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MHA Research Heater

photos by Norbert Senf

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Firebox Exit Modification Dec 20/15

During the MHA research heater build, our first firebox ceiling was vermiculite board, which cracked.

We wondered if a floating piece would still crack in that location.

Note that we have a piece of 8" stainless liner extending down into the firebox as an experiment
A 22" x 12" piece of vermiculite board was suspended below it, sitting on 4 steel tabs at the corners,
that were inserted into the horizontal air slots.

Some flames went directly into the pipe, whereas others circulated in the space above.

Stack temperature at 37 minutes is 140F.

Note the slight bend in the vermiculite board.

At 50 minutes steam is still coming from the stack.

90 minutes., well into the charcoal phase.

Very small amount of steam, barely visible.

The board did not crack, but sagged about 1/4" at the centre.

Round 2.
 2 stainless steel angles are laid across to support a 12" x 12" piece of vermiculite.

In the vein of Peter van den Berg's early exit baffle experiments, we put a perimeter of ceramic glass cutoffs
around the exit pipe, to force the gases to downdraft before entering, and maybe provide some extra mixing.
Our instrumentation is not set up yet, therefore this is only a visual experiment.


The ceramic glass initially got a light soot coating.

Flaming is happening to the left side of the firebox, and at 10 minutes the soot is burning off the left side of the glass.
You can see a flame through the glass, curling down.

Now more soot has burned off, and you can see the flame curling up into the bottom of the pipe.

Steam at 14 minutes.

Stack temperature is 105F.

At 19 minutes the exhaust flow picks up speed.

Stack temperature is  130F at 24 minutes.

The right side of the firebox is cooler. Notice the circle at the top where the initial soot is starting to burn off.

At 27 minutes we cut the air back approx 90%, to see the effect.

With less flaming, notice that the pipe is glowing dull red, as is the top surface of the vermiculite board.

2 minutes later the stack temperature is down 5 degrees.

At 55 minutes into the burn, the air has been reduced for the last 28 minutes.

Stack temperature is down to 110F. Air is opened back to full.

Three minutes later stack temperature is at 135F. Air is turned back down

112 minutes. Note the action at the rear air slots.

Steam is still visible, but much decreased. At 113 minutes, after this photo,  the air is shut down.

Surface temperature near the top of the channels is 268F.

Update Dec 21/15:

The next day, we had a fire with 59 lbs of dry hardwood, with full air.
Stack temp peaked at 180F and surface temp at top was 337F.

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This page was updated on December 29, 2015
This page was created on December 20, 2015