How much wood do you load in a wood furnace?

[tom reinbolt]

Been tinkering with my DS Stoves 400-09. The firebox measures 16"x29". The maximum log length is 26 inches. I'm burning 14"-18" splits now--mostly ash with some hard maple and red oak. We put in usually
5 splits max to 'fill'.

I'm lucky to get 6 hours burn--we wake up and the house is cold--62 degrees.

So how much can I cram into this thing without damage?

The interior of the box has brick linings. Above the brick is the secondary burner tubes that run vertical up to the top. Can I load wood into the 'metal' section of the firebox above the brick?

Would like to get 10 hours--load at night, load when I wake up, load when I get home from work and then repeat the process.

Thanks

 

[Marshy]

Sure you can, it just increases the risk of warping the area above the bricks. My wood stove has one row of bricks on end for the sides with enough space above them for a second row (gives ya an idea of how much room I have) and when loaded to the roof I swear I can see a noticeable difference in the bow of the walls above the bricks. I try to avoid doin this very often because I can get the same or more heat transfer with less wood but the burn times are shorter too, that is the down side. Good luck.

 

[newyorker]

I put two large splits on bottom and two med-small splits on top and that hold the house to 68 in morning supposed to dip to 0 or maybe below this week so I will prolly cram a few fillers in

 

[laynes69]

I looked up the specs, it says there's a 8 cu.ft. firebox. So I would assume it will take more than 5 splits, unless the splits are massive. Our old furnace had steel sides like you've described, and we filled it to the baffle. There never was any problems, but I think that was due to the blower keeping things in hand. Load it up, just don't burn it cherry red. If the furnace has a secondary burn, you should be able to lower the air once hot and it should remain hot.

 

[svk]

Also load it with larger splits from slower burning hardwood to achieve a more uniform release of heat versus lots of smaller fast burning splits.

 

[newyorker]

Holy crap 8 cu ft that is huge

 

[Haywire Haywood]

That was my only complaint with the jotul oslo I had. Small firebox vertically. Getting up at 2-3am to refill the stove was just something I had to do. I got to where I don't think I really woke up to do it. Chucked a few pieces in and went back to sleep.

 

[066blaster]

My dad has a wood furnace. We never split anything under 12 inch diameter for his use. use the big ones for overnighters. I couldn't amagine only using small splits in it. Basically if it fits in the door it doesn't get split. You don't really need a rip roaring fire in it.

 

[brenndatomu]

My Yukon has a monster firebox too. I actually stacked more fire brick in it to make the firebox smaller (narrower) so that small loads on warmer days in the spring/fall will burn hotter. I was pleasantly surprised to find that I didn't have to take the bricks back out for more wood capacity during colder weather. For me, that, and a few other mods helped cut my wood usage quite a bit.
It takes a bit of time until you learn your heat load and what it takes to keep the furnace warm without smouldering the wood.
One suggestion I have would be to have different lengths of wood available. Long wood to stack 'er full on cold days and shorter stuff to run on warmer days. It is pretty easy for me to have two different length wood because I cut at 22" for the furnace and 16" for the stove upstairs. I find the fire burns hotter/cleaner for me if I can stack the wood higher (tall/narrow) so less length allows less #s loaded but still get that height that burns so well.
Another thing that I tried this fall was to stack the splits on end (on an angle) at the back of the firebox (tall firebox with firebrick to 18" high) I really liked the results. Seems to give me a hot/clean fire with good secondary burn almost right off the bat, and burn times still seemed good too. Doing this made my ash bed grow on an incline, which so far this winter I have left it that way
I wouldn't worry about stacking wood a bit over the firebrick level but I also think you shouldn't really need to go much higher unless you have a HUGE heat load. Now, having said that, keeping the fire below the brick level would probably help make the furnace last dang near forever.

We never split anything under 12 inch diameter for his use

I'd have black unburnt chunks of wood in the morning if I tried to burn unsplit rounds that size unless they have been stacked/drying for 10 years!

