Outdoor wood burner idea for my house..help me

[LanceA0]

well i do most of my time reading on here rather then posting. let me tell you a little about myself. my name is lance, im 24, im from Michigan and i bought my first house in may. its and old 2 story (1300sq ft) from 1930's. ive been spending all of my time fixing it up and im slowly getting it as effiecent as my budget will allow. i installed a new 90% 2 stage carrier furnace, energy effiecent water heater, CFL bulbs, and im about to add 18" of insulation to the attic.

right now the house stays a lot warmer then i though it would. but im the type of guy that always wants more. my uncle gave me an old wood fireplace insert that im planning on putting in my garage/shop to heat it durning the winter. i want to turn that into a "outside wood burner" style burner and use it to heat my house. i plan on building a water holding tank that sits on the top and hangs down on the side. i will have an in/out on the tank  where i will pump the heated water to my furnace  and into a radiator then back to the burner. i would also like to find a way to preheat my hotwater heater.

there is still a lot that i dont know about these system thats why i posted on here. here are some things i know i need help on.

• will it work or am i crazy?
  
• how big of a water tank on the wood burner?
  
• how big of pipe do i need for my feed and return.
  
• drain back or not?
  
  

here is some picture of what i got right now.

ATV radiator to use for the heat exchanger(mount in duct work) will seal up pressure release and install one by the wood burner.

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view¤t=4a3d_1.jpg

map of house and layout. the red square is my furnace(basement of house)  the blueish grary square is the wood burner located in garage. its about 47' away from the furnace. the orange pipe is the out from the burner. it then goes the the exchanger. on the way back to the burner it goes through a home floor radiator located in my shed to help heat that then back to the burner to heat up again.

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view¤t=house.jpg

here is the wood burner. 20"D x27"W x23"T with an 8" hole for the chiminey.

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view¤t=P1040496.jpg

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view¤t=P1040501.jpg

please give me some imput, good or bad.

 

[hamitduk]

In my younger years I would travel allot and in Costa Rica I would stay at a hotel in San Jose, across the street there was a chicken stand that was open 24-7.  The reason for this was, in the flew there was a large coil of tubing and the storage tank for the hotel next door to it. Great Chicken and lots of hot water!

Hami

[zeusmorg]

 It will work, if designed properly. There is a lot of information regarding using hot water for heating at garygary's site.  http://builditsolar.com/   I would suggest reading up as much as you possibly can before building.

 In your climate you would either require a drainback system or ample antifreeze in the system to prevent freezing. A 50/50 mix of anti-freeze will be expensive but then again so will a lot of the other components.

 You could design solar collectors to heat the water on nice, sunny days. Using a radiator for heat to air transfer may require a larger radiator than what you have pictured. (or more of them). A hot water system is a lower grade heat than a fire. so the output of air temp is lower. This is why most hot water systems use radiant floors.

 Of course any piping running to the house needs to be VERY well insulated to keep losses down. Do remember that water expands with heat, so a low pressure or open system would be the best in this application. The radiator you show won't take any high amounts of pressure.

 It may be better to use a system with a large inground storage tank which stores heated water from your wood burner and any solar that you wish to add then install a heat exchanger in the tank to transfer the heat to your house and shed.

 that way you could easily automate a lot of the functions you'd have pump loops form your heat source to storage tanks, then a pump loop to the house which could be controlled directly by a differential thermostat.

 As far as pre-heating your domestic hot water with this setup, I'd recommend doing a heat exchanger on that, also, which could easily be built. Just remember you want double walled pipe for such an application. You do not want to have the possibility of contamination of your fresh water.

 Just try your best to eliminate any losses which would decrease overall efficiency.

You will also want to watch anything that will lower your chimney heat which can cause creosote buildup, a chimney fire is VERY dangerous! You would need to at minimum want to clean the flue once a year..

[12AX7]

Hello..

I'd suggest you check your local codes and with  your insurance company.

Local codes here states you can NOT have an open flame heat source in a garage and I'd guess your codes are the same way.

The reason they build "out door" wood burners is to meet code requirements.  Most need to be a min. of 25ft. from any buildings.

From your pics it's hard to tell size, but I think your fire box is a bit small and will require frequent trips out to keep it burning.  

Most outdoor boilers have an "open" water heating tank, to prevent any pressure build up, also requiring to monitor water level.

Besides the insulated pipe that runs between the boiler and heat exchanger you need a worthy pump and their not to cheap.  

