Let's design a smoke pipe setup

Thanks to those who are still tuned in.

I disassembled and cleaned my stovepipes last night and took a few measurements from inside. I also estimated the chimney at 32 feet from ground, with the thimble about 7 feet above grade so let's call it 29 feet from the outlet of the furnace.

The clay flue measured about 7"x9" inside. The pic shows the 7" width. It's connected to my furnace room by an 8" ID clay thimble, 12" long. (I forgot to dig out a level and check if it's sloped or just horizontal). Math: the 7x9 flue is 63 sq in. The 8" stove pipe is 50 sq in, and the 6" stove pipe is 28 sq in. If 6" is the ideal size then I need to plan for a liner to reduce this.

Referring to the table handily provided by Coaly, that means my current setup can "handle" in excess of 275k btu. My Big Jack furnace is rated for less than half of that. With my 28' flue I could go down to 6" round.

Inside my smoke pipe I found about 1/8" of black, bubbly, dry, flaky creosote. Reaching into the flue I felt a similar amount, maybe less. I cleaned most of it out of the stove pipe by scraping with a random length of pvc pipe and got maybe a pint glass worth. Is that a little bad or a lot bad?

Is it reasonable to fit a 6" round liner into the 7x9 rect flue?

 

dgeesaman how much have you burnt to get that much creosote?

 

About a cord so far.

I've used different wood sources over the last couple of years but this year I'm burning the first wood that I CSS myself. It's been stacked for nearly 2 years but it was uncovered. I think the oak in particular is not as seasoned as it needs to be.
I have everything covered now and I'm inclined to burn next year's wood now since it seems drier in general and contains more maple and less oak.

The other issue is we started burning back in late October and this furnace seems to have capacity more in line with our mid-winter demand. So it's spent a lot of time in low idle. I don't think the flue temps are high enough.

 

I would say that is a lot of creosote for a cord.. do you have a moisture meter? make sure your horizontal runs have a minimum 1/4 inch rise per foot.. I an not as knowledgeable as others.. I do not have that much creosote after a winter and 5 cord.. I believe this type is more dangerous than my brown fluffy... I did when I burned a little 2 cubic foot NC 13 type stove,, but put 12 cord thru it in a winter...

 

I do have a moisture meter - but I need to get off my can and split some of the "seasoned" pieces to confirm their actual moisture content. It's not very splittable by hand.

 

I use a Dr Meter which claims to be temp compensating and we're well above freezing today.

I grabbed a chunky piece of oak from my furnace room and carried it back out to my splitter to get a true moisture reading. The result: It's time to turn in my FHC members card.

That piece of oak read 3-10% on the outside and 35-45% on the inside. I know wood dries from the outside in but I had no idea it could hide so much moisture.

I went thru my stacks and split samples and found anywhere from 18 to 25 on the insides.

I'm half tempted to make a few calls and load up on properly seasoned stuff while I can still buy it for the rest of this winter. It pains me to spend the cash but burning half green wood isn't economical or safe either. Then move my half-dry stacks inside of my storage building for next year. Even though it won't get sunlight there at least it can never get wet and it should dry as fast as possible.

 

Well wet wood explains the creosote ... don't know what you got for wood cut and split... can you pull out oak and burn cherry soft maple ash elm... it's what I'm burning this year..

 

Actually your flue is for approx. 380,000 BTU input. I only posted 6 and 8 inch. At 30 feet, 9 inch or 78 sq in. is 490,000 and 10 inch (113 sq in) is 740,000 ! You can see how it multiplies by diameter.
You should be able to get a 6 in there with no problems. Again, this isn't just to make it work, it allows the damper to run open more (slowing draft) for the same draft with less heat used for the chimney. You should see a fuel savings. Your velocity will be almost twice as fast giving smoke particles half the time to dwell in the flue. That's why if you can, it should be the same size as appliance outlet all the way up.

Don't feel bad, I heat with a Kitchen Queen 480 ONLY and when we have "less than optimal" wood, we dry it in the over before the next reload. That takes 6 months off the seasoning time right? About 350 for 4 hours.



This stove has a 7 inch outlet and manufacturers instructions that came with it caution against reducing flue or pipe to 6. I did the calculations and reduced to 6 when I installed it. (hoping it wasn't needed for circulation around oven) It works fine even with an added thermostat intake. The stove was recently retested and passed with 6 inch ! The thermostat passed as well as an option.

 

It will not finish drying very well at all in there unless it can at least get a lot of air flow. Sitting outside in direct sun in a breezy spot is the best, I don't worry about covering the stacks until the last couple months before I'm ready to move it into the woodshed for the coming winters use, and even then it is top covered only.
As long as the wood is stacked up off the ground then rain really doesn't make it "wetter" other than a bit of surface moisture that will evaporate in day or two...unless maybe it gets under the bark, that may take a few days more of wind/sun to dry up...but even then it doesn't "soak into" wood that is already well on its way to being good and dry....well, except maybe some real low BTU softwoods that tend to punk up quickly.
As you are finding out, Oak gives up its moisture slowly...I won't even think of burning it until at least 3 years CSS.
If you can buy wood that is actually dry, like as in you split a few pieces and moisture test it with your meter before you buy it, then yeah, may be worth buying a cord or two to supplement the wood that you have now that is ready to go. You can also mix in some kiln dried stuff to "average out" the moisture content of your loads, construction cut-offs, old (free) pallets, ECO bricks (any brand)

Do you have a tstat hooked up to it?
As you said, it often idles a lot, so part of the learning curve on these things is learning how to "load for the weather"
I gave up trying to run a wood furnace in warmer weather (say, 40s and up) we have a small 1.8 CF insert stove in the fireplace that gets used a lot in the spring and fall. The other thing that is nice about this is the stove happily chows from my shorts/chunks/uglys pile instead of having to cut shorter splits for it.

