Rocket mass heater refuses to pull draft after summer rest.

Hello all.  

I've not been active in the forums for a few years.  I bought the RMH book (which I cannot seem to find to reference) and built a RMH in my greenhouse a few years ago.  The heater is ABOUT 30-35 feet (I think - its been so long (firebox and manifold under barrel plus 20 foot straight pipe plus 5 elbows then 15 foot vertical chimney)) long including corners at 5 foot per, and it has worked VERY well for a few years now.  Every time, split kindling, light it with a torch, and it goes.  if weak, heat exhaust with torch to help draft and it goes.  Today, while its 15 degrees outside and dropping, I decided its about time for a fire.  I tried to light the thing but no draft.  I heat the exhaust, no draft.  I light a fire under the vertical chimney and it has a strong draft in there, but nearly no draft in the firebox.  AFter working for over an hour, I develop a WEAK draft in the firebox by heating chimney, lighting fires in chimney and back of firebox, and blowing.  I was thinking that with the bone chilling cold outside and 69 inside the greenhouse there was a "cold plug" in the chimney, but after everything I'd think i'd have had it pushed out.  I ended up walking away from it after fighting for 2 hours and getting increasingly smoked out by the lack of draft.  It would pull, then puff, then pull, then puff in my face.  You know that time when you realize you're getting too irritated to continue without acting a fool?  I was there.  I had to walk away.  

Please help with some ideas and forgive the fact i have not been here in years.  Everything was working great for a while.  Ive got a 3 year old lemon tree, a lime tree, a banana tree thats 12 feet tall, and reaper peppers in there.  

Also help me out with this site.  its changed a lot in a couple years.  Thanks for your understanding.  

thanks everyone.  

Matthew

Are you sure there's not something blocking the chimney or other part of the flue? An animal nest would do a number on the draft...

theres a draft in the chimney, but its weak in the mass.  i dont really want to tear it apart to find out, but nothing changed other than the date.  perhaps spider webs within?  

If you have a blower, you can jam it in there, and then seal really well around the edges with an old blanket or something. Make sure to close all air intakes, or anywhere else where air could puff into the house. Then put it on the highest setting and blow. I have used this method to clear out fine ash. No immediate neighbors. There was quite a plume.

A hot fire in the fire box, does not equal hot gas going up the chimney. That's what we're aiming for - efficiency. You might be able to drop some burning newspaper or something from the top in order to burn out some obstruction.

There are very small cameras meant to go in tight places. I would try one of those before ripping anything apart.

good idea, dale.  I will try this tomorrow when the sun comes out.    

That's why cleanouts in the heat exchange ducting are recommended - so you can find and clean obstructions without tearing anything apart.

Took a blower to it.  no nasty plume came out.  draft is better ish.  had a fire going, but it kept "burping" smoke at me and i had to shake it and mess with it every 30 seconds to keep the draft going down.  noticed a few places where smoke was coming out around the manifold so perhaps there are small cracks i dont really see that kill the draft?  

What is the exact layout of your flue path? Are there places where you can't reach a pole or snake? Are there any cleanouts at all? If so, I would try a little indicator fire in each of them, starting nearest the chimney, to see what kind of draft you have. If you find the draft significantly diminished between two spots, I would try to access that run for blockages.

A nest in a duct might not blow out with a fan, maybe diminish a bit, and would be the kind of thing that would cause a drastic difference from the last fire in spring to the first fire in autumn.

For me, when my stove started to do this, I had a buildup of ash at the bottom of the barrel and manifold area. Have you removed your barrel (assuming you use one) to check this area? At the base of the heat riser/ back of the burn tunnel is another spot that builds up ash. You said you noticed smoke coming out of the manifold area... seems to indicate that this is where the problem is.