Don't forget you need controls.   Controls for the pump and some sort of control for the "burn".   Most outdoor boilers have hi and low temp controls for both the pump and burn (normally an automatic damper).

Not saying it "can't" be done, but the devil is in the details.   It's not just heating water...

Good luck and post lots of pics!

ax7

[jonas302]

first thought is look for a differnt stove check craigs list or freecycle for an old wood boiler that went in the basement they are out there  also used outdoor stoves can be had also

If you still have to modify that stove I'm thinking a run of steel pipe inside the top of the firebox leave it an open system with room for expasion when hot don't try to heat much mass your fire is to small maybe 5 gal at the stove

Is the garage attached? 3/4 inch is good for pipe size  insulated piping can be made cheaply let me know if you need detail

A taco pump can be left running constantly you will just need to manually control the stove temp no drainback if your worried about freezing use antifreeze talk to you local salvage yard very cheap used about 1.50 a gal

hope that helps a little

[Airstream]

I've not done anything like this before - but I am collecting bits and pieces to build my own and have read up on it over the last bunch of years. Here's some thought on the your supplementing heating using a remote wood burner.

The ATV machine has a lot of surplus energy they add parasite loads like water pumps and electric cooling fans to; the radiator heat exchanger is too restrictive in air flow to demand an existing furnace set up to accommodate it.

The effort required to push X amount of coolant through that radiator for cooling that specific motor was an exact calculation - the potential waste heat counting on a large (100°F+) temperature differential between air and water will allow a small amount of flowing water to carry off a lot of heat without cooling the combustion engine too much to lower its efficiency.

You really don't want to make steam even by accident. Think supplemental heat, not pressurized boiler. Instead of counting on super hot or pressurized water in a small radiator you would do well to go with lower temperature water with a larger flow through a larger radiator surface.

Useful heat exchange from water to air starts at around 40°F differential from ambient; designing a system that can provide a constant flow of liquid heated 50°F above household air temperature to a loop of baseboard radiators (3/4 copper pipe w/ aluminum fins with steel housing) would not be that hard to accomplish. Finding huge ancient cast iron radiators and using them may be even easier.

120 to 150°F heated water drawn from a reservoir like an old water heater, with the circulation pump pulling from the top tank, through the loop and pushing the now cooled liquid back to the reservoir would avoid any chance of steam flashing through the living areas and lower the likelihood of injury to occupants.

How you accomplish transferring heat into the reservoir, convection or electric pump and the specifics on modifying a wood burner to heat water I got to leave to someone else...

[LanceA0]

there is a lot left for me to learn thats why im here.  this site different then the ones im used to. im not sure how to reply to multiple posts with out repling to each persons post. so i will do it all here.

zeusmorg:

• if i can get away with a 50/50 mix i would like to do that. my basement is only 400 sq ft so space is rather limited.
  
• im tring to keep this system as simple as possible. pipe running from garage to house will be insulated. i got a couple of ideas oh how to do it and there are some on BIS. com  that ive seen.
  
• as far as controling to system im not sure exactly how i am going to do it. i got to talk to my heating a cooling buddies to see what my options are. i do know that the circuation pump will be running all that time.
  
• for my hot water set up do you have a links to nice exchangers for that. ive seen some in the past when i was searching the site. however when i was looking last night i couldn't seem to find them again. im sure BIS has some on there that i can search for too. i dont think i will be able to heat my hot water totally by the wood burner but i would be nice to atleast warm up the cold water some as its entering the tank.
  
  

12AX7:

• i will deffently check the the local codes. i know my neighbors on both sides of me have wood burners in their garage/shops.  mine is a 17x18 garage that will be strictly a shop. i might pull the front of a truck in there to work on it but nothing with gas will be stored in there. all that stuff will be in the shed.
  
• frequent trips to the garage to keep it burning  wont be a problem for me. im kinda new to the whole wood burning thing other then the yearly trips to deer camp. i could see maybe having to load the fire 5-6 times a day.
  
• as far as controls im just looking for a simple system. the pump will run all the time. the water temp should stay pretty constant once everything gets warm (at the exchanger). when the furnace fan kicks on and it starts blowing air through the heat exchanger  i know the water temp will drop. thats why i was wondering how big the tank should be on the burner.
  
• "Not saying it "can't" be done, but the devil is in the details.   It's not just heating water..."   in my eyes its is heating and transfering hot water. the hard part is doing it safely and efficently.
  