 

[tla100]

I have one row bricks in the Heatilator WS-22 and almost always load above it. Not much room above, but helps for longer burns. Most time wood doesn't touch the sides above, have not noticed any warping at all. Have burned some large rounds that just fit in door, usually long dead standing trees. Burn just fine.

 

[outdoorsman0490]

2 splits that are maybe 5"-6" on the bark side of split; then a round that just fits through the door. Good dry oak, close up the dampers and it I do this at 10:00pm, at 7:00am the blower is most often still running, the house is still 70-75 and a bed of coals. Getting these times out of my hotblast.

 

[zogger]

Been tinkering with my DS Stoves 400-09. The firebox measures 16"x29". The maximum log length is 26 inches. I'm burning 14"-18" splits now--mostly ash with some hard maple and red oak. We put in usually
5 splits max to 'fill'.

I'm lucky to get 6 hours burn--we wake up and the house is cold--62 degrees.

So how much can I cram into this thing without damage?

The interior of the box has brick linings. Above the brick is the secondary burner tubes that run vertical up to the top. Can I load wood into the 'metal' section of the firebox above the brick?

Would like to get 10 hours--load at night, load when I wake up, load when I get home from work and then repeat the process.

Thanks

Mix into your stacks double (or even triple) size your normal splits or full rounds larger than your normal splits, these will last longer.

I burn one inch to around twelve inch wide/diameter stuff. This, along with species selection, is how I adjust heat output. Air intake only for adjustment, no exhaust damper.

Not the best in the world, but it works.

 

[CTYank]

Storage is a big help, too. Ever see or hear about the "Hill Boiler" that Richard Hill, ME Prof, UMO designed back in the '70s? You could run its burner hot & super-clean an hour a day with its heat exchanger heating a storage tank of water. Draw heat from the tank a/r. In the interest of efficiency, complete combustion was a primary requirement. Forced-draft primary air made stack draft unimportant only for the secondary air.

Storage ccan be done with air, too, and room objects. My stove is in a room that serves as an accumulator. Temps swing from 85-115. Wood is stored in there too to complete drying. Rooms that air is fed to from there see much lower temp swings. I make minor changes as to species & amount of wood depending on ambient. Close-enough works fine.

Just doesn't work (IMO) to try to match wood-burner heat output to the load moment to moment. Spidey tries that. I'll pass, thanks.

 

[ChoppyChoppy]

Holy crap 8 cu ft that is huge

Our shop stove is about 4ft roundx7ft long, about 90 cu ft. Will stuff it to the gunnels when it's cold out. Takes 2 heaping wheelbarrow loads. Do that 2-3 times a day.

In the firewood dog thread there is a photo of it with my dog laying under it sleeping.

 

[Whitespider]

Can I load wood into the 'metal' section of the firebox above the brick?

Not being familiar with your furnace I can't say with 100% sureness that you can load the box to a point above the brick without consequence (actually I'm covering my azz)... but I find it really hard to believe it would hurt anything.

In most fireboxes, more wood means more heat per minute, per hour, etc., not necessarily longer burns... unless you change the rate of burn. Back-in-the-day, people would stuff the box full and choke down the fire to get the "long" burn. But they could have got near (I said near) as long a burn with just half, or even a quarter load choked back that way... but less heat per minute, per hour, etc.

Your furnace has an automatic forced air draft... rate of fire changes automatically according to heat demand. If you want longer burns you need to reduce how often the draft blower starts, and reduce how long it runs when it does. There's only two ways to do that...

1. Turn the thermostat down... which means the house will be colder when you come home, and require more wood burned at high rate to warm things back up. Chances are that alone won't increase burn time by all that much... only by the length of time it takes for the house to cool to thermostat set point.
2. Put a larger load of wood in the box (and/or use heavier, denser wood)... which will make more heat per minute, per hour, etc. when the furnace is idling, thereby reducing how often the draft blower starts, and will make more heat per minute, per hour, etc. when the blower is running, thereby reducing how long it runs.

