Masonry Heater

[sailawayrb]

As many of you know, we built our retirement homestead in southern Oregon a couple years ago.  I thought I would share some photos of the masonry heater that we built and report on its performance.  This is our second Winter using it and I can report that it works amazingly well in our high efficiency 2400 SF home.  One 30 pound wood firing every other day will easily keep our home at 70F for this 48 hour period.  

I should also add that our home is a passive solar design so about 40% of of our daily heat comes from the sun shinning through the south wall windows.  Our other heat source is hydronic radiant floor heating.  When we are not using the masonry heater, we can heat both our home and our detached 1800 SF garage/shop/guest quarters building for about $30/month just using small electric boilers located in each building that are expressly designed for hydronic radiant floor heating.  When we use the masonry heater, this heating cost reduces to about $12/month.

I built a masonry heater performance calculator:

https://www.borstengineeringconstruction.com/Masonry_Heater_Performance_Calculator.html

Here's some specific info on our masonry heater core and the fire mason we used to construct it:

https://www.borstengineeringconstruction.com/Masonry_Heater_Builders.pdf

Here's some info on the NexGen boiler we used for the hydronic radiant floor heating:

https://www.borstengineeringconstruction.com/NextGen_Boiler.pdf

And finally, you can find construction photos of both buildings here:

https://www.borstengineeringconstruction.com/About-Us.html

Anyhow, I hope someone finds this info useful in the future.

Cheers,
Bob

[sailawayrb]

Another photo

[sailawayrb]

Another photo

[sailawayrb]

Another photo

[LowGear]

What an absolutely wonderful home.  I'm sure we all feel some envy for the outcome of your hard work.

Aloha,

[mike90045]

We also, heat a 2 story 2400ish square foot house, with a masonry heater.  We used a company from Canada - Tempcast for the "Core"  and then a local mason added the layers of brick.  The house was designed around the heater, and the first floor, with all that radiant heat from the brick, gets up to about 110F, is comfortably warm. The air is only about 66F, but the radiant heat is like basking in the sun.
We only wish we'd made enough provision to have a hot shelf niche to hold a tea pot or some such, we have a black oven built in, but only seldom use it.

I have a facebook album showing the construction process of the refractory core and the finished brickwork.

we burn about 2.5 cords of hardwood a year, and sweep the chimney every 3 years - and the sweeps say " such a nice fireplace, you should use it more often, we didn't need to come out and clean it. "

questionable links to album
(look for Kachelofen Konstruction (Masonry Heater) album )

Albums
https://www.facebook.com/Lucky-Monkeys-Ranch-120212794718849/photos/

https://www.facebook.com/Lucky-Monkeys-Ranch-120212794718849/photos/?tab=album&ref=

If none of those work, search facebook for https://www.facebook.com/Lucky-Monkeys-Ranch and maybe you can find it from there
  ( sorry,  the old facebook used to have an easy share link for albums )

[sailawayrb]

Yes Mike, I recall seeing your beautiful masonry heater several years ago.  Our masonry heater uses the Norbert Senf Heat-Kit core (photo attached) that we had shipped from Quebec Canada to Portland Oregon and which we then trucked to our construction site.  

Our single story 2400 SF home was also designed with this masonry heater in mind.  We located our masonry heater in the center of the home with the core glass door facing our living area and the white oven door facing our kitchen area.  The masonry heater rests on a footing that is 2' thick.  Our home has a large amount of interior thermal mass (e.g., 2' thick masonry wall, 5" thick concrete floor slabs and lots of granite/marble window sills, counter tops, etc.).  Soap stone is often considered the best facing for masonry heaters for typical homes because it can store heat well and release it relatively fast.  However, for our highly energy efficient home we needed something that would store even more heat and, more importantly,  release it much slower and for a much longer period (i.e., for 36-48 hours)...hence my reason for developing the calculator...and discovering that Argillite Stone had the properties needed to accomplish this goal and which we had trucked in from Montana.  Our masonry heater facing surface temp peaks at about 150F about 10 hours after the firing.  I instrumented, tested and calculated our masonry heater efficiency to be 81%.

I suspect that many folks don't fully appreciate how vastly different masonry heaters are from fireplaces, rocket stoves, or wood stoves.  The following are excerpts from the masonry heater calculator instructions that provide more info about the motivation for using these devices and how they function:

"Energy efficient homes may only require 3 to 5 British Thermal Units (BTU) of heat gain per hour per square foot of living space.  This would be equivalent to only 8,000 BTU/hour for a home having 2,000 square feet of living space.  For most conventional woodstoves, this is well below their critical burn rate for operating cleanly and they will start to smolder.  If you operate most conventional woodstoves at or above their critical burn rate, you may easily overheat an energy efficient home.  The only solution for this dilemma is to have many small firings, which is not very convenient.  Therefore, wood burning and energy efficient homes are not normally compatible unless you have some way to burn the wood at or above the critical burn rate to allow operating cleanly and you have a way to store the excess heat that is created and slowly release it as needed without having to accomplish frequent, inconvenient firings.  

