Masonry stoves appear to be more effective - why aren't they more popular?

[rashomon]

I mostly love my new(ish) Green Mountain 60. But as I've been learning about the benefits of thermal mass, all while shoveling in more wood to keep my stove rocking, I'm wishing I went the route of a Masonry stove. They keep warm all day even with just an few hours burn in the morning. Repeat for warmth all night. Therefore they use way less wood if that's important to you.

I'm also seeing they aren't that expensive!? They capture way more heat to be used for warming your home. They are inherently super efficient, and I just learned this also made them exempt from EPA testing!

I'm not sure what a "kit" entails, but here's one you can buy for under $9000 that includes an oven!

I love this company's but they seem to out of business! Anyone heard of Biofire Inc.?

This guy sells plans look seem very affordable.

People here have pooped on Rocket Mass Heaters in the past which are basically the same thing. Paul Wheaton over at Permies has put great effort towards awareness of them (for a number of reasons) but he's mostly rejected. Interesting because no can disputes how awesome Masonry Heaters are, some here putting them on the highest of pedestals.

 

[stoveliker]

Because of the space they take and support they need (mass).
Second, yes, they are very efficient. Maybe even 90%.

But your 75-80% efficient stove (I presume) is not far behind.
You will still need the BTUs you need now to keep your home warm. Rather than spreading them out as you do now, you release them at once from the wood but then store them in thermal mass to let them in your home over time.
Your stove keeps the BTUs stored in the wood until it burns. A masonry stove keeps it in the mass until it leaks out - and note that you don't have much control over that: once fired it's done. Physics takes its course.
Your stove you can change the setting halfway through a burn to adapt the BTU release into your home.

So the wood use gains may be there but are not all that large. The controllability is less (no adapting once fired; you're forced to live with the heat release as it goes).

I like them though. Nothing wrong with them.

 

[blades]

Masonry heater systems are very costly to install , do not lend themselves well to simple installation in an existing home. I am not talking about prefab units ( most of the time these do not do much to heat a home) The average wood stove cost including the stove & flue can be less than $3000 up to $ 6000 or even a bit more. It all depends on stove cost and flue length Pellet stove are more just because the stoves cost more. Your price of $ 9000 seems way low considering labor costs, and is not something the average home owner could accomplish on there own.
Rumford style masonry systems are quite involved. Even the rocket stoves you mention combined with a large physical mass get involved and pricey. There are 4 rocket stove based designs that I know of but none of these include the huge mass for the exhaust heat transfer system . they relie on the mass of the stove itself just like convention wood stoves.

 

[rashomon]

Hi Stoveliker, those are all great points.

In my case my home is always cold at least 4 months of the year. We have lots of inefficiencies in our home construction. I would probably use a Masonry stove twice a day for those 4 months just to get our home in the ball park of where my normal stove can take over and be adjusted for the additional heat I need.

I feel it's ideal for our cold basement (with open staircase to the main floor) where I would otherwise need to keep an eye on a stove throughout the day adding wood. We never use the basement because the only way to warm it is baseboard electric. The floors on the main level are always cold. Insulating them would probably cost as much as a masonry stove.

I could burn more gas, but honestly, I don't trust, respect, or endorse the petroleum industry and can't wait to get rid of that utility--the sooner the better.

Blades, outside Denver my Green Mountain 60 cost $6200 including flue and install, and my flue went straight up. You're probably right about labor costs adding a lot to masonry stoves. It's something I would love to help or do myself because I easily spend more labor every summer with other projects around the property. Which are the 4 Rocket Stove designs you speak of? All the designs I know of include the mass. I know the Liberator is a stand alone unit, but the only reason that appeals to me would be if I hooked it up to a mass. Especially considering you can't get the tax credit with it.

