interesting simple hot air wood furnace

[mikeyny]

I recently got a good look at a simple hot air system that really got me re-thinking about how to heat a house. My tarm set up is great but somewhat complicated with pumps and relays and the like. This guy (somewhat of a hippie) had an old coal furnace from the 30's. The fire chamber was shot so he removed the coal burning chamber and slid a large airtite wood stove right into the center of the unit. All of original duct work and plemnum remained in place. There is no blower, no moving parts or thermostat. He burns wood from his property so it costs nothing except his time. He burns the wood very slowly so as not to over heat the house. Naturally this causes some creosote problems so he cleans the chimny quite often. The simplicity of this system is very appealing to me. Nothing can go wrong. He actually has a lever upstairs in the hallway connected to the damper so he can turn the heat up or down without going down to the cellar. If I had an existing hot air system I would definitly consider doing one of these.
Mike

 

[jdemaris]

This guy (somewhat of a hippie) had an old coal furnace from the 30's. The fire chamber was shot so he removed the coal burning chamber and slid a large airtite . . . Mike

Those old coal/wood furnaces, down the basement with huge hot-air pipes and gravity flow worked great and were extemely simple. Wish I had one now. Hard to install unless the house was planned around it. Needs a deep cellar and a high vertical house, not a sprawling ranchhome.
I lived in the northeast kingdom of Vermont with one in an old farmhouse.

I came close with what I did in my large workshop and three story barn. I built a dedicated, three-sided furnace room attached to the 1st floor back with a sloped ceiling and lots of heat shields. Big old Thermo-control 500 wood/coal furnace. No heat pipes, just planned convection. Worked out much better than planned and you can't get much more simple. No electric, no heat pipes, just a bi-metal ait intake control.

 

[mikeyny]

One nice thing about a boiler is storage and flexibilty of firing times though. With that hot air no fire no heat.

 

[jdemaris]

One nice thing about a boiler is storage and flexibilty of firing times though. With that hot air no fire no heat.

Yes, and also a very slow recovery. If the house was cold, and you fired it up, it took a long time to get the house warm. But, unlike modern forced-air systems that constantly cycle on and of, the old gravity systems gave nice steady heat and were extremely simple. They give out heat for a day after the fire was out. And if it got warm outside, and house got too hot, you just opened up all the windows.

 

[mtnmizer]

Some of the older house builders in this area were of Scandinavian decent,(swedes, finns)
and built houses with massive fireplaces in the center of the house.
They had a fireplace both in the basement and on the
main floor. The ones I'm familiar with just took a fire in the basement
once a day in mild weather and maybe twice in below zero and kept the
whole house toasty when all that stone heated up. They had hollow chambers around
the fireboxes that work very well at circulating the heat. Some of the later ones
had blowers with outside air and burned very hot. One builder had a Russian stone
mason that did one for my dad, very artistic guy.

A daylight basement makes for easy access to the wood pile but some had a dumbwaiter too.. If
they had a fire on both floors at the same time you had to open the windows and doors.

These guys have mostly passed on but their ingenuity lives on.. I wish I had a fireplace like that
but when I priced it out it was over 25K and out of my budget.

 

[slowzuki]

There are books and kits to make masonry heaters like what you're talking about. Those old natural circualating wood furnaces in the basement were common around here. They certainly don't give off heat after they go out, at least not more than an hour or two.

Mostly they died out here because the heat in the house was not even.

 

[jdemaris]

Those old natural circualating wood furnaces in the basement were common around here. They certainly don't give off heat after they go out, at least not more than an hour or two.

Mostly they died out here because the heat in the house was not even.

The one's I've used gave out heat for a long time after the fire died. Maybe your definition of "go out" is different than mine.

With a forced-air system, heat is delivered only when the blower fan is turned on by the control swith. Off and on and once cooled to a certain point, no "on."

With an old gravity coal/wood furnace, after the active fire burns, and all that is left is coals and a lot of hot cast-iron, steel, and firebrick - the heat continues to rise and heat the house and can do so for a day with no active fire with flames. Some longer then others depending on what sort of thermal mass they have.

As far as their demise, I'm sure lack of control and fast response was one of many factors. It took up a lot of room and was not suited for modern petroleum fuel systems which was probably more of a factor.

