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About to buy an outdoor wood furnace... advice?

Started by Thomas-in-Kentucky, December 12, 2006, 03:49:51 PM

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I have searched and read all of the archives here to learn as much about outside wood furnaces as possible.  But now that it is time to commit and actually buy a unit, I thought I'd revive the topic and see if anyone has any more advice to offer. 

I am leaning heavily toward the Taylor **whoops - meant to say Hardy** H4 or H25, primarily because of the stainless steel construction, because the company has a good warranty, because the compay has been in business for 30 years, because I've been able to see one in operation (for 6 years without a hiccup), and because there's a dealer within 30 miles. 

Thanks to another local dealer, there seem to be a lot of "Hicks" brand outside wood furnaces in this area.  I haven't seen that brand mentioned on this board, but there are about 75 in our county.  They have a generously sized firebox (albeit unlined, and regular carbon steel) and appear to hold a lot more water than other models - other than that I don't see anything very unique about them.

Anyone have any advice... good bad or indifferent.... about these or other outside wood furnaces?  I need to buy something soon so I can work on my house in-the-warm!

Thanks in advance for any tidbits of information!



Getting a unit with oil back up would be a good choise that way if you want to get away for a weekend you don't need anyone to feed the stove while your away.


Hoo boy.  I could write all day about mine.   I have a Central Boiler 5648 (which is now the 6048 model).  The only other brand I considered was Heatmor.  I looked at the stainless versions of both (I think Heatmor is only stainless, no carbon steel) and decided that the regular steel was better.  Why?  The non-stainless conducts heat better, and the grade of stainless that is used on most outdoor boilers is a fairly low grade stainless.  It will still rust.  If you do the regular maintenance required by the company, you will get 20-25 years or more out of the firebox anyway.  Unless the mfr. offers a lifetime warranty on the stainless firebox, I'd not bother.

Anyway - mine holds 385 gallons of water.  I am heating a SIP-skin timber frame totalling 4300 square feet, and it is currently being heated using only a single zone, five loops of 1/2" PEX tubing in the basement floor slab.  The basement thermostat is set at 68 degrees, and the temperature in the coldest part of the house never gets below 63 degrees.  Very comfortable.  The only problem at the moment is that with very low demand on a reasonably warm day (32 degrees or higher), there is no place for 'excess' heat to go and the boiler literally boils.  Big clouds of steam coming out the top.  That problem should go away once we start using hot water regularly (the house is under construction and unoccipied for another few weeks).   As for fuel, I am using about a wheelbarrow's worth of wood per day.  Sometimes more, sometimes I don't even bother on those warmer days.  On a 30-degree sunny day, the house temperature will hold without a demand call on the boiler.  Overnight, still with no demand, the temperature will drop 2-3 degrees.  About as stable as a walk-in cooler, which is essentially what the place is. 

For me, feeding the monster once or twice a day is worth the little effort it takes, especially to save the $6-$8 per day I have been spending on fuel oil for my current home.  Where we live now eats $2500 a year in oil and it's literally half the square footage.  Not an old drafty house either.    $2500 a year will pay for the boiler in six years and leave me enough for some really nice woods tools, chainsaws and equipment.   It's not worth the money if you're not willing to put in the effort.

I could add a lot more little comments and anecdotes, but I've only been running the boiler for a total of six months.  Two last spring and four this fall and winter.   I can't complain at all. 


I have the same furnace that Engineer has. It works well and puts out a lot of heat. One thing to had to Engineer's comments is that the Central Boiler does not have an ash pan.  I have the carbon steel version also. On my second year and am happy with it. I have seen the Taylor around Mo. but do not have any idea how well it works. Heatmor and Hardy are the most prominant around here.

Sawing part time mostly urban logs -St. Louis/Warrenton, Mo.
LT40HG25 Woodmizer Sawmill
LX885 New Holland Skidsteer


I got my first Taylor back in '88.  Have had one ever since.  When I built my new house, I didn't even bother putting any other heat in it.  I do have a small oil fired boiler gathering dust behind the Taylor, just in case I go out of town during the winter. 

