My improved homemade boiler

[cumminstinkerer]

so I thought I'd start a new thread since the last thread seems to have gotten off track and I haven't updated regularly. I built my own OWB back in 2010, just a standard box in a box with forced induction. It worked very well but along about this time last year i started wanting to make it more efficient and use less wood. I found Hearth.com and a couple other sites and started learning a lot. I decided to try and get some secondary burn out of it, knowing full well it would be difficult. I already had an exhaust box in it that forced the exhaust to the very rear before exiting the central flue. I went in below that and added a steel supported firebrick baffle and then routed secondary air inlets along the lower portion of the box from the rear to the front then up to the bottom of the baffle where they turn 90 degrees and run under the baffle with outlet holes. These are connected to my draft fan which also supplies primary air under the entire length of the fire through multiple openings. After visiting with several very helpful folks on here I drilled a small peep hole in my loading door, the peep now remains open after some investigation. After a fair amount of experimenting I found that my secondary tubes needed to be turned to form a vee shape under the baffle, I would then get some secondary flames but not consistent. The air outlets in the secondary tubes started off at 5/32 but it appeared my air velocity was too high, I began drilling the holes out and retesting. I have now settled with them at 3/8 and pointing at approximately 1:00 on the left tube and 11:00 on the right. Now after considerable adjustments to the butterfly valves made into the feed lines for primary and secondary air, one to two minutes into a fresh load the secondary flame lights up and increases in intensity until I have a rolling flame that is from clear color to an incredibly intense bright yellow at the very tips. Once the secondary flame lights the chimney goes completely clear. The only piece of the puzzle left for me at this point other that some final tuning once I get an O2 sensor is my flue temps are somewhat high, I'm running 475-500 surface temps on single wall measured with an IR gun about a foot above the boiler top. I'm in the process of designing a flue tube style HX in hopes of recovering some of this heat and lower flue temps. That however will not be done this year for two reasons, cost and time, and the boiler is my only heat source and therefore cannot shut down at this point to do the install. I am also planning on adding some storage next year, just need to work out the details of where with the wife to make sure and leave her as much storage space in the basement as possible. Thank you to everyone on Hearth for all the help and just general knowledge sharing I have learned a tremendous amount.

 

[Bob Rohr]

Invest is a flue temperature gauge, they are available online. I have a magnetic type with a probe into the the flue. IR guns may not be accurate, depending on the surface you shoot, and they don't see the hottest point mid flue.

With a good gauge you get instant results of any adjustments you make. Keeps the piping safe also.

 

[cumminstinkerer]

 

[cumminstinkerer]

the chimney photo is after all of the mods including drilling the secondary air holes out, that is roughly two to three minutes into a fresh load, the inside of the fire box is way cleaner now, that pic was before i drilled the holes out, the baffle and pipes are white now and no lumps of creosote except on the fire box walls there is a little.

 

[cumminstinkerer]

more updates to the boiler, I added more air holes in the secondary tubes and have lined the lower 2/3 of the chamber, incredible difference for sure, secondary flame is very quick to light and creates a huge amount of heat very quickly

 

[cumminstinkerer]

The lined boiler is no running completely clean in the lower chamber the walls and air tubes air a nice white color. I know I said I wasn't going to do it this year but I am adding the fire tube HX. I wanted to revive this thread so the two were tied together. I also have an additional 250 gallon of water capacity plumbed in and valved off for now until the HX is finished. I am hoping to Get the HX installed this weekend and test things out, still have a lot of welding to do.

 

[cumminstinkerer]

I am gaining on the Hx still on track to install it this weekend. I want to send a huge thank you out to warno for all of his advice and help.