Outdoor wood furnaces
Experiences with outdoor "water stove" heating systems. March 20, 2001
Question
Has anyone had experience with outdoor "water stoves" (Taylor, Central, etc.)?
Forum Responses
I have had a Taylor for three years now and it has already paid for itself. I heat my hot water, house and 28 x 48 shop with it. You can expect about 10 years out of them. Compare what you'd pay for heating and hot water over those ten years to the price you would pay for the stove.
I have a similar question. Will I be able to run hot water through my steam fin piping and what temperature can I hope to achieve?
Regarding changing a kiln from steam to hot water, the fin pipe will transfer heat out of the hot water just fine, although at a lower btu/ft rate, because the water will not be as hot as the steam. (Theoretically, you'd need more fin pipe if you use hot water, but the difference might be negligible in a small kiln).
The bigger problem is getting the water to move through the heat system. Steam will naturally move under its own power, condense as it gives up heat, and the condensation flows back to the boiler. A steam trap controls the flow of the condensation out of the cool end of the system. If you use hot water, you have to pump it somehow, in a controlled manner, to control the dry bulb temperature.
I heat my kilns with a Mahoning Outdoor Furnace. Mine burns waste oil - great free fuel, and cheaper if I have to buy it.
I've heated my home with a Hardy furnace for eight years. It doesn't cost me a cent. I use firewood cut from treetops instead of slabs when it gets really cold. The domestic hot water feature cut my electric bill about $1 per day. You never run out of hot water as long as there's a fire in the box.
I've used a Heatmor for 1 1/2 years to heat my house and domestic hot water. It works well, but slabs from my bandmill are too thin to use -it takes too long to fill up. All I burn is hickory and oak of poor quality. I burn large pieces (50 lbs) on really cold nights.
The Heatmor has a few nice features - it is all stainless steel and the incoming cold water goes through a hollow door, so it is never hot when you add wood. It also has a bladder, which helps keep steam from oxidizing your pipes, etc.
Get a paper by the Ag extension service of the North Carolina State University called "Getting into Hot Water" (A Practical Guide to Hot-Water Heating Systems).
I understand these stoves are extremely smoky. Are they inefficient because of this?
There are poorly designed stoves that have a tendency to smoke if they do not have enough combustion air. They do not have enough water capacity and tend to cycle too often. You load the stove with wood and fire it. With a small water capacity, the water reaches setpoint temperature and the stove shuts down. You still have a good load of wood in the firebox that sits there and smolders.
If you have a large water tank capacity, you can burn the total load of wood with good draft, burn and efficiency. You may only have to fire once a day or even every other day.
Wood usage depends a good deal on the kind of house you have. My home is 100 years old, and not insulated well. I fire mine morning and night. How much wood left over after a 12-hour cycle depends on the kind of firewood and the weather. My brother has the same furnace, in a pretty well insulated house trailer. He fires a maximum of once a day, and uses less wood.
My Hardy is made of stainless steel. The firebox walls' maximum temperature is 180 degrees or so. With proper care, it ought to outlast me.
Excessive smoke has never been a problem for me. It will roll smoke for a while after you fire it. Otherwise, it produces a small amount of smoke with a pleasant wood odor.
My only change would be to add a portable generator and wire the system up so I can operate my furnace in a power failure.
My brother bought a Pacific Western outside wood boiler. It cost a lot of money, but with a large log home it has paid for itself.
I have built three. The first worked well, but had to be filled three times a day. My current boiler burns 24 hours on one filling. It has 350 CDN gallons water storage. I built it from large bullet style propane tanks and metal from scrap yards. I heat a 135 year old home, about 2500 sq feet.
If you can weld and scrounge, you can build it yourself. Manufacturers have cutaway pictures of their designs. I took principles from Central Boiler for my design, and I burn about 2/3 the wood that my brother burns in his factory unit.
I've read you have to put the fire out in a hot air furnace in the event of a power outage, because the fire would melt the furnace. Is this true?
With my hot water stove, there is no danger of melting if the power goes off. It just takes electricity to operate the pump and fans to transfer heat to the house. I suppose that would be true of any unit with a water jacket.
