Question:
How does the outside wood stove/boiler built from this plan work?
Answer:
This stove is basically, a very large firebox that is completely surrounded by water. A thermostat on the boiler waterjacket, energizes and de-energizes a forced air, powered damper and draft assembly, to maintain a constant user-set boiler water temperature. A low wattage pump moves this heated water to the house and back. The electricity to power this setup costs the author, about $10.00 per month at .06 KH.
Question:
What is the design of the delivery system that supplies the heated water to the house?
Answer:
I used 1-1/4" galvanized pipe that I obtained for free. Otherwise I would recommend, using 1"flexible copper or PEX tubing. Use long enough coil lengths to eliminate underground splices. The tubing should be well insulated with lengths of thick foam, pipe or fiberglass, insulation, or encased in 4" PVC, non-perforated sewer pipe, to keep moisture out of the pipe insulation. Do not use black poly pipe. It cannot take the heat, and will eventually crack. These supply and return waterlines, should be buried at least 12" deep.
Question:
How often do you have to fill the fire box?
Answer:
That will depend on the outside temperature, and the size and insulation properties of your house. With my house (2300 sq. ft. plus a full basement) here in Wis., I fill the stove twice a day using softwood, until the temperature gets down to 0 degrees Fahrenheit. At that point I burn hardwood, but still only load twice per day. When the temperature is at, or above 20 degrees, once per day is sufficient.
Question:
Can I use the boiler for other heating applications such as heating domestic hot water?
Answer:
Yes. It can be used to heat domestic hot water, a swimming pool as I do, or a hot tub/spa. This requires only a liquid to liquid heat exchanger, plans for, which are available from DEB Design.
Question:
I have a forced air furnace in my house. Can this stove work in this application?
Answer:
Yes. There are 3 main ways this boiler can be used with any existing furnace system:
1) In a hydronic (hot water system) the hot water could be pumped directly to the boiler distribution manifold, and delivered to the various zones of the system as dictated by the zone thermostats. This is the method I currently use.
2) In a hydronic system, a liquid to liquid heat exchanger could be installed. The wood boiler water would be pumped into the exchanger, which would then heat the house system water, when the zone thermostats open and allow water flow through the exchanger.
3) In a forced air system, the boiler water would be pumped continuously through a liquid to liquid heat exchanger that is installed in the furnace plenum, just like an air conditioning "A" coil. A simple control is installed to keep the furnace burner off, if the boiler supply water is
hot enough. Then, when the house thermostat calls for heat, only the furnace blower is energized. In methods 2 and 3, the exchangers serve two purposes:
1) Supply heat to the house heating circuit.
2) Supply heat to the wood boiler circuit, too prevent freezing when the boiler fire goes out, if no antifreeze is used.
DEB Design offers construction plans for a liquid to liquid heat exchanger. Liquid to air heat exchangers are available through most plumbing and heating retailers.
Question:
Does it take superhuman welding skills to weld this boiler? I am interested in building such a outdoor heating apparatus. I would like to know what welding skills are necessary as I am a novice.
Answer:
I feel average welding skills are required to complete this project. It is constructed from cold rolled steel with mostly long straight 90 deg. butt welds. If you don't have average skills, I recommend you have a qualified friend, or even a welding shop, weld it for you. For a budgetary quote, plan on 60 hrs. to complete the welding. Unfortunately, if you are considering paying someone to weld or build your stove, you might just as well purchase a commercially built stove.
Question:
How easy is it to change the plans? Could 7 gauge steel be used? Can the plans be modified to include a slide out ash pan and grate system?
Answer:
This design is real flexible. The material list specifies the component sizes and assigns each piece a number. The plan drawings explain the assembly sequence, and show how the numbered pieces fit together. Using thicker steel would not be any problem. Extending the firebox length to 6', as an example, would involve adding 24" to the length of the appropriate pieces. This could take a bit of studying, however, it could easily be done. I once thought about installing an ash pan and did use a grate system, for a while. The grate didn't stand up very well, so I finally just left the ashes to serve as the bed. This has worked out quite well for me. I usually remove the ashes every 2 to 3 weeks. I do this prior to a reload session. I push the embers over to one side, and then shovel out half the box, and then repeat with the other half. Once done I refill the firebox. The residual embers easily restart the fire. It does get a bit smoky on occasion, but otherwise it's quite trouble free. If an ash pan/grate system was desired, I feel that one could be designed and installed, without too much trouble.
