Woodstove catalytic combuster retrofit??

[Tom Myers]

Does anyone know of a presently available, commercial source for a 6 inch catalytic combustor that can be installed in the chimney of an airtight wood stove?

We presently heat with an airtight wood stove with a heat exchanger and a draft fan installed in the chimney.

This stove is the primary heat source for our 1800 sq/ft home and we only use the backup oil furnace when the Minnesota winter temperature drops below -10 degrees.

The heat exchanger is controlled by a thermostat and the duct fan is controlled by a timer.
These two units have worked quite well for increasing the efficiency of the stove but the heat exchanger does tend to increase the soot buildup in the flue above the unit.

I am thinking that a catalytic combustor replacing the flue immediately above the stove top would raise the flu temperature thus reducing the soot buildup and also increasing the heat output of the heat exchanger.

I remember that a few years ago, there were quite a few of the retrofit units available for sale but it seems that now the new wood stoves that already have the combustion unit installed have almost completely eliminated the supply of retrofits.

I found one unit available that was exactly what I had in mind, but it was for an 8 inch pipe and adding the reducing adapters to my existing chimney would make the unit too long to install.

The catalyst in this unit can be rotated 90 degrees to either enable or disable the ignition of the catalyst.



Any thoughts or recommendations would be appreciated.

[Battis]

I don't know if this relates to your situation, but I had a Vermont Castings woodstove many years ago that had a built in catalytic converter. Nice stove, great idea...but it did not work out well. The catalytic converter did its job - if the temp on the stove was, say, 800 degrees, the temp on the pipe leading from the stove was around 200 degrees. The problem was that the chimney was a high, outside chimney and not compatible with the converter. The chimney stayed very cold so any creosote released built up immediately. The inevitable result was a really bad chimney fire, one week after having the chimney professionally cleaned. It was then determined that a high outside chimney and a catalytic converter do not mix. I returned the stove and got one with secondary air and it works great.
For what it's worth, it seems that an inside chimney works well with the converters.

[Tom Myers]

I don't know if this relates to your situation, but I had a Vermont Castings woodstove many years ago that had a built in catalytic converter. Nice stove, great idea...but it did not work out well. The catalytic converter did its job - if the temp on the stove was, say, 800 degrees, the temp on the pipe leading from the stove was around 200 degrees. The problem was that the chimney was a high, outside chimney and not compatible with the converter. The chimney stayed very cold so any creosote released built up immediately. The inevitable result was a really bad chimney fire, one week after having the chimney professionally cleaned. It was then determined that a high outside chimney and a catalytic converter do not mix. I returned the stove and got one with secondary air and it works great.
For what it's worth, it seems that an inside chimney works well with the converters.

Battis,

Thanks a lot. This is the kind of information that I need to hear about.

This stove is in a mobile home so the stove pipe above the ceiling line is fully insulated and only reaches 3 feet above the inside ceiling and doesn't build up soot really bad. I only need to give it a brushing twice a year.
My main reason for considering a catalytic insert was to increase the exhaust temperature up through the heat exchanger.
The insert in the unit rotates so that the initial cold exhaust can bypass and can then be rotated back into position when the flue temperature is high enough to start the heat exchanger fan.
The exchanger fan kicks in at 300 degrees and supposedly the catalytic unit will ignite at 300 degrees.

[beemer]

I have a Buck with a catalytic unit, the unit can be by passed until the it is hot enough to ignite. It is a little fussy to operate but works well to keep the flu cleaner. I put regular 8" pipe to the ceiling and 8" double wall insulated stainless flue straight through the attic and out the roof. I give things a good cleaning once a year, this year the stainless flu needed nothing. I have had this unit for 10 years and it has saved me a lot of trouble and wood. I did find that pine or wood not seasoned properly gives trouble. The increased temps in the heat exchanger is what makes these stoves heat better and decrease soot and creosote.

I think the Buck could have been designed better, I think it should be easier to clean around the catalytic unit. It is hard to heat with wood without some creosote buildup.

I heated for years with a cabinet style heater with an automatic draft and outside flue. The flue was 8" x 10" masonry and the heater was 6". Goin to a larger flue and to many turns slows down the flow, going into an outside flue cools things off and causes condensation. Keep all your flue the same size, use insulated flue the attic and out the roof and straight up and out. Got to keep things hot and moving.

I think you are on the right track, let us know how it ends up.

Dave

[Petrol & Powder]

Although I no longer heat with wood I used wood exclusively for many years.
Rather than relying on a catalytic converter to complete the combustion of un-burned gases and particles, you would be better off doing that in the firebox itself, IMO.

The overall concept is sound - By burning those gases at the catalytic converter you are capturing energy that would have been lost up the flue and helping to keep the flue clean in the process. The problem is the practical application of that concept.

It's just simpler to burn everything in the firebox and have a conventional flue without a converter.
A properly sized flue that remains hot all the way to the top will accumulate little creosote.

It's ALWAYS better to burn a small fire hot and completely than to let a large fire smolder and lose a lot of heat in the form of unburned gases. The downside of that is the smaller fire and firebox must be tended more frequently.
I completely agree with beemer that keeping the flue gases hot and moving results in a cleaner flue. That can also mean some lost heat but that's the compromise for less creosote. The catalytic converters can help that process but you're adding complexity to the system.

I would prefer to have a simpler system and skip the converter. YMMV

On a similar note, one of the best small stoves I've ever seen for extracting all the potential heat out of a small quantity of wood are the Jotul model 118 stoves. They're not cheap but they are very efficient.

[beemer]

P & P, I agree with you. I have seen people keep a very hot fire all the time and have very little trouble with their flue. Like you said a small hot fire doesn't last long and we need heat overnight.

My brother was in Romania several years ago, he talked about the heating-cooking heater they used. It was some type of masonry and laid in the center of the house. The firebox and oven were small but it had a lot of mass. It would burn small wood very hot and clean with almost no smoke and build up heat during the day that would keep the small house livable at night. Wood is not as plentiful as here, they learned to make do with what they had.

[Petrol & Powder]

New England folks are known to be frugal and an old New England floor plan shows that. The house would have a massive central chimney that would hold and release heat long after the fire died out. Similar concept to what you describe in Romania.