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[Jd79]

I've been reading for a week or so, and I appreciate all the free knowledge available on this site.  Looking for comments, concerns, questions, and suggestions to improve my plan.  I am planning to build an outdoor wood boiler, relying heavily on my father-in-law who is a retired welder/fabricator with over 40 years of experience, which is a good thing considering I hardly know how to turn my mig welder on, much less use it to weld watertight.  Here’s the plan:  I have a 300 gallon diesel fuel farm tank that I have had for years that I plan to use as the water jacket (hasn't had fuel in it in over a decade).  It’s relatively thin metal (probably 1/8”?) but if it’s designed to hold fuel, I figure it would make an OK water jacket.  It measures 38” in diameter and is 60” long.  I plan to have a piece of 3/16 steel rolled into a 24” cylinder for the firebox.  Not sure on how long to go.  I don’t want it to go completely the whole 60” length of the tank, so I’m not sure if I should use a rear exit flue or a top exit.  I will have the blower with damper controlled via either aquastat or ranco controller, not sure which I plan to use yet, so I’m open to any suggestions.  I would like to install an ash pan in the bottom of the box with some grating, but cannot figure out how I want to build the door or where I can buy a pre-made door.  Also, I would like to put the air in from the back side of the firebox rather than at the door if possible, but that would likely mean I would have to run the firebox the full length of the water jacket, so I’m still pondering how to do this.  I am planning on buying pre-made insulated pex, so I am trying to make this work with only 1 pair of 1” lines due to cost (rough estimate of about 130-150 feet of run, depending on my exact location of the boiler).  My plans are to have a 20-plate 5X12” brazed plate heat exchanger on the water heater (82 gallon electric water heater) first in the circuit, then to the air/water heat exchanger in the ductwork, then returning to the boiler.  I also plan to put a “T” in the return line to the boiler and tie into my domestic water supply via a ¼ turn valve for a means to top off the boiler without having to stretch out a garden hose.  I’m thinking I should come off the hot water side of the water heater to keep from shocking the boiler so much with cold water during top offs.  I do plan to install a thermostatically controlled anti-scald valve to the water heater to prevent kids from getting burned by the hot water in the house.  My current setup has a heat pump with 15kw backup electric strips, which have proven to be very costly, not to mention the dual 4500 watt elements in the water heater eating $$$, especially in the winter time.  The house is 1800 sq ft of living space, and is fairly well insulated (built in 2003).  Since my heat pump has a variable speed blower, from what I have read, I should be able to utilize a second aquastat surface-mounted on my supply line from my boiler and have it hold the contacts open on my yellow wire to my outside unit on the heat pump unless the boiler water temp falls below say 120 degrees (indicating fire went out) whereby it would then close the contacts to allow the heat pump to run normally and allow the backup heat strips to function as normal, and I would be able to continue just using my normal thermostat.  Otherwise, I would run into issues of the blower not wanting to spin up to high speed.  Since I’m only planning on one set of lines from the boiler for heat and hot water, I would just run my circulator 24/7 as many people do, and I’ve heard that the circulators seem to hold up pretty well like this and don’t use a whole lot of electricity anyway (about similar to a 100 watt bulb).  I am open to any and all suggestions, and I have looked at a number of different builds on this site and continue to be impressed with everyone’s ingenuity and the amount of thought and design that go into these builds.  I've run various calculations on the size of the firebox, determining how many gallons would be left for the water jacket, etc., just not sure how much of each is enough or too much.  Looking forward to some good advice!  Thanks in advance.

[BoilerHouse]

I'm not sure I can add much.  It seems like you have a lot of things thought out.  If you run the flue out the back, make sure you allow for a clean out.  (You probably already knew that).  One thing to point out- the trench preparation is as important as the type of underground pex you use.  The pex should sit on a few inches of sand or gravel, and than be back-filled with nice clean fill, sand or gravel.  If a root or stone tears through the pex "O" pipe, even a good quality pex will be worthless.  Some are now putting a 4 inch "O" inside a 6". 