 

I'm curious what the material is above the flu pictured (the black pipe) and what the distance is?

 

Coaly,

Great question - it's drywall and it's about a cinder-block high - too close for single-wall.

Brendattomu - it is on a thermostat and we only burn when it's 30 or lower. The heat pump has its own t-stat and handles 30-70 temps.

I basically did what you describe. This wood was on plastic pallets for two years.

Shopping for firewood I'm going to pick up a few pieces, take them home and split them and decide if its' worth it.

 

I thought I had already shared this with you but after looking around a bit, apparently not.
An easy little trick I learned that worked really well in the Big Jack is to flip the fire around.
Lay some old steel or some cheap firebricks on the grate covering it all except the back 6" or so. Then get some ceramic or mineral wool insulation and stuff it in the "secondary air" slot, all except the back 6" or so. (that's the 1" gap between the top of the firebrick and the bottom of the firebox "barrel")
Now, let the ashes build up 2-3" (4"?) deep and when you go to re-load, use the poker tool to only knock enough ash through the grate to make a small hole where a little air can come up through the grates, right there at the back where the grate is still uncovered. Then you'll rake the hot coals around the "hole" you just made. Load the wood toward the back of the firebox only. This keeps the early part of the fire more so back under the baffle plates and gives better secondary combustion for sure, especially with good dry wood.
Wire in one of those cheap spring wound bathroom fan timer switches on the combustion blower, and set it for 5-10 minutes so the fan can get the new fire stoked up without having to babysit it or get distracted and forget about a totally manual switch. Obviously if you are using a tstat and it is already calling for heat, then using the timer switch is unnecessary.

 

About the shed - it breathes like a ziploc bag. Which is why I followed the idea you mentioned about it's better to have sun and wind working for you. But since this is also my hay storage building with a leaky roof, I'm already planning to install an exhaust fan. I have louvers on the back end near the hay and I could locate the exhaust fan up front where I would stack wood. That should keep a slow, steady airflow in all conditions. Combined with the extra high temps in there in summer it might work very well.

I realize now I'm low on wood because I focused on CSS of the oak early on because it needs the most time, and worked on the tulip poplar, cherry, and maple later. It seems that right now it's all partly seasoned. Oh well can't win them all.

I have access to some kiln-dried wood cut ends at work. I intended to harvest that source and now I have motivation to use it to sweeten my loads.

BT, I think I'll have to try that when I have wood that really wants to burn. Right now I have the opposite problem.

I hooked up my manometer again, this time about 10" above the damper control. I'm seeing .04 to .05 tonight with a good warm fire and no call from the t-stat.

 

Do you know what your flue temps are, at 32 feet that chimney should suck your hat off.

 

I don't. I can dig out my ir gun and measure the pipe surface or install a proper flue thermometer.

 

Mines not fancy but remember they only work from up close. If you want to get finer details you'll need to use a flir camera or need to get up there.

Oh, I get it now your IR gun was off by 36 degrees - yeah that's not going to help.

I seriousness though the temp guns can vary based on the material it's aimed at, so it's best to read a target at a known temperature before reading it to find its current temp.

 

Yes, they are most accurate on a smooth flat black surface...taking temp readings on shiny metal will give you goofy results often times. If you need a shiny surface temp, put a piece of black electrical tape on it and then shoot that...

 

I just called this back up today to review against the recommendations of the chimney guy currently working to clean last year's mess. Your reply matches his first comment.

He recommended to remove or at least foil over the baro damper because he saw evidence of a cold stack. The creosote on the back of the damper door was even glazed (!) while the rest of the smoke pipe had >1/4" of "ash" creosote from just the latter part of last winter. I considered the wisdom of removing it entirely but the previous install had none and kept the chimney pretty clean. I asked about the need to limit draft on very windy nights but he felt overburn won't happen once the damper is gone. I think I'll foil it and keep it accessible in case of a very windy night. I'll also install a flue thermometer.

He also recommended to install a "stove adapter" fitting right off the stove outlet to get the male/female pipe fittings reversed. This follows the concept that you'd rather have liquids creosote coming down toward the stove. Not a big problem but easy enough to fix.

He did not recommend to install double-wall smoke pipe, yet but he did want us to install a zero-clearance panel between the clay pipe and ceiling. Double-wall is another solution at much higher cost, in his opinion.

They recommended two other things: 1) line the chimney (using "two-ply" round liner and insulation) 2) instead of repointing the chimney, replace the top cap, lengthen it 3 more feet, and encase the existing chimney with 2" of mortar. The liner was more important in his mind and the new crown can be done later.
The repointing is coming due and about the same cost - so maybe line this year and recrown next year.