  

jonas302:

- a different stove isn't an option. i wish it was but this has to be a budget build. im not looking to cut corners on safetly or key things but i dont want to spend a bunch of money. im looking for a decent return on my investment and to actually do it. ive been reading and reading on here and Home power and i want to build something. i came up with an idea and im here now tring to get it perfected.  by the way i did look on craigslist. nothing much of anything came up. there were some companys tring to sell new out door burners and a couple of people wanting wood boilers. please dont take my reply as me tring to be a jerk. i know i could probably seem that but thats not what im tring to imply. i value your reply thanks.

Airstream:

• as far as the ATV radiator that is something i have laying around so i figured i would see of i can use it. it is probably 8"x16"  so i figured that when it was mounted in the duct work most of the heat would go around it rather then trough it. however it is still X degrees hotter then the air so it should still warm the passing air. however im sure there is a better heat exchanger out there that i can use. what about a  A/C coil?
  
• im looking for a open system that way no steam will accumlate and build pressure. does it matter were the system is open at? could i add a  vented over flow tank to the tank that will be sitting on the wood burner. that way if a the water started evaporating or turning to steam it would have a place to vent and get more water if it was getting low. kinda like a car radiator system but with out it being pressureized.
  
  

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thanks for all the replys please keep them coming.

Lance

[Clifford]

I think the subject had been on Fieldlines a couple of times.

Here are a couple of links you might find interesting.

http://www.fieldlines.com/story/2008/1/11/2545/59486

http://www.boomspeed.com/bofh1968/stove/index.html

I'm not sure about the heat exchanger.  

Many of the new wood stoves/inserts have a re-burner, either catalytic, or non-catalytic to reduce the smoke.  

Anyway, if your system has the re-burner, then you will need to capture the heat after the re-burner.

You could, of course, use plain ductwork rather than a heat exchanger.  

Earlier I was also thinking about the difference between the ancient cast iron steam radiators, and the automotive radiators & fans.

There is something nice about the radiant heat of those old steam radiators.

[zeusmorg]

 Some more thoughts.. there would be different ways to capture the heat off the firelpace insert. Probably the safest would be a large tank,less likely to overheat than a run of steel pipe.

 I personally would not put pipe inside the fireplace, but on the outside. Any tank, or pipe system you do install I would have either an expansion tank/pipe on the top (highest position) or some sort of pressure relief on it. Probably both. you will need a considerable amount of surface area on your radiator to transfer the heat to the air.

You also do not want to restrict normal airflow of your current blower or you will decrease the efficiency of the current furnace(if you choose to put this in the hot air ductwork). In other words the area through the radiator must exceed the current duct airflow.

 As far as automation. A differential temperature control switches on a pump(or fan) when the temperature at one sensor exceeds the temperature at the other. Some are designed to accommodate setting this difference, and can also be set to switch on at a given temp at one sensor. If you pumped water to a tank. then you could have the pump  switch on when the fireplace sensor exceeded the holding tank temp. Then water could be pumped from the tank to the radiator(s),(and also switch on the blower fan) when the house thermostat kicked the system on. Also you could put in this tank a loop of copper pipe, acting as a heat exchanger on the cold water inlet of your DHW heater. A tempering valve would also be a good idea in case the temperature becomes scalding in the DHW system. (this mixes hot water output of the tank with cold water to lower the temperature if required)

 Doing it this way would require two pumps, but they wouldn't be running constantly, only as needed. The initial cost would be more, but savings in running the pumps would pay for that rather rapidly.

 If you're just looking for an easy supplemental heating system you could build one that deleted the tank and used a totally separate system to heat part of your house. Several radiators encased in a box, with an attached blower recirculating the air through either freestanding system or a separate ductwork. This would just be switched on by the water temperature exceeding a certain point. Like 110-120 degrees,and a pump switched on likewise, with a thermostat located on the fireplace tank. This system would require a lot more manual intervention though, and would only give you usable heat when the fire was fed.  

[LanceA0]

this is what im thinking as far as a design. the measurments are rough, seeing as im not sure how many gallons of water i need to heat.  tell me what you think.

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view&current=woodburner-1.jpg

http://s2.photobucket.com/albums/y39/LanceA0/house/?action=view&current=woodburner1.jpg

[zeusmorg]

 I would put cold water intakes on both sides, and a hot water output at the top...otherwise you'll run into flow problems.

