Vermont Castings "Defiant" vs Quadrafire "Isle Royale" vs Jotul "600 firelight"....

Yeah unfortunately eight inch pipe is EXPENSIVE, although Duravent is significantly cheaper than some other brands.


Eight inch is also a little heavier too, making it all that much more fun to install.

Yes, you'll have less heat loss from a 6 inch chimney based on surface area, since all other parts of the heat transfer equation would remain essentially equal between the two pipe diameters. As long as the volume of gas isn't choked by the 6 inch flue (and the manual indicated it isn't), its probably a better choice. Plus its cheaper.


Of course when the manual is speaking about large chimney cross-sections, they're really talking about venting the stove into something like an 8x12 masonary flue, not the differences between the 6 and 8 inch flue.

Pine doenst contain any more creosote then any other wood, how wood is seasoned is what determins the creosote buildup in the chimney. Pine, IMO has less chance of creosote buildup due to the low density and a high combustion rate.

Stick with the 6". 8" chimney is more forgiving at your altitude then someone at sea level, but your stove will perform better on a 6 inch flue. 30' is plenty of pipe for 6", i would be afraid of overdrafting the stove on 8". I have 24', 6" chimney at 9000' and my stove drafts perfectly. Remember, manufactures are going to be conservative with there recomendations.

My last point would be that most modern stoves run on 6" flues, the trend seems to be going to smaller flues with every new generation of stove. When your stove wears out, i think you would be better prepared for a replacemnet with a 6" chimney in place, who knows, in 10 years the standard might be 5...

here is a quote from http://www.mastersweep.com/wood.htm

"Back in the early 1980's, tests were conducted to discover which kind of wood created the most creosote in a regular "open" fireplace. The results were surprising. Contrary to popular opinion, the hardwood's, like oak and madrone, created MORE creosote than the softwoods, like fir and pine. The reason for this, is that if the softwoods are dry, they create a hotter, more intense fire. The draft created by the hotter fire moves the air up the chimney faster! Because it is moving faster, the flue gas does not have as much time to condense as creosote inside the chimney. Also, because the flue gas is hotter: it does not cool down to the condensation point as quickly. On the contrary, the dense hardwood's tend to smolder more, so their flue gas temperature is cooler. Thus, more creosote is able to condense on the surface of the flue. So, saying that "fir builds up more creosote than oak" just isn't true! It is a misunderstanding to think that it's the pitch in wood which causes creosote. It's not the pitch that is the problem, it's the water IN the pitch. Once the water in the wood has evaporated, that pitch becomes high octane fuel! When dry, softwoods burn extremely hot! "

Actually pine grown at our elevations have much more density then pine grown at sea level. I burn about as much pine as our hardwood burners here burn in a given season. When i fill my non cat up with a load of wood i get at least 7 hours and more commony 8-10 hours on a burn cycle. I burn 4 cords a year to heat ~ 2000 square feet home with good insulation at 9000' feet. Not bad. You will get longer results with the cat stove, you just have to carefully watch the cat temp before you engage it.
Glad i could help!
MSG

Back to the heat loss stuff for just a second. Using simple radial one-dimensional heat flow, assuming the inner temperature of the flue is the same, the insulation is the same, etc etc, you're going to lose more heat with an 8 inch pipe because it has a large external surface exposed to the cooler air. Also, an eight inch chimney will have a larger inner surface area but the flue gases will still contain roughly the same heat and you'll end up with that heat spread over a larger inner area on top of what I already mentioned.


I can do the calculations for real with the two pipe sizes if you guys would really like to see the math. Using fourier's law and the simple approach above gives a pretty good idea of the difference based on the increased external area.


The ONLY way I can see that the 8 inch pipe might present less heat loss is if the velocity dropped significantly below that of the 6 inch pipe. Then you could use the formula q (heat loss) = md * cp * (Tpipeoutlet - Tpipeinlet) and you'd see a decrease in heat loss IF the exit temperature of the gases was the same between 8 inch and 6 inch, which I doubt would be true.


I guess I'm just beating around the same bush with that. Ultimately an 8 inch pipe will lose more heat when compared to an identical 6 inch pipe.

I think you will be fine with 6". If it was me , I'd go with the 6", just because you have a 30' chimney. I have 22' with a 5.5 " liner, and when it gets really cold I think it drafts too good sometimes.

I'd spend the money on the Dura-Tech. Besides it isn't really that expensive in the world of chimney products; I can think of quite a few other insulated brands that are as expensive or worse.

Hi MSG. I'm confused. Why would 30' of 8" draft better than 30' of 6".

I am really confused, are we at the point of green paint drafts better than blue paint? Volume of air is a basic fact of moving air. If you need to move a lot of air, the bigger the tube the more air you move. In a stove if you move too much, you over burn (that's too fast, too hot). If you want efficiency you use the draft appropriate to the burn. That translates to the engine determines the size of the exhaust, not the huge exhaust needs an even bigger engine to work effectively. Regardless of profession or trade, if you move air you should understand the importance of having the right size flue for the source of the exhaust air. If you are too large in flue, you will not have adequate pressure to move your exhaust out. The best is the level of pressure that maximizes the movement of air, at the same time you don't want a ram jet to make the stack the place your fuel burns.

All that said, has anyone seen anything about the actual temperature of a stove, or fuel source during a chimney fire??? My guess is it is less than the ambient temperature?

I'm an engineer and I'm not comfortable with VC's chart on chimney height versus altitude. It would be helpful to see how they arrived at their calculations.
Hoping we can look into this a bit farther..... Scotty

are you talking about draft because draft is not thwe same thing as moving air threw duct work unless you have some sort of power vent hooked up moving the exhuast out of the stove is a function of the chimney that is created by tempeture dif. that is what creates draft and the a lareg pipe will not increas draft in alot of cases it will acctually lessen draft as the gas will cool quicker as they expand i belive corrie stated this before and he is dead on.