Rocket mass heater temperature questions.

In another thread (this thread ) I asked about my rocket being not enough rockety.
Well, I thought I solved the problem as it worked well but now it pulses, meaning it will suck air fine and then, suddenly, I'll have a backdraft, the flames will come right up the hole with lots of smoke.
Enough to drive my wife crazy as she hates smoke.

I'm this close to giving up.

I suspect that I have a choke point somewhere and I will investigate that this weekend. I hope I won't need to open the barrel as I couldn't find one with a cover so it is literally sealed with mud.

This brings me to my main question:

What surface temperature should I expect on my barrel surface? ( I have a 6" system)

I just got a thermometer today so it is the first time I can test it but I got a pitiful 175 F or 60 C. on top of the barrel. I'm not going to go very far with that.

Could the reason be because the whole burn chamber is encased in fresh cob? Before I got the cob, I could get temperatures that felt (I didn't have a thermometer) hotter. After running the rocket all afternoon, the exhaust pipes were really hot to the touch, but bearable for a second or two.

So, what surface temperature should I expect and what to do if it is not hot enough?

Thanks in advance,

Hugo

Hugo; I have only built one rmh ,an 8" so i am not sure about temps on a 6" system. What i can tell you is that until your cob drys out you will not get good heat out of it. As far as your system puffing back, we need pictures or at least a better description of what you have built. My understanding is that you need the top third of your barrel uncobbed to allow rapid cooling to create a siphon effect pulling even more hot air up your heat riser and pushing it into your horizontal transition area. From your description it sounds like you have cobbed your whole barrel? I have seen pictures of completely cobbed barrels that worked just fine so maybe yours just needs to dry out ? Bring your wife some flowers and tell her that you are still working on it,don't give up ! My wife was not sure about our rmh but now that it is working she loves it!

My 6" system with a 55gal barrel gets up to 750deg on barrel top. I have a 2" gap between riser and barrel. It takes quite a while for some reason to get there. I can get it to 500+ in the first 30 minutes, 600 in an hour plus, but it takes up to 3+ hours to max it out at 700+.