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.


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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.