stack temps - how low?

[pybyr]

after a nearly all-nighter and somewhat quick and dirty "better get this thing running before I freeze" completion of at least the initial install of my Econoburn 150 last night (or should I say wee hours of the morning) and having it do a champion job of heating the house overnight--

I got out my instruments (the combustion sort, not musical- )

I set my barometric damper per the Econoburn manual (which says between .02 and .05) to hold a consistent .03 (it was pulling .05 -.06 WC before I adjusted it)

stack temps are running in the high 200s to low 400s F depending upon how much wood is in it and how hard the fan is running

my instruments are Bacharach Analog bought new old stock a couple of years ago (the big, good draft gauge + Tempoint thermometer), so it is pretty decent stuff, even if not the latest digital whiz-bangs

from an efficiency standpoint, and also based on how this Econoburn seems to belt out more heat per piece of wood than I'd even hoped, the stack temps seem great

that said, I don't want to rot out my terracotta flue with condensation

flue is 8" round terracotta tile in a masonry chimney, sorta indoors (the upper half goes through an unheated attic)(total height from furnace pipe's thimble to top of flue estimated at about 24 ft. )

never thought I'd need to wonder about a wood combustion appliance being so efficient that stack temps might be too low

I'll be glad to find out if I can simply do a happy dance, just don't want to wreck the chimney...

Thanks, as always

 

[Nofossil]

Congratulations on getting it running!

I'm no chimney expert, but I don't think condensation will hurt the chimney. Rain falls into it all the time, right? My brother's is washed clean on the inside from condensation, as his flue temp leaving the top of the chimney is never above 120.

 

[DaveBP]

his flue temp leaving the top of the chimney is never above 120.

A temperature sensor at the top of the chimney would be a very enlightening source of data, wouldn't it?

Some of the wisdom and rules-of-thumb about flue temperatures for residential sized wood burners may have to be modified as more gassifiers come online. At least some of the components of the exhaust that become aqueous and corrosive when the steam condenses will be almost nonexistent in a gassifier's exhaust. You'll still have carbonic acid from CO2 but it's got to be less nasty than the usual gore that drips down the inside of chimneys. I've demo'd a few old New England chimneys and the limey mortar is the first thing to go, long before the bricks. But ceramic tile and refractory cement (we always use refractory cement, don't we ) I don't know about. More to learn over the years.

I use a stainless steel cap on my chimney. I think a lot of the deterioration of chimneys is due to freeze/thaw damage by distilled water (rain). On my new house (under construction 12 years and counting) I went one further and transitioned to Metalbestos as the masonry chimney comes out of the 15'' of blown in insulation in the attic. Keep those flue gases as warm as possible and not expose my dubious brickwork to the elements.

 

[LeonMSPT]

I have conventional wood/coal boiler... only way to maintain 250 degrees in the stack is to leave the combustion blower on... or open the air shutter much farther than New Yorker recommends.

So I said, "PEE" on it... don't care what it is at idle... when the thing is up on step it's between 450 and 500 degrees, and will dry anything out that happens to be in there or burn it off. I check it weekly, daily... and am well aware of what is going on in there.

I burn coal during the week, wood on the weekends. Like the long burn time with the coal.

 

[flyingcow]

just fired up( at 910pm) the Innova-30 and heating 820 gals of storage(love the square tank system). Its roaring like there is no tomorrow. Heating my zones in the(2000 sq/ft) house + heating the tank when the zones aren't calling.It is -18 below, wind about 10mph.Stack temp has been about 400. Not sure if I got really good gasification, but I'm tired and it's working well. I'll update tomorrow

 

[jebatty]

My stack usually runs 400-550 as shown by the probe thermometer, and at that temp I get the heat I need. I can run cooler, but BTU output suffers. The Tarm just purrs in this range. I have the chain turbulators, and I would be running about 100 hotter without the turbulators.

Yesterday checked the chimney (17' Class A through unheated attic), been burning since Sept, and there only is light brown-gray haze on the inside, also clear at the cap.

 

[NNYorker]

My magnetic thermometer never seems to go above 250* --stuck on my adapter directly off the boiler flue pipe--the only single wall pipe I have . Usually ranges from 200-250*. I guess I'll have to buy a probe type online--no one carries them locally.

Where should I mount the probe? My single wall 8-6" adapter runs 5" off the Eco. flue then is hooked directly to a double wall tee/double wall black pipe to the ceiling. Mount in the short single wall run off the boiler or in the double wall vertical run?

Moisture content-I'm still dealing with less than ideal wood.

 

[jebatty]

Rough rule of thumb is that interior flue = 2x exterior. 250 exterior is roughly 500 interior. I don't use double wall black (I assume not insulated, only an air space), but single wall to Class A. My guess is that it's OK to drill the probe hole through double wall black. If so, I would put the probe about 12-18" up the vertical from the T.

 

[pybyr]

after having done a bunch more burns under a wider range of weather and heat load conditions, and with different batches of wood (varying species, varying degrees of how well-seasoned), I've noticed that the inside-stack temp seems to vary during different parts of the burn-- which I guess is not surprising. No precise correlation even between the stack temp and the quality of the gasification- under some conditions, gasification seems to yield high or rising stack temps- under others, it seems to settle in at a nice 350 F (inside stack).

I am still definitely in the early stages of learning how to get the " mojo workin' " at its best with this unit- but I have to say, I am already getting more comfort per unit of wood- by FAR- than ever before.