[LanceA0]

in the side picture you will see dotted lines those are plates  welded on inside of the tank used to direct the water from one side to the other. however your idea would be cheaper and easier do you think it would be efficent?

how does the design look? you think this will work effiecently?

i also figure i will put the pump on the pipe heading back to the wood burner. that way the water temp should be cooler and posibly prolonging the pump a little bit longer.

i have been researching for the past 3 hours on ways to heat my hot water. i found the DIY pipe in pipe heat exchanger on homepower. i am also thinking of finding a free hot water tank on craigslist, cutting it open and putting a coiled copper exchanger in it. i would probably make it a 15 gallon tank and bypass my current gas one for the winters. i would have to install a anti scalding valve too. i wish i would have spend the extra money for a tankless waterheater when i replaced mine 4 months ago. it just seems like that would have made things a lot easier. i could have just ran the exchanger just before the tankless water heater to control the temp.

[zeusmorg]

 Even with the baffles(which i did notice) you want your hot water to exit from the highest point of the tank..

 If you do it as you drew, you'll have some water trying to rise from the hot water outlet side to the highest point of the tank. (heat naturally rises)

 If you put the cold water into the lowest points, and remove it from the highest, you will get the hottest water out.

 Yes it is fine using the pump on the cold water side.

 I would also install a sight glass on your expansion tank. that way you know when the water level drops. It may even be worthwhile to install a float valve for automatic water replenishment.

 The problem with a tube in pipe heat exchanger is the surface area and the fact you will have to be pumping water when your water is incoming into the water heater.. otherwise you will get no heat exchange. That is one reason (amongst others) I like the idea of a storage tank.

 It would be prudent to look at garygary's system on his house which is very well designed, although it is mainly solar heated.

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

[LanceA0]

your idea makes sence now thank you.

my drawing showes a vented overflow tank. the vent is to eliminate any pressure build up. will that be enough or should i install a pressure releif valve too? the over flow tank will probably be a gallon tank. i will keep some water(1/2 gal) in there that way if the tank gets low gravity will fill it back up. then if the water expands it will expand back into the over flow tank. similar to a car radiator system.

do you think my idea of the coiled heat exchanger in the 15 gallon hot water tank will work?  how many ft of coils would i need?

 

[southpaw]

Hi Lance

Here are some suggestions regarding your proposed system.

Check this link regarding a heat exchanger to preheat your domestic hot water.

http://www.fieldlines.com/story/2006/6/6/144733/0442
<img<p>
It is a single wall exchanger so may not meet plumbing code but because the inner pipe

(cold water supply to water heater) has no joints the chance of developing a leak

is small and if it did leak the higher pressure in this pipe would dump fresh water into your heating loop and overflow your woodstove tank and not allow antifreeze into your domestic supply.

Check this picture for my idea on your radiator placement, over the black hole in

the return air shoe, not the grill he is pointing at.

src="http://www.otherpower.com/images/scimages/7822/DuctAtFurnace040DFss.JPG" width=80%>

I think your tank on your wood stove would work if you could keep it in close contact to the stove shell for maximum heat transfer.

You would probably be better off with a larger tank, in order to have a cushion, if

you are not drawing heat from your radiator or heat exchanger, the 7 cubic feet of

 water in your tank  (437 lbs.) will heat from 112 degrees to 212 degrees (boiling)

(437X100=43,700 btu) in 1 hour if you had a 87,400 btu fire and a 50% heat transfer

from your fire box to tank.

The reservoir should be at the same level as your tank with a loose cover to prevent

excessive humidity into the shop and allow easy access to check level and fill.

With the reservoir in this position and a large open vent if the water does boil it

won't be blowing a gallon of scalding water out at roof level (think hot shower)

The circulating pump is designed to handle hot water and should be below the tank level to eliminate air locks. If you put it in the return line and any leak develop

it will suck in air and airlock, with it in the supply line any leak will show

immediately and can be dealt with. You may want to insulate the outside of the water

 jacket to prevent overheating the shop.

here's a crude drawing of my idea.

Some ideas and suggestions, feel free to poke holes in them.

