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  1. #1
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    Default Anybody convert a wood furness to boiler?

    Wood boilers are very expensive and I'm not sure I want to invest in a system that will just get used during the coldest times of the season. Our house is going to have radiant heat in the slab. And AC ducting for Summer.

    Here is what I'm thinking; Get a common used wood furness made for hooking up to the air duct system. Remove sheet cover and wrap with 1" copper tubing. Replace sheet cover. Plumb to storage tank. Keep the duct work attached. Then by thermal siphon and or pump, circulate to the storage tank. Radiant heat system would pull from storage tank as a pre-heat. Keeping the duct system intack would allow to have the squirel cage "cool" things off if it reach excessive temps. Other wise, all heat transfer would be the copper pipe.

    The storage has a duel purpose, I'd like to have hot water solar panels feeding this tank as well. So in theory, sunny days the solar would pre-heat and during cold cloudy days I'd have a fire.

    Comments?

    Patrick T

  2. #2
    Bronze Member zukota's Avatar
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    Default Re: Anybody convert a wood furness to boiler?

    Quote Originally Posted by Paddy View Post
    Wood boilers are very expensive and I'm not sure I want to invest in a system that will just get used during the coldest times of the season. Our house is going to have radiant heat in the slab. And AC ducting for Summer.

    Here is what I'm thinking; Get a common used wood furness made for hooking up to the air duct system. Remove sheet cover and wrap with 1" copper tubing. Replace sheet cover. Plumb to storage tank. Keep the duct work attached. Then by thermal siphon and or pump, circulate to the storage tank. Radiant heat system would pull from storage tank as a pre-heat. Keeping the duct system intack would allow to have the squirel cage "cool" things off if it reach excessive temps. Other wise, all heat transfer would be the copper pipe.

    The storage has a duel purpose, I'd like to have hot water solar panels feeding this tank as well. So in theory, sunny days the solar would pre-heat and during cold cloudy days I'd have a fire.

    Comments?




    Patrick T
    I didn't completly follow your description, but look into the construction /install of an 'outdoor' wood furnace - there is NO magic there..
    - Max

    1 Machine 2 shades of Orange.

  3. #3
    Super Member Highbeam's Avatar
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    Default Re: Anybody convert a wood furness to boiler?

    You are installing radiant heat in the floor slab. How do you plan to heat the water for the slab other than wood? Is there a conventional boiler for that? A water heater? Since the floor is a circulating system there is no "preheat" benefit as there would be with preheating water prior to the domestic water heater.

    Just buy a wood boiler. It's not worth destroying a perfectly good wood furnace to create a hokey boiler.
    Kioti CK30HST, FEL w/toothbar, 60" RC, 60" BB, PJ 10k trailer. Weekend warrior hauling 50 miles each way.

  4. #4
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    Default Re: Anybody convert a wood furness to boiler?

    Highbeam,

    Yes we will have an ele boiler as the main heating source. Have to be prepared to leave town on short notice. There are plenty of plumbing schematics for adding solar or wood heat to a boiler. As I said, wood boilers cost $10,000 and used wood burners are $300 -500, so to me worth looking at. I have seen photos on web searches where this has been done. Wrapping copper pipe around a wood burner would not destroy it in either case. Just take time and $$ in copper tubing.

    Some examples I have seen are simple copper coils wrapped around the stove pipe. This is bad because it cause flue gasses to cool to the point of creasote. In Europe they use what they call "back boilers". This is a small tank strapped to the back of a stove. There most heat is via water.

    Patrick T

  5. #5
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    Default Re: Anybody convert a wood furness to boiler?

    Zukota,

    The problem with those outdoor boilers are they have a water jacket. The water has max temps of 212 deg F, and that is far lower temp than complete combustion. In the end, they burn real smokey. Some places are banning them. Indoor boilers have high burn temps and burn clean. extracting too much heat become a big issue.

    Patrick T

  6. #6
    Bronze Member zukota's Avatar
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    Default Re: Anybody convert a wood furness to boiler?

    Quote Originally Posted by Paddy View Post
    Zukota,

    The problem with those outdoor boilers are they have a water jacket. The water has max temps of 212 deg F, and that is far lower temp than complete combustion. In the end, they burn real smokey. Some places are banning them. Indoor boilers have high burn temps and burn clean. extracting too much heat become a big issue.

    Patrick T
    I really don't think the water jacket causes the outdoor stoves to be smokey. Those boxes are big enough for the center of the fire to get well above 212 deg. They smolder because the water is hot enough that the jacket thermostat never calls for much draft. - My brother in law has built a few.

    I guess my point was that you would need to make the wood furnace to be like the outdoor stove and have it automatically 'shut down' when the water got too hot - yes you would have a creasote issue to deal with. I've never used a wood furnace, maybe they have that issue solved?
    - Max

    1 Machine 2 shades of Orange.

  7. #7
    Elite Member
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    Default Re: Anybody convert a wood furness to boiler?

