Need some information on wood furnaces
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pdboilermaker
New Member
Obviously here is a great place to start. Another good one that is broken down by manufacturer is http://www.outdoorwoodfurnaceinfo.com/forum/
I think that most makes are represented here, I have a Woodmaster 4400 and love it. Heating a 4400 sq ft, 100 yo farm house in north central Indiana, no windbreak, r-19 in the walls r-38 in attic. I use 10-15 cords per year running an upstairs furnace, a downstairs furnace, and dhw.
Mine is 5 years old, the only issue that I have had is I had to replace my draft fan. Boiler sits about 50' from the house with pex in the ground at 48"
I think that most makes are represented here, I have a Woodmaster 4400 and love it. Heating a 4400 sq ft, 100 yo farm house in north central Indiana, no windbreak, r-19 in the walls r-38 in attic. I use 10-15 cords per year running an upstairs furnace, a downstairs furnace, and dhw.
Mine is 5 years old, the only issue that I have had is I had to replace my draft fan. Boiler sits about 50' from the house with pex in the ground at 48"
WoodNotOil
Minister of Fire
Please describe your current fossil heating system so that we can give you ideas...
http://dhs.wi.gov/eh/HlthHaz/fs/waterstoves.htm
Be cautious about installing an OWB. Read the above from your state. More and more states are regulating these stoves and in some states even current owners must alter their systems to comply.
Considering the inefficiency of the design and cost of OWB boilers, you are better off installing a gasification boiler.
http://dhs.wi.gov/eh/HlthHaz/fs/waterstoves.htm
Be cautious about installing an OWB. Read the above from your state. More and more states are regulating these stoves and in some states even current owners must alter their systems to comply.
Considering the inefficiency of the design and cost of OWB boilers, you are better off installing a gasification boiler.
I have a 3000 sf 2 story house including the basement with a 90,000 BTU high efficiency NG furnace which sits on the original pad. Currently, my wood stove is using the existing utility chimney with a 6" flex liner that is coming in from the opposite side of the original opening. I'm in town so doubt anything can go outside. I also have a tankless water heater.
WoodNotOil
Minister of Fire
wendell said:
I assume this is a forced air system by your description and not a hotwater system. Your options are a forced air wood furnace or a wood boiler with water to air heat exchangers. I have heard that the wood furnaces require frequent filling to keep the NG from coming on. I have heard there may be some with secondary burn for higher efficiency, but am not familiar with them.
The more efficient option that many here have done is a gasification wood boiler with the water to air hx. Check out my site to see some of the boiler options, but others will chime in with their experience with these. Lots of brands to choose from. However these systems can cost a lot to get up and running.
Do you have access to a flue in the basement? Another option is to put it in its own structure or in a garage (codes may prohibit it though).
Yes, it is a forced air system. Although I would like to keep the stove in the basement the only way I could see this working is to pull it out and use the chimney for the wood furnace. My other option is to add a second wood stove so I'm not looking to spend much more than that would cost so most likely a boiler would cost much more?
WoodNotOil
Minister of Fire
wendell said:
Yes it would... a second wood stove would be much cheaper if cost is an issue and if that would meet your needs. The advantage of a wood boiler is that your system would run off of a thermostat and you would have much better control over room temperature. Gasifiers with heat storage can also give you the more flexibility to burn wood when it is convenient for you. BUT it comes with a large price tag. Just read the threads on here about choosing wood boilers and look at some of the retailers that run ads here for prices and I think you will see what I mean.
That said, I wouldn't trade my gasifier and storage for anything...
WoodNotOil
Minister of Fire
wendell said:
Two options for wood furnaces would be the Yukon Superjack and the Caddy EPA wood furnace. Both run in the $2500 range and have secondary combustion making them more efficient. I haven't seen the numbers so I can't say whether they are as efficient as the gassification boilers or not.