Question:
Some heaters use an insulated door instead of a water filled door. Wouldn't that be simpler?
Answer:
Yes, it probably would be simpler. I was concerned about safety, and insuring that no exterior boiler surfaces became hotter than the boiler water temperature. This also could be left to the builder's discretion.
Question:
What would be the life expectancy of the 11 gauge steel.
Answer:
That will depend on how leak free the fire box is made. The enemy here is rust, not heat. If the inside of the firebox stays moisture free, I would expect it to last many years. I also think that using a rust inhibitor (automotive) in the boiler water, would help promote a long boiler life.
Question:
The first thing that I was wondering is how do you fill your boiler with water? Do you fill it with a hose?
Answer:
I have a water supply line plumbed into the circuit, inside my house.
Question:
How many gallons do you think you fill each week?
Answer:
I usually only have to add a gallon or so each week.
Question:
Have you thought of installing anode rods similar to water heaters?
Answer:
No, but that's an excellent idea. They would need to be installed along either of the sides where there is enough depth.
Question:
I am concerned about heat loss through the door of the unit. Any suggestions on insulation in the door to take the place of the water? Possibly vermiculite?
Answer:
The primary reason the door is water filled, is safety. This unit will sit outside, probably unprotected. Using water as a coolant will keep the fire door at a more reasonable temperature. The secondary reason for a water filled door is to keep it from warping under high fire/heat conditions, burning pallets, as an example. If the door were to warp under these conditions, you would lose your draft control, and end up with a run away stove, a very undesirable condition. I know it's more complicated with a water filled door, but I think the peace of mind is worth it. My advice in this matter would be to keep the water filled door, but use vermiculate insulation, as you suggested.
Question:
Would four or five pieces of metal tubing run horizontally in the top of fire box be an easy way to improve efficiency?
Answer:
It might. There are any number of ways to improve the efficiency of the design. The plan, as built, was meant to be a starting point, for stove builders. More capable and advanced builders, could easily add modifications of their own.
Question:
Wouldn't insulation put under the floor of the unit help hold heat.
Answer:
Yes, It would. Perhaps 1" or 2" foam insulation could be safely used here.
Question:
In your design, your supply and return lines both go to or near the top of the boiler. Why don't you return to the bottom of the boiler?
Answer:
This method provides protection in the event of a major, rubber, door hose break. If the outlet is positioned properly, the boiler water level would only drop to 1" above the firebox, which would keep water above the thermostat level. This would then keep the stove from thermal run-away, and subsequent destruction, and/or possible fire.
Question:
In your design, you weld spacers on the side pieces to make up the baffle system layout. Would it be better to cut the boiler sides out in one piece?
Answer:
Yes, probably, but this method allows all the parts to be sheared by the steel supplier.
Question:
Many commercially distributed wood boilers boast a firebrick lining in the firebox. Your plan doesn't. Do you recommend it for your boiler design?
Answer:
I don't know what the advantage of the firebrick would be in my design.
Question:
I am interested in ordering plans for a wood stove-boiler. Can you tell me the difference between Plan I and Plan II?
Answer:
Boiler Plan I is made with all new steel components. It is quite flexible and more efficient, but more costly, and complicated to build, than Boiler Plan II. Boiler Plan II is made with tanks and fuel oil drums, which can be salvaged locally. It is cheaper and easier to build, but is not as flexible as Boiler Plan I. It would be a good "starter" wood boiler.
Question:
Do the plans show how to hook up the boiler to a forced air heating system?
Answer:
No, the plans provide details for a hydronic system only, including details of the delivery system. You should consult a heating contractor for that phase of the project.
Question: If the inside of the fire box and flue baffle system become coated with creosote wouldn't this act as insulation and rob the boiler of efficiency?
Answer: Yes, probably, but the design of the firing system uses a forced air blower, resulting in high flue temperatures to minimize the build-up.
Question:
Are there any provisions in your design to facilitate flue baffle access for cleaning?
Answer:
In Boiler Plan I the baffles can be accessed for cleaning. Boiler Plan II does not contain a baffle system.
Question:
Have you found creosote fouling to be a problem with your set up?
Answer:
To date I've had no problem at all.
Question:
I'm somewhat reluctant to build a boiler such as this as I'm not an experienced welder. What are your thoughts on this?
