Wood Stoves

[thollandpe]

I expected I'd get a unit that ducted in outside air for combustion, because why suck warm air up the chimney? But it looks like there are some fire hazards associated with it and it isn't neessarily any more efficient. I'm surprised. This is the kind of stuff I've been reading; I can't assess how sound it is: A non-commercial service in support of responsible home heating with wood - The Outdoor Air Myth Exposed

That article didn't pass my sniff test. Just because there are combustion air systems that don't work correctly doesn't mean the whole concept is wrong. One, be sure to account for wind when you locate the inlet. And two, almost every natural-draft system I've seen is undersized.

Building code specifies combustion air sources for fuel-burning appliances. For something the size of a medium/large wood stove (50,000 Btu/hr) you'd need to provide 2000 cfm from the room. That would be one big and leaky-as-feck room, given that a range hood should draw 250 to 400 cfm. And we rightfully worry about that backdrafting stuff.

If your room isn't big enough or leaky enough to provide that, code requires two ducts (one low and one high) with a cross-section of 25 sq.in. (6" diameter) each. If you have openings direct through an outside wall, these can be half the size, 12.5 sq.in. or 4" diameter.

Or you can power vent the combustion air, 17 cfm. That airflow is less than half a bathroom exhaust fan, and a 3" diameter duct.

The code has evolved around appliances that burn oil or gas, because carbon monoxide is bad. Granted, a wood stove will smoke you out before it knocks you out, but I don't see why you should treat it differently just because you can.

Disclaimer: I'm quoting code numbers from memory and that's bad practice but hey this is a bike blog and I'm not billing anybody for this time.

[Mark Kelly]

I've run the numbers on this looking at heat loss from a ducted and non-ducted intake sytem in a house we are building with a 90%+ efficient HRV system and air infiltration around 1 m³ / m² / hr (predicted, not yet tested).

The ducted system is about 10% more efficient than the non ducted system. The HRV ensures that delta P is minimised and takes care of any concerns about air supply (non-ducted) by continuously supplying 300 m³ per hour of fresh air into the house.

We are currently undecided about installing the wood heater at all, given that the predicted energy balance of the house comes out to around 200 MJ / annum without it, so it should cost about AUD$1 per day to run (not counting hot water and cooking). The big plus of the wood heater is IR irradiation of the passive storage surfaces designed into the house, which provides significant subjective warmth.

[caleb]

The ducted system is about 10% more efficient than the non ducted system.

Does the 10% figure account for the energy needed to heat the non-ducted air before combustion? The greater the temperature differential between the outdoor air and the indoor air, the more that inefficiency would seem to be. But I'm certainly not an engineer.

Our final stove walkthrough is this Thursday. Assuming everything goes as planned and we sign off, we should have a 2020 certified Hearthstone Manchester operational before Thanksgiving.



The install will have fully ducted outside air, which is the installer's standard practice.

[Mark Kelly]

Does the 10% figure account for the energy needed to heat the non-ducted air before combustion? The greater the temperature differential between the outdoor air and the indoor air, the more that inefficiency would seem to be. But I'm certainly not an engineer.

The model was run with air supply at the appropriate temperature (T_ext = 0 and T_int = 20). The major energy difference is that the internal heater draw unbalances the flow through the ERV heat exchanger. If you don't have ERV installed you will get different results.

[caleb]

I never did close this thread out. After only 18 months or so of back and forth with different shops, we finally had a Jotul F400 Castine installed at the end of January. We've been using it all the time, and we love it.

Here it is before getting the wall and trim sorted back out:



And last night after an afternoon out in the woods:



As you can see, it's mostly a dog accessory.

[monadnocky]

That's a beast of a stove - I had one in my former house. Good choice on the enamel finish.
Love the way the first photo suggests that there is no flue at all! It's a MIRACLE!

On second look... what's the distance between the back and the wall?

[caleb]

On second look... what's the distance between the back and the wall?

About 8". You can't see it in the photo, but we have the rear heatshield installed, which reduces the clearance to combustibles to 7". We had a reputable brick and mortar shop do the install in its entirety. Amazingly, the rear wall stays cool to the touch even when the stovetop is at 600 degrees.

[monadnocky]

Sounds good and right. Photos can be so deceptive.
Great stove.

And that wood looks beautifully seasoned.

[caleb]

And that wood looks beautifully seasoned.

I was out scouting the firewood situation yesterday, and I found some medium maples that came down over the winter along with some red pine castoffs from a logging cut over the winter. I didn't spot any birch that came down over the winter, but I'm going to keep my eyes open.