The advantage I see of the boiler with air to water hx is the ability to add heat storage to increase efficiency and store heat for when there is no fire and for off season direct hot water. Direct hot water is definitely a benefit. Also, you can add radiant heat to your house, garage, additions, etc. Gasification boilers however start at around double what the above mentioned furnaces run. Plus the heat exchangers, plumbing, and eventually the cost of setting up heat storage. I think it is worth it in the long run. Compared to the cost of burning fossil fuels, these systems usually pay for themselves in just a few years.
I agree, the only good furnace options are superjack and caddy, some may disagree, but thats my opinion. As far as a gasification boiler and storage - well I hate plumbing, and if I had to do all the plumbing, I'd just burn propane - but only having to have one or two fires a day and also taking care of the hot water sounds enticing.
I'll just tell you about my superjack, which I am pretty happy with. It heats a very big house, over 4000 sq ft, and it is very efficient when the weather is cold. Shoulder season is hard (but it is with a wood stove I think too), and the house gets too hot or the fire smolders too much. I think it is indestructible, very solid, everything works well. The lack of a window on the door bothers me, but the way it is engineered it cannot have a window on the door (uses the door to heat incoming air). My first year (last year) I smoked up the garage (where it sits) a bunch, but not once this year, that was just part of the learning curve. It will burn wood over 20% and still do a good job heating - I know this for a fact from last years wood, and even some of this years wood, but that produces a lot of ash. Yukon-eagle is very helpful, and have answered all my questions, and I think they have great customer service. I am not sure that they are developing any new wood burning products, they seem to be just content with what they have, that concerns me some.
I think the caddy has a much better secondary burn, and a window you can see it with, but I just am not sure it could keep up with my house size. It was not available when I bought, so it was not an option.
If you had any specific questions about my superjack or yukon, I'd be glad to answer them.
I'll just tell you about my superjack, which I am pretty happy with. It heats a very big house, over 4000 sq ft, and it is very efficient when the weather is cold. Shoulder season is hard (but it is with a wood stove I think too), and the house gets too hot or the fire smolders too much. I think it is indestructible, very solid, everything works well. The lack of a window on the door bothers me, but the way it is engineered it cannot have a window on the door (uses the door to heat incoming air). My first year (last year) I smoked up the garage (where it sits) a bunch, but not once this year, that was just part of the learning curve. It will burn wood over 20% and still do a good job heating - I know this for a fact from last years wood, and even some of this years wood, but that produces a lot of ash. Yukon-eagle is very helpful, and have answered all my questions, and I think they have great customer service. I am not sure that they are developing any new wood burning products, they seem to be just content with what they have, that concerns me some.
I think the caddy has a much better secondary burn, and a window you can see it with, but I just am not sure it could keep up with my house size. It was not available when I bought, so it was not an option.
If you had any specific questions about my superjack or yukon, I'd be glad to answer them.
WoodNotOil said:
How does the add on hook into the existing furnace? I assume that when the thermostat calls for heat, air into the firebox is increased and the heat is pulled from the add on? Where does it need to sit and how far from the chimney can it be? Will the existing 6" flex I already have in my chimney be OK?
Gooserider
Mod Emeritus
wendell said:
The configuration and details like you ask vary with the unit - you pretty much have to pick a few likely candidates and then look at their install manuals... The smaller units will probably be fine with a 6" liner (assuming it's properly rated for your wood stove) some of the larger ones would want an 8" flue. Typically you tie the add-on into your existing ductwork, but the details depend on the exact unit you choose and the details of your existing setup.
As a comment on the difference between a furnace and a boiler, in the cold season, you probably wouldn't see a big difference with a properly sized unit, as both would be running pretty steadily. The big difference is in "shoulder season" - with a furnace, there is no way to store heat, so you have to essentially keep the fire going 24/7. This you get a lot more problems with possibly over heating the house, and / or excessive idling if you put a lot of wood in at a time (makes for creosote) or a need to run a small fire that needs frequent feeding...