CTYank is wrong, I do not "try to match wood-burner heat output to the load moment to moment"... I load the box for expected heat demand and walk away from it for 6-12 hours, depending. If I was trying to match it moment to moment... I'd be needing to sit beside it and babysit. The auto firing rate (i.e., draft blower) makes that a simple thing, it allows you a large margin of error... there's no reason to ever over-load and over-heat the house...

Keep experimenting and trying different load sizes... you'll catch-on to what it wants/needs for conditions.
*

 

[fixit1960]

When I used my add on wood furnace in the basement from 1984 to 1997 I would have to jam it with wood in weather like this (-0). It was old school. No fire brick. It had thin cast iron insets on the side of the firebox that came up about 1/2 way on the side. These warped and broke after a period of time. I removed them and installed new ones I made out of 1/2 steel plate. I also made them higher to cover more of the interior skin. Worked fine after that. I would get about 7 hours burn time and very seldom ever had any oak or what some would call premium hard wood to burn. Hackberry, ash, elm, soft maple and mulberry were the main supply. It kept this old 2 story 2000 sq ft farm house warm for us. I had an adjustable snap disc blower control on the back that I could adjust if necessary.

In fact I sold it about 4 years ago to my friend who lives in town. He has run it since with no problems. Almost overkill for his 1000 sq ft house.

You may look into lining your firebox higher to prevent warpage, but try loading it heavier and see how it performs. As Spidey said you need to experiment a little and see what works, no two stoves will work the same in different homes. Good luck...

 

[Whitespider]

Something else I should add... something that's been true for any firebox I've used with a coal grate and air coming in under it...
During times of high heat demand (i.e., extreme cold weather), run it with a deep coal bed... both heat output and burn times will be increased noticeably.

It was cold here yesterday, we reached a high of only 3°, and it dropped to -10° by this morning. Yesterday late afternoon/early evening I started building the coal bed by loading a couple smaller loads, a bit sooner... by 8:00 PM last night the coal bed was a good 8-10 inches deep when I gave it the final loading and turned it. When I rolled out 9 hours later, at 5:00 AM, there was still a good 3 inches of screaming hot coals on the grate (draft blower was running) and warm air was coming from the heat vents. Now, truthfully, the house had cooled to 64°, but that's not as bad as it sounds... it's only 2° below the overnight thermostat set point of 66°. I opened the door, gave the coal bed a quick rake, tossed in an armload of firewood, slammed the door, and went upstairs to pour a cup of coffee. An hour later, when the wife rolled out at 6:15 the house was 68°, and by 7:00 it had risen to 71°. When I left for work at about 8:00 there was a good, deep coal bed... I tossed in a couple more splits, the wife likely won't add any more until mid-to-late afternoon (if she even does, were lookin' for a high of about 10° with relatively light 10 MPH winds, and sunshine until the snow moves in). When I get home tonight, about 5:30, I'll start building the coal bed again.
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[olyman]

CTYank is wrong, I do not "try to match wood-burner heat output to the load moment to moment"... I load the box for expected heat demand and walk away from it for 6-12 hours, depending. If I was trying to match it moment to moment... I'd be needing to sit beside it and babysit. The auto firing rate (i.e., draft blower) makes that a simple thing, it allows you a large margin of error... there's no reason to ever over-load and over-heat the house...

*[/QUOTE]

 

[brenndatomu]

they could have got near (I said near) as long a burn with just half, or even a quarter load choked back that way... but less heat per minute, per hour, etc.

Absolutely right! Took me a long time to figure this out, more wood equals more heat, not longer burn, well, not very much longer anyways...
The exception to that would be with the modern secondary burn stoves. More wood can equal longer burn there (more heat too), the bigger the firebox, the longer the burn, well, some models are better than others...
But since OP is talking about a furnace I agree with spidey (even though this model is supposed to be a reburner) That brings up a point, OP, you wouldn't want to get us some pics of the top half of your firebox (inside) would you? I love to see if this thing has secondary"EPA style" firebox since they claim it has secondary burn...

 

[stihly dan]

Longer splits, or a few sideways in the back then your 16's.