 

[stoveliker]

If it's always cold, then indeed you need additional heat, or reduce heat loss. Insulating and air sealing seems like a very useful approach then - in particular if you can do things yourself. First the attics: remove all insulation and air seal all penetrations (ceiling lights, electric wiring) with silicone (nonflammable), and seal gaps between top boards and drywall with foam (spray can).
Then either put insulation back and add, or only use new. I did this, going up to r-57. It cut my heating bill by more than 50% (before I had wood heat).

Go around with caulk at your window frames. Seal outlets in walls etc.

If your basement is not insulated, adding heat there is going to be hugely inefficient.

I'm not sure adding heat input with a masonry stove is going to be the most (wallet) efficient way...

 

[mellow]

Some Masonry heaters can be had for around $7k:

Products | Hestia Stoves

Soapstone stoves from Hestia Stoves

www.hestiastoves.com

 

[rashomon]

...Insulating and air sealing seems like a very useful approach then ...

I should have described it better. I have no attic-- instead cathedral ceilings. We have tons of giant windows (yes all have cellular shades and window coverings). The basement is finished with R-19 in 2x6 framing. I've long insulated outlets. Windows aren't leaking.

When previous owners redid the cedar siding they did not add a housewrap (Tyvek or other). The entire house is covered in only OSB with plenty of air gaps. They simply burned more gas. Fixing that is not an option until we change the siding which will be decade(s) from now.

My cousin is an energy auditor. To fix even part of the problem would cost more than a masonry heater. Just this winter I did the insulation in a drafty B-vent (decorative) fireplace. I added XPS foam to the foundation. It's been a piecemeal process.

 

[rashomon]

Some Masonry heaters can be had for around $7k:

Products | Hestia Stoves

Soapstone stoves from Hestia Stoves

www.hestiastoves.com

That's a lot of soapstone! My GM60 is lined with soapstone but this is another level. Not a bad option, although the other kinds of masonry heaters I mentioned weigh over 5000lbs on the low side (guessing). So not sure how these compare.

 

[stoveliker]

Given that insulation situation, a low maintenance steady heat output source (possibly in the basement - for that look at how to move the heat upstairs, see link below) could help.

A (high mass!) masonry stove could help with that.
Or you could go with a Blaze King King model. Not everyone's taste pleaser visually, but going 40 hrs on one load and not sacrificing the control (mid-burn) you have versus a masonry stove (mid heat-release phase), could be useful.


Generally, though, I would note that most places where masonry heaters do work nicely are places that are built around the masonry heater. Not the other way around.

Surely I'd ask advice from an engineer as you'd be adding a ton of weight in one location.

Moving heat from basement

How many people heat their house with a wood burning stove that’s in a uninsulated. Basement rim joists that are insulated. beside the basement walls ?

www.hearth.com

 

[rashomon]

Given that insulation situation, a low maintenance steady heat output source (possibly in the basement - for that look at how to move the heat upstairs, see link below) could help.

A (high mass!) masonry stove could help with that.
Or you could go with a Blaze King King model. Not everyone's taste pleaser visually, but going 40 hrs on one load and not sacrificing the control (mid-burn) you have versus a masonry stove (mid heat-release phase), could be useful.


Generally, though, I would note that most places where masonry heaters do work nicely are places that are built around the masonry heater. Not the other way around.

Surely I'd ask advice from an engineer as you'd be adding a ton of weight in one location.

Moving heat from basement

How many people heat their house with a wood burning stove that’s in a uninsulated. Basement rim joists that are insulated. beside the basement walls ?

www.hearth.com

Great advice. And the link confirms what I've been thinking, using the basement itself as thermal mass and let the heat rise-- ultimately warming the main level's floors and continuing up our large basement open staircase.

The weight is another reason why I thought the basement, it would be awesome to have a masonry heat on the main floor, but ultimately need something for the basement and like you mentioned earlier I can better control the normal stove on the main floor anyhow.