I have been impressed with the Taylor from day one, it heats my home, the hot water, the Spa, and the shed.  Oh Yea!  it heats the 2000 BDFt kiln too. 

I have the 450 I think, the small homeowner model.  Holds around 300 Gal of water. 

Look out for the ones that only hold 100 gal of water or less, they do not have a good enough thermal flywheel.
2001 LT40HDD42RA with lubemizer, debarker, laser, accuset. Retired, but building a new shop and home in Missouri.


I'm lookin too, but I think I will wait on woodmizers sawdust burner. I ran what specsI have past my engineer son, he was impressed.
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men


like othres  have said:   size matters and water volume helps stabalize the boil cool down.   also many units don't have ash pans, and what you need to watch out for is that any ash that sets long periods of time aginst steel or even SS can/will cause rusting.   keeping the corners clean is critical.   summer shut downs it is very particular to make sure the ash is all gone if you are not firing it long periods.   keeping it hot & ash dry is OK for ash in there it is when it gets cool & starts condensing moisture that it really becomes caustic...

mark M
I'm looking for help all the shrinks have given up on me :o


  Taylor gets my vote.   SS is not a good conductor of heat so alot is loss up the stack.  FIL had a Hardy and does not like it.  Does not hold much water and has rusted out.  (pretty good SS I guess)   He had it 8 years and sold it this fall for $1,000 and was glad to see it go.   When I put one in at the yard it will be a Taylor.

Bro. Noble

We are on our third season with our Taylor and like it real well.  I'm not sure what modle it is,  but it holds 450 gallons and is made to service two houses and an outbuilding if it were needed.  I didn't shop around because I had confidence in our heating and air-conditioning man and he said it was the best.  People who have seen others comment on how well built it is.  Ours is hooked into the duct work along with an electric furnace/heat pump.  There is a heat sensor on the waterline that goes to a relay.  When the water from the furnace gets below 120 degrees,  the relays allow the electric furnace to come on.  My wife sure appreciates the unlimited supply of HOT domestic water ;D
milking and logging and sawing and milking


I have a Hardy and had no problems with it. Only had it for about 10 months but use it to heat the house and a greenhouse. Also used it on a kiln that is still under construction and have been able to get the temp up to 145 to 150. One thing to consider is the location. I have mine over 100 ft from the house but in a good location for handling the firewood.  I handle the firewood on pallets that can be moved with a FEL. (see my photo gallery). If I had to handle the firewood very much, I would not have gone with the furnace.


I think that lots of water is good.  I have a 6 year old CB that holds 400 gallons.  I have filled the stove at 6 in the morning when it was -20f and come home to a fire that did not burn and a warm house.  There are a lot of btus stored in 400 gallons of 180 degree water.  I was told the same things about stainless by the dealer that sold mine.



Great advice!  Much appreciated.  Please keep it coming!

Pinenut - What model Hardy do you have?  I like your system of palletizing the wood!  I have a FEL as well, and I can see the advantages of stacking it this way - very little handling... now if you could just load the stove with one of those pallets.  :)  BTW, the crane photo was entertaining, if not sobering!

Engineer - I'm heating a timberframe home as well... about the same size.  R-24 SIP walls, and R-50 PolyIso ceiling insulation.  Your experience is encouraging.  I have radiant tubes installed in the basement, but not on the first and second floors (yet).  House is still under construction.  Hoping that the basement tubes will be enough to heat the house up some and take the edge off while we're working inside this winter.  Question - did you use water-to-water heat exchanger or simple mixing valves when you tied your outside furnace water (hot hot) to your radiant heat water (medium hot)?

I've wondered about water storage.  The Hardy that I'm looking at stores only 160 gallons of water, whereas the Hicks stove stores a whopping 1,000 gallons of water.  But it looks like one could store additional water inside the house - so long as the Taco pump is circulating enough volume?  I haven't done the calculations, but there has to be some water storage in the 3000 feet of radiant tubing I will have as well. (albeit at a lower temperature).

