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Small Cabin Forum / General Forum / Controlling heat from a cabin woodstove
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Mccoun
Member
# Posted: 17 Nov 2009 21:27
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I have a small 12' by 20' frame insullated cabin that I use my fathers old woodstove to heat. It's either off or 85 degrees in the cabin. Does anyone have any suggestions as to how to controll the temp? We have been leaving the outside door open but you tend to wake up cold. Thanks MM

CabinBuilder
Admin
# Posted: 18 Nov 2009 10:30
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Yes, that's the issue with wood stoves - its mostly on or off. I picked the smallest stove I could find for my small cabin. We keep window open as well.

I assume you are controlling the woodstove's burn rate by adjusting
the air intake. We can get the steady slow burning by setting it to a certain level. But don't close too much, as lack of oxygen may cause creation of carbon monoxide (although I believe most wood stoves are made to have a safe minimal opening)

Mccoun
Member
# Posted: 18 Nov 2009 17:30
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Yes We have tried air flow control but like you said hot or not. I actually considered boxing it in w/ proper air space and venting that outside. Kind of like a little room but I feel it will get too hot and unsafe.

Clay N Feathers
Member
# Posted: 22 Nov 2009 14:52
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I also have a 12'x20' frame cabin. 5' lofts at each , center 10' open. I bought a small wood stove because I thought it would probably run me out with a bigger one. I also installed a new propane heater 11,000 btu's. I can pretty much control the heat in te wood stove by the amount of firewood and heat controller. The propane heater is placed opposite end of cabin for really cold weather. I'm in Alaska. Also for summer use the propane is ideal to take the chill off or set at low so when the wood stove goes out. Good luck.

Clay N Feathers
Member
# Posted: 24 Nov 2009 00:43
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Reference the above. The stove I bought is a "Aspen" by Vermont castings. Heat control works very well.
Specifications:Log length: 16"
Burn Time: Up to 5 hrs.
Heating Cap: 600sf.
Max heat output: 18,000 btu's hr.
Efficiency rating: 69.5%
EPA emissions rate: 4.3 grams/hr.
Weight: 240 lbs.
Flue collar: 6" round, reversible
Cost: $900.00 Alaska price
The propane heater I installed is a "Homecomfort" #DV8, 7,500 btu's, not 11,000. approx 25" high and 12" wide and 5-1/32" deep.
Cost: $459.00 in Alaska. Like both real well.
I like the option of not using the wood stove until colder weather and the propane to just take off the chill or supplemental heat in the coldest winter days.

flatwater
Member
# Posted: 30 Nov 2009 00:46
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Once we get the cabin warm we let the fire go out and the propane fridge and regular cooking pretty well keeps things toasty.Our rule of thumb is never put in that last piece of wood.

denny
# Posted: 3 Dec 2009 19:11
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First, a bit of background. Since May 2008 I've been living full time in a 12x16 cabin in Missouri, about 90 miles south of St. Louis. Standard 2x4 walls with R-13 insulation, R-19 in the ceiling and inside walls finished with plywood beadboard. While the floor is not properly insulated I did very carefully stuff MANY layers of bubble wrap in this fall with rolled wrap tightly stuffed into each end to block the wind. It's not real insulation but I'm certain that there is FAR less wind and air movement under the space that had previously been open. I've also got stacked rock along the base of the cabin from ground up a couple inches past the outer 2x8 rafter.

For this winter I stacked concrete blocks around my wood stove with excellent results thus far. I've got a total of 24 solid blocks (3.5" x 7.5" x 15.5"). They're stacked on the the two long sides and behind the stove and up about 2.5 feet on the back side of the stove pipe. On the sides I've got them stacked two thick (about 7"). On top I've got a big enamel canning pot full of water which leaves just enough room on the stove top to put my coffee pot. I also reinforced the floor deck under this corner of the cabin using a couple concrete blocks placed snuggly under the floor rafters.