But.... yes... I do see the best benefit of a masonry stove being when you can build your house around it. We have a B-vent in the basement with decorative rock wall. Probably makes sense to place a stove there, but would need to pipe up to the roof. The rock wall is nice but more a facade than thermal mass. A rocket stove would be a great trial, very affordable and I have the time and energy to build, but it's not approved for our county so not a fan of it.

 

[bholler]

I mostly love my new(ish) Green Mountain 60. But as I've been learning about the benefits of thermal mass, all while shoveling in more wood to keep my stove rocking, I'm wishing I went the route of a Masonry stove. They keep warm all day even with just an few hours burn in the morning. Repeat for warmth all night. Therefore they use way less wood if that's important to you.

I'm also seeing they aren't that expensive!? They capture way more heat to be used for warming your home. They are inherently super efficient, and I just learned this also made them exempt from EPA testing!

I'm not sure what a "kit" entails, but here's one you can buy for under $9000 that includes an oven!

I love this company's but they seem to out of business! Anyone heard of Biofire Inc.?

This guy sells plans look seem very affordable.

People here have pooped on Rocket Mass Heaters in the past which are basically the same thing. Paul Wheaton over at Permies has put great effort towards awareness of them (for a number of reasons) but he's mostly rejected. Interesting because no can disputes how awesome Masonry Heaters are, some here putting them on the highest of pedestals.

You have to be very careful believing all of the hype about things like this. Yes masonry heaters can be very efficient so can Rocket mass heaters. But that all depends upon the design construction and use of the units. A good woodstove will be almost as efficient and doesn't take a highly skilled person to install it at generally a very high labor rate.

The claims of massive wood savings just are not backed up at all. There is only a certain ammout of btus available in wood and an extra 5 to 10% of efficiency isn't going to save you the ammount of wood they claim.

One of the links claimed 3 to 5 hours of burn time for wood stoves. That is absurdly short. Most stoves on the market easily double that

 

[stoveliker]

My point was that the long steady heat is achievable with modern stoves too.
The BK King goes 40 hrs (at a low(!) output), their other models go 30 hrs at a low output. I have one, I reached 36-37 hrs (before the cat dropped out the active zone) on one 2.9 cu ft load of wood.

Of course, depending on your BTU need, you would have lower burn times (e.g. now, with nights in the upper 20s and days below 40, I get about 16-22 hr burns depending on how full I stuff the box, but bholler needs a lot more BTUs in his home so his burn times are quite a bit lower).

The thermal mass of the basement is a bit of a misnomer; yes it's a reservoir (of warm air and in my case a library, sowing station of my wife, and lego's of the kids...), but it's not that much mass. It's only helping with the stove "off" when the outside temps are so high (45 or so) that I really don't need a lot of heat; the little bit it can still supply then is enough to keep the home warm a day longer.

(Regarding your rock wall thermal mass: any efficient thermal mass should have insulation between itself and the outside world - which is why masonry fireplaces on an outside wall leak so much heat. Bricks heat up and radiate half of their heat inwards, and half to the great outdoors...)

In the end, you'd still be loading once or twice a day with a BK - as with a masonry stove.

My point of this is that if you want to "only load twice a day" - there are many, many stoves that can give you that, AND that give you the option to change the heat output mid-burn which is nonexistent for a masonry stove.

As bholler said, and I mentioned earlier, the efficiency is not that different. Maybe a bit better, but in my view the variability in wood quality, moisture content, weather outside, packing density in the stove etc. are likely washing out any measurable difference in efficiency of 5-10 pct.

 

[rashomon]

You have to be very careful believing all of the hype about things like this. Yes masonry heaters can be very efficient so can Rocket mass heaters. But that all depends upon the design construction and use of the units. A good woodstove will be almost as efficient and doesn't take a highly skilled person to install it at generally a very high labor rate.

The claims of massive wood savings just are not backed up at all. There is only a certain ammout of btus available in wood and an extra 5 to 10% of efficiency isn't going to save you the ammount of wood they claim.

