Hearthstone Mansfield not hot enough

[mopfoot]

We just installed a Mansfield and the hottest I've been able to get it is 400 but usually it only gets to 300-350 and only for a short period of time. How can I tell if secondary combustion is occurring? Any tips on maintaining high temps?

- The thermometer is placed on the center stone next to the stove pipe.
- Dampers fully opened
- Coals red to almost white hot
- 30' Stainless chimney with pair of 45s
- outside air kit installed
- Fuel is unsplit 6" juniper seasoned 3 years with mix of fir
- looks like gasses emitted from the pipes on top are igniting in certain sections
- no visible smoke from the chimney
- when I turn blower on, surface temp drops to 200 or lower

 

[mikeathens]

SLC, it takes a while to heat these babies up. Mine will heat up to about 400-500 and stay there for a while. I usually reload the stove at the 200 to 300 point. Do you have a chimney thermometer? If I want the stove to get above 500, I keep the air control set to where the chimney is 600 to 700.

If this is your first experience with a wood stove, or first experience with a soapstone, keep at it. The soapstone can take 3 hours to get up to temp sometimes.

EDIT: Reread your post...if you're not seeing smoke from the chimney, you're likely getting good secondary combustion. Most of the time, you should see nice "ghost flames" dancing at the top of your firebox around the burn tubes.

EDIT 2: don't have experience burning juniper or fir, but I believe these are relatively low Btu woods, which would make sense that you're not going to get as hot for as long as using oak or ash or other hardwoods.

 

[edthedawg]

"Dampers fully opened" sounds like the problem. You need to run it wide open to fire up a reload, then after 10-15 minutes, with a good hot fire going, back it down about halfway. Then after a few more minutes, back it down to about 1/4.

Try that and tell us how it works...

If you're not seeing secondary flames on the tubes, it's not happening. It sounds like you are sending all your heat right up the flue, instead of heating the firebox and surrounding room w/ it...

 

[mikeathens]

Nice, Edthedawg. I missed the primary-air-full-open comment.

If you don't have a chimney thermometer, get one. If you are leaving the primary air full open the whole burn, you are gonna see some scary flue temps.

 

[edthedawg]

OP also says "dampers" which makes me wonder more... is there a flue damper installed? it may be recommended (30' is the max height for a Heritage - I don't know what the mansfield manual says) and would probably do a great deal of good to reduce the draft further, if that is pulling harder than the primary can control. I know lotsa folks say "they aren't needed on today's EPA stoves...", but I will gladly swear up and down that we would never be able to get the heat we do without ours...

One final concern - is this a NEW Mansfield? or an old/used one?

 

[wellbuilt home]

Hi , CLS I had the same problem . When the secondaries lite up you will feel like you are sitting next to the sun. The whole top of the stove will be a blaze . I don't know how juniper burns but 6" un split logs don't burn to good in my equinox . I have been using one large log and then filling the fire box full with 2x6" splits . I have a 30'+ chimney and could not get my stove hot with out a damper in my flue . It seems that the HS stoves can be over fire when the fire box is full of coals and you pack it full of wood for the night . The temp creeps up while your sleeping over time . My temps shot up to around 550 last night and i killed the air intake to cool it off. Most of the guys like a flue thermometer also . John

 

[mopfoot]

Wow! You guys are fast. I didn't expect so many quick posts.

Yes, I do have a flue damper and have experimented with it a little. I can close it almost completely and the fire will continue to flame (and I hear the exhaust being sucked through the crack). I don't keep it that way because I'm not sure that it's safe. Any tips on how to determine the right amount to dampen the flue would be appreciated.

I'm a little confused about the primary air control. I assume that the more air it gets, the hotter it will burn. Why do I shut it down to get hotter?

Juniper is a fairly soft wood so I expect the burn cycle to be shorter but just as hot. Let me know if that's an incorrect assumption.

 

[mikeathens]

Make sure you read your manual...the primary air control is located under the door, to the left. You use this to control the rate of burn (the amount of air getting in). All the way to the left, it's full oepn. All the way to the right, it's closed all the way. If you leave it open all the way, all the time, you can A) overfire the stove, B) overheat your chimney, C) waste wood. Anyone want to add anyhting else?

As stated, when you're up and running, most of the time you'll run at 25% air. If this won't control your stove, then you can use the flue damper in tandem.

From my experiences, during a steady burn , my flue is at 400-600 and the stove is 400-500. I open the air a bit more to keep the chimney at 600-700 in order to heat the stove up more.

I think I rely on my chimney probe more than others, but I think it is a really good indicator of how the stove is performing...

 

[edthedawg]

I get the best performance w/ the flue damper FULL SHUT. Granted, this is a damper plate that fits loose inside the 6" single-wall pipe, and has like, 4 holes in it, each about 1" dia... So it'll never shut the flow down completely, but you can definitely hear it slow things down. next time I crack this pipe open again, I will seriously think about putting in a more fully closeable damper plate.

it is totally safe to run it like this.