We prefer masonry heaters which provide the solution to this problem and have actually been the most efficient way to heat a home with wood for over a hundred years.  Unlike fireplaces or woodstoves, there is very little heat loss because the exhaust gases are circulated through the masonry heater several times before going up the chimney.  There is very little pollution because masonry heaters burn the wood very quickly and operate at about 1700 degrees so as to fully burn what even certified woodstoves cannot burn.  Masonry heaters store and slowly release radiant heat over a 24 hour period accomplished by only one or two firings per day.  Masonry heater surfaces never get extremely hot like stoves and will not suddenly overheat your home, which your sinuses will greatly appreciate.  A masonry heater may be located to absorb solar radiation and store this form of heat energy too.  Therefore, masonry heaters are similar and compatible with hydronic radiant floor heating and passive solar heating.  As a side benefit, you may have a nice masonry oven that is available for energy free baking duties perhaps 10 hours per day and you may have heated benches for you, your guests, and your pets to enjoy all day.  Constructing a masonry heater is a relatively simple DIY project and there are many good kits available in the marketplace to do this.  Please be sure to fully research and comply with all the local building code requirements.

Masonry heater overall efficiency is the total measure of how well the masonry heater converts the chemical energy of the wood into heat energy during the combustion process (combustion efficiency) and how well the masonry heater delivers this heat to the house instead of out the chimney (heat transfer efficiency).  The heat loss out the chimney consists of the chimney stack temperature which is typically 300-400 degrees Fahrenheit and the water latent heat loss from converting the water in the wood to water vapor.  Masonry heater combustion efficiency is typically 96 to 99%.  Masonry heater heat transfer efficiency is typically 57 to 80%.  Overall efficiency is the combustion efficiency times the heat transfer efficiency.  European testing methods ignore the water latent heat loss which is around 9 to 13% depending on the moisture content of the wood.  North American testing methods include the water latent heat loss.  The theoretical maximum overall efficiency obtainable from any wood burning device using North American testing methods is 83%.  Actual masonry heater overall efficiency is typically 55 to 79%."

[sailawayrb]

Another photo

[sailawayrb]

Another photo.  Note that the exhaust only gets to finally go up chimney after first going to top of core (around white oven), down the sides of the core to floor, and through the side and front benches.  When core temp is about 1900F, flue temp is only about 280F and exterior of stainless steel flue pipe is only about 110F.

[LowGear]

I used to run small wood stoves and wood was the most important decision.  I got pretty hooked on vine maple.  Not easy to find but fantastic heat.

Are these masonry furnaces as well choosy and what are the fuels of choice?

[Tom Reed]

Around here the hot ticket is Madrone. The split wood is clean, it burns clean, leaves little ash and has more BTU's than Oak. I've seen Mikes heater and it's quite nice. We head exclusively with wood here and I'm heating a 2100 sq ft house with a heated 1500 sq ft basement with about 2.5 cords of wood a year using a Lopi Liberty stove. The house was designed with a lot of thermal mass and a concrete main floor, so the stove is run hard for a short while and the house holds the heat, usually until the next evening. Our concrete floors have hydronic heating in them that are heated by the cooling water from our Listeroid. It works well, except now that we have LiFePo batteries the Listeroid rarely needs to be run.

[sailawayrb]

We use Madrone and only about 0.9 cords per year...we only need a 60-90 minute fire every other day.  You can use any wood as long as it is dry.  You just pile the wood into the chamber, place some paper/kindling on top of the wood pile, light the paper and close glass door.  As soon as the temp gets over about 800F (maybe after about 10 minutes) the wood pile goes into full gasification mode and the temp quickly rises to 1700F +.  Flame color quickly changes from yellow/orange to white to wispy blue/purple plasma-like state.  It has a small ash tray that we only empty about once a month. 

[mike90045]

here's a 90 video overview of a Masonry Heater
https://www.youtube.com/watch?v=udk0uCnLOeA&feature=emb_logo

It turns out our new, modern windows leak air like a sieve.  We burn about 3 cords a year, about half oak, half madrone.  As long as it's dry, it will burn well. We us the top down burn method, big logs at bottom, and some small stuff on top, seems counter intuitive, but it works and very little smoke. 
We found bringing in wood with a 5 gallon bucket is the cleanest way to load the thing, the canvas carriers just dumped a lot of debris on the floor. An average day we burn 2 batches, 1.5 buckets  each firing.   Also the bucket is a great sizing tool, wood the length of the bucket is just right, an inch longer, we have to stack diagonal.
No fussing, light it and close the dampers in 90 minutes when it's out.

[sailawayrb]

Yes Mike, a very good masonry heater link and I have watched it before!

We use the canvas method to bring in our wood.  And yes, it does leave some debris near the masonry heater.  However, we have a central vacuum system and a vacuum port and small hose next to the masonry heater just for this purpose of keeping it tidy. 

We also use the top down method too as it has been shown to reduce smoke during startup.  Of course, there is zero smoke once the inferno stage is quickly reached.  One could not tell by looking at the chimney exhaust that there was even a fire.  We have been told that there is no need to ever sweep the chimney because of the lack of creosote and the relatively low stack temp.  However, I will still scope/inspect it from port at base of heater about every 5 years.