Need Help with efficient wood burning on a hearthstone mansfield stove

[tbrickner]

Hi all:

4 months ago I had a Hearthstone Mansfield stove installed and am still trying to figure out the nuances of the unit.

I live in the Elkton, Maryland area so it doesn't get super cold here averages around 22-25 F during the winter months. I also have a 17ft stack (details as follows)

3ft double wall black pipe from stove to a 90 Deg. elbow 1 ft section straight through the wall to a double wall stainless stack clean out piece on the outside of my house straight up to the cap 14ft.

The stove has no damper installed on the stack.

I typically load up the stove from a cold start and open the air intake to full. Then after about 20 min cut it back to half way and get the temperature typically up to about 300F in about an hour and a half. Next I put another load in at 300F open the air intake to full for about 10-15 min to get a good flame, cut back to half for about 15-20 min and then close off the intake. This will get me between 450F to 500F. I just can't seem to get the temperature above 500F with out throwing in another load around 450F. It seems that I am loosing a lot of heat potential out of some very dry wood and am having to load the stove very frequently at the 400-500 F range.

Does anyone suggest adding a damper to the stack?

If I add a damper to the 3' section where would you folks suggest I drill a hole for the stack thermometer?

I was thinking 1-1/2 ft up from the stove on the double wall black pipe 3 ft section. Do you treat it like a flow meter or other sensing deice where you try to keep the thermometer about 3 diameters distance from any bends. At 1-1/2ft the thermometer would be about 3 diameters distance away from the stove and about 3 diameters distance away from thermometer to the 90 deg elbow to allow the hot air a straight uninhibited path past the thermometer?

I know that these closed system stoves don’t typically have a damper with the stack so I need some suggestions?

Any help would be appreciated.

Tom

 

[Backwoods Savage]

Tom, I'm not sure why you think you need a damper. You only need a damper if you have excessive draft and what you describe does not indicate that.

If you can't seem to get the stove up to temperature, then cutting the draft won't help in the least. That is, cutting the draft with a damper. Cutting some draft on the stove itself might help. But what you are describing sounds more like poorly seasoned wood.

What type of wood are you burning and how was it seasoned?

Also, when you are reloading with more fuel at 300 degrees and again at 450 degrees, is it because the stove temperature is starting to go down at that point or are you just thinking more fuel will get it hotter? Don't forget that when you add fuel it is normal to lose just a little heat at first because that cold or cooler wood will take some of the energy to heat it up so it will burn. Perhaps you are adding wood too fast and the secondary has not had a chance?

btw, I would never think of adding wood to a 450 degree stove!

Now I'll let some Hearthstone guys chime in here.

 

[Backwoods Savage]

Tom, one more thing popped into my mind. When you leave the draft open for 15 or 20 minutes, what does the wood look like? It should be well charred. Sometimes you have to leave the draft open for longer periods, depending on the wood.

 

[Todd]

Soapstone is slow to react to the inside firebox temps. I think your cutting back the air too soon, leave it at about half way for longer and see what happens.

 

[tbrickner]

Thanks for your input.

I'll try to describe some further detail.

I am using some 1 year old mix of hard wood oak and softer wood maple. Some is punky but most of it is solid dry wood. You may have a point that this may not put out as many btu's per load.

You are also correct in that when the stove gets to 475 deg F it stays there a while when I set the intake draft to 1/4 open but after about an hour starts to drop off and about two hours later will drop to 350 deg F. To avoid this drop and to try to get the stove back up to a higher temperature I will load with wood at 400 or 450 deg F with draft full open to get the wood to catch. By opening the draft and loading I typically drop about 25 degrees then after 15 minutes of good full intake open burn I will start cutting back to 1/4 open intake draft and in abut 45 minutes the temperature goes up again but typically stalls out between 500 to 525 Deg F. Again the temperature will start to drop back to about 400 degrees to 300 degrees after about 3-4 hours at outside temperature of about 20-25 deg F. I am definitely getting a good char on the wood so that I can get a nice burn when turning the draft down.

I understand that opening the stove I will loose some heat and by having the intake draft full open I will increase air velocity through the stove and loose more heat through the higher speed air flow as well as the energy it takes to heat the newly stoked wood. I also understand that the whole idea of the soap stone is to heat it slowly and capture the heat in the stone so that it radiates out over a longer period of time. My problem is that I don't seem to be getting much time out of my stove from the 350 to 550 Deg F temperature range. On a cold night here in maryland we may get 20 deg F weather and I need to keep the stove arround 475 to 525 to keep the house warm. I know people use these stoves in Minnesota and other really cold areas where they are at temperatures in the -20F range why can't i heat my house in the 20+F range. My house is 2400 square feet area that I am heating with 10 ft ceilings if this may help. I typically can heat the house between 66 to 71 deg F between 20 to 30 deg F outside temperature.

