firebrick vs redbrick in rocket mass heater combustion unit

Considering an 8" system with a metal pipe heatriser , is there a major the difference in performance when using common red bricks instead of refractory bricks for the combustion unit? where in the system is it noticed?, radiating barrel temperature?, the amount of time the thermal mass remains warm?what is affected most?

thanks

Leonard

Leonard Allen wrote:
Considering an 8" system with a metal pipe heatriser , is there a major the difference in performance when using common red bricks instead of refractory bricks for the combustion unit?

Common red bricks will decay rapidly in the feed and tunnel assembly, these are made for a different purpose and cannnot stand the heat for long. The same goes for the metal riser, this will spall very badly and burn through in one or two seasons. It will fail at the most inconvenient moment, according to the law of Murphy. Even steel of 1/4 inch or more will burn away, stainless will hold out longer but will fail in the end as well.

But you are welcome to find out those things yourself, of course.

Leonard: Within the limitations of the system you describe, using a metal heat riser,there are two issues in using soft red brick rather then 'fire brick'.

With two identical systems | Except for different bricks | the softer brick will degrade faster, more so with the 'Rockets' hi temps !

The 2nd thing is the softer bricks are less insulative, this means that it will take longer for your 'rocket' to reach it's maximum and most efficient burn/2ndary
burn temps.

There is certainly no good reason to say that you can't use soft red brick for your first build, also the stove pipe used to form your heat riser can be considered
to be nothing more than a form to hold your clay / perlite mixture in place while they cure !
Many people who build 'Rockets' this way report that the eventual failure of the stove pipe merely exposes the highly insulate clay/perlite to the hot 'heat riser' gas flow !

If you have the brick, you can also build your heat riser totally out of brick, the resulting rough,craggy surfaces of the inside of the heat riser is usually
considered to improve turbulence, and air/gas mixing ,improving the 2ndary burn !

Be safe, keep warm, Pyro magically Big Al

Yea, i want to make the riser with bricks and use the pipe i have as part of the flue system instead,but don't have enough bricks yet, only for the combustion unit, which i started building,
the other option as you say is to let the clay cure , in this case though how should the mix be?, same as the perlite/clay for insulation ? or should it have more clay?

Listen to Peter!  I did.  I am now casting my second dragon heater style core (6 inch) with factory made refractory cement.  Add water and then cast.  The cylindrical riser is also cast from refractory cement.  Absolutely no metal that will certainly fail when internal temps reach 1000-2000 Fahrenheit.  The cost of this method was comparable to refractory brick (not red fire brick!). Further, on top of my 55 gallon containment barrel I have placed another water filled 55 gallon barrel to absorb the btus.  As the high temp exhaust (2000 Fahrenheit?) from the riser crashes into the bottom of the upper water barrel it cools dramatically and consequently shoots downward to exit out the side of the lower barrel (a normal design).  This is in effect a powerful heat pump.  How powerful?  Strong enough to push the exhaust 35 feet horizontally through a heat sink, then 10 feet diagonally to connect with 25 feet of vertical!  Crazy but if you listen to Peter it can be done.

Leonard Allen wrote:.... , in this case though how should the mix be?, same as the perlite/clay for insulation ? or should it have more clay?

Hi Leonard, you might want to buy Erica and Ernie's book as it lists all the mixes for clay slip and clay stabilized perlite insulation and lots of good rules of thumb for RMHs.

Sincerely,

Ralph