Thanks again for all of the advice so far.



As a neighbour to one and in my research, buy the smallest one that will work cause when they run under part load or have the solenoid damper slamming shut all the time they smoke like crazy!  Some of the good models as far as smoke is concerned have a power induced draft fan on the stack that seems to really clean up the burn.  Also, the ones that smoke less normally have firebrick liner so the fire can burn hot and clean.

Have been looking for myself but the best wood boiler I have found has been out of production for almost 10 years.  Dr. Richard Hill from Orono Maine was involved in several water storage wood boilers that were built from the early 80's till the mid 90's but people have been burning less and less wood so companies stopped producing the Jetstream furnace.


Well, unlike others, I have don't even have dos colones worth of advice for you.   

But I think cabin fever is starting to set in enough for some folk so I won't mention why...  ;D
So, how did I end up here anyway?


I have had a Heatmor for 2 years and really like it.  We heat our house (about 1800 sq.ft) and our office/warehouse (2000 sq. ft.).

Before we installed it we heated the house with wood and also a propane wall furnace  and the office with propane hot water baseboards.  The house used about $800/yr in propane as well as 3-4 cubic cords of hardwood.  Domestic hot water was propane.  The office/warehouse used $2200/yr in propane.

We burned around 6 cubic cords last winter and I expect around the same this year.  I agree with a previous post about getting the oil backup burner as you can go away and not have to get someone in to load the stove.

The heatmor doesn't boil the water.  It heats it to 180' F then shuts off the electric fan/draft.  When the water drops to 155'F the fan starts up again.  As the firebox is airtight when there's no draft there is just a wisp of smoke coming out the chimney. There is a pump that runs all the time circulating the hot water.  We haven't noticed higher electricity bills so it must not draw much.

Overall we like it because both buildings are WARM!

The only downside is the extra wood I don't have a lot of time to cut, haul, stack, etc.
100 acres, Lucas 618, Universal Tractor w/loader, chainsaws, cant hooks and not enough time to play!
Fear is temporary...regret is forever.


Quote from: Thomas-in-Kentucky on December 13, 2006, 08:42:01 AM
Engineer - I'm heating a timberframe home as well... about the same size.  R-24 SIP walls, and R-50 PolyIso ceiling insulation.  Your experience is encouraging.  I have radiant tubes installed in the basement, but not on the first and second floors (yet).  House is still under construction.  Hoping that the basement tubes will be enough to heat the house up some and take the edge off while we're working inside this winter.  Question - did you use water-to-water heat exchanger or simple mixing valves when you tied your outside furnace water (hot hot) to your radiant heat water (medium hot)?

I used a copper-plate heat exchanger.   The radiant in the basement does more than take the 'edge' off - it's actually comfortable living space.  My only issue right now is 'dumping' excess heat - I'll give you an example.  It's been in the upper 30's and 40's, day and night here, since Sunday.  Yesterday morning I fed the boiler and it boiled over and steamed up.  I haven't touched it since then, checked it this morning and there is still a half-box full of firewood and the boiler temp is at 190 degrees.  I have no good way of gettting rid of the excess heat.

EDIT:  I think I've figured out how that monster boils.  The draft door solenoid kicks the door open when the boiler water temp is 169.  Usually, there's just some small coals or buried coals and a large pile of firewood that has spent several hours "cooking" (for lack of a better word), and is good and dry and partially charred.  When those coals catch and the draft kicks in, that pile of hot, dry wood turns into an inferno.  I've had flames coming three feet out the door when I've opened it up toward the high end of the draft cycle.  What happens is, when the water temp hits 180 and the solenoid shuts the damper, that fire is still so hot and no place to dump the extra heat (especially on a relatively warm day), the water jacket boils.   The residual fire/heat/coals drives that temperature up another 20 degrees, even without a draft.    It won't boil if either A) the inside circulator pump is on a demand call and is feeding the floor loop, or B) it's a cold day, usually below freezing.