Do you think it may be the wood or is it some bad techniquie I am using?

My thought was that I may need to put a stack damper on to hold in some of the heat lost in the stack. Would this help out at all?

Right now I am getting a bit frustrated because I thought I was doing everyting right but I seem to be missing something with what I am doing.

Please let me know what you think. I am out of ideas at this point. Also what temperatured do you typically reload at? Let me know if there is any more information that could shed some light to what is hapening.

Thanks again,
Tom

 

[tbrickner]

By the way.

Another piece of information is that after I leave the draft 1/4 to 1/8 open I will get a lot of chunks of coal at the 200- 250 deg F range. Does this indicate a poor draft or some other symptom.

Thanks,
Tom

 

[jdemaris]

Red or white oak isn't going to be dry if it's only one year old - at least not in my area of northeast with short summers. Soft/red maple is a different story. It's possible part of your problem is the wood itself.

As to the specific temps by the numbers - I can't comment much. Can't think of good reason to use a thermometer and I've been heating with wood for close to 40 years.

I'll say this. I bought the Hearthstone Mansfield as a moderate-weather source of heat when outside temps are 30 F and above. Gets used fall and spring mostly. When weather is really cold, I heat with our forced hot-air wood furnace and don't use the Mansfield. Before the Mansfield, I had a large pot-belly stove built in 1900 which was hard to control and wouldn't not hold a fire more than a few hours.
With the Hearthstone, I've noticed it's hard to get going on mild days unless wood is good and dry - and NOT one-year old oak or hard maple. Sometimes with days of poor draft, I start the fire with the door open a crack since the fully open air-intake is not sufficient. After maybe ten minutes, I close the door, draft gets going, and all is fine. As far as monitoring temps, I use the glass door clarity. When it's clear, I assume the fire is hot enough and that's worked fine. Good clean burns, very little chimney pipe build up, especially in cold weather even when the air-intake is turned way down. In general I'm impressed with Mansfiled over older "air-tight" stoves that were the rage in the 70s, or the stoves with few controls built earlier. It's sometimes harder to get going, but burns cleaner when turned down.

My Mansfield is hooked with 6" black pipe going up the ceiling straight - to a large ceiling-passthrough where it changes to triple-wall stainless for three feet. Then back to black pipe to a 90 degree bend and into a brick clay-flue 6" square chimney that starts upstairs. Kind of unusal nowadays, but my 1820 house has three chimneys built on top of chimny closets that all start upstairs.

 

[jpl1nh]

Tom, I'm curious what you mean when you say "load the stove". Do you cram it full, loose, 3/4's of a firebox full? It's got a pretty big firebox and an 80k heat rating. After only a couple of hours when you go to reload there can't be too much room for new wood in it. In my much smaller Keystone, when I really need lots of heat, I can keep topping the load off every 1 1/2 to 2 hours for up to 8 to 12 hours and I can keep my stove in the 500 to 600 range running it a bit more open. By the end of a day of doing that I have such a massive bed of coals I have to let them burn down so I can fit wood in it again. More typically I run a load and let it burn down to 250 to 300 stove top then load it full and start the cycle again. I would agree with others here that one year old oak is probably not as seasoned as you'd really like and may be part of your problem. Buy a few packs of the kiln dried stuff from the conveniance store and see if running that makes a difference.

 

[jpl1nh]

Just reading over the Mansfield operation manual, they suggest full primary air for a high burn and 1/2 primary air setting for a medium burn. Could you be damping down too low and actually running at a low burn? Are you getting good secondary combustion?

 

[Backwoods Savage]

Tom, the more I read this and think about it, your wood definitely has to be the problem. You won't get much heat from punky wood (we throw all that on brush piles) and oak needs a good 2 years to properly season. In order to keep burning what wood you have you no doubt will have to start leaving the draft open more. Again, a damper in your chimney would not help, but would hurt you. With not so good wood, you need all the draft you can get. To keep more heat in all you need to do is close your draft, but with poor wood, you can not do that.

I keep thinking about how it is not that cold in your area and you should be baking with that stove. Believe me, you will when you get some very good wood. You will get a lot more heat from each log and will not burn as much wood either. There will be a world of difference in how that stove works depending upon the fuel.

Someone asked if you are getting a good secondary burn. My guess is that you are not getting any.

 

[tbrickner]

Thanks again for the replys.

You all may be right. Maybe my wood hasn't dried long enough. Would you say 2 yr minimum for the hard wood?

By the way jpl1nh your description of the way you load is similar to what I am doing except I am letting it burn down quite a bit. I am typically loading to within an inch below the secondary burn jets with 2-3" diameter wood for my first break in hot fire for coals. Next I will load with 2-3" plus some 4-6 inch wood on top for my second burn. I am getting a good secondary burn every time but like you have to load about every 1 to 1-1/2 hours to keep it at that 500 deg range. I will also end up with a lot of coals left over which I mix up and then burn down with my intake full open. Typically I just get about 250 deg F with the coals just burning and air intake full open.

