Non-Cat Insulation Question

[Dillier23]

Reading through the "how to choose a stove" article on the site i ran across a confusing comment about the cat vs non-cat comparison that I need some clarification on.

The article states the non-cat need to have a very insulated firebox to achieve a temperature high enough to achieve the secondary burn required to meet EPA regulations.

With no experience in the stove world this suggests to me that the firebox insulation would prevent the heat from reaching it's target, the outside environment the stove sits in? I also gathered that the cat stoves did not require that amount of insulation because the cat dropped the temps required for re-burn. If this is the case, it leads me to believe that the cat stoves by design would offer more usable heat because of the lack of insulation. Are my assumptions off base?

 

[begreen]

Combustion efficiency is not the same as heat transfer efficiency. There are many non-cat stoves that don't have firebrick and minimal side wall insulation. Typically they are cast-iron stoves. These may not be as combustion efficient but they do easily pass current EPA phase 2 emissions. And often they are very good heaters too.

 

[Ashful]

With no experience in the stove world this suggests to me that the firebox insulation would prevent the heat from reaching it's target, the outside environment the stove sits in?

I also gathered that the cat stoves did not require that amount of insulation because the cat dropped the temps required for re-burn. If this is the case, it leads me to believe that the cat stoves by design would offer more usable heat because of the lack of insulation. Are my assumptions off base?

A given load of wood has a fixed number of BTU's, and your stove's efficiency tells you how many of those BTU's end up in the room, versus going up the pipe to the sky. Yes, cat stoves generally run cooler flue temps, and so less of the heat is going up the pipe, and they generally have higher efficiency. However, this does not translate to insulated fireboxes causes less heat to end up in the room, as an insulated non-cat still puts WAY more of the heat into your room than a non-EPA ("traditional") stove. Both cat and non-cat are dramatically more efficient than a non-EPA stove, with cat generally being a little more efficient than non-cat.

BTW... a cat stove generates the majority of its heat in the catalytic combuster, which is insulated VERY well from the room. Don't get caught up too much on the insulation, instead focus on firebox size, burn time, and efficiency.

 

[JA600L]

What is lost by the insulation is gained by the combustion efficiency (higher internal temperatures) . In a non cat stove, high heat is needed to burn the smoke. It's the same principle as a diesel engine running very high compression ratios. More heat- more complete combustion.

 

[branchburner]

Once a non-cat is up to temp, it is going to throw a LOT of heat, regardless of insulation. Perhaps very early in the burn there is less output due to a highly insulated firebox, but not over the whole course of the burn... that heat has to go somewhere.

But I think you are on the right track... because a cat can burn smoke at lower temps, you can likely run it with a cooler flue that can still prevent creosote formation. In theory, that would mean you could burn less wood to get the same amount of useful heat, losing less heat up the flue, and some cat users insist this difference is very real based on their own observations.

Some stoves (like mine) end up running with average flue temps that are much higher than the minimum needed to keep a clean stack and re-burn most of the smoke. This is less of an issue in severe cold, when you are running the stove very hard anyway, but more of an issue in the spring and fall when it is harder to run a "small" fire, To burn clean you end up generating much more heat (for both the house AND flue) than you really want to. I may switch to a cat one day, for the ability to "dial down" a clean burn.

 

[Dillier23]

Good responses so far, I was thrown by the comments in the article. From what I've read a cat stove with good wood is hard to beat for efficiency.

 

[Ashful]

Here's the list of the top 30 most efficient stoves sold in the USA today. Note that the top 10 all use a catalytic combustor. Some non-cats make it into the top 30 (at the bottom of the list), mostly because there aren't that many good cat stoves on the market today.

That said, efficiency isn't everything. The reason I don't own one of the catalytic stoves on this list is because that none of them (excepting the Ashford, which wasn't available until just last year) appeal to my sense of what a stove should look like.

 

[BrotherBart]

there aren't that many good cat stoves on the market today.

How true, how true.

 

[Ashful]

There was some talk last year, in fact repeated to me by one of the Jotul tech's, that Jotul would be forced back into making cat stoves if the "new efficiency legislation" passed... whatever that was. I seem to remember the state of Washington was driving it. Whatever happened there?

BK makes fantastic stoves, but their styling is not for everyone. Same could be said for Woodstock.