The primary - assuming Mansfield ~= Heritage function - pumps its air directly up the front bottom center of the stove and into the bottom of your fire. It's a great little power-blast for refiring from a hot coal bed - that's the time to keep it wide open. Once your fire is going, you don't need to be blasting it with combustion air, so you crank this down and slow down your burn.

I'm assuming you are seeing really tall, kinda wind-blown flames in the firebox? If you are, then (with such flames happening) try closing the flue damper almost all the way (if not completely - listen for the "intake roar" and how it changes w/ the damper - you should hear it noticeably "slow down"), and closing the primary control til its about 1/4 of the way from closed. On the Heritage the primary lever moves about 4", with full closed being all the way to the right. so i'm talking about leaving it at about 1" away from the far right stop.

Your secondary is always wide open. You cannot modulate it without dampering the main intake on your OAK. Your fire will get plenty of combustion air, even with the primary closed. We run our overnight and at-work daytime fires w/ the primary and flue damper both full shut. maybe a 1/32" nudge open on the primary if the fire is being stubborn and i have to leave, but probably no coals 8 hrs later if i do that.

One final caution - WATCH BOTH FLUE AND STOVETOP TEMPS. I'm giving you recommendations to (hopefully) really heat up the stove - you risk overfiring it if you're not careful, especially w/ the good seasoned wood you appear to have. Open your damper and/or primary if you feel the stove is running away from you, but don't under- or over-fire the chimney either and risk creosote buildup there.

Good luck!

 

[edthedawg]

If you leave it open all the way, all the time, you can A) overfire the stove, B) overheat your chimney, C) waste wood.

(A) - not really - maybe a local hotspot or two, but he's complaining that the stove is not hot enough w/ it full open. We've had a lot of posts here recently w/ people complaining about cold stoves when running w/ the primary full open, and it typically is corrected by backing down the primary. So if wide open = cold stove... how would that overfire the stove again?

Overfire the chimney (B)? yes. waste wood (C)? absolutely...

 

[mikeathens]

Well, I'm speaking from experience...If I leave mine all the way open, my chimney will quickly be >1000 F, and my stove temp will quickly be >600 F. No kidding. I have been wondering if my stove suffers from poor draft, which might explain that. Anyhow, it can happen.

 

[edthedawg]

ah - great data point! I have been looking for field experience on low-drafting flues vs high-drafting flues. Did the Heritage you used to have operate the same way for you? How high is your chimney again?

(I almost asked "how long is your pipe?" but you'll note the restraint i exhibited...)

I'm surmising that:
- Long flues = high draft = cold stove w/ primary full open.
- Short flues = low draft = WAY too hot stove w/ primary full open.

Wonder where "Happy Medium" is in that equation... we may never know (those folks don't come here to complain!)

 

[karri0n]

Ed, it seems this is stove dependent. I've overfired my IR pretty badly by leaving the primary full open for extended periods. I've never once seen it go up by backing down a bit, but this is different for all stoves, especially since heat transfer through stone will take longer than through cast iron.

SLC burner, As to your question about why the primary would lower the temp, it doesn't look like that really got addressed. It's a good question, as it's counter-intuitive. Basically, with the primary full open, you are feeding a lot of air into the stove, through a very small opening. This creates a large amount of air velocity. this air rushes over the fire, through the airwash, over the baffle, and up the flue. While it does feed the fire more than if you had the primary closed, the velocity is the issue here. A soapstone stove especially requires the stone to be in contact with heat for a longer period. as it is now, the air is rushing right past the baffle and right underneath the stovetop. If you close the primary down, it will slow the air velocity and keep the heat in contact with the stove surface for a longer period, and transfer more of the heat into the stones and therefore into the room before it goes up the flue.


On a side note, Ed, why do you keep your "before" pic as your avatar? Until your recent thread, I just thought you had an insert. Come on , we wanna see the stove porn!


edit: Not sure about your equation ed. I have about a 30' flue in an interior fireplace, and my draft is like a vacuum cleaner with a cold chimney. If I take the elbow off, I can shoot a piece of paper up my cold chimney. I think it's more of a heat conductivity of the material issue.

 

[struggle]

SLC,

The best thing you can buy right now is a probe thermometer for your flue pipe above the stove. It will give you all the feed back needed to determine how much heat you are losing going up the chimney.

Chimneys over I think 25 feet are considered to high and do require a dampener like you have mentioned having.

(broken link removed to http://www.elitedeals.com/cpf-41120.html) you will not regret getting a probe thermometer, it is one of the best tools for this stove. It will make dialing in the stove a cake walk. All you have to do to install it is drill a 0.25" hole in the pipe and your done in five minutes. Using four minutes to get the drill and put it away.

 

[edthedawg]

Good point. The OP note of "white hot coals" kinda confirms this. That's what I was talking about above...

"It’s a great little power-blast for refiring from a hot coal bed - that’s the time to keep it wide open."

if you blast those coals w/ fresh air, they'll stay white hot like that...

 

[mopfoot]

KarriOn - Good explanation, thanks!

 

[edthedawg]

On a side note, Ed, why do you keep your "before" pic as your avatar? Until your recent thread, I just thought you had an insert. Come on , we wanna see the stove porn!