Best of luck

Kurt

[LanceA0]

i love all the replys im getting here.  keep them coming.

kurt thanks for the input. the hot water heat exchanger you linked me to is the tube in tube one i was talking about earlier. i like the idea and i think it would work well in a different applacation. i got a 40 gallon gas hot water tank right now. if i do a tub in tube on the cold side of my hot water it will preheat my water some which will allow the hot water tank to not have to work as hard. but when the water is sitting it the hot water tank all day the heater will have to keep the tank hot.  if i build another hot water tank(15 gal) and use the coiled heat exchanger inside it to keep the tank water hot all the time i would have used no gas to keep the tank hot.  this also brings up a good idea i wonder if i could keep the gas water heater but put the coil in it. i could turn the gas heater down low so it will never have to turn on but if i dont have a fire going it will still keep the tank somewhat warm. hmmm.

yeah im thinking a bigger tank on the stove too. i figure the more water i can heat the better. im not sure if i will have a problem heating more water seeing as my fire will be small. any ideas?

the water tank will be sitting right on top of the stove so it should get great contact, the only thing i see is the wood burner has a air duct on the inside that runs from the bottom of the stove(blower) up the back and and on the top of the stove to blow hot air into the room/shop. that will create an air gap that might hurt the time it takes to heat the water. i also plan on building a box(on the outside) and stuffing bats of insulation in between the box and the stove to help insulate the water. i would like to be able to hold as much of the heat as i can in the water. that way if the fire goes out i will still have heat for a little bit.  

 

[southpaw]

Hi Lance

Its really tough to put a coil into a water heater, if you cut the tank you will

destroy the liner and it will rust out quickly.

If it has fiberglass insulation you can remove the shell and insulation and wrap

your heating coil around the tank tightly and then replace the insulation and shell.

You must remember if your water heater is warmer than your wood stove and the circ pump is running you will be trying to heat your shop and shed with your water

heater. A 110v thermostat on the stove tank to control the pump, set higher than

the water heater setting will prevent that.

I see what you mean about the air duct around the fire box, that will definitely

interfere with the heat transfer, perhaps you could fill it with something with

high heat transfer properties.

Kurt (Southpaw) not to be confused with Kurt the moderator

[LanceA0]

how many coils will i have to run around the hot water tank to make an impact? to me it seems like a lot.  

as far as the air duct, i need to keep it there so the blower will heat the shop. how much of a burdin will it be? it will still transfer through the sides and some on the top with the air duct there.

[southpaw]

Hi Lance

It is going to be difficult to get the water in the tank as hot as the water in the

 water heater if you are blowing cool air through the heating jacket on the wood stove

but you will probably have enough heat coming off of the exposed parts of the stove not covered by the water jacket to heat the area in the shop and will probably have

too much heat for a 17X18 shop if you keep the fire fed well enough to supply heat for

 the house and domestic hot water.

If you dont have enough heat in the shop a box fan blowing over the entire assembly

will probably extract enough. My brother heats his leaky old 32X32 shop with an old

car rad with a thermostat controlled box fan behind it even at -40 in northern saskatchewan.

Regarding the coils around the water tank, more is better and any are better than none.

Extra insulation over the original will also increase the heat transfer and reduce heat loss while sitting idle. There are commercially available blanket wraps available for this purpose.

southpaw

[LanceA0]

so i looked at my stove a little better and due to its size and the 8" chiminey the top surface of my stove is very small. i will have to redesign the top of my tank. if you look at it from the side it will have to be skinny and tall. this will leave most of my contact surface on the sides.

as for the coils on the hot water tank could i use PEX? i found insulation for the hotwater heater for around $30.

for the pex running from the tank to the house what degree should it be good for?  

[Vince]

You've zeroed in on a question I've been wondering about for some time. Can you really connect pex directly to the water tank atop the wood burner without it melting ? Or do you have to run a length of copper and then switch over to pex, and how far away ?

[MattM]

So what happens when you leach off the heat from the top of the stove and it becomes relatively cooler than the sides?  Are you prepared for the gases in the stove becoming cooler than the design of the stove intended?  You need to be prepared to meet the challenge of regular cleaning the exhaust pipe when the creosote accumulation in the pipe becomes enhanced.

[taget]

Hi, i tried something like this almost identical last winter, sorry if this is a repost but. when trying to wrap the system with copper lines to a holding tank it was damn near impossible to tune the length of line and keep it from boiling as it came out of the other end, the best way is to have the firebox submerged as that takes care of your energy storage and delivery at the same time, the moment you start boiling your fluid you are going to lose whatever it is you have put in. and if its antifreeze, its to damn expenxive to lose. once again sorry if it is a repost but i didnt have time to read the enitre thread. good luck there is no better way to learn that by doing.

[LanceA0]

just wanted to thank everyone for the help, and give you an update.  i decided against this. i just would hate to spend all this money and not be positive it was going to work how i wanted it to.  so im going to put the wood burner in the house.  running the chemney pipe up the side of the house. i still however want to heat my hot water with it.