Getting heat out of the fireplace

[sean donato]

Don't worry, I am not but sore or defensive. But I am skeptical about efficiency claims. I have tried to research how efficiency is measured, and the methods are clear enough, but they do not explicitly state the conditions. It is my belief that even with secondary combustion, burning slow is less efficient overall than a fast, hot fire. Therefore, I suspect the efficiencies were measured under ideal conditions (fast burn) rather than the actual conditions most people use. As a side note, there are home gas furnaces and water heaters that go above 90%, but to do that, they actually have to extract heat from the combustion water vapor and condense it, resulting in flu gas temperatures below 150F, so they need a blower to drive the flu gas up the chimney, which is often made of PVC. No good in a power failure, though. I get what you say about wet wood. That is why I stack wood in the round for 2 years before I split it, and then I split it between March and the end of May each year, putting the split wood under an 8' overhang on the back of my garage, where it gets plenty of air and sunshine but no direct rain. My moisture meter typically reads between 8 and 15% moisture when I burn the wood. I have not measured the flu gas temperature on my Tulikivi, but the manufacturer says 250-350F is typical even though it is a short, hot fire because the soapstone absorbs 80-85% of the heat. THe masonry heater stays warm or hot to the touch for at least 24 hours after the fire goes out.

Efficency testing has greatly changed over the years, hence one of the reasons there's fewer and fewer epa certified stove (furnace) manufacturers and models they offer.
Yes I'm well awear of condensing furnaces. For gas/oil they are more or less standard these days. I do not have a wood stove, I have a wood furnace. No I don't have the forced draft hooked up. The secondary combustion works amazingly well without it, given i maintain 300* flue temps. Which isn't difficult heating 2600 sq ft with it. It's sized well for what our heat needs are. Ie, it's burned within its optimal parameters. I have never had any build up issues in my chimney. I don't claim any efficency ratings, other then it burn much less wood then the last wood stove i used at my old house.
You can believe or not believe, really it doesn't matter, whom ever you've gleamed your information from to make these assumptions doesn't know how to run a wood stove, has an ancient inefficient pos, and or has never experienced a decent wood furnace. Night and day difference.

 

[Hermio]

Yes I read this book recently, it was excellent. The factors that affect draught was fascinating and how it needs to be just enough (to remove all the smoke) but not too much (to take all the heat with it). Also it covers the concept of having a forwards sloping rear back to a very shallow fireplace to help throw heat out into the room.

In the medieval ages, fireplaces started off simply being bonfires in the corner of a room with a huge hood over it. Design evolved over time to this smaller shallow design. Most modern fireplaces seem to have forgotten this fact and seem be too deep (maybe builders do this to be super safety conscious as it contains the sparks) or maybe because rebuilding a chimney if the draught was too poor would be such a massive job?? Its easier for a builder to make a super conservative system with masses of draught, but is utterly useless at producing heat as an open fire?? Or is this big hole easier to fit a stove??

Well worth a read.


View attachment 1210653

Cool! I have that book also.

 

[Hermio]

Efficency testing has greatly changed over the years, hence one of the reasons there's fewer and fewer epa certified stove (furnace) manufacturers and models they offer.
Yes I'm well awear of condensing furnaces. For gas/oil they are more or less standard these days. I do not have a wood stove, I have a wood furnace. No I don't have the forced draft hooked up. The secondary combustion works amazingly well without it, given i maintain 300* flue temps. Which isn't difficult heating 2600 sq ft with it. It's sized well for what our heat needs are. Ie, it's burned within its optimal parameters. I have never had any build up issues in my chimney. I don't claim any efficency ratings, other then it burn much less wood then the last wood stove i used at my old house.
You can believe or not believe, really it doesn't matter, whom ever you've gleamed your information from to make these assumptions doesn't know how to run a wood stove, has an ancient inefficient pos, and or has never experienced a decent wood furnace. Night and day difference.

One thing is for sure. An efficient wood stove or wood furnace is much less expensive than an efficient masonry heater. One thing I like about masonry heaters, though, is that they radiate heat over a large area at a lower temperature rather than a higher temperature over a smaller area, making the heat more even, so you don't feel uncomfortably hot when you are near the unit. The surface temperature of a masonry heater is generally between 150 and 220F, and my unit has an effective radiant surface area of about 50-60 square feet.

 

[SS396driver]

I replaced a 30 or so year old Dutch west stove a few years ago with a Drolet HT2000 . Best thing I ever did wood wise uses way less wood and heats better and the flue stays super clean this is on low
View attachment IMG_5088.mov

 

[snobdds]

I am aware that the features you mention improve efficiency. But it is simply a fact that a smoldering fire is less efficient than one which achieves complete combustion. The catalyst may prevent creosote but it will likely get clogged at some point. Would you trust such a system to go 20 years or more with no chimney cleaning?