One of the links claimed 3 to 5 hours of burn time for wood stoves. That is absurdly short. Most stoves on the market easily double that

I appreciate your thoughts. I believe the claim regarding massive wood savings are because the exit gas temps are much cooler (like hundreds of degrees cooler). So although the design does only have 5-10 (or maybe more) % burning efficiency, it's the efficiency of it's design (and use of thermal mass) which makes better use of the heat that's otherwise sent out the chimney. And it can do that thanks to not needing high exit temps because of the way they burn. That's just what I've learned.

Unfortunately my Green Mountain 60 does only get 3 hours of burn time (maybe more if you count coals slowly dying). I would love to have a load last 5 hours! Hearthstone does claik it offers 24 hours of heat, which might be the case in a test on Key West. That's a little joke I say regarding my hottub claiming to only use $200 of energy a year (yeah, right!).

So I believe there's stove out there with longer burn times. I unfortunately didn't know this when I bought mine. Do they have large fireboxes? Mine is only 2cu ft.

Stoveliker is echoing what you're saying though, so I do believe that's the case!

 

[stoveliker]

The efficiency of stoves is determined by measuring how many BTUs get released into the home/room, and how many got in. The rest goes out the chimney.
So the warm chimney is already accounted for when comparing (standardized tested) efficiencies. That's the 5-10 percent. There is no "additional efficiency" somewhere hidden there that can be claimed by masonry stoves.

Anyway, a 2 cu ft stove should last longer than 3 hrs. So something is awry here.

How full do you stuff it (pics)?
How tall is your chimney?
Do you have a flue probe thermometer in the flue above the stove? If so, what does it read?
What is the moisture content of your wood? (Measured after having a large split in the home for 24 hrs so it can reach 70 F ish, then splitting it in half, and measuring on that freshly exposed surface with the moisture meter pins parallel to the grain.)

 

[rashomon]

My point was that the long steady heat is achievable with modern stoves too.
The BK King goes 40 hrs (at a low(!) output), their other models go 30 hrs at a low output. I have one, I reached 36-37 hrs (before the cat dropped out the active zone) on one 2.9 cu ft load of wood.....

The thermal mass of the basement is a bit of a misnomer...

(Regarding your rock wall thermal mass: any efficient thermal mass should have insulation between itself and the outside world - which is why masonry fireplaces on an outside wall leak so much heat. Bricks heat up and radiate half of their heat inwards, and half to the great outdoors...)

In the end, you'd still be loading once or twice a day with a BK - as with a masonry stove.

My point of this is that if you want to "only load twice a day" - there are many, many stoves that can give you that...

As bholler said, and I mentioned earlier, the efficiency is not that different. ...

Hi, well everything that you and bholler have said does make me want to rethink my situation. I will look into the BK King for one.

When I said thermal mass for the basement I meant if I had a way to get my basement temps up to 80 (using a stove), since right now my basement is nothing but a heat sink.

Yeah, my rock wall facade is insulated behind it. That was one think I double checked when I fixed my leaky b-vent.

Regarding burning efficiency not being too different, what about the lower exit gas temps showing how masonry stoves make better use of the heat with no creosote buildup? I always assumed this was part of their attraction.

EDIT: I see your posted another comment. I'll answer that now!

 

[rashomon]

The efficiency of stoves is determined by measuring how many BTUs get released into the home/room, and how many got in. The rest goes out the chimney.
So the warm chimney is already accounted for when comparing (standardized tested) efficiencies. That's the 5-10 percent. There is no "additional efficiency" somewhere hidden there that can be claimed by masonry stoves.

Anyway, a 2 cu ft stove should last longer than 3 hrs. So something is awry here.

How full do you stuff it (pics)?
How tall is your chimney?
Do you have a flue probe thermometer in the flue above the stove? If so, what does it read?
What is the moisture content of your wood? (Measured after having a large split in the home for 24 hrs so it can reach 70 F ish, then splitting it in half, and measuring on that freshly exposed surface with the moisture meter pins parallel to the grain.)

