Outdoor Furnace

[skent]

I have been struggling with the decision of switching over to using an outdoor furnace. I hoped the wisdom of the board could help.

For those of you who are not sure of what an outdoor furnace is, Basically you have a small shed, located outside, that contains a wood fired boiler, with underground pipes connecting the heated boiler water to a water to water heat exchanger (for heating domestic water) and a water to air heat exchanger located in the air plenum of the existing heat pump. The outdoor furnace has a damper to control the fire that is controlled by the boiler water temp. When water hits 140 to 160, the damper shuts back and the fire goes into a slow burn. When needed, the damper opens and fires up. Water is in a loop and is circulated by a small electric pump. To see an example of an outdoor furnace, go to www.centralboiler.com Other companies make wood fired boilers that are not packaged in the weatherproof shed, to be installed indoors.

Prices of complete outdoor systems range from $4500 to $7500. (does not include installation) Other systems that could be installed in an existing pole barn range from $3500 to $5000. In my location, with my size house and from history of electric usage, I am expecting to use 5 to 6 cords of wood per heating season (mid October through mid April) The higher priced system has a 10 year boiler warranty, cheaper systems have a 3 to 5 year warranty. Cheaper units will need refueling every 12 hours, more expensive units can go as long as 48 hours between stoking, depending on type of wood used.

I have 8 to 9 acres of wooded area that could supply fuel. I have been cutting and splitting firewood in the past (to sell) and estimate it actually costs me 20 to 30 dollars a cord (chainsaw gas/oil, wear and tear on saw and blade, gas for splitter). Time wise I can process (cut/transport/split/stack) a cord of wood in less than a day.

After careful reviews of heating costs over the past six years, I have carefully figured the electricity used per month and have determined my current heating costs are in the range of $600 per heating season. Our heat pump has a very high efficiency and was sized one size larger than what was minimum for our size house. It has a 15KW resistance back up that is only used (and then in 5KW steps) when the Heat Pump can't keep up, usually only occurs when outdoor temps drop below +15 degrees.

If I go with a boiler in my pole barn, one with a 10 year warranty ($5000), its going to save me $450 per year ($600 saving in electric minus $150 wood processing). Time to recover my initial cash outlay is 11 years. I could be faced with having to replace a boiler at my cost before I achieve payback. Up side is we all know energy costs are going to increase over the next decade (but how much?), thus shortening my payback. Re fueling with this unit would be once a day, ash cleanout once a week, wood could be stored in polebarn and residual heat would keep polebarn slightly warmer. Downside is the labor involved in harvesting/storing/moving wood (six days to process six cords) and feeding a wood boiler, cleaning ashes out, boiler maintenance, electric used to run circulator. I am 45 years old and in reasonably good shape. Will I be able to harvest wood at this rate in 10 years? 20 years ?

Does anyone on the board have experience with outdoor furnaces'? Good or Bad.

At this point, I am tempted to wait and see. . . . . . what do you think?



Steve

 

[StoneHeartFarm]

Steve,

I have seen several of these systems in operation (they are quite popular here), and have talked with owners (independently of any dealers). /w3tcompact/icons/wink.gif I have even helped construct one from scratch (air powered) and talked with a machinist who was building one from scratch (water powered). There are basically 2 different system types. One pumps in air from around the heat chamber, and the other heats water and pumps that in. The first commercial unit I saw in action was a water pumper that the owner had used for 3 years. It fed water throught a "single side arm" exchanger connected to the domestic water heater and then ran through a heat exchanger on his furnace's air plenum. There were 2 thermostats (one for the blower and one for the LPGas furnace). The owner reported he felt the furnace had paid for itself in the 3 years he had owned it. (Winter nights here average about 10+ with a couple of weeks of 40- early in january).

There are ALOT of different manufacturers of these furnaces. Check carefully before you buy. You can probably put one in your pole barn, but they make furnaces for this application. Furnaces that MUST be put inside. The outside ones (the ones that have a little metal shed around them) usually put out a LOT of heat. I have been investigating them for about 5 years. Here, a $5,000.00 (uninstalled cost) unit would be rated to heat my house, pole barn and maybe a hot tub and part of the driveway. (Yes, you can use them to heat your drive). There are extra costs to install, and you might want to check them out. The dealers I have talked to usually do the installation. Water is pumped into the house through a (deep) trench with a water line (pex pipe) laid inside a 4" or 5" insullated and water proofed PVC pipe. The good news is that pex pipe appears to be able to handle freezing and I've never heard of an estimated life span for it, so once it's in, it's good for a lot longer than the furnace.

Also, I checked the pumps on these furnaces, and they only draw about 1 amp or so. There are solar kits that can be added to keep the pump going in the event of power failure. (not much use unless you have HW heat with radiators or radiant floor.)

So, don't forget to consider your domestic hot water usage when comparing costs. New 50 gallon electric water heaters are estimated at about $300-$400 per year to operate.

Good luck /w3tcompact/icons/cool.gif

SHF

 

[Anonymous Poster]

Since you already have a high efficiency heat pump why don't you just put in a high efficiency fireplace insert or a wood stove? The payback period would be much shorter. The other thing that concerns me is that you will have quite a bit of wood cutting to do into your twilight years. The downsides that I can think of are that the fireplace insert will not heat your whole house and it would probably be easier and less messy to stoke the furnace if it was outside instead of in the house. Don't forget to add in the value of your labor while you are wood cutting.

