Back Puffing

Hi, folks.

I'm new to the forum, but I know that my issue has probably been covered at some point, at least, around here somewhere. If anyone could direct me to any resources that might help, please do so.

I built my Rocket "Room" Heater (I rent, so I couldn't use "mass," so to speak, so it's more of a convection/radiation heater in my basement) and just finished cobbing at the base of the 55 gallon barrel around the base chamber of bricks and around the exhaust.

My exhaust is an 8" diameter pipe, which extends from the heater for about 4', and I reduced it to a 6" diameter pipe that bends at 90 degrees to go out a cat-door. The exhaust rises maybe 20 degrees over the span from heater to outside. The 6" pipe is extended out the cat-door by about 5'. So it's essentially pointing almost directly North. Surprise: I'm getting back-puffing and a slow draw for the burn.

I figure that the reduction is probably an issue, and I could change it to a complete run of 8" diameter pipe if I make some alterations to the cat-door. But I'm also considering a "chimney cap" outside if I cut the straight section and bend it upward at 90 degrees, like a standard chimney. I figure the winds would create a consistent draw with a cap installed. The pipe going outside is also HVAC metal pipe, so there's no insulation, and it's single-wall.

Otherwise, the RRH seems to work pretty well--for my first build--and I'm chinking spots in the cob where smoke is escaping. The pipes are actually dripping onto the basement floor from so much vapor in them.

ten fires : I expect that where I amgoing to send you will turn out to be just a part of your problem, But! This is a very good source to explain why Rocket Mass Heaters 'mostly'
don't work in basements ! In effect your whole house starts working against you. There is a lot of Information on this site, which is a working/outreach arm of Alaska University!

Please go to - ' makinghouseswork.cchrc.org/2013/what-is-stack-effect-and-how-does-it-affect-your-home/ ' For a couple of years now the best of the Workshop Trainers have
been pointing out the handicaps we have been fighting against, trying to place a R.M.H. in the basement, and recommending that it is given "Pride of Place' i.e. no more than an
arms reach from the heart of the house ( heart of the home/house is what hearth originally meant, now it is used to name an architectural feature ) Enjoy Big AL

Late note : pay attention to what is happening at 5:50 >>>> A.L.

Hello. I will tell you I am not an expert and have only built a test unit out side but have been doing alot of research. You can not reduce the pipe or you won't have the correct flow for your gasses, if you needed to be at 6" for the exhaust, the whole system needs to be 6". Plus the math for your riser and feed tube need to be correct for a good draw, also the gap between the riser and the barrel.
Since you already built your core , just change to 8 " and see what happens. I am sure that will fix your problems.
Good luck
Carter

Thanks, folks.

I switched out the 6" pipe for 8", and I put a 90 degree elbow on the end that extends from the house (cat door) with a rain cap on it, hoping to use the winds, even if they shift, to pull draft.

I lit the stove, and I found that it was VERY difficult to prime. What was interesting was that it wouldn't prime with a positive draw unless the basement door was open. Once it was going, I could shut the door, but I needed to keep a rather large opening available to allow for air exchange. (At this point, the drying cob was also presenting cracks that were allowing smoke to enter the basement. That was frustrating.)

So now I'm seeing, what I believe Allen was showing me regarding Stack Effect. I understand the physics, but now I need to come up with a solution. This is a 3-story house, and though I've sealed houses before (animal proofing), I think making it air-tight is going to be all but impossible--if I'm lucky.

Otherwise, maybe I can use the Stack Effect to my favor somehow in order to create an even better draw on the Heater. Right now, the fire burns less than enthusiastically, and it takes a long time for the top of the barrel to heat up (like 20-30 minutes).

What I'm willingly ignoring, for now, is that I probably need to take the whole base apart and cob the inside of the chamber, as well as clean it out. The barrel is cobbed to the base, and the exhaust is cobbed-in as well.

I've potentially cobbed myself into a corner.

Guys, guys, guys!


Jeff, i bet you have a barrel gap or flue junction problem. It's not your pipe, nor the bassement. Ok, you need the presures to equal between outside and inside.


Carter, it's perfectly possible to use smaller pipe at some poin,t. I go from 6 to 4 on a batch rocket with about 28' before the restriction.

The key is to have the restriction as short as possible, and have a smooth transition from big to small. From small to big is less important, tho, it might create turbulences which would impede the flow. Actualy having a smaller vertical tube, insulated might be a better option in some casses, since it would speed up the flow. And remember, a venturi can generate depression.

Jeff, check your gaps and transitions. And make sure your basement is not air tight. You need a fresh air intake.

I found that after changing the 6" to 8" exhaust, it became necessary to open the basement door just to get enough incoming air to prime the heater. It's been relatively warm outside, so it follows that the warmer outside air isn't putting enough pressure to force cool air into the basement at a high rate of displacement.

I put a hole in the exterior wall and place a length of 4" pipe from the hole directly to the feed tube. That seems to help significantly. Still, opening a window partially also facilitates a nice draw. Unfortunately, I need to seal some leaks in the cob and the exhaust, because the basement is filling with smoke. I've also found that even if the basement door is kept closed, the top floor of the house gets a little smoky, too, reinforcing the Stack Effect dynamic.

I figure that if I keep enough ventilation open in the basement, then the fire will heat up the area enough that a cold-air exchange will only cause a negligible impact on the efficiency of heating the basement. In other words, I'm hoping the cold air coming in will stoke the fire enough to cancel it out in the basement and leave me with a net gain of heat to rise into the rest of the house.