I am wondering if I use smaller splits in the 2"-3" range If I would get a hotter burn due to the better surface area exposure. I am afraid with the 2-3" diameter splits I wouldn't be able to sustain a long burn as I would with a 4-6" diameter split. Am I wrong on this, will the smaller diamter splits last as long as the larger diameter ones If I load the stove up?

I thought that I would get more ash and less 1" pieces of coal with a hot burn. Is there a reason the wood doesn't burn down all the way into white ash?

 

[Backwoods Savage]

You will get hotter burns with smaller splits and with your wood I'd recommend you try it. But you will still get coals and probably more because of not totally seasoned wood.

The reason the wood doesn't burn down as well is it is not totally seasoned. Sorry to keep harping on this but it is just one of those facts of wood burning that we all have had to learn.

 

[tbrickner]

Thanks Backwoods savage:

This makes sense now. The moisture in my wood would draw away any usable energy to evaporate the water out of the wood leaving me with the incomplete burning of the coals.

This has to be what is happeing. Thanks so much, I didn't realize it takes up to 2 years to get a dried set of hardwood. I'll take everyones advice and invest in a few store bought logs to verify this and see what type of coals are left.

You folks have been fantastic.

Thanks agin for all your wood wisdom,

Tom

 

[Highbeam]

The Mansfield is rated as follows:

80,000 BTU/hr
1800 - 2500 sq. ft.

You wrote:

"On a cold night here in maryland we may get 20 deg F weather and I need to keep the stove arround 475 to 525 to keep the house warm. I know people use these stoves in Minnesota and other really cold areas where they are at temperatures in the -20F range why can’t i heat my house in the 20+F range. My house is 2400 square feet area that I am heating with 10 ft ceilings if this may help. I typically can heat the house between 66 to 71 deg F between 20 to 30 deg F outside temperature."

The SF figure assumes normal ceiling height of 7-8 feet so your 10 foot ceilings mean you need even more stove than the ratings offer. The mansfield is on the edge of being too small for your needs even if you are an expert woodburner and have excellent firewood. It is not easy to run a soapstone stove at max output all of the time since the stove has a very low maximum temperature and once it falls a couple of hundred degrees it doesn't make much heat.

Good luck in getting the most out of your stove. Please don't be too disappointed in the stove if you can't get the job done on those cold nights.

 

[FDUTTON]

Tom, I'm burning 2 year season oak, my normal process is, load the stove in the morning on a hot bed of coals (stove temp around 300*) I leave the primary air open all the way while I get ready for work (about 45 minutes) then before I leave (7:15)I'll put whatever I can fit in the stove and turn the air off.

When I get home I fill it again, dump the ash pan and leave the air open. If it is cold out (teens) I'll add a few splits and then before I go to bed (about 11:00) I'll fill it up with large splits and turn the air off. I have been doing that same process for 4 years or so and it has worked great. When I'm home to keep an eye on the stove temp it will be between 350* and 550* for hours with out touching it.

Over the years I have burnt some wood that was wet and like others have said it does not burn real well. I would get my stove burning good with a nice bed of coals and then mix the 1 year old wood with the 2 year stuff and it burned great.

I only put a few splits in this morning because it was going to be 50* today and at 5:00 I put a few more in (stove temp 300* all day) In a few minutes I will load it up for the night and start the process over in the morning. This is the best stove I have ever owned, it heats my home (about 2000sqft) with no problem at all. We will see how it does when I finish my upstairs (about 1000sqft). My chimney is about 16' double wall stainless, straight up. I believe when your wood is good and seasoned you wont have a problem. Good luck

Frank

 

[tbrickner]

FDUTTON:

Thanks for the detailed description of how you load your stove. This was very helpful to me. I loaded some smaller dried pieces of wood 2-3" diamter and got a good heat out of the stove as well as a low amout of coals when the unit cooled down to 300 F.

I wanted to ask what size splits you use to get the hot bed of coals ? (1-3"? Square/round?)
When you load on the hot bed of coals for the overnight burn do you load the bottowm with 1-2" diameter splits and the top with larger diameter splits 4-6"? What way do you load the stove front to back layout or left to right or do you create a front back left right mix stacking them in the stove. I hope this makes sense. Basically how do you arrange your wood when loading and what size do you use.

When you load before work and come home do you find you have a lot of coals left over or do you have a good bed of fine ash left?

I appreciate your help.

Tom

 

[jdemaris]

FDUTTON:
When you load before work and come home do you find you have a lot of coals left over or do you have a good bed of fine ash left?