Smoldering fires happen only after a hot burn to start things going and heat everything up.

At that point efficiency is not really important. People put less wood in because the heat is no longer needed in the quantities needed initially.

Burning a fire is like a bell curve. Not a straight line linear up sloping line.

 

[Hermio]

Smoldering fires happen only after a hot burn to start things going and heat everything up.

At that point efficiency is not really important. People put less wood in because the heat is no longer needed in the quantities needed initially.

Burning a fire is like a bell curve. Not a straight line linear up sloping line.

Indeed. People skilled in the use of woodstoves get a sense of how often to add wood and how much to add to maintain a comfortable temperature. That is very different from how a masonry heater works. Such heaters store heat and release it gradually, so if it is fired too much, the room will be warmer than desired for a day, and if not fired enough, it takes close to a day to get the stone up to the desired temperature. So, it takes either ESP or a reliable weather forecast to anticipate how much firing it needs. I generally let my ground source heat pumps do most of the work, using my masonry heater as supplemental heat. I burn about 6 cords per year. I have found that with 3 firings per day, I can keep the two main rooms it heats about 30-35 degrees warmer than the outside temperature. The two rooms amount to about 1000 square feet floor area but have a ceiling height of 21 feet, so the wall area is equivalent to a home of 2000 square feet. We have two "wings" that are single story adjacent to the main two rooms, but they do not get much heat from the fireplace since they are separated by walls.

 

[sean donato]

One thing is for sure. An efficient wood stove or wood furnace is much less expensive than an efficient masonry heater. One thing I like about masonry heaters, though, is that they radiate heat over a large area at a lower temperature rather than a higher temperature over a smaller area, making the heat more even, so you don't feel uncomfortably hot when you are near the unit. The surface temperature of a masonry heater is generally between 150 and 220F, and my unit has an effective radiant surface area of about 50-60 square feet.

Mine has a low speed blower and is ducted to the entire house, even without power it still convects fairly evenly throughout, there's no "hot spot" again, stove vs furnace.

 

[snobdds]

Indeed. People skilled in the use of woodstoves get a sense of how often to add wood and how much to add to maintain a comfortable temperature. That is very different from how a masonry heater works. Such heaters store heat and release it gradually, so if it is fired too much, the room will be warmer than desired for a day, and if not fired enough, it takes close to a day to get the stone up to the desired temperature. So, it takes either ESP or a reliable weather forecast to anticipate how much firing it needs. I generally let my ground source heat pumps do most of the work, using my masonry heater as supplemental heat. I burn about 6 cords per year. I have found that with 3 firings per day, I can keep the two main rooms it heats about 30-35 degrees warmer than the outside temperature. The two rooms amount to about 1000 square feet floor area but have a ceiling height of 21 feet, so the wall area is equivalent to a home of 2000 square feet. We have two "wings" that are single story adjacent to the main two rooms, but they do not get much heat from the fireplace since they are separated by walls.

All fire places transfer radiant heat. Even If you don't have a masonry heather, the objects in the room absorb the heat and in turn radiate it back into the room.

Everyone who has a woodstove also has a masonry heater via the objects around the woodstove. The principle is the same, the only thing that differs is the objects transferring the radiant heat.

 

[Fried Chicken]

I just looked at the fireplace, but the styling isn't quite what's desired.

I still can't figure out why a special flue is needed when I can just burn wood normally without much trouble. The previous owner had it without a flue. Didn't want to sell it, but his wife is forcing him.

Also it looks like the government has gotten involved in fireplaces and is causing a pain in the ass and headache for everyone. New super strict regulations for all newly sold inserts as of 2020....

 

[Mad Professor]

I just looked at the fireplace, but the styling isn't quite what's desired.

I still can't figure out why a special flue is needed when I can just burn wood normally without much trouble. The previous owner had it without a flue. Didn't want to sell it, but his wife is forcing him.

Also it looks like the government has gotten involved in fireplaces and is causing a pain in the ass and headache for everyone. New super strict regulations for all newly sold inserts as of 2020....

Flue has to match the size of the appliance, or you won't get proper draft, and flue may not heat up to prevent creosote formation.

 

[Hermio]

What is radically different is the temperature distribution. With a woodstove, you have a rather hot spot in a small area. The objects in the room absorb some of the heat and re-radiate it, but not enough to even out the temperature. And when the fire goes out in a woodstove, the room chills down rather quickly, because you really don't have that much thermal mass in a typical room. My masonry heater weighs 9000#, and it is warm to the touch 24 hours after the fire goes out.

All fire places transfer radiant heat. Even If you don't have a masonry heather, the objects in the room absorb the heat and in turn radiate it back into the room.