Now I just need to seal the exhaust and the lower area of the heater and keep to burning extremely dry and thin sticks of wood. If I can get away with heating this place with less than 4.5 cords (I'm hopeful for 2 cords or less), then I'll consider it a success, and I'll be happy.

Jeff Rycha : This may work well for you only if you are willing to shift much of your daily activities into the basement. Two things, you would lose 1/2 or better of your problems by
moving up a floor and you really need to tighten your house up, starting from the attic and working down, The increase in air being supplied to the basement only increases the
amount of Your Yearly Heat Energy Bill that comes from the large number of Air exchanges! Cold air in the basement, Hot air leaking out all over! You are significantly increasing
the Percentage of Your total heating bill that goes to Air Exchange ! I am betting that you are at or higher than 50% of that total now !

Just so you can get an other answer from a respected pair of Rocket Mass Heater Instructors/Builders I am asking you to go to villagevideo.org/products/rmh/scenes
scroll down and click on Preparing for your stove ! (the second short video I think !)

A third good choice is to look at the paperwork that comes with your Utility Bills, and see if you are eligible to have you house get a free energy audit, there is probably a series of
charts showing your total usage and a average cost of heating for your neighbors ! Think about it, people who take advantage of this program are paying the Utility company less,
and as a monopoly can not be Allowed to lose money so YOU are paying for their savings ! I hore this is timely And Helps ! Big AL !

Any reason you can't hook it up to an existing flue?

This is the Rocket Stove from bones to soup.

The rest:

Jeff Rychwa : Your wood looks O.K. remember that this is not a use one match fire, See if you can find some old pallets that have been setting undercover and split them
down fine ! They make excellent kindling and Squaw wood !

For a 1st build I see lots of progress and good ideas, From your pictures you did a Great Job on insulating the Heat Riser/Internal Chimney ! It also looks like you built directly
on top of the concrete floor without using any insulation except bricks between the combustion chamber and the floor, this will work, and certainly drives heat into your floor
so that you have some Thermal Mass, but it also retards that magic point where your combustion chamber finally gets to glowing red hot and the next chunk of wood you put
in there seems to spontaneously burst into flames! From that point on you can increase the size of your wood chunks, so that the number of chunks of wood you are burning
drops to 3-5 chunks of straight dry wood !

Instead of getting up a 1/2 hour early to start a fire and bringing it to that magical temperature before you turn it over to your wife to tend to while you go play in the woods
It may take you as long as 1.5 hours to get it to the point that you can turn it over to your other adult supervision ! (please make sure you leave her with a nice big stack of
dry wood, we want her to like this thing !)

Be grateful for the nice high ceilings, I see it is new construction, you do want to keep your landlord happy if he will let a family of Seven move in ! I do feel that there must
be some glaring short cuts committed, especially in sealing the second floor from the attic space ! Definitely fix the up high leaks 1st !

I have one thing that may be a Big Help, assuming that you do not have a gas fired clothes dryer, get one of those water filled buckets that attaches to the end of your dryer
discharge hose and cleans the exhaust air and traps moisture with the lint ! This will stop the drier from trying to pull in its operating air from outside. As someone has to do
several wash loads every day, you will be greatly reducing your puff back with every load. And cap and seal the dryer vent hole! You only need to vent the dryer outside when
its hot and you are not running your R.M.H. ! If you are really lucky you have or can have a signally device on your washer or dryer signal when it is time to check the clothes,
this will allow for a quick check on your R.M.H.. You will quickly learn to set the timer to match the load of clothes with your Rocket. This should help! For the good of the Craft !

Think like fire, flow like a gas, Don't be the Marshmallow ! As always your comments and questions are solicited and Welcome ! PYRO - Magically Big AL !

Thank you, Allen. I totally forgot about the dryer exhaust in the winter! I made a "vapor filter" out of a 2 liter bottle once, but it didn't even cross my mind here.

As an update, I just finished cobbing the heater base again after installing the new piping. I now have a 15-20 foot stack outside under the eaves, and I have cobbed the base of the feed tube, as well. I just lit the unit, and it's CRANKING like a dragon now, with only minimal smoke coming out the stack. The rain cap protects the stack, and so does the eave, and the draft is pulling beautifully. My only "anxiety" now is waiting for the real cold to set in. It's 54 degrees (F) out right now, and it's a sunny, windy day, so all's in my favor...but we'll see the mettle soon enough.

Jeff very good to have you tell us that your system is much improved, Some people have been successful in putting panty hose over the end of the drier vent hose,
! like the wet bucket it seams to collect some of the moisture along with the lint, your bathroom fan and the fan over your range in your kitchen can add to your
problems Even be your problems if you have an extremely tight house! and I have seen that happen in New Home oner build homes, but never in contractor built
homes !

I know you will find lots of penetrations of electrical wires even D.W.V vent stacks from kitchens and bathrooms into attics in some homes ! It's usually hidden under the
insulation, if you find any dirty insulation you have a penetration !

One of the happiest sounds I have ever heard is the deep throaty purr of a contented and well fed house dragon ! Congratulations ! Big AL!

Speaking of pallets: Has anyone burned pine or hemlock with success? Do they burn so efficiently that buildup (resin) isn't an issue, or are they still considered not appropriate to the exhaust system, like a typical chimney?