home made outside wood stove
By electrondady1, Section Heat Posted on Sun Jun 10th, 2007 at 05:42:00 PM MST
what lengh of copper for good heat transfer?

i ran out of time last year to finish my stove. lots of desigh changes too. http://www.otherpower.com/images/scimages/2793/outside_wood_stove_001_Small.jpg relocated the contraption next to the little shop i want to heat http://www.otherpower.com/images/scimages/2793/outside_wood_stove_002_Small.jpg i will run air duct all around the stove and  through the wall i have a thermostat and blower ready to go.once the ducting is inplace i will put up the insulated walls and roof and fill the space with sand . http://www.otherpower.com/images/scimages/2793/outside_wood_stove_003_Small.jpg i would also like to run a hot water system to move the heat to my house next year. i can't go any further (build walls and fill with sand ) untill i get the plumbing in place. my question is what lengh of flexable copper pipe should i use to ensure a good transfer of heat? also, if the copper pipe is installed (wrapped around the fire box) with out a fluid inside to help cool it, would it be damaged by the heat?

home made outside wood stove | 18 comments (18 topical, 0 editorial)

Re: home made outside wood stove (3.00 / 0) (#1) by electrondady1 on Sun Jun 10th, 2007 at 11:53:38 AM MST (User Info)

sorry the links don't work i will try another way ok that seems to work. i am getting the sand from under my cabin as i dig out for a basement so everything is on hold untill i get this working.

Re: home made outside wood stove (3.00 / 0) (#2) by harrie on Sun Jun 10th, 2007 at 08:52:24 PM MST (User Info)

Well, I have built a few wood stoves in my time, so here is what I think. First, it scares me alittle that the unit is so close to the siding on the building, but than I dont know what will be used between them, anyway, if you are planing on completely inclosing the stove, than I would reccomend a blower that would direct air from the floor area of your shop into the stove unit, and than just a different duct that would direct the hot air back into the shop at the highest area of the stove. As far as using the copper pipe Im not sure why you would want to do that if you do not plan on have water in it?? I dont beleve you would ever get the stove hot enough to melt the copper, unless you had soder fitings, than of course that would not work. I have built a wood stove that has 3/4 inch flex copper right in the fire box that coils around the 36 inch dia pipe line pipe that I used for the stove. I had a transfer pump that moved the water thru the coils, and into a heat exchanger in my shop. Of course you also need a expancion tank, and a pressure releif valve for this system, or it will go boom!!!! this unit used very little wood to keep the water hot. when I needed it. I think for shop heat, you are on the right track, using just heated air with a blower, but make sure you eithe keep a air space, or some kind of nonflamable matl. between the wall of the building and the stove, I would hate to see you have to build a new shop. Ha. [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#3) by electrondady1 on Mon Jun 11th, 2007 at 06:30:26 AM MST (User Info)

thanks for the words of warning harrie. a shop fire is something i am trying to avoid. i have almost no experience with wood stoves. this thing does get hot . the space between the siding and the stove is 16" it will be filled with sand. i believe the sand will dissipate the heat so that there is no risk of fire. i spoke to the fire chief of my town he felt it would be alright. i intend to place a temperature sensor through the wall . something like the ones they use when roasting meat. it should give me the temperature of the sand next to the siding . the air duct will loop around the stove . then be backfilled within the sand. so i will have a stove inside a pile of sand 4'x6'x5'. i idea is to create a thermal mass that will retain the heat even if the fire goes out. i was thinking that here might be enough heat to run a hot water system to my house eventually.(next year) that's about a 30 foot run. i have no time this year to put that in place(digging insulated trenches and what not) so i was simply going to wrap the copper pipe around the stove and place the ends were i could access them later. still curious as to what lengh of pipe should be wrapped around the outside of the stove in order for it to pick up the heat . maybe that would depend on the rate of flow of the pump i may use. [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#4) by wdyasq on Mon Jun 11th, 2007 at 08:21:27 AM MST (User Info)

"still curious as to what lengh of pipe should be wrapped around the outside of the stove in order for it to pick up the heat . maybe that would depend on the rate of flow of the pump i may use." And 'Delta T'... and pipe diameter ... and wall thickness of pipe ... and pipe material (I know you stated copper) ... and size of pump ... and amount of heat desired ... and inlet temperature ... and the run distance ... and the run insulation ... and the knowledge to put all of this together. Of course someone will give you the answer you want if you only ask the question enough times. I would not go as far as saying the answer would be correct. Ron Adventure is just bad planning." -- Roald Amundsen

Re: home made outside wood stove (3.00 / 0) (#5) by electrondady1 on Mon Jun 11th, 2007 at 05:04:48 PM MST (User Info)