The real reason - i LOVE that tile job. And I only got to look at it finished like that for about 4 days. I did it the week before our stove install. I built that flush hearth as an expanded restoration of the original, 100+ yr old hearth which was cracked all to heck, and way too small - after looking at it and pondering just what to do for over 10 years.

THEN i discovered that we had still underbuilt it due to both the R-value needed and the minimum clearances required behind the stove. Oops. RTFM! Grrr...

No more tile available. Way oops.

Very quickly designed and built the new one over it. Hate the new one. HATE it. Can't wait to destroy it and re-tile w/ the correct pattern this summer. I *MIGHT* be tempted to rip out the flush one and rebuild it to the proper size and R-value, knowing what I know now... I SO wish i had found this site before i did...

oh well, live and learn...

 

[karri0n]

Well it IS a nice tile job. I didn't think the other one looks half bad either, but we are our own worst(best?) critics.

 

[mopfoot]

I'm going to read between the lines of the posts and make some statements, please let me know if I am understanding correctly:

- Flue temp should be 400-600 and the best tool to moderate it is the flue damper
- Primary air of course trumps the flue damper in that it can cut off oxygen and moderate the overall burn rate
- Both can control velocity and slower is better as long as combustion is happening

Anything else?

 

[karri0n]

Best tool is the primary air, not the flue damper. Flue damper is kinda a bonus feature, but once you get the stove going and the primary phased down, close it off to extend your burn even more. Bear in mind that *most* epa woodstove burners do not have a flue damper. 85% of the time your primary air will be closed most or all of the way. It should really only be full open if you have stubborn unseasoned wood or you are getting the fire going after a load/reload.

Flue temps will be much higher during startup, and will be much lower once you close down the primary. I would keep my eye on stovetop temp more often than flue temp, since it's the device, not the flue, that is heating your home.

 

[mikeathens]

ah - great data point! I have been looking for field experience on low-drafting flues vs high-drafting flues. Did the Heritage you used to have operate the same way for you? How high is your chimney again?

(I almost asked "how long is your pipe?" but you'll note the restraint i exhibited...)

I'm surmising that:
- Long flues = high draft = cold stove w/ primary full open.
- Short flues = low draft = WAY too hot stove w/ primary full open.

Wonder where "Happy Medium" is in that equation... we may never know (those folks don't come here to complain!)

OK, ed...I have a "flat" roof (not exactly flat, but pretty damn close). Let me try to remember this from memory...4' single wall connector into metalbestos SS; There is 12' of this class A. Of the total chimney height (16'), there is approximately 10' outside.

I have some factors working against me: I live in a narrow valley with lots of close trees (draft redustion). The majority of my chimney is exposed to outside temperatures, resulsing in reduced internal temps (more draft reduction). I've yet to actually accurately measure the draft, but I suspect I really don't want to know since I can't don anyhting about it...and leave my pipe length out of this.

I am planning an addition in the next couple years that will replace the falt roof with a 10/12 pitch gable, and give me a lot more chimney height, as well as keep most of enclosed in an insulated area.

 

[edthedawg]

SLC,

https://www.hearth.com/econtent/index.php?ACT=24&fid=2&aid=18673_yUkTPI4Wn8tVBjAz3drk&board_id=1

I have no idea if that url will work - look for jeffman's "Cracked stone on Tribute" thread, page 6 - shows the Condar probe thermometer. Struggle's post above links to the same thermo. You want the flue gases to be about 600F - not running consistently over 800. Not sure if you have single wall or double wall or what, but if single-wall, you can approximate the flue gas temp as ~2X the metal surface temp.

metal temp != gas temp


Primary moderates overall burn rate, but its sensitivity is GREATLY enhanced by having the flue damper in place. Without my damper, the primary effectively gives me on/off control and that's it. With the damper, i get much finer control.

 

[mikeathens]

I'm going to read between the lines of the posts and make some statements, please let me know if I am understanding correctly:

- Flue temp should be 400-600 and the best tool to moderate it is the flue damper
- Primary air of course trumps the flue damper in that it can cut off oxygen and moderate the overall burn rate
- Both can control velocity and slower is better as long as combustion is happening

Anything else?

Keep in mind my flue temp numbers work for me. these are my guidelines...maybe a starting point for you.

I would start by controlling the stove with the primary air control on the stove. As suggested, maybe set it at 25% open once you get a nice fire going. Keep note of your flue temps and stove temps. If you still are experiencing short burns with low stove temps, play with the flue damper to see if you can slow down your burns and keep more of that heat in the firebox.

I like to periodically check the stack for smoke. If you have a nice show going in the top of the firebox and no smoke, you're probably in business. BTW, those flames from your secondaries should slowly dance around - they shouldn't look like a raging campfire or boiler fire.

 

[mopfoot]

Looks like Condar has a store on eBay. I just bought a probe.
http://members.ebay.com/ws/eBayISAPI.dll?ViewUserPage&userid=woodstovepro

Thanks for describing the dancing secondary flames. Mine were more like a boiler fire.

 

[karri0n]

Remember the mantra: "the primary is your friend". You will probably be pretty shocked at how long a fire lasts in that beast once you get pretty good at working the primary.