Non-Catalytic vs Catalytic Woodstoves

Non-Catalytic vs Catalytic Woodstoves

Non-Catalytic vs Catalytic Woodstoves

Question: Vermont Castings catalytic compared to non-catalytic

I was wondering if you could share your opinion about the Vermont Castings “Defiant Catalytic” woodstove compared to non-catalytic. We had to replace the catalytic converter two years after installation, and now must replace several burned-out internal parts not covered by the warranty. We’ve also had trouble since day one controlling the fire. We were told this stove is cutting edge technology. I really like how the cast iron looks with the porcelain finish, but frankly, we don’t like the catalytic converter. We notice that all the woodstoves on your web pages are all noncatalytic. Are these not required to reduce emissions?

Vermont Casting Defiant Catalytic

Answer: How catalytic stoves were developed

Regulations across many countries limit the amount of particulate matter, measured in grams per hour, that may be emitted by a woodstove. They don’t tell the manufacturers which method to use to achieve this level. Certificates such as EPA, EN13240, 15aB-VG, DIN+, I.BlmschV Stufe 1/2, Nordic Swan, Flamme Verte all indicate different parameters of efficiency and emission. Incorporating a catalytic converter is only one way to clean up woodstove exhaust, and it is far from the most popular.

Vermont Casting Catalytic

The story of the catalytic woodstove

The story of the catalytic woodstove begins over two decades ago when only a handful of places had as yet passed a woodstove emissions regulations. At that time, manufacturers who wanted to sell woodstoves in regulated regions found that by simply incorporating a catalytic after burner into existing models was a relatively inexpensive way to clean up the exhaust. (Your “Defiant Catalytic”, for example, is basically the same stove as VC’s old Defiant model, but with a catalytic converter added). This “band-aid” approach produced several models which, while clean-burning enough to sell in regulated places, didn’t turn out to perform as reliably in the field as the high-emissions models the woodstove manufacturers such as Pacific Energy continued to sell in the much larger, unregulated marketplaces.

Back in the ’80s, we dealt with a few catalytic woodstoves, but dropped them almost immediately because of negative customer feedback (the need to “babysit” the stove until it came up to catalytic ignition temperature before activating the converter, lack of control of the fire, the frequent need to service or replace the expensive converter element, etc.). By and large, these complaints remained unresolved by the manufacturers, presumably because:

  1. Solutions didn’t readily present themselves
  2. The numbers of catalytic stoves sold at that time were relatively small.

Vermont Casting problems

Emission testing certificates

When the certificates stepped up the level and announced their intention to outlaw high-emissions models, many manufacturers (Vermont Castings among them) were left with only their “band-aid” catalytic models to sell; suddenly, catalytic-equipped woodstoves were being sold in large numbers all over the country, and consumer complaints multiplied proportionately whereas Pacific Energy continued to innovate and design its Alderlea woodstove.

One by one, manufacturers grew tired of the customer dissatisfaction, expensive warranty repairs and poor performance associated with their catalytic models, and began to reject the trouble-prone catalytic technology in favor of an alternative, non-catalytic, clean burning technology that had been developed in other countries, where woodstove emissions had already been a hot topic for over fifteen years in countries like Canada, Denmark, Austria, NewZealand, Australia. With some design improvements, technology was developed to comply with the stricter standards, and was easily applied to woodstoves of plate steel construction, where only a few changes on the assembly line were needed to convert from catalytic technology to the non-catalytic secondary burn designs.

Cast Iron Stoves

Not so with cast iron stoves like your Defiant,  or other cast iron stoves like Jotul or Dovre. Manufacturers of plate steel woodstoves could weld up a prototype in a few hours, then test, modify, reweld, and retest it as needed until standards are met, cast iron stove manufacturers would be faced with a tedious and expensive process involving design engineering and foundry work, as all preliminary parts would have to be cast in custom-made molds, one at a time, prior to assembly and testing. Thus, manufacturers of cast iron stoves tended to lag behind the rest of the industry in adapting their models to the new non-catalytic technology. Meanwhile, the basic non-catalytic design underwent further refinements, and other secondary burn designs were developed until non-catalytic technology became the standard in the marketplace.

Vermont Castings has for some years now been actively engaged in the process of adding non-catalytic models to their product lineup one by one, starting with their smaller models (the non-catalytic design is easier to implement in smaller stoves).

In the meantime, catalytic technology has also continued to improve. Repositioning of the converter relative to the flame path addresses the flame impingement problem, which had previously shortened the lifespans of the converters in earlier designs. Changes in both the substrate and the catalyst itself have resulted in longer lifespans and more consistent performance. Re-designed access openings and holding brackets have made cleaning and replacement the element less of a chore. Consumer education has perhaps been the biggest factor: today’s catalytic stove owners seem better informed about what not to burn, and are generally more knowledgeable about care and maintenance of the converter itself (like keeping it clean, and replacing it when needed).

Pacific Energy Alderlea non-catalytic woodstove


You asked for our opinion, so here you go: if the problems you describe have become more than a nuisance, the best solution we can come up with would be to trade your Defiant in for a non-catalytic stove. All new woodstoves sold should hold some kind of certificate unlike manufactured self-welded stoves, so any stove you buy will be a low-emissions design, whether it has a catalytic converter or not. Pacific Energy, Lotus and TermaTech have sold non-catalytic woodstoves for over 20 years now. Pacific Energy approaching 40 years and in our experience, non-catalytic technology has proven itself effective, reliable, and easy to operate. Since you mention above that you really like the looks of your Defiant, you might consider an Alderlea T5 in porcelain finish or an Alderlea T6 from Pacific Energy with extended burn technology which combines modern interior design and a very similar traditional cast iron exterior, which is, as you might have guessed, is non-catalytic.