I'm not FDUTTON, but here's my input anyway. My Mansfield always burns very clean, pretty much just pure ash and no coals or clinkers left over as long as I don't last ashes build up too high. I never use small splits, just big pieces of red oak, hard maple, ash, cherry, etc. Hasn't made any difference on how I stack it, just needs good dry wood, that's all. When being used, I fill it as full as I can and shut all the way down when we all go to bed. I have found one or two old maple syrup spiles and chunks of barbed wire now and then, but that's it.

 

[Highbeam]

Ha! I just found some barbed wire in my ash bed yesterday. About a 6" long section.

I have begun just putting the big wood on and letting the fire smolder until it eventually ignites into fire. I know it isn't the cleanest way to burn but I have found that as long as there is a good bed of hot coals beneath the load of big firewood, it will eventually ignite and burn clean enough to keep the glass clear even with the air all the way shut. So yes, stuff it full and close it down, go to bed. With good wood, I haven't been able to kill a fire all the way dead.

 

[FDUTTON]

FDUTTON:

Thanks for the detailed description of how you load your stove. This was very helpful to me. I loaded some smaller dried pieces of wood 2-3" diamter and got a good heat out of the stove as well as a low amout of coals when the unit cooled down to 300 F.

I wanted to ask what size splits you use to get the hot bed of coals ? (1-3"? Square/round?)
When you load on the hot bed of coals for the overnight burn do you load the bottowm with 1-2" diameter splits and the top with larger diameter splits 4-6"? What way do you load the stove front to back layout or left to right or do you create a front back left right mix stacking them in the stove. I hope this makes sense. Basically how do you arrange your wood when loading and what size do you use.

When you load before work and come home do you find you have a lot of coals left over or do you have a good bed of fine ash left?

I appreciate your help.

Tom

No problem Tom, When I load it up for a overnight burn (or all day) I will put in about 5 or 6 6" to 8" splits (12" round split in half about 18" long) and if its really cold I'll slide a few smaller pieces in, if I have the room. I have found that if I rake the coals around and empty the ash tray every night I get very fine ashes on the bottom and nice coals that dont fall thru the grate (I leave the grate open), but if I dont empty the ash tray every day, the ash will build up and the fire will not burn very well.

If the coals are not going the way I want them to, I open the ash door and get them good and hot (about a minute, I know your not supposed to, but I keep a eye on it) A few years ago I would load the wood front to back and that was because the wood was smaller (I had 2 cords left over from my old Hearthstone II, it was very small) Then one day I was helping a buddy split wood up in P.A. and he told me I was splitting the wood to many times, just split it in half. The rounds were about 12" to 14" and I was making 4 splits so I just split them in half. His family has been doing it that way for 100 years, the wood was great, very clean and dense, I think it was ash.

They had about 50 acres of dead standing trees, no bark and pretty much seasoned, sorry I'm getting off the subject. I load my stove from the left to the right, but if I have room I will slide a few smaller pieces on top (front to back). Good luck

Frank

 

[tbrickner]

Frank:

So you load up a 6 to 8" split over hot coals and that is it. My wood definitey needs more seasoning.

By the way do you just put the splits on the hot coals and cut the intake all the way closed or do you load the splits, open the intake full open to catch flame and then turn down the intake air. If I read your other post correctly you load with the splits with intake full open for 45 minutes then cut it back to closed before going to work or going to bed at night. What is the exact detail on this?

Did I read your post right? Did you say you leave the ash grate open while you run your stove?

I unload my ashes with my ash shovel from the front when the heat is down. I find the ash pan a pain but if I can do what you are saying and leave the ash grate open I'll do the same thing you are doing.


Thanks again for the detailed explinations.

Tom

 

[swestall]

Try leaving the stove open almost all the way (maybe just 1/4 shut) for a whole load just to see how it does. Then try leaving it that way for about an hour, then shut it down to about 1/3 and see how that goes. For coals, try opening it all the way and just put on a small piece or two every few hours to burn the coals down. The more open you leave the draft, the fewer coals you will get.
These stoves like to cruise at 450-550, you can get them up to 600 but you have to work at it to keep it there. As others have said,a lot easier with really dry wood. You don't want this stove much hotter than 675 and 700 is tops.
You will also notice that the colder it is, the better the stove will work for you.
You have to burn the wood to get the heat, but the secondary burn boost the output. You will find that the secondary burn starts at about 1/2 close. All the way shut will give you a longer burn, but at 400-450. (depends on what your high temp is when you shut it down)
It takes quite a bit of getting use to the Soapstone. I think folks that never had a steel or cast stove might get use to it easier because they have no habits to change.
I am going to try the damper next year just to see what effect it has, some say it holds more heat in. But, you might need a great draft for that to happen. I also want to see what happens with the draft more open and the damper somewhat closed. I think that's kind of "advanced soapstone" operation. We'll see.