Regarding the efficiency, please correct me if needed, but what I'm saying is less heat is wasted or "goes out the chimney". Are you saying the BTUs of the wood are accounted for and compared to the room? I've always heard the exhaust from mass heaters are much less because the mass absorbs the heat to be released later. Also, it appears (most?) masonry stoves aren't even able to be tested which is why they're exempt (although I'm interested in seeing the data from the Hestia stoves mellow posted to better understand this).

My wood is always pine, I live in a Pine forest with no shortage of trees I need to remove for fire mitigation. I have the details of my chimney in my signature line - Double-walled 6" pipe - Straight up from stove 18' total (10' exterior). If I stuff it absolutely full maybe it is over 3 hours. I often can't stuff it cause it's so hot with the door open and I don't have gloves. In another thread I did mention how I do get a lot of ash (compared to others that claim to only remove ash once every two weeks, or not at all which seems impossible). It's been 3 hours as I type this and I've only got coals on the bottom. For this load I've been burning medium-high, but admittidly in these cold months I'm definitely always higher than medium (and I know for this stove just 1/2" out from all the way in is already medium-high, even though high has another full inch of travel from there).

I do have a flue thermometer, and in my efforts to extract as much heat as possible I generally try to get it to 350-400 using my fan. Not sure if that's bad, but I asked about this in another thread.

Yes, some of my wood is wetter, and I do notice it. I live on a very steep hill and I've already exhausted the wood I seasoned last summer. But I have a ton of sticks under 5" that burn super hot. This summer a friend is going to help me winch up a ton of trees so I hope this won't be a problem. I admit that's a variable in my situation.

I imagine +7% moisture would take a hit regarding heat, would that affect burn times? I've seen some logs up to 15%, but those are rare.

 

[mellow]

You might want to check out the Hearthstone threads and read up on the green mountain 60 issues:

HearthStone

This forum is for discussions and information regarding Hearthstone Stoves

www.hearth.com

 

[stoveliker]

Regarding the efficiency, please correct me if needed, but what I'm saying is less heat is wasted or "goes out the chimney". Are you saying the BTUs of the wood are accounted for and compared to the room?

Efficiency ratings of wood stoves are precisely that: 100% of fuel goes in, 80% (in a good stove) goes to the room, 20% goes out the chimney.
That is the 80% rating. (or 70% for whatever the model is)
And that is what should be compared to masonry stoves (at 85%?).

So yes, for standardized (and independent!) testing, which is where the efficiency number comes from, the BTUs are accounted for.

Low exhaust temps can mean an efficient stove (if the BTU flow to the room is high; I can get low exhaust temps lighting a match in my stove - problem is that not many BTUs go to my room either, hence efficiency is a *ratio* ).

I've always heard the exhaust from mass heaters are much less because the mass absorbs the heat to be released later. Also, it appears (most?) masonry stoves aren't even able to be tested which is why they're exempt (although I'm interested in seeing the data from the Hestia stoves mellow posted to better understand this).

I can run my stove below 200 F exhaust temps...

My wood is always pine, I live in a Pine forest with no shortage of trees I need to remove for fire mitigation. I have the details of my chimney in my signature line - Double-walled 6" pipe - Straight up from stove 18' total (10' exterior). If I stuff it absolutely full maybe it is over 3 hours. I often can't stuff it cause it's so hot with the door open and I don't have gloves.

Chimney sounds not bad. Pine is fine, as you know.

In another thread I did mention how I do get a lot of ash (compared to others that claim to only remove ash once every two weeks, or not at all which seems impossible). It's been 3 hours as I type this and I've only got coals on the bottom. For this load I've been burning medium-high, but admittidly in these cold months I'm definitely always higher than medium (and I know for this stove just 1/2" out from all the way in is already medium-high, even though high has another full inch of travel from there).