I'm finding that I can do two very distinct fires, morning and late evening. Thus far each fire is 3-5 logs for a fairly hot burn of 1.5 to 2.5 hours. The result is that the concrete blocks moderate the hottest peak of the burn because they are of course absorbing lots of heat. About an hour after the fire has burned out the heat finally really makes it's way to the outer edges of the concrete. They are hot to the touch but by no means hot enough to burn anything. I type this at 3:15pm and the blocks and pot of water are still noticeably warm. My morning fire was over at 8:15am - that's seven hours of steady, slow warmth. I expect that they'll radiate heat for another hour, maybe two before diminishing. A huge improvement. Rather than peaking at 85 (or higher!) and fairly quickly dropping to 60 I'm peaking at about 80 and VERY slowly dropping. In fact, there is a moderation of temps even past the time that the blocks feel warm. I'm going out this evening and won't be back till 9pm to rekindle the fire but if the past week is any indication the cabin will still be at 60 or above at that time... 12 hours past the morning fire. Outside temps today: 30 at sunrise, 40 at 3:30pm. Inside temps today: 60 at sunrise, 68 at 3:30pm. I've just started keeping track 9 days ago and in that time I'm seeing an average difference of about 22 degrees at sunrise and sunset before the morning or evening fire is built.

My guess is that in the colder part of winter when nights regularly dip to 20 or less and highs only in the lower 30s that I'll be burning my morning and evening fires longer with more logs but I'm hoping that each fire will still be fewer than 10 logs. Based on what I've seen thus far I don't think it is unrealistic to estimate that I'll burn about 40-50% less wood than last year. I wish I'd thought to keep track last year with no blocks so that I could compare by numbers rather than memory of numbers. I routinely heated myself out of the cabin. It would warm very quickly but also cool fairly quickly, especially at night. Each day I'd try to get the fire up then let it go to very low coals and re-ignite. At night I'd try to keep the fire going till bed at midnight when I'd stock it up as much as I could without getting it too hot to sleep. If I failed to wake up at 2 or 3 am to get it going again I regularly woke to 40 degrees, sometimes less on really cold nights. Constantly up and down.

Regardless of how much wood I save I know for certain that the less extreme temperatures and warmer mornings will greatly increase my comfort level as well as the time I spend tending the fire. Well worth the $52 spent on concrete blocks! This is not even close to an original idea. There are many variations on the concept. Masonry stoves, cob.... the important thing is to have as much thermal mass around your stove as you can afford and safely place on the floor. If I had planned better I would have built this section of floor much stronger and would have 40 or 50 blocks rather than 24. The more mass the better the moderating of temps.

geekinthegarden
Member
# Posted: 4 Dec 2009 13:29
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Meant to post a pic with the above. Here's the stove with thermal mass:
wood stove with thermal mass
wood stove with thermal mass


flatwater
Member
# Posted: 4 Dec 2009 22:23
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Looks nice and funtional

lawnjocky
Member
# Posted: 4 Dec 2009 23:20
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That is really cool! Right away I started thinking about those water jacket hot water heaters for wall tent stoves for the sides of the wood stove and for the flue making double wall pipe by using the standaed single wall flue pipe and the a second several inches larger and filling the gap with concrete.

Jocko

JRanch
Member
# Posted: 5 Dec 2009 09:35
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Hi geekinthegarden,
Could you post some pics of your cabin and o on. I am in the process of designing a 12x16 and am looking for some ideas, roof picth, loft and things you would have done different if you could do it again, and so on.

Also, are you of the grid and if so what are you using for lights and cooking?

Thanks,
Jranch

geekinthegarden
Member
# Posted: 7 Dec 2009 18:52
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Hey JRanch, I've got gobs of photos on this flickr set. Not off grid but use as little electricity as possible... about 2-4 kWh a day. Use propane for cooking. Haul water by hand from well.

JRanch
Member
# Posted: 7 Dec 2009 21:44
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Hey geekinthegarden,
Nice spread you have going there, I like it. How long have you been working on your place(s)?