My plan is to try the solar kiln drying method over the summer to see if I can get them down to <20% in a single year.



I'll also cut and split some oak with the plan to stockpile it and leave it for at least two years. Unfortunately, ash is out as a source due to the bugs.

[monadnocky]

I was out scouting the firewood situation yesterday, and I found some medium maples that came down over the winter along with some red pine castoffs from a logging cut over the winter. I didn't spot any birch that came down over the winter, but I'm going to keep my eyes open.

My plan is to try the solar kiln drying method over the summer to see if I can get them down to <20% in a single year.



I'll also cut and split some oak with the plan to stockpile it and leave it for at least two years. Unfortunately, ash is out as a source due to the bugs.

I don't know about that method of drying....but I am always loath to completely encapsulate my firewood in plastic, as that can do more harm than good in terms of trapping moisture. But I will scan that conversation.
Ash? Plenty around here, waiting to be felled and split. It's all dead, of course, but it will be good to burn for a a few years. Heartbreaking.

Nothing I enjoy more than peeling back the bark of my ash firewood, finding some larvae, and tossing them into the woodstove. Bastards.

[caleb]

Wood storage has been a work in progress. Started with some posts and 2x4s, then built a platform with sides, when added a basic roof to the platform last night.



Hopefully this will make it through the winter, and I'll be able to redesign the roof next spring when the rack is empty.

[caleb]

We're over three and a half cords stacked out in the dog yard now. I might try to put another one up before the fall in anticipation of another COVID shutdown and WFH orders over the fall and winter.






There's not much I can do about the state of the world right now, but I can make firewood.

[ides1056]

I share your sentiment. When I came back from Florida in March I went to work clearing fields with firewood as a byproduct.

[j44ke]

Well, kindling burns. Fingers crossed on the real stuff.

[Mabouya]

Cool.

What happens to all the heat that's generated by the fire? Is it blown into the living space? (I assume the black strip around the door is where the firebox gets it's air, but that may be incorrect)

Or do you just get what's radiated through the glass?

[j44ke]

The inside of the stove has a bunch of plates and holes and vents. As the box heats, unheated air gets drawn in at the bottom and heated air exits at the top, somehow without smoke.

The air intake slide control (bottom front) is key of course. When I remembered to shut down the air a bit, I got a better burn rate. Wide open, the wood disappears. Way too hot. The better setting makes more glowing coals. Plenty of heat and the wood lasts longer.

Need more practice. Trying not to burn the house down.

[j44ke]

Wow maple burns nicely doesn't it? I just took all the lower limbs off a maple that's been down for a year and a half and cut them up. The thickest piece is 2-3", but most of it is 1-1.5" in diameter. Made a bag of ash log chips, dumped a pile in the stove, got it cranking and now the maple is cleaning out my stove for me. Wonder if the biggest difference is that the limbs were all sticking up in the air, drying all the way around in a nice sunny spot. Each piece makes a nice "clink" sound when you knock them on the floor. Definitely going back for the rest.

Learning stuff is cool.

[ides1056]

That clink sound, like a bat hitting a home run, sounds like firewood ready to burn.

[j44ke]

Today my friend Jeff and I spent several hours dragging out the last piece of the giant black cherry that fell over in a storm a month ago. First we got it down a small rise in the forest and then up a small rise and then into a clearing where we could load it into Jeff's truck. We used a ratcheting winch (come-along), a strap, some chain, and some rope, plus a couple peaveys and a rock bar (very heavy bar for moving rock). And rollers made out of small trees that got crushed when the cherry fell. Then we used Jeff's gantry, that he made three trees ago and is still going strong, to raise and swing and roll the trunk into the van. 21" diameter at the base but more than that at the top where it split into two trunks. I think in addition to this one, we got nine 8' logs out of this tree. Nice workout.









Not technically about wood stoves, but this tree produced all the cherry wood sitting next to our garage that Jeff and I split a while ago out from the limbs. However, Jeff is a cabinetmaker, so he's going to mill the big trunk to make a dining room table - eventually when it all dries out in a few years.

[Bewheels]

Well, kindling burns. Fingers crossed on the real stuff.

Jorn - This cannot be a real photo of a living space. Where is all the stuff randomly covering surfaces (tables, chairs, floor)? This looks like the cover of a scandinavian home and garden magazine cover. Post a photo of this same room perspective during mud season.