[Stoves] Stoves Digest, Vol 95, Issue 8

Crispin Pemberton-Pigott crispinpigott at outlook.com
Mon Jul 9 14:58:22 MDT 2018

Dear Friends

There is something interesting emerging from the development of this new generation of coal-burners. It is that the emissions of PM are not substantially the result of incomplete combustion, but the lofting of fly-ash. I think this is significant. If fly-ash is an unimportant ambient air contaminant, it puts a creates different perspective on air pollution.

Having tested some of the high performance domestic products from Kyrgyzstan now for 18 months, it is clear that fly-ash I an on-going issue and that VOC’s, PIC’s, PM2,5 BC and OC are not.

The high velocity of air through the combustion zone (which is constricted in order to generate adequate turbulence and mixing) lofts fly-ash and gets it flying, No big surprise there.

Fan stoves like the Mimi Moto and others will have the same problem, save that wood ash is usually finer than coal ash. Dung ash can be very fine – to the point it is difficult to remove from the stove without creating a cloud of fine ash in the room. In fact, we had to add an ash drawer to the Model 2.5 heating and cooking stoves to address this problem. Never before had people seen a stove that completely burned the dung, and the pure white ash from such a fire is extremely fine. Sweeping it out of the stove from an ash collection area proved to be a major source of IAP. So we added a drawer at the request of the homeowners.  This allows the ash to be removed carefully without disturbing it until it is tossed into the field as mineral-fertiliser.

If the mass permitted by the EPA is ‘bad combustion’ (up to 18 g/hr) that is going to be an air quality problem, whereas 18 g/hr of fly-ash is what, exactly? That is the sort of air pollution experienced in Beijing years ago – fly ash from boilers with strong fans pushing as much through the heat exchanger as possible.

We are going to need epidemiological studies on health impacts based on the PM2.5 composition to make valid claims.


Hi Andrew:

This is specifically for domestic wood fired boilers.
It is part of a Federal Rule known as EPA NSPS (New Source Performance Standards).
It also covers wood stoves and pellet stoves, although those are regulated in g/h.
For boilers including those with storage, there is an additional upper limit of 18 g/h, no matter the size of the boiler.

It would be a non-issue for gas or oil fired boilers, and I'm not aware of any domestic scale coal fired boilers
for sale in the US. Google has info for coal fired power plant boilers, and they seem to be individually permitted,
and the PM limit is 0.01 - 0.02 lb/MMBtu. (Compared to 0.32 lb/MMBtu for domestic wood)
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