Delta-T stands alone as the world's foremost designer of higher-tech alcohol plants ... Delta T, delta-T, deltaT, ÄT, or DT is the time difference obtained by subtracting Universal Time from Terrestrial Time. Universal Time (UT) is a time scale ...  Values of delta T before AD 1600 pre-date the telescope and are based on historic records of naked eye observations of eclipses and occultations. ...  85 million, 800 thousand listings for delta T on google . i am just guessing ron but if i subtracted universal time from terrestrial time during an eclipse,  would i be able to get everything done before winter ? [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#6) by wdyasq on Mon Jun 11th, 2007 at 05:42:07 PM MST (User Info)

I think Robinson Crusoe had everything done by Friday. Ron Adventure is just bad planning." -- Roald Amundsen [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#9) by finnsawyer on Wed Jun 13th, 2007 at 08:31:56 AM MST (User Info)

T can also stand for temperature, and delta T can stand for the temperature difference between the outside of the pipe and the inside of the pipe.  The temperature difference then determines the rate at which heat flows through the pipe.  At least I think that's what he is getting at.  While copper would have superior heat transferring properties, perhaps inside the firebox one might rather use iron pipe.  It might withstand the effects of the fire better.  Also, with iron one can extend the pipe through the wall of the firebox and weld it in place so as eliminate the possibility of leaks. GeoM [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#10) by Darren73 (darren2604 at hotmail dot co dot uk) on Wed Jun 13th, 2007 at 03:41:41 PM MST (User Info)

Hi Geo, I think you missed the sarcastic wit in the replies above. :-) (Spell checked using UK English) [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#15) by finnsawyer on Sat Jun 16th, 2007 at 07:58:02 AM MST (User Info)

Must be the heat. GeoM [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#7) by vawtman (vawtman(at)charter(dot)net) on Mon Jun 11th, 2007 at 07:23:41 PM MST (User Info)

Edaddy  Not sure if this would work but maybe imbed a water heater tank in the sand.  Is this sand filled system your idea or something youve seen before?  Seems cool(oops meant warm)  Have Fun

Re: home made outside wood stove (3.00 / 0) (#8) by electrondady1 on Tue Jun 12th, 2007 at 06:04:27 AM MST (User Info)

vman, the sand idea is just another one i've picked up from the good old other power discusion board! i think it will work! [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#11) by electrondady1 on Wed Jun 13th, 2007 at 09:00:04 PM MST (User Info)

thanks for the interest fellas , i have been google searching the board for a few days now. using the terms "woodstove" and "copper tubing" as search perameters lots of different configurations have been used. i couldn't find anything that i could apply directly the primary fire box is 16" dia. so i could get 6 turns from a 25" roll . if i use two such rolls i could run them parallel or in series.  just like the electrical coils.   [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#12) by electrondady1 on Wed Jun 13th, 2007 at 09:25:07 PM MST (User Info)

since i am just at the thinking stage on this one , it just occurred to me that two more coils could be placed around the secondary burn chamber. four in all. if i can run them in parallel  it would reduce the speed of fluid as it passed through the heating area allowing more time for it to acquire the energy. thermodynamics! you gotta love it. [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#13) by TomW on Thu Jun 14th, 2007 at 05:04:51 AM MST (User Info)

Edaddy; Since you seem to be flying by the seat of your pants here as it were. Maybe a setup where you have 2 independent coils with appropriate valving. Then you can either parallel or series the flow to get different results. Run in parallel when you have high heat or series when you have low heat. Just seems it would give you more control after it is installed. Maybe even several coils. Do not mistake me for an expert. Just popped into my head as a way to expand the options after its installed. Cheers. TomW "Education consists mainly of what we have unlearned."--Mark Twain [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#14) by electrondady1 on Thu Jun 14th, 2007 at 06:49:41 AM MST (User Info)

tomw , i think your right, and i think thats the way i have to go. 4 independant coils that can be run in what ever configuration that is required. add to that maybe, a speed control/flow control on the pump and it should give the options i need. i've done some test burns on the stove as is but it's dificult to anticipate the the effects of having it buried in sand. [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#16) by electrondady1 on Wed Jun 20th, 2007 at 06:46:26 AM MST (User Info)

just priced copper tubing  what a shock! 30 ft. of 3/4" =97.48 canadian dollars. with a 14% sales tax, $111.12 $444.50 for four lenghs. ouch! [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#17) by electrondady1 on Sat Jun 30th, 2007 at 10:47:08 AM MST (User Info)

i will take a pass on the copper tubing . perhaps next year . the air ducting is done . time for more sand! [ Parent ]

Re: home made outside wood stove (3.00 / 0) (#18) by Kevin L on Tue Aug 28th, 2007 at 11:25:26 AM MST (User Info)

Water will carry 500 BTU/h * F or 500 BTU per Hour degree F  Thus 1 gpm will deliver 10,000 Btu/h for a 20 degree drop in temp. [ Parent ]

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