Looks good.

flatwater
Member
# Posted: 7 Dec 2009 22:23
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WoW neat pics. The dog looks like a cross between a pit bull and a pug

geekinthegarden
Member
# Posted: 8 Dec 2009 14:06
Reply 


Thanks JRanch. We started work on the site in May of 08, so a year and a half. I'm pretty happy with the progress thus far. There's always more to do but I'm settled in and plan to stay so there's time.

Flatwater, yes, that's my crazy talula. She does kinda look like a pit bull in her coloring. not sure about the pug though, her face is not really squished flat. I always thought she might be a pit bull and Chihuahua... scary to think about that one!

lawnjocky
Member
# Posted: 8 Dec 2009 18:44
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Nice place Geek.

Jocko

Moontreeranch
Member
# Posted: 8 Dec 2009 23:39 - Edited by: Moontreeranch
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Denny has the right idea, the key to sustained heat is thermal mass. If any of you have read much on solar home design, one of the big mistakes made in early designs was the lack of thermal mass, lots of big windows (too many sometimes) and not much thermal mass the sun would shine in...the temps would soar and as soon as the sun went down, it was cold. Allowing the energy to be adsorbed by something then re-radiated back (during the night with solar) was key to getting it right. The happy balance between windows and mass.

We put in our wood stove in our 12 x 20 cabin over thanksgiving break The first night it was into the low twenties,and we had not yet finished the insulation, we ran the propane "bottle top" heater it runs at 8,000 to 15000 btu we ran it at the lower setting and it was still chilly in the morn. the second night we ran the wood stove for the first time. we had more insulation in and the stove is a little scandia 150 (about 50000 btus) it got a bit hot, and our plan for the future is to add more thermal mass. We have a passive solar design, and plan to have tile through out the cabin, with 1/2" wonderboard as backer.. at about 60 pounds per sheet it should temper the extremes. Our next visit we will add a damper to the stove pipe to control the burn more and add a few more sheets of backer to the place. (we currently have three sheets about the stove floor is insulated to r-30) our final floor mass should be close to 800 pounds for the backer, and almost that much more for the tile. If we still need more mass I might built something like denny has.

elkdiebymybow
Member
# Posted: 11 Jan 2010 18:25
Reply 


We have found the best way to regulate is how much wood we put inside the stove. After a few hours our 14' x 24' cabin gets 70 degrees at a 5' height in the cabin- warmer the higher up you go and a little cooler towards the floor. We just spent 10 days up there- outside lows were around 10; highs in the low 20's. Once we get the cabin warmed up, we toss one or two logs in to keep the fire burning. Temps fluctuate a bit and when it gets around 60 we toss in another log. I stuff it with some apple wood just before bed and if I don't add to it by morning our inside temp is between 40-50 degrees. We find that we dress in layers and adjust our clothing as the inside temperature fluxuates.

We'd love to rig up a weighted fan that operates kind of like a coo-coo-clock in principle, but can pull air down from the peak of the cabin and circulate it to the cooler air on the floor. Has anyone seen such a thing? I'm going to build one if I can't find something out there.
winter cabin
winter cabin


fasenuff
Member
# Posted: 10 Apr 2010 21:47
Reply 


We used to have a wood stove in the garage that we would load up in the morning and it held an even temp all day. We used a heater thermostat from a Volkswagen Beetle to automatically open and close the air dampers on the stove. Those thermostats are the type that expand as they get hot and can be used to move a damper as much as 2 inches or more if you set up some type of lever. They have threaded ends and are easy to install.

I am preparing to start on my new cabin soon and I will be building my wood stove from scratch and will install one of these to make a more even temp from the wood stove.

island guy
# Posted: 13 May 2010 17:11
Reply 


a clock mechanism to control a fan is an idea i've looked at. Basiclly, a weight driven fan, with the speed regulated by an escapement mechanism. There are some fans available, however, which run solely from the heat produced by the wood burner itself. They are available through Canadian Tire, and many other stores as well.