I do have a flue thermometer, and in my efforts to extract as much heat as possible I generally try to get it to 350-400 using my fan. Not sure if that's bad, but I asked about this in another thread.

I don't know why you only get 3 hrs then... but I do not your stove. I see mellow above was helpful for that.

Yes, some of my wood is wetter, and I do notice it. I live on a very steep hill and I've already exhausted the wood I seasoned last summer. But I have a ton of sticks under 5" that burn super hot. This summer a friend is going to help me winch up a ton of trees so I hope this won't be a problem. I admit that's a variable in my situation.

I imagine +7% moisture would take a hit regarding heat, would that affect burn times? I've seen some logs up to 15%, but those are rare.

15% is fine too. Anything below 15% is great.
Once one gets above 15-20% one can notice the decrease in heat output, at least here.
I have run on 13% pine (in a 3 cu ft box) for 20 hrs.

If nothing is wrong with the stove (...) I think you just need more BTUs than your stove was made for. You need a bigger stove.
Even then, adding 50% capacity (2 cu ft to 3 cu ft) would in your mode give you 4.5 hrs... Which is ridiculously low.

Do you have high ceilings (windows)? Ceiling fan pushing down pooled warm air there?

 

[rashomon]

You might want to check out the Hearthstone threads and read up on the green mountain 60 issues:

HearthStone

This forum is for discussions and information regarding Hearthstone Stoves

www.hearth.com

Thanks, I've browsed before but it's been awhile!

Efficiency ratings of wood stoves are precisely that: 100% of fuel goes in, 80% (in a good stove) goes to the room, 20% goes out the chimney....

I can run my stove below 200 F exhaust temps...

If nothing is wrong with the stove (...) I think you just need more BTUs than your stove was made for. You need a bigger stove.

Do you have high ceilings (windows)? Ceiling fan pushing down pooled warm air there?

(Sorry, I don't know how you separated each point to respond to like you did for me) Also, thanks so much for taking the time today to respond to me. I know it's been a significant amount of time!

If the 100% BTUs from the fuel are accounted for, and the efficiency rating takes into account the heat that's wasted out the chimney, how do manufacturers make sure they aren't wasting valuable BTUs with hot exit gas temps thus giving them a lower score? I'm beginning to understand but still trying to reconcile the heat that goes out my chimney. Especially if you say you have 200 F ext temps!! I'm talking about temps at the ~18" above the stove flange where the flueguard goes. Everything I've read here, including the warming on the thermometer itself, says you need minimum 350 degrees, which is one of the reasons why I've been interested in the masonry stoves which claim to be much less (I'm assuming they don't waste the heat since they get fully combustion by design).

YES, I most certainly need more BTUs if I want to be more comfortable and not use gas. I'm looking at the Blaze Kings right now and particularly like "...our built in thermostat to control your heat output ..."! It looks like the King 40 is the only wood burner that offers up to 40hrs? That's important to me having been duped by Hearthstone's claim my GM60 has up to 24hrs of heat. I would love to set it and forget it in the basement for long lasting heat!

I do believe you're convincing me! And yes, there is a high ceiling near my stove. I can't say I've noticed a difference when I turn the fan on. Using an infrared dongle on my iphone (Heat Thermal) I noticed my ceiling tempertures went up with the fan on. I thought they should go down?! Here's photos, I could redo the experiment though.

 

[Prometeo]

It is clearly indicated on the epa.gov website many manufacturers indicate efficiency, the heat produced with a quantity of wood, and NOT necessarily the amount of heat that enter in the house, masonry stoves are more efficient exactly for this reason, they retain a lot of heat, and combustion is better, but the heat that enters the house is much lower.

 

[stoveliker]

Thanks, I've browsed before but it's been awhile!

(Sorry, I don't know how you separated each point to respond to like you did for me) Also, thanks so much for taking the time today to respond to me. I know it's been a significant amount of time!

