4" RMH for small urban spaces, revisited

I know that, previously, 4" rocket mass heaters were abandoned because the internal drag on the natural draft was too much to work.  However, I was listening to one of Paul's recent podcasts wherein he discussed a RMH in an apartment.  I got to thinking, could an urban & stealth RMH be developed that could share the exhaust vent normally reserved for a tenant's clothes dryer.  I know that, permies being geared to off-grid, independent lifestyles, developers of the RMH don't like to introduce grid-dependent technology to their research.  However, I was wondering if anyone has tried a forced draft method to allow the 4" RMH to work?  What I mean is, attach a vent fan; preferably one with a variable speed, to the exhaust end of a 4" RMH in order to force air to move in the correct direction and out the side of the apartment building via an existing dryer vent.

Hi Creighton;
4" J-Tubes were abandoned as too finicky.
4" batch boxes work fine if you like feeding twigs until it heats up.
In-line fans that can take wood heat and keep on spinning are not cheap.
Real smoke, not steam will come out while lighting and warming it up.
Even a fan cannot overcome wind gusts into a horizontal pipe.

I'm sure it has been attempted, and probably even worked until management found out.

Would something like this work for the riser on a micro-RMH? Could these be clustered to increase the diameter?

I imagine it would fit into a co2 or other compressed gas tank

https://duralite.com/shop/ceramic-tubes/mullite-tubingsingle-bore0-75-in-outer-diameter/

Well, you are really talking micro! It is only 3/4" ...
That is a bit too small.
Temperature rating, they are great.
If they had them in a larger dia then maybe.

I've thought about sourcing such fans.
Power vent water heaters have a fan that expels heated exhaust.
I have one I kept for just such a build.
More universal would be using any old  fan to create draft via a venturi effect:

Here's a thread with a forced draft rocket mass heater:
https://donkey32.proboards.com/thread/3473/mini-rocket-forced-induction?page=1

My 4" J-tube RMH in the greenhouse isn't all that fussy. The first burn of the season can be a little touch and go at startup, but as soon as the tunnel gets warm it's off to the dragon races. Replacing the cast fireclay/perlite riser with a 5-minute one really helped, as did putting twin wall flue pipe on the exterior run. It isn't pushing through a lot of mass...the flue goes about 2 m through the cob bench and then exits. The few times that I have had trouble were caused by a big rust flake peeling off the top plate and blocking the outflow from the riser, but now that part is easily removable for inspection.

I could easily see a system like this serving the needs of a tiny house or sleepout.