Answer:
You might want to consider Boiler Plan II. It's easier, and cheaper to build than Boiler Plan I and would provide you with valuable experience, should you ever want to build a more complex version.
Question:
What is the difference between a closed system and an open system?
Answer:
A closed loop system is not vented to the outside atmosphere (such as a hydronic heating system) while an open system is.
Question:
What advantages and disadvantages do they each have?
Answer:
The main advantages of a closed loop are:
1) There will be very little oxygen in the water, which can shorten heating system component lives. (pumps, valves, etc.)
2) There won't be any evaporation of the boiler water. The main advantage of an open system is that the components do not have to be as strong to withstand the higher pressures prevalent in a closed system.
Question:
Do you have any plans for a system that holds less water?
Answer:
No, but the plans can be easily modified by the builder.
Question:
Can you use a boiler to heat two buildings?
Answer:
Yes, all you do is run a plumbing (including pump and thermostat) loop from the boiler to the building to be heated.
Question:
Can this unit be setup, so that if the fire goes out the gas furnace will take over?
Answer:
I have no direct experience with this type of setup, but it can be done. A liquid to air heat exchanger is usually installed in the forced air furnace plenum. A thermostat keeps the forced air furnace ignition circuit from energizing if the incoming water loop (from the wood boiler) is hot enough. This water loop runs continuously. If the boiler loop temperature drops, the thermostat would enable the ignition circuit so the house furnace could heat the house and the boiler through the exchanger and boiler loop. (This would keep the wood boiler circuit it from freezing until restarted)
Question:
I currently have a 4,600 sq. ft. home with a 430 sq. ft. garage and a 16 by 30 ft. indoor swimming pool. We are using a 225,000 B.T.U gas boiler to heat our home. This boiler operates at 18 p.s.i with an expansion tank. Will your wood boiler work with our present system with the gas boiler used only for a backup?
Answer:
I've estimated the DEB Design plan design boiler at app. 125,000 BTUs. You'd need to use liquid to liquid heat exchangers to integrate the outside wood stove into your existing heating system. I've estimated the DEB Design exchanger plan design BTU rating at app. 50,000, so you'd need at least 5 of the exchangers and a large enough wood boiler to match your current stove capacity. (Plus a whole lot of wood to fuel it)
Question:
How large of a boiler will I need in the previous question?
Answer:
About twice the size of the plan design, which has a 36 cubic ft. capacity firebox. (In theory)
Question:
Are the plans for Boiler I and Boiler II different size boilers?
Answer:
No, they have the same size firebox.
Question:
What are the BTU ratings of the plan boilers?
Answer:
Approximately 125,000 BTUs.
Question:
Do you ever, or frequently have problems pushing water with your small ground Grunfos pump? Have you ever had the situation where your pump won't push air, but it will push water? Do you have any ideas as to why I am running into so much trouble with the pump quitting pumping the cycle?
Answer:
Yes, I've had the same problems with air in the lines, especially the first year, when I used poly pipe for supply and return lines. Leaks will cause this. Also, the Grunfos pump may not pump water up hill very well. A critical design element is the nipple length, shown on the "Side View" of Drawing 15. (Size the pipe nipple length to end 1" above the firebox) This creates a fluid locked water circuit, between the boiler supply and return outlets. Once all the air is purged from the lines, the Grunfos pump can "move" water continually, with out problems, as long as there are no major water leaks. If you don't construct the boiler return entry like this, you won't be able to use a Grunfos pump. You may need a stronger pump. (More electrical power consumption) In my own installation I placed an old jet pump ahead of the Grunfos pump, that I use for purging air out of my system. (It also serves as a back up pump)I must always be careful to insure that at least 1 heat circuit is open, otherwise the pressure from the auxiliary pump will trip the high pressure relief valve on my natural gas commercial boiler (usually set at about 30#). As you can surmise, I have my heating systems integrated. Once all the air is purged from the system, the auxiliary pump is shut off, and the small circulating can pump just fine. If you are using a radiator as a heat exchanger, the auxiliary pump should be installed on the return side. This would insure that the radiator is not exposed to excessive pressure.
Question:
How do I seal around the chimney, high temp silicone?
Answer:
Use a chimney collar. This is a piece of steel that wraps tightly and fastens around the flue pipe. It flares down and out, a few inches. High temp sealant could be used to complete the seal between the collar and flue pipe.

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