Anonymous
# Posted: 16 Jul 2010 12:12
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talking about thermal mass, here's Russian stove

Stove

Ozarks
Member
# Posted: 31 Jul 2010 00:18
Reply 


Other than installing a small stove designed for the small space like one for marine use like the Little Cod etc. or a VC Aspen.

My only suggestion is to build a small fire of three small splits.

A catalytic stove can be better controlled for burn time and temperature stability but I am unaware of any stove designed for such a small space.

poppasmurf
# Posted: 21 Nov 2010 19:32
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I have used both blocks and granite rocks for fire rings and they always crack and crumble from the heat of wood fires. I am concerned that the same thing might happen to cement blocks stacked near and around a wood stove and then building a hot fire in the stove. I would recommend fire bricks to keep this from happening.

seesaw
Member
# Posted: 8 Jan 2011 16:15
Reply 


"There are some fans available, however, which run solely from the heat produced by the wood burner itself. They are available through Canadian Tire, and many other stores as well."

I looked on Canadian Tire and I'm not seeing. Can you direct me?
Sounds like a great solution for those of us who want wood or propan heat but don't want electricity

islandguy
Member
# Posted: 8 Jan 2011 16:34
Reply 


Click on "heating and air conditioning" then woodstoves and pellet stove accessories" or just search for ecofan.
These fans get good reviews from users, although they cost about $100 and up. We will be installing one as soon as our woodstove is installed.

seesaw
Member
# Posted: 8 Jan 2011 16:41
Reply 


Found it thanks island guy. looks like they don't last forever but if you figure $50 a year, sounds worth it....

debbijo
# Posted: 13 Jan 2011 11:17
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I'm enjoying this web site. I am planning on building a cabin off the grid this year and have a couple of questions that maybe someone could answer. My plans are to build a brick fireplace in the center of the home with two sides open. One side opened to the living area and the opposite side open to the two bedrooms and bath. I have been told that a fireplace is not as effecient as a wood stove, but I already have the brick. So...could I build this fireplace now and eventually put in a woodstove insert with this type of construction? And, if this would work, would the brick heat up like the concrete blocks and reduce the wood consumption as you speak of here? Thanks!

MikeOnBike
Member
# Posted: 13 Jan 2011 13:22
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Our current cabin plan is for a long 12'x40' cabin to maximize the view we have. The wood stove will be at one end of the cabin. I need to move some warm air to the other end so I plan to install a 35' long, 4'-6" heat duct near the ceiling with a duct booster fan to move the air. That's the plan, hope it works.
The View
The View
The Plan
The Plan


seesaw
Member
# Posted: 13 Jan 2011 13:53
Reply 


Sweet MikeOnBike!

larryh
Member
# Posted: 13 Jan 2011 19:23 - Edited by: larryh
Reply 


I like wood heat. But as you say a small area can be tricky to heat a small home. The best suggestion so far is that you burn it with small amounts of wood and let it go out or nearly out to keep it from getting too hot. I would wonder if a upright circulating type coal stove with a small pot would produce less heat than a stove with the amount of firebox and radiating sides as the box type stoves. Unless you can find a very tiny Jotul or Morso which came in really tiny sizes your going to have trouble in any small area. Be very careful with you distance from combustibles. A chimney pipe that gets hot can really throw considerable heat to that rear wall if it is less than 18 inches or so from the wall. And even then it can be very hot. It should never be hotter than you can touch and hold your hand too without it being too warm. I do like your radiating idea of the blocks. As also shown its pretty much the principle of the european masonry stoves. If a person had the skill to build one they might be the answer to small spaces as they never give off the direct hot heat of an iron stove. I have two wood stoves, one heats the home of 1000 sf and I have a large kitchen stove which will take the 11 x 17 kitchen up to over 100 if you run it very long. One can buy newer small cooking stoves that have enough power to heat a cabin your size easily. Any small stove is going to take more tinkering because of not wanting too large a wood which will run longer than small pieces for sure.

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