[Jd79]

After doing some looking, I like the design that WoodMoJoe used on his, and am attempting to go that same route.  I decided that the old diesel fuel tank I had was too thin for what I wanted to do, and if I'm going to spend the time and money, I might as well make something that will last.  I acquired two propane tanks yesterday (about a 120 mile round trip to get them, but they appear to be in pretty good shape, and I don't think I got a bad price on them)  One is a "short fat 500 gallon" tank that is 41" X 100" and the other is a 250 gallon that is 30" X 94".  For placement of the boiler, I was thinking of putting it near my shop with future plans of heating it as well, but not now.  The location is slightly downhill from my house, so the circulator will have to pump up to the heat exchanger in the house.  Total change in elevation is probably going to be approximately 10 feet or so, give or take.  I remember reading somewhere that you shouldn't have any "appliances" (or I suppose they meant heat exchangers) higher than the elevation of the water level in the boiler jacket.  Could someone please elaborate on this?  It seems to me that a circulator with enough discharge head should be able to accomplish this with no problem.  I would post tank pics on here, but everybody knows what a propane tank looks like, and I don't think they make them any different here in Kentucky than anywhere else.  I will post updates over the coming months as we progress on this project.  We won't be starting until the weather breaks because I can't purge the propane tanks with any water until the weather gets above freezing for at least a couple of days.

[skorpyd]

Looks like good tanks to start with.  Good luck keep us updated and pics are good.

[skorpyd]

That 11" tank diameter differential I think will be great.  You can just add length to get the size or amount of gallons you are shooting for.   

I wouldn't mind getting ahold of a couple more tanks those sizes.

[WoodMOJoe]

That sounds like the same tank sizes I used.

If you haven't seen it yet there is an ACAD sketch of my build in my thread here that has a lot of dimensions on it.  Some of them changed a little when building but they will give you an idea of some of the things I did.

[Jd79]

I saw the CAD drawing, and I printed it off to show my father-in-law so he could see what I was wanting to do.  I'm not any good at drawing things on paper, so that was a real life saver to have the dimensions already figured out.  I will probably make a few mods to it to fit my particular case, but I really appreciate that information being made available.  My father-in-law is sold on the idea that we can fabricate the door, but I'm still thinking I need to just buy it pre-made.  Anybody have any drawings of how to build one from scratch?  I'm afraid it will be more trouble than it's worth trying to build it ourselves, but time will tell.  I'm really anxious to get started on this project, considering I'm looking at two back-to-back outrageous electric bills, and tomorrow is supposed to hit 0 degrees again.  When I built this house, propane prices were all over the place, and natural gas wasn't available out here, so we went all electric with heat pump and 15kw back-up heat strips for furnace, but it is proving to be increasingly cost-prohibitive to heat that way.  The power co-op that provides our electricity raised rates in October and again in January of this year due to their wholesale supplier losing their biggest industrial customer to open market pricing.  It's hitting everyone in their wallet right now.

How much are you heating with yours?  I am thinking of adding a second loop to heat my 32X50 poorly insulated shop in the future, but not sure if the water capacity and BTU output of this size unit will be able to carry that kind of load.  I'm already looking at heating 1800sf of fairly well insulated house plus 82 gallon domestic water heater with plate exchanger.  Just not sure if there is enough BTU output and recovery ability to handle another HX in the shop.  Thoughts?

[Jd79]

Just getting started, but at least we got the tanks cut open!  That was the part I was most uneasy about of the whole project.  My father-in-law is the torch expert and my buddy is helping in the other pic while I try to lift the cut tank with the backhoe.  Those tanks are difficult to maneuver!

[skorpyd]

Looks like a good start.   

My friends backhoe sure came in handy with my build also.

[mlappin]

How'd you handle the cutting of the LP tank?

The sale barn in the next county gets used LP tanks in for consignment sometimes, they'll cut em as well if you want.