In a boiler with storage, you have a tank full of water that you heat and then draw the house heat from the storage tank if the boiler isn't burning - Thus the use pattern is different - you build a fire, and let it run flat out while you heat the tank, and then let it go out - ideally you never idle. This can mean 2-3 fires / day during peak heating season, depending on the boiler and storage sizing, load, etc... However in shoulder season you might only need to build a fire every 2 or 3 days. Some of our members that also use the boilers for DHW in the summer time report needing to build a fire only once a week...
Gooserider
A real-life example of what Gooserider said - this is my first full winter with my Tarm Solo 30 and 670 gallons of storage, also used to heat my DHW. We got up and running about a year ago. We're heating a 2500' sq ft house plus keeping the basement fairly warm, and we used to use just over 1,000 gallons of oil a year. This summer, just about 1 fire a week took care of 100% of the DHW for my wife and I. Starting in September, a fire every 2 or three days let us run a little heat when the house got chilled. October and November saw a fire every night providing enough heat to last until I got home from work the next day. Since early December I usually have a fire in the morning and one in the evening, but it absolutely never gets stoked by my wife while I'm at work, and the final loading is never later than 9pm or so, we haven't had any weather severe enough to require a midnight stoking, but it might be necessary at 20 or 30 below with a wind. On weekends, I often have a single fire and charge the tank up to its max rather than having the morning and evening ritual.
I know yukons sight www.yukon-eagle.com has a manual that you can download so you can see clearances, how to hook it up to existing ductwork, requirements for chimney, ect. Also a quick call to them will get you those answers. I would guess the same applies to the caddy sight.
wendell said:
laynes69
Minister of Fire
You should get an idea on your heat load of your home. The caddy is a nice furnace, and does require a 6" chimney and good seasoned wood. I would recommend you figure out how many btus you will need to heat your home. When running a wood furnace, you get a steady supply of btus to your home unlike a gas furnace where it shuts on and off. How is your square footage divided off in your home per level. The caddy can close down and burn cleanly which puts it ahead compared to most woodfurnaces. If your current wood stove is a non-cat then the operation of the caddy wouldn't me much different. Just all the heat would be ducted and distributed through the home. You can do an add-on which would cost less and would use your central furnaces blower (series), or you could get a unit with a blower housing built into the furnace and run a parallel install. The caddy requires 6" for the first 6 feet of ductwork of clearances.
Gooserider
Mod Emeritus
wendell said:
Square feet estimates are guesses at best - you MUST do a "heat loss" calculation on your house, something formally known as a "Manual J" after the standards book that describes how it's officially supposed to be done. I have a couple of links in the "tidbits" sticky to sites that will let you do reasonably good approximations. Slantfin used to have a free calculator program download that was really nice, but they've taken it down a while back, and I don't think it is back up. I've heard that some of the stuff on the Taco site will also do it, but I haven't checked personally.
The problem with square foot estimates are that there are to many variables - how "tight" is your house? How cold does it get in your area? How warm do you like it inside? etc... The rate at which a house loses heat is a function of the difference between the inside and outside temperatures and the construction of the structure. The greater the difference, the more heat a given house will lose per hour, and thus the more heat output you will need from the heating system - Essentially to keep a constant temperature, your heating system needs to put out exactly as many BTU's per hour as your house loses... Thus you will calculate your load based on "design day" conditions - the coldest day of the year expected in your area, and the inside target temperature you want to maintain. You will need good measurements of the sizes of all the walls in your house, plus the areas of doors and windows, and what sort of construction is used, etc.
The knowledge that you have a 90K furnace is a decent starting point - your heat load is probably less, as most heating installers tend to put in oversized units (Truism in the industry, "nobody complains about having to much heat...") You probably want a wood unit that is reasonably close to that, or maybe a bit more (but do the calcs to be sure!) The cyclic nature of a wood fire does cause a bit of a problem - the output numbers on wood units tend to be the peak outputs, figure that your average over the course of a normal burn will be more on the order of 75-80% of the rated output...
Gooserider
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