Another thing, your payback period will only be valid if you do not spend any extra money on maintenance of your new unit. You are already accounting for replacing the boiler but are you sure nothing else will go wrong? What will the price of a boiler be seven years down the road? Please note that I am not necessarily trying to talk you out of doing this as the heating and air-conditioning system in my house is going to be the victim of some drastic changes also, it is just that since you already have a high-efficiency unit, I think your payback may be too far out there. However, if you can get free hot water out of the deal then maybe that tips the scales in the direction of the outdoor furnace. Good luck with your decision.

 

[Corm]

I looked into outdoor furnaces quite a bit last fall. I found there pro's and con's, and for me there were more cons.
PRO'S * All the mess is outside * Only stoke it once or twice a day * Don't have to haul firewood into the house * Could heat my shop with it as well as the house * No chimney to clean. CONS * Expensive * Only a few have an oil burner attachment, and those that do are NOT efficient * If you don't get an oil burner attachment, then you have to maintain a 2nd furnace in your house that will run on auto-pilot when you leave your house overnight in the winter time * They smoke a LOT, I mean a real LOT.

For me, the con's outweighed the pro's. I would really like to have one because I think they are pretty neat, but I just couldn't justify one. If I may give a bit of advice, it really pays to shop around and look at them all. For the shopping I did, I felt the Heatmoor was the nicest unit, with the Mahoning a close second. Good luck with whatever you decide to do.

Corm

 

[M. Sullivan]

I second kubotadrivers thoughts on an indoor burner. Check-out Lopi brand, they have everything from rustic to contemporary. Had one in a 65x35 ranch, and it did the job fine all Michigan winter. I think the top of the line is around $2500, with an average around $1200. Can do the installation yourself if you're a bit handy.

Don't think I would want to chop 6 cords a year in my 60's, might consider the cost of a splitter in your analysis. Good luck, let us know what you end up with.

 

[ejb]

Seems hard to justify with an 11 year payback, especially if you factor in what you could possibly be doing with your time instead of processing wood. Something to consider is picking up a second-hand furnace. They can be found and sometimes only a few years old and at 1/3 to 1/4 the cost. That would really help your cost/benefit analysis.

Good luck.

 

[geneP]

Skent, I haven't considered an outside furnace since our winters are typically much milder than yours, but I have cut/hauled wood for a wood heater when I was younger. The last time my central AC went out, I replaced it with a heat pump, figuring that I would get too old to want /be able to cut and haul wood. I continued to use my wood heater until I had to remove it from the fireplace to have the chimney cleaned. While it was out of the house I decided to use the heat pump for 2 or 3 months just to see how it worked and how much it cost to run. I've not put the heater back in since then. The heating costs are smaller than the cooling costs, and there is no mess from burning wood to contend with. While this might sound like an endorsment for the heat pump, I'm really stressing that as we get older, it gets harder to do the manual chores that come easily while we are young. And the body takes longer to recover from these attacks on it, especially if we have non-manual daily jobs and only "work" occasionally. I think you're at the age that cutting wood might not be fun by the time the furnace reaches it's payback. We're all different and you might be more industrious than I am.

On the plus side, You can figure some cost savings for the wear and tear you'll be saving on your heat pump's longivity.. Maybe you can't exactly quantify the wear/tear cost, you can consider it if you're right on the go/no go line.

 

[skent]

Already have a splitter, hydraulic pump runs off the pto of the Kubota. Its still labor intensive.

It's alright now, and maybe even five years from now. but how about when the splitter needs repairs, or chain saw wears out or when Stevie wears out. . . . .

Steve

 

[bpence]

We added a wood fired boiler to our home heating system in 1981 and generated about 75% of our total heat from the wood boiler for 14 years. We cut, split, hauled, moved, stacked, moved again, and re-stacked more wood than I can even remember. We burned about 4-6 federal cords per year, depending on the severity of the winter. The last few years we burned seriously we bought logs by the semi-load from Michigan's UP. All in all it was very cost effective to heat with wood. I didn't mind having a full-time part-time wood management job, but my wife and I just got tired of handling wood all the time.

Although we didn't use an outdoor furnace, I thought I'd share my experiences so you could maybe get a grasp on the size of the task you're talking about taking on. It's great physical exercise, and it's also back-breaking work that goes on month after month, year after year. Gotta keep next year's woodpile growing and when an opportunity to get some good wood at the right price pops up, gotta go. Other folks may say that it's not all that much work, although I think maintaining a woodpile to feed a furnace is a huge undertaking.

Just think seriously about it before you jump in. I quit feeding the wood boiler when I was 45. I could still handle it physically then, today, and into the future for a while. My wife and I just decided we wanted to do other things and the price we had to pay was to heat our home differently. That's my two or three cents worth.

Bob Pence

 

[ejb]

4-6 cords doesn't sound too bad to handle. My brother in law lives in Maine and heated a very big old (read poorly insultated) farmhouse with a wood furnace for about 15 years...he used 25-30 cords of wood a year...now thats a lot of work. (and yes, he cut, split and stacked all of it..with some help from friends and family)