Their method is to pull all the fittings, place a cement block down, place the torch on the cement block then weight it down with bricks, light it and head around the corner of the building and wait.

Did I mention their family tree has very few branches?

[hondaracer2oo4]

When I cut my 500 gallon tank I filled it with water to purge any remaining gas that was in it out. I then rolled it over and dumped the water out. It STUNK like mercaptan for a month. My wife was not pleased. I then filled it with water again and cut it with a Metal cutting circular saw that doesn't spark. I would suggest using one to cut. Makes a really nice cut and is fairly quick. Took me about 30 mins to do that whole cut. My torch would have been faster but would have left a jagged edge.

[Jd79]

DISCLAIMER: I am in no way an expert and if you try this yourself, I assume no liability for any damages, explosions or anything bad that can or may go wrong. You are on your own and assume all risks associated with cutting propane tanks.  Having said that, what I did was fill the tanks first with water, dawn dish soap and TSP (trisodium phosphate). I filled the tanks until they were overflowing, then shut off the water. I would see the oily residue from the mercaptan floating to the top, so I'd add more water to get that stuff to float out. I did this a few times. I left the solution in there overnight and the next day I dumped the tanks. I probably should have rinsed them, but I didn't. About a week later I had some weather good enough for cutting the tanks, so I hauled them out of the field over to the gravel by my building and set them down. I figured up the volume in cubic feet of the tanks (about 100 cubic feet total for the 2 tanks) and bought 20 lbs of dry ice, which will make about 170 cubic feet of co2 (roughly 8.5 cu ft per lb) and put it into the tanks for extra insurance before cutting. Once the dry ice was in the tanks, I added about 1 gallon of water to each tank to get the co2 rolling nicely. We checked the tank with a torch over the open holes and there was nothing. We proceeded to cut with no issues-no pops, woofs, or flame-ups of any kind. I did make sure the bottom drain plug was in when we added the co2 so it wouldn't run out the bottom being heavier than air, but all the top plugs/fittings were removed before cutting. I'm not saying this is the best way to do it, but it's how we did it, and to me it seemed safer than the car exhaust method since carbon monoxide IS flammable in the right concentration. Use your best judgment and only do it in a way you are comfortable is my only advice because this stuff can be deadly if done wrong.

[mlappin]

slick ideal with the dry ice.

I've welded a few fuel tanks on our straight trucks, drain em out empty as possible then stick the steam cleaner wand in and let it run, when the steam no longer smells like whatever fuel it had in it, good to weld.

Wouldn't work on your tanks though, too much volume.

[Jd79]

Torching out the opening for the flue pipe.




Flue pipe tacked in place.




Installing slugs and pipe plugs to be welded in place.




Firebox squared up and tacked in place to front plate.





We tried everything to get the paint off the firebox.  I tried a wirewheel, liquid paint stripper, and even hit it with a grinder for a little bit.  I figured if it was that hard, it wasn't coming off.  Everything loose is off, but the rest will just have to stay and bake on I suppose.  Since the only things that will be supporting the firebox are the front plate and the flue pipe where it attaches to the water jacket, we decided to upsize the front plate from the original plan of 1/4" to 3/8".  That is one stout piece of steel!  I fabbed up a small rolling platform so we could roll it under the chain hoist to set the firebox on the plate.  Not sure how we are going to set the water jacket on yet since my building isn't tall enough to use the chain hoist to get it to clear the firebox.  I guess we will have to get creative and figure something out.  If you're wondering why the flue pipe is so short, it's because we had to allow clearance for the waterjacket to slip over and then back.  Once in place, it will stick out of the water jacket about 2" and we will weld on the flue pipe extension from there.  Inside the firebox, the flue pipe extends to about 8" off the bottom.  It will be a few days before we have a chance to do anything else to it due to weather (today) and my work schedule.  I'll post more pics as progress continues.

[mlappin]

If you placed some regular plywood down outside can you roll it out and use the backhoe to set the outer tank in place?