    Current wood boilers are loaded up technology wise. Your method is how they used to be made. Much depends on a viable wood source. Heating air is much easier for a wood appliance or I should say more efficient so much wood wil be used to heat the water. There is a reason wood boilers are 10 grand. Look at what they must do for a continuous burn viable enough to heat water that is now going to be looped. It seems to me the most important aspect here is how well insulated the storage tank is and it has to be of several hundred gallons as exchange will rob many btu's. My personal favorite method for heating with wood is the wood furnace that is ducted thru-out the house. I hope your combination works but you are going to have to feed that furnace/boiler often when you get a cloudy day. I think the best part of your idea is the combination of solar and wood. Don't forget to install the safety valve if you go thru with this. In the end, it might be cheaper to duct your bottom floor and use a wood furnace with the solar backing up your radiant floor heat. You'l use less wood and you won't be bothered with the tie in. Ducting is rather simple with feed and returns.

  8. #8
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    Default Re: Anybody convert a wood furness to boiler?

    arrow,

    Water heating does have it's advantages. Water holds much more BTUs per unit volume. Heated water can be stored for quite some time. This allows Batch heating. Heated water can be moved a long distance with minimal heat losses, (easy to insulate a 1" dia pipe). With all the floors being concrete on a steel joist structure, warm floors will be primary way of heating. Radiant heating requires much lower source temp, 85 to 95 deg F. There is a lot of thermal mass in the concrete and water. We are using ICF and they are tight and insulated. Hope the BTU need is nearly as low as I hear.

    Patrick t

  9. #9
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    Default Re: Anybody convert a wood furness to boiler?

    Quote Originally Posted by Paddy View Post
    arrow,

    Water heating does have it's advantages. Water holds much more BTUs per unit volume. Heated water can be stored for quite some time. This allows Batch heating. Heated water can be moved a long distance with minimal heat losses, (easy to insulate a 1" dia pipe). With all the floors being concrete on a steel joist structure, warm floors will be primary way of heating. Radiant heating requires much lower source temp, 85 to 95 deg F. There is a lot of thermal mass in the concrete and water. We are using ICF and they are tight and insulated. Hope the BTU need is nearly as low as I hear.

    Patrick t
    I am not arguing that. Thermal mass absorbs large amounts of unutilized energy until needed. The problem here is that one must create large amounts of of btu to even get to storage point. This is another heat exchange however and before I jumped in, I'd know for sure if your temp assumptions are indeed correct. If you look at the curent batch of wood boilers, there are several types. Some practically gasify the burn and others rely on a very hot , quick fire to heat up hundreds of gallons. One even has its water storage surrounding the fire box with a container of 1500 gallons. Coils have proven to be problematic in that to even approach the heat output of say an oil fired boiler, burns long and hot enough have caused a breakdown of the old traditional copper coil open to a fire box. Cost is a large consideration for you and I know you are trying to avoid as much as possible. You want to tie in your current water based system to a wood fire. If you are determined to utilize water, I think what I would do in this case is not even invest in a wood fired furnace just yet. I would buy a couple of 55 gallon drums and build the double drum wood stove. I would then add the heat reclamation tubes that you plumb into the stove that are available or build your own, mount them into the top drum and see what you get with this set up. This way you have not invested alot of money to turn something into something else and you can customize to kingdom come. My idea for the wood furnace was just to make it easier for you to involve yourself with heating with wood.
    They in their own right are not an inexpensive start point hence my suggestion for the barrel stove along with the fact you are kind of starting from scratch which in my mind opens up a host of customizing availabilities.

  10. #10
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    Default Re: Anybody convert a wood furness to boiler?

    Quote Originally Posted by Paddy View Post
    arrow,

    Water heating does have it's advantages. Water holds much more BTUs per unit volume. Heated water can be stored for quite some time. This allows Batch heating. Heated water can be moved a long distance with minimal heat losses, (easy to insulate a 1" dia pipe). With all the floors being concrete on a steel joist structure, warm floors will be primary way of heating. Radiant heating requires much lower source temp, 85 to 95 deg F. There is a lot of thermal mass in the concrete and water. We are using ICF and they are tight and insulated. Hope the BTU need is nearly as low as I hear.

    Patrick t
    I am not arguing that. It is another heat exchange however and before I jumped in, I'd know for sure if your temp assumptions are indeed correct. If you look at the curent batch of wood boilers, there are several types. Some practically gasify the burn and others rely on a very hot , quick fire to heat up hundreds of gallons. One even has its water storage surrounding the fire box with a container of 1500 gallons. Coils have proven to be problematic in that to match the heat output of say an oil fired boiler, burns long and hot enough have caused a breakdown of the old traditional copper coil open to a fire box. Cost is a large consideration for you and I know you are trying to avoid as much as possible. You want to tie in your current water based system to a wood fire. If you are determined to utilize water, I think what I would do in this case is not even invest in a wood fired furnace just yet. I would buy a couple of 55 gallon drums and build the double drum wood stove. I would then add the heat reclamation tubes that you plumb into the stove that are available or build your own, mount them into the top drum and see what you get with this set up. This way you have not invested alot of money to turn something into something else and you can customize to kingdom come. My idea for the wood furnace was just to make it easier for you to involve yourself with heating with wood.
    They in their own right are not an inexpensive start point hence my suggestion for the barrel stove.

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