Everyone who has a woodstove also has a masonry heater via the objects around the woodstove. The principle is the same, the only thing that differs is the objects transferring the radiant heat.

 

[Fried Chicken]

Flue has to match the size of the appliance, or you won't get proper draft, and flue may not heat up to prevent creosote formation.

Ah I see; you want the flue to heat up. Now it makes sense. It also makes sense why the Flue would have insulation.

 

[Fried Chicken]

It is a hot as my wood stoves, an Aarrow and a Danish Aduro and has never smoked even when lighting. Behind the smoke shelf I installed a hinged metal door which can be opened and the chimney swept with the throat flap firmly shut and the soot going outside

That's unbelievable. How can it be more efficient than a stove? Franklin's whole point of the stove was that the heat should enter the house, and then the smoke carried away

 

[snobdds]

What is radically different is the temperature distribution. With a woodstove, you have a rather hot spot in a small area. The objects in the room absorb some of the heat and re-radiate it, but not enough to even out the temperature. And when the fire goes out in a woodstove, the room chills down rather quickly, because you really don't have that much thermal mass in a typical room. My masonry heater weighs 9000#, and it is warm to the touch 24 hours after the fire goes out.

You are correct that thermal mass plays a big role in the equation. But I don't experience a rapid cool down in the house after the fire goes out. The fire usually burns for over 10 hours and the heat energy transferred around in the house makes it comfortable for a long time after the fire goes out. That is my point...radiant heat is transferring energy to objects. Even for you, the objects in your room have no choice but to absorb the energy coming off your heater. Energy is always transferring from hot to cold. Storing it is impossible in both of our situations, it's just the rate of transfer that changes. You have a slower rate of transfer than I do.

 

[Hermio]

You are correct that thermal mass plays a big role in the equation. But I don't experience a rapid cool down in the house after the fire goes out. The fire usually burns for over 10 hours and the heat energy transferred around in the house makes it comfortable for a long time after the fire goes out. That is my point...radiant heat is transferring energy to objects. Even for you, the objects in your room have no choice but to absorb the energy coming off your heater. Energy is always transferring from hot to cold. Storing it is impossible in both of our situations, it's just the rate of transfer that changes. You have a slower rate of transfer than I do.

In a sense, energy is stored for a while, due to a slow rate of transfer. Of course, the whole universe is headed towards uniform energy distribution, leading to cessation of life and other complex systems. But in our houses, we just have to be concerned with how long a given heat input will last. And though the furniture and walls do hold some heat, they won't hold quite as much as 9000# of soapstone. I do notice that furniture near the fireplace is warmer than furniture further away. Interestingly, though our walls are well insulated, the interior walls feel warmer to the touch after a sunny day than an overcast one. We have brick veneer on the outside, and I am sure that can hold a lot of heat.

 

[dboyd351]

I replaced a 30 or so year old Dutch west stove a few years ago with a Drolet HT2000 . Best thing I ever did wood wise uses way less wood and heats better and the flue stays super clean this is on low
View attachment 1210673

Drolet makes a good stove.
I have an Osburn 2300, which is a slightly fancier and slightly larger version of your stove. I was very interested in the HT2000, but decided on a little larger stove.
I have had mine 12 years and am very, very happy with it. The only things I have had to replace were a couple of cracked firebricks and just replaced the door gasket this spring
It is a wonderful stove!

 

[Fried Chicken]

I've looked at a few of the stove inserts. Were I up north and doing more serious heating, would these options be more viable for me. As it is, they're frankly not that attractive. The stupidity of the vanity isn't lost on me.

Based on reviews I'm seeing, I'm increasingly gravitating towards the grate wall of fire with a fireback. The price for new units floats around the $600 or $700 mark. A used stove insert sits around the $500 to $1500 mark, and then requires repair/restoration, parts, and installation including the addition of a flue.

I like the idea of heating the whole home entirely with firewood; I could use the central HVAC blower for that, but the investment seems too high to make sense.

Do fireplace doors/windows serve any particular purpose with regards to heating?

 

[dboyd351]

A fireplace is for ambience, a woodstove for heat, an insert is between the two.
There is really no way to get around the fact that a woodstove standing free and ckear in the room radiates heat in all directions, while most of the heat from a fireplace goes up the chimney, not into the room,

 

[Fried Chicken]

A fireplace is for ambience, a woodstove for heat, an insert is between the two.
There is really no way to get around the fact that a woodstove standing free and ckear in the room radiates heat in all directions, while most of the heat from a fireplace goes up the chimney, not into the room,

You're right. This offers clarity.

My options are: enjoy the fire for show or find an insert stove, either new or used, and install that along with a flue.

 

[sean donato]

You could always get an add on wood furnace, just duckt it into your existing vents for ac/heat.