I haven't figured out the trick to timing the feedings yet so that it won't boil on me, yet won't go out entirely so that I have to start the fire from scratch again.



Have you thought of setting the temp down on the furnance to a lower temp on the days that are warm. I have not experience the problems you are having but I have a house, hotwater heater and a shed running all the time. I using force air in both the shed and house.   Also have you consider putting a smaller load of wood in the furance and let the coals burn down a little furthur.

I would think that the problem you are having would happen with most outdoor furnance. My dad has had the problem with his (aque therm) funance when the electricity goes out and the pumps can not circulate.


Sawing part time mostly urban logs -St. Louis/Warrenton, Mo.
LT40HG25 Woodmizer Sawmill
LX885 New Holland Skidsteer


I have had the similar experience as you with my wood boiler. I partially shut down the draft opening to lessen the air intake. That way their isn't such an inrush of air. It was a matter of learning over time just how much draft opening was enough, but not too much. If I want a roaring fire, then I open the draft full.
The other thing to learn over time, is how much wood in the firebox is needed when it's not cold out, and the wind is or isn't blowing, and a number of other tricks needed to have good control and not blow off any steam, or have a cold house. Knowing your wood supply is an important factor in the equation as well.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others


It's a learning experience.  As I said, I've only been running it for a total of six, non-continuous months, and I'm not there all the time as the house is still under construction.  Another factor is that most of what I've been burning is offcuts and scraps from the house project - mostly pine.  I have a huge pile of it that I'm trying to get rid of, and along about February I'll have burnt thru most of it and can start on some hardwood.


I have the Hardy H4, 130 gallon, 180,000 BTU. Most people around here have the smaller H2, 100 gallon, 120,000 BTU. I wanted the larger one so I could put a larger load of wood in it. It also provides the extra heat for the green house and kiln. As I mentioned earlier, it is very important to set it up for the ease of firewood management. I have a metal carport right next to the furnace for the firewood. No problem to load it in the rain. I have not had any problem with boiling the water except when I failed to close one of the doors. I don't have the domestic hot water connected yet. I just can't seem to find that round tuit. Seems like I saw the literature on a furnace you could load with the FEL but I think it would be a bit large for a home.


What do you do for hot water in the summer? LeeB
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.


Quote from: LeeB on December 13, 2006, 05:30:31 PM
What do you do for hot water in the summer? LeeB

Either feed the boiler or let the backup propane burner take over.


For the water BOILING over you need to adjust the high temp shut off temperature down a bit lower. OR go to a different type of thermostat which can sence WHERE the temp is and when it shut down sooner to prevent this.   One of the guys at work has recently changed his and now uses alot less wood as well as 0 boil overs since then.   His was a simple bulb stat and he upgraded to a better unit with beter control features...    Anyhow one other thing is to make sure you're DOOR seal is goo all way around and making contact, any I mean ANY air leaks can cause boil over too...   Also make sure all dampers are closing fully..  some use dampers on both stack and intake air, others use pressure blower on inlet and dampers on stack ect.   all of these work in conjunction to maintain temp inside the water jacket.   

Mark M
I'm looking for help all the shrinks have given up on me :o


I won't be much help since i built mine, I've turned my water temp all the way down to 160 degrees. Mine gets the heat in the trailer VIA an water to air heat exchanger under the furnace. Furnace blower moves tha air across it and through the ductwork. At 180 degrees I was getting boil overs. Part of the problem is the door design which I'm working on changing. Also at 180 degrees you couldn't step on a register without getting a minor burn.

I also found burning green wood on warm days helps keep the heat down

Breezewood 24 inch mill
Have a wooderful day!!


Engineer, I think Spiker has answered your boil over problem, with the thermostat. I have the 5648 also and have never boiled over. Our house is 1800 sq. ft so the furnace is way over kill. I bought this size in anticipation of taking it with us to the farm when we move there.
Grass-fed beef farmer, part time sawyer

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