at the end of my burn box its only about 4 1/2in high. this doesnt seem to hurt it much during the burn although it can be overfilled and sort of snuffed out if i cram against this lip/mistake. I have noticed this creates a warm air pocket inside my burn box that lasts hours after coals are no longer hot. I read and saw many designs over the past few years and saw much debate on length of stovepipe through the mass. I have a mass 15ft in length so in all about 38ft of stovepipe including cleanout, elbows, and 5ft up pipe at the end. Is this too long? I am pulling 140F from the last of the stovepipe before it makes the turn up and about 100F steam/smoke out of the end. I dont have a thermometer that reads above 250F at the moment but the barrel and first 10ft of stovepipe exceed 250F easily. The barrel definitely gets hotter than any wood stove ive been around. My system takes about 2 hrs to fully get hot. when fully hot will stay above 100F roughly 8hrs later. I forgot to mention my system is OUTSIDE! I am heating an area for my outside pets (used to be indoors but no room for them inside new place.) I plan to build a shelter house around my RMH. Right now I have a huge tarp covering my camper with it extended over  the RMH. It is not sealed up nor insulated. pictures to come once i find out how to post them here. Temperatures in my area have fallen to 20F with highs mostly in the 40s during the day. when my tarp room is better sealed (before big wind storm) i was keeping it 58F overnight with near 80F during the day with help from the sun (60F on cloudy days.) that was with last restock at around 10pm. I am very impressed with the way they work. I am and will continue to talk all my family and friends into RMH as their main source of heat. just in this past month ive had mine ive convinced my brother to build one. I have a decent size yard with many mature trees i hope will give me all the wood i need. I have future plans to build more RMH to heat a greenhouse and a barn. I also plan to design a RMH into my future house building plans. I am having blow back issues at winds of 10mph or more. Does anyone know of the best and cheapest way to block wind from my stovepipe opening. ive looked into some caps but they are more expensive than i spent on my whole RMH thus far. i am a tight spender but if i need to buy a $129.00 cap/topper to make work correctly i will. I attempted to make a directional wind cap. it successfully turns away from the wind but did not help but blow back issue. i have abandonded sealing my tarp until i resolve the blow back issue. please help. thanks in advance.

One way to reducethe effects of blowback upon your exit flue is to mount a T on the end, and leave both sides open. This has two primary effects; first it pretty well blocks direct wind from that side, which is likely your greatest problem.  Second, it sets up a venturi vacuum effect from cross winds.  As they blow through your tee from one end to the other, it creates a tiny bit of vaccum in the correct direction through your RMH.  Which, if anything noticable happens, will slightly increase your working draft.  If this doesn't work for you, a commercial cap may be in order, but this is pretty much how most of them work.

Thanks for the T idea. I have talked to others that say a vertical turbine topper may be helpful. I will try both and see what works best. Update to my final bench design. I plan to build a park bench over my mass. Under the bench for the last covering over my stovepipe I plan to put lava rock. Hidden within the lava rock i am going to put some dim red LEDs to give the illusion of hot coals. Thoughts?

Aaron Marco wrote:. Hidden within the lava rock i am going to put some dim red LEDs to give the illusion of hot coals. Thoughts?

That sounds awesome!