The default position for the damper (or blower motor) for these units is closed. When the power is out, the fire shuts down and smolders. It cannot burn out the firebox. Also, it is surrounded with water that will help to keep it cool.
These boilers should last a long time as long as the heating system is a closed loop. Do not tap hot water off of the system or corrosion will eat holes. Use a closed loop also for heating the hot water.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor C:
I have a Pacific Western outdoor wood furnace. It works OK, I guess, but I wish I would have bought one that had grates in it and an auger system like the Mahoning so I could burn coal also.
The Pacific Western I have is wood only, I did put a grate in it and it works a little better. FYI, I've heard that Pacific Western is in danger of going out of business, something to consider before you buy...
Comment from contributor A:
The answers in this message board so far only begin to touch on the basics. Type of wood, actual heat load, design characteristics of the unit and location are all factors in how well each unit will perform. I have used a Central Boiler Classic for six years. I have talked to over forty owners of various brands. The best is easy to see if you understand the physics of these systems. In lab tests and field comparisons, the Classic has high efficiency, easy maintenance and few parts requiring service. Keep it simple and efficient.
Comment from contributor D:
I just purchased a Central Boiler this past year and I love it. It cut our electric bill in half, and never used any LP at all. I wouldn't trade it for anything. If you enjoy cutting and burning wood, this is a good investment.
Comment from contributor B:
We have a Wood Doctor Boiler Plate and we love it. We burn any type of wood to heat our huge home, hot water, pool and hot tub. Smoke issues are dependent upon user. When first firing it will smoke if blower is on, but our system lets you adjust the air flow and the temp so you are controlling the burn. Ours sits 20 feet from our newly sided home and no problems. It has saved us a ton of money as people bring their "unusable wood" to us and drop it off. It saves them money, cleans up and saves us a lot of money.
Comment from contributor E:
We have been using a Heatmore for seven years now. It heats the house, hot water, shop, greenhouse and drying kiln (5*6*19', heats to 140F). We also use a 1/2" pipe under the living floors. I use all the slab wood mostly during the milder days. The best move we ever made.
Comment from contributor S:
We've had a Taylor 750 for six years now. Operating in Oregon's temperate coastal area we burn about nine cords per fall, winter and early spring to heat 3,000 sq ft house via radiant floor heat (1999 construction standards; five radiant floor heat zones) and all domestic hot water. It is a good unit - smokes when starting up, but when the unit is to temperature, 180 degrees, it burns clean. Load the cubic yard fire box once a day in temps in 50s; twice in 30s or below. Emergency generator runs pumps and fan that "stokes" the Taylor when it needs more heat. Good buy. Good unit, although the metal sheeting on the roof next to the chimney rusted through after the 3rd year. Replace with galvanized steel... all is well in Oregon now.
Comment from contributor G:
I live in Central Ontario, and we have long, cold winters. I have a 120 year old log house that is composting into the earth. It is not insulated well. I just about burned the place down with the aging and poorly installed wood stoves that came with the place. Insurance was to be thousands, so I had a Heatmore installed by the local sales rep. Best decision I ever made. I heat my shop and house and water. It runs year round. On cool summer nights I can circulate the hot water to heat my 80 gallon tank and it keeps the old place dry, working also as a dehumidifier. As simple as plugging it in and opening a valve. I am very rural, so smoke is not a problem. Smoke is created by moisture, so a lot depends on how wet the wood is. The amount of fuel needed in the summer is very little compared to winter consumption. Sticks and trimmings dried in the July sun make very little smoke. My clothes drying line is right beside my stove and it is not a problem. I run it at 150 in the summer and as high as I can get it in the winter, usually about 185. It then peaks about 190 and the fan kicks in at about l80. The magic is that water at this temp carries a lot of heat energy. This old place has never been warmer and it has already paid for itself. Having the oxidization chamber inside the home now seems so ridiculous. Ash, bugs, molds and everything else that belongs out in the forest comes into your home. So I am obviously a big supporter of these systems.