If the 100% BTUs from the fuel are accounted for, and the efficiency rating takes into account the heat that's wasted out the chimney, how do manufacturers make sure they aren't wasting valuable BTUs with hot exit gas temps thus giving them a lower score? I'm beginning to understand but still trying to reconcile the heat that goes out my chimney. Especially if you say you have 200 F ext temps!! I'm talking about temps at the ~18" above the stove flange where the flueguard goes.

Sorry. I was not precise. i can run my stove with 200 F in the flue 18" above the stove.

Everything I've read here, including the warming on the thermometer itself, says you need minimum 350 degrees, which is one of the reasons why I've been interested in the masonry stoves which claim to be much less (I'm assuming they don't waste the heat since they get fully combustion by design).

Yes, because no one has 100% efficiency. Therefore, unburned stuff goes up the flue. To avoid that caking on the walls, you want zero water condensing there as that's what captures smoke, then dries out ,creating creosote.
So I *can* run below 200 F 18" above the stove, I try to avoid it.

YES, I most certainly need more BTUs if I want to be more comfortable and not use gas. I'm looking at the Blaze Kings right now and particularly like "...our built in thermostat to control your heat output ..."! It looks like the King 40 is the only wood burner that offers up to 40hrs? That's important to me having been duped by Hearthstone's claim my GM60 has up to 24hrs of heat. I would love to set it and forget it in the basement for long lasting heat!

I can't vouch for it being the only one. I can vouch for BK not lying with that. BUT again, it's at a low low output rate.
I don't remember the King model low rate, but for my stove (advertized 30 hrs, I got 36-37) that is with a heat output of not more than three and a half 1.5 kW electric plug in heaters.
Clearly you need more BTUs to heat your home, so you'd never run 40 hr cycles in the King model (unless it's a base load you do, with the other stove modulating it on top of that).
Generally, people forget that "longer burn times" equate "less heat output per hour" (given the same fuel amount).

I do believe you're convincing me! And yes, there is a high ceiling near my stove. I can't say I've noticed a difference when I turn the fan on. Using an infrared dongle on my iphone (Heat Thermal) I noticed my ceiling tempertures went up with the fan on. I thought they should go down?! Here's photos, I could redo the experiment though.

Not sure how to interpret the pics below, but is your fan pushing down the air (rotating clockwise, I believe) or pulling it up?

View attachment 324821

View attachment 324822

 

[stoveliker]

It is clearly indicated on the epa.gov website many manufacturers indicate efficiency, the heat produced with a quantity of wood, and NOT necessarily the amount of heat that enter in the house, masonry stoves are more efficient exactly for this reason, they retain a lot of heat, and combustion is better, but the heat that enters the house is much lower.

I'm sorry, but the *efficiency* given by independent (EPA) standardized tests is precisely that: the amount of heat coming in the home versus what goes out of the chimney (or, equivalently, the amount of heat coming in the home as a fraction of what the BTU content was of the fuel load).

Masonry stoves are indeed very efficient. Maybe even a little more than modern stoves. (My contention is that it's only a little more, and that it's not worth giving up *control* of that heat release rate for that little increase in efficiency - no knob to turn on a masonry stove to "turn it down" as I can on my stove.)

 

[stoveliker]

EPA Overall efficiency is the percentage of heat that is transferred to the space to be heated when a load of fuel (e.g., firewood, pellets) is burned.

The "Combustion efficiency" is of little value. Mfgs advertize the overall efficiency - as that is what you want to know (how much heat do I get for a certain amount of wood (i.e. work, or $$)).

 

[bholler]

I have to add masonry heaters need to stay above the condensation point until the exhaust leaves the chimney as well or they will have creosote issues. Believe me I have seen it in poorly designed ones or ones using wet wood. No matter what claims are made they are not achieving complete combustion

 

[mellow]

The King40 requires an 8" liner. Something to keep in mind.

I regularly got 12 hour burns with my BK sirocco 25, and that was with useful heat.