 

[pybyr]

I just took out a still functioning wood hot air furnace to replace it with an Econoburn 150. My wood/ air unit used a blower, not gravity. Gravity systems do have wonderful simplicity, but they also often take up _vast_ amounts of space with all the needed ductwork and the need to size and slope it for good flow.

I also seem to be getting what seems like double the heat output per unit of wood from my gasifier, as compared to the wood/ air furnace. And even though I purposely don't idle my gasifier much, it seems better able to do long burns in a non-smouldery mode. With the old wood/ air unit, in order to avoid fires that I could tell would be "asking for" creosote, I had to run hot, fast fires that really would not sustain for long if I was going somewhere, going to bed, etc.

For someone who's around a lot, though, and can cut their own wood and is not too worried about how much they have to cut/ handle/ tend the fire, wood/ gravity hot air would probably remain an excellent option

 

[cguida]

Some of the older house builders in this area were of Scandinavian decent,(swedes, finns)
and built houses with massive fireplaces in the center of the house.
They had a fireplace both in the basement and on the
main floor. The ones I'm familiar with just took a fire in the basement
once a day in mild weather and maybe twice in below zero and kept the
whole house toasty when all that stone heated up. They had hollow chambers around
the fireboxes that work very well at circulating the heat. Some of the later ones
had blowers with outside air and burned very hot. One builder had a Russian stone
mason that did one for my dad, very artistic guy.

A daylight basement makes for easy access to the wood pile but some had a dumbwaiter too.. If
they had a fire on both floors at the same time you had to open the windows and doors.

These guys have mostly passed on but their ingenuity lives on.. I wish I had a fireplace like that
but when I priced it out it was over 25K and out of my budget.

The Masonry Heater/Russian Fireplace tradtion does indeed live on, and may be experiencing a renaissance. Kuznetsov the Russian stove designer reports that there is alot of house construction going on in Russia these days, and that most of it is taking place on the fringes of cities. That is, beyond the range of the usual centralized, community-wide hydronic facilities, and beyond the existing natural gas lines and also beyond reliable electric power. So they build their houses around masonry heaters, like the old days. Chernov (Kuznetsov's collegue in N. America) says Kuznetsov and his team have built over 4000 of these things, and are still going strong.

Chernov has an interesting explanation of why the traditional designs are the way they are...

"It is well known that each change of direction in the gas flow weakens the draft. The more "turns" - the weaker is the draft. Therefore, there is always a limit of how long the channels can be in these designs, and how much heat can be stored. Here, it is always a question of achieving the perfect balance: maximum length of channels without having the stove smoking and compromising the cleanness of burn. No wonder that such balance is difficult to achieve as many factors affect the gas flow. This is why, such systems are usually designed with "draft reserve" that means that "it is better to loose some heat than have the stove smoking". Obviously, this "reserve" lowers the overall possible heat retention. "


"It has been said above, it is hard to achieve the perfect balance between the heat retention and sufficient draft in these design systems. This is the reason why stoves, belonging to these systems, usually have a standard unchanged sizing of the firebox and the channels that has been refined in numerous installations over the centuries. Finnish contraflow stoves, Swedish contraflow stoves, grundofens and kachelofens: they all belong to such systems. Wee call these "forced gas movement systems".


http://www.stovemaster.com/html_en/designsystem.html
Http://stove.ru

By way of contrast, the new interior designs ("free gas movement") allow for much more flexibilty -- to the extent that one might consider building one of these things and have some hope of success.

Nowdays, the beauty of elegant masonry heaters might still cost $25000. But the 'heat' part is pretty straight forward, and not that expensive. Chernov said the materials cost of the Perth (Ontario) boiler was about $3500, and that included $1500 for the heat exchanger.

This is probalby more than you ever wanted to hear about masonry heaters and such, but if you want to see what they look like on the inside, try this link -- lots of pictures!
http://www.heatkit.com/html/lopezs.htm

 

[applewood]

Neat idea.... I scrapped the old coal furnace once it got beyond patching after ? years of coal, about 20 years of an oil burner in the draft door, then 20 years of wood burning in her. But there's more to these than large pipes and slopes..... The whole duct system is backwards. Hot air ducts are in the center of the house and therefore near the furnace and cold air returns are on the outside (under windows) to take advantage of that nice cold air for nature convection. Summer kitchens were additions and had east and west windows to vent the heat and winter kitchens were in the main part of the house the capture the heat from the cook stove. Who said the old timers didn't know what they were doing?????