Comment from contributor J:
I have had a Pacific Western #3 for two years. I heat a 9,600 square foot home and 900 square foot garage in Iowa. We also use a heat exchanger for hot water. We re-piped the system inside the house after the first year because the installer did a sloppy job. We have thermometers throughout so we can determine temperature loss and really know what is going on. There is a lot of BS said about these units, but we really know.
The unit is 160 feet from the house. 1" Pex pipe is insulated and enclosed in 4" corrugated plastic pipe. Temperature drop is about 12 degrees F from the boiler to the house when the outside temperature is zero. At zero, we burn average quality dry oak and load wood about half full morning and night. Loading more than half full uses more wood but doesn't produce more heat (just wastes it), so we believe that the best way to use the boiler is to plan for a 12 hour loading; then when you reload, there are still a few pieces of wood burning with a deep (6") bank of very hot coals.
Even with 15 people at our home, we never run out of hot water. We designed our own potable hot water recirculating system with a return line from the furthest bathroom to HWH #1 drain valve. Cold water comes into tank #1 inlet, out to plate heat exchanger, in to tank #2, then to house. Return is back to HWH #1 drain, as mentioned. Small Grundfos pump recirculates potable hot water continuously. Aquastat on HWH #2 bypasses hot water from boiler away from plate heat exchanger when water temperature in second tank is over 135 degrees.
Boiler water goes from HWH plate system to furnace #1 with water to air exchanger is plenum, then to same systems for furnace #2, then to plate heat exchanger for in-floor hydronic heat system for basement, then to space heater for garage.
The heat quality in both the hot water and in the air is far superior to gas, is much cleaner inside the house, and we think the system is great.
Comment from contributor R:
I also own a Pacific Western outdoor furnace (model #1). It heats well enough and would heat better if my house was a little more airtight. I have read many things written about the horrible smoke that outdoor furnaces produce. I cannot speak for other makes of outdoor furnaces but My Pacific Western cold killer model (which has a tube all the way around the firebox blowing air from all sides onto the fire) smokes hardly at all. Once up to temp, there is no smoke. When the blower shuts off, there is very little, if any.
Comment from contributor N:
In another forum someone was saying how bad these furnaces are with all the smoke. I disagree. I watched the smoke from a Shaver Outdoor Wood Furnace that a friend has one day and from the chimneys of two fireplace in two homes (one mine). The winner? The outdoor wood furnace. Why? The fire is much hotter in the outdoor furnace. There's a lot more wood burning at one time. Contrary to what has been said, the wood burns completely.
Also the smoke is kept outside which is much better than smoke in the house because most of the winter you're in the house. I know from personal experience that every time you have to open the door to add wood - several times a day - that smoke gets in the room. Not so with an outdoor furnace - no smoke gets inside. The chimneys can be extended on outdoor wood furnaces so that the smoke doesn't get anywhere near other homes.
I definitely prefer the outdoor wood furnace and it is the clear winner as long as the owner fills it with good, dry hardwood.
Comment from contributor M:
I have had my Taylor T-450 for 13 years and have no problems with it year after year. I heat a 3,000 square foot home and my shop that is 1800 square feet. I checked all the models out before I bought the Taylor and will buy another when I wear this one out.
Comment from contributor I:
We have had a Heatmor for for years and love it. It heats our 4,000 sq. foot home plus heats the water. We went from a $700 a year LP bill down to almost nothing (except for backup). As far as the smoking goes the stove only smokes when new materials are put into it (once a day) but after that it mostly burns clean. I can burn anything - pine, cardboard, scrap wood and very large stumps. No more wood chopping - just cut and load.
Comment from contributor F:
I have a turbo burn from Spokane, Washington and it heats a 2000 square foot house. The upstairs is heat exchanger; downstairs is hydronic. The stove has a 750 gallon tank that I heat in a couple of hours while I also heat the floor. I heat once a day if it is under 20 degrees. I have 35 yards of concrete as a heat sink in my floor. I have used it for 16 years or so and it has been a great system. The fire is hot and quick as it is fan driven.
Comment from contributor V:
We bought a Taylor Woodburner ten years ago and the only thing I don't like about it is the hot water coil gets clogged up and I have no hot water. I guess everyone else has city water. They should put some kind of filter